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Commercial Cooking Appliance Technology Assessment

FSTC Report # 5011.02.26

Food Service Technology Center 2002

Prepared by:

Don Fisher, Principle Investigator

Contributors:

Todd Bell Judy Nickel Charles Bohlig Greg Sorensen

David Cowen Richard Young Victor Kong Fred Wong

David Zabrowski

Fisher-Nickel, inc. 12949 Alcosta Boulevard, Suite 101

San Ramon, CA 94583

Prepared for:

Enbridge Gas Distribution Pacific Gas and Electric Company 500 Consumers Road

Toronto, Ontario M2J 1P8 245 Market Street, P.O. Box 770000

San Francisco, California 94177

© 2002 by Fisher-Nickel, inc. All rights reserved. The information in this report is based on data generated at the Food Service Technology Center.

Acknowledgments

California consumers are not obligated to purchase any full service or other service not funded by this program. This program is funded by California utility ratepayers under the auspices of the California Public Utilities Commission.

Los consumidores en California no estan obligados a comprar servicios completos o adicionales que no esten cubiertos bajo este programa. Este programa esta financiado por los usuarios de servicios públicos en California bajo la jurisdiccion de la Comision de Servicios Públicos de California.

A National Advisory Group provides guidance to the Food Service Technology Center Project. Members include: Advantica Restaurant Group Applebee’s International Group California Energy Commission (CEC) California Restaurant Association Carl Karcher Enterprises, Inc. DJ Horton & Associates Electric Power Research Institute (EPRI) Enbridge Gas Distribution EPA Energy Star Gas Technology Institute (GTI) Lawrence Berkeley National Laboratories McDonald’s Corporation National Restaurant Association Pacific Gas and Electric Company Safeway, Inc. Southern California Edison Underwriters Laboratories (UL) University of California at Berkeley University of California at Riverside US Department of Energy, FEMP The FSTC specifically acknowledges Enbridge Gas Distribution for co-funding the update of this technology assessment.

Policy on the Use of Food Service Technology Center Test Results and Other Related Information

• Fisher-Nickel, inc. and the Food Service Technology Center

(FSTC) do not endorse particular products or services from any specific manufacturer or service provider.

• The FSTC is strongly committed to testing food service equipment using the best available scientific techniques and instrumentation.

• The FSTC is neutral as to fuel and energy source. It does not, in any way, encourage or promote the use of any fuel or energy source nor does it endorse any of the equipment tested at the FSTC.

• FSTC test results are made available to the general public through technical research reports and publications and are protected under U.S. and international copyright laws.

• In the event that FSTC data are to be reported, quoted, or referred to in any way in publications, papers, brochures, advertising, or any other publicly available documents, the rules of copyright must be strictly followed, including written permission from Fisher-Nickel, inc. in advance and proper attribution to Fisher-Nickel, inc. and the Food Service Technology Center. In any such publication, sufficient text must be excerpted or quoted so as to give full and fair representation of findings as reported in the original documentation from FSTC.

Legal Notice

This report was prepared as a result of work sponsored by the California Public Utilities Commission (Commission). It does not necessarily represent the views of the Commission, its employees, or the State of California. The Commission, the State of California, its employees, contractors, and subcontractors make no warranty, express or implied, and assume no legal liability for the information in this report; nor does any party represent that the use of this information will not infringe upon privately owned rights. This report has not been approved or disapproved by the Commission nor has the Commission passed upon the accuracy or adequacy of the information in this report.

Contents

5011.02.26 iii Food Service Technology Center

Page Executive Summary ................................................................................... xiii 1 Introduction ......................................................................................... 1-1 Objective and Scope....................................................................... 1-1 Background ..................................................................................... 1-3 Standard Test Method Development ............................................. 1-4 Appliance Energy Efficiency........................................................... 1-8 Gas/Electric Consumption Ratios .................................................. 1-10 Higher Efficiency ............................................................................. 1-12 Ventilation Requirements ............................................................... 1-16 Emissions from Commercial Cooking............................................ 1-28 Conclusions..................................................................................... 1-32 References...................................................................................... 1-34 2 Fryers ................................................................................................... 2-1 Introduction...................................................................................... 2-1 Cooking Processes......................................................................... 2-2 Types of Fryers ............................................................................... 2-3 Controls ........................................................................................... 2-4 Heating Technologies..................................................................... 2-4 Fryer Performance.......................................................................... 2-7 Benchmark Energy Performance................................................... 2-11 Fryer Energy Consumption............................................................. 2-17 Ventilation Requirements ............................................................... 2-21 Research and Development........................................................... 2-22 Industry Market Focus .................................................................... 2-22 References...................................................................................... 2-23 3 Griddles ................................................................................................ 3-1 Introduction...................................................................................... 3-1 Cooking Processes......................................................................... 3-2 Types of Griddles............................................................................ 3-2 Controls ........................................................................................... 3-4 Heating Technologies..................................................................... 3-7

Contents

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Griddle Performance....................................................................... 3-11 Benchmark Energy Performance................................................... 3-17 Griddle Energy Consumption ......................................................... 3-19 Ventilation Requirements ............................................................... 3-23 Improving Performance .................................................................. 3-23 Research and Development........................................................... 3-23 Industry Market Focus .................................................................... 3-25 References...................................................................................... 3-27 4 Broilers ................................................................................................. 4-1 Introduction...................................................................................... 4-1 Cooking Processes......................................................................... 4-2 Types of Broilers ............................................................................. 4-2 Controls ........................................................................................... 4-9 Broiler Performance........................................................................ 4-10 Broiler Energy Consumption .......................................................... 4-16 Ventilation Requirements ............................................................... 4-19 Research and Development........................................................... 4-19 Industry Market Focus .................................................................... 4-21 References...................................................................................... 4-22 5 Range Tops .......................................................................................... 5-1 Introduction...................................................................................... 5-1 Cooking Processes......................................................................... 5-2 Controls ........................................................................................... 5-3 Heating Technologies..................................................................... 5-3 Advanced Technologies ................................................................. 5-7 Range Top Performance ................................................................ 5-10 Benchmark Energy Efficiency ........................................................ 5-12 Range Top Energy Consumption................................................... 5-13 Ventilation Requirements ............................................................... 5-14 Research and Development........................................................... 5-14 Industry Market Focus .................................................................... 5-17 References...................................................................................... 5-18

Contents

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6 Chinese (Wok) Ranges ...................................................................... 6-1 Introduction...................................................................................... 6-1 Cooking Processes......................................................................... 6-2 Types of Chinese Ranges .............................................................. 6-2 Controls ........................................................................................... 6-4 Heating Technologies..................................................................... 6-5 Chinese Range Performance......................................................... 6-6 Chinese Range Energy Consumption............................................ 6-6 Ventilation Requirements ............................................................... 6-7 Research and Development........................................................... 6-7 References...................................................................................... 6-9 7 Ovens ................................................................................................... 7-1 Introduction...................................................................................... 7-1 Cooking Processes......................................................................... 7-3 Types of Ovens............................................................................... 7-4 Controls ........................................................................................... 7-12 Heating Technologies..................................................................... 7-13 Oven Performance.......................................................................... 7-16 Benchmark Energy Efficiency ........................................................ 7-19 Oven Energy Consumption ............................................................ 7-20 Ventilation Requirements ............................................................... 7-24 Research and Development........................................................... 7-24 Industry Market Focus .................................................................... 7-27 References...................................................................................... 7-29 8 Steamers .............................................................................................. 8-1 Introduction...................................................................................... 8-1 Cooking Processes......................................................................... 8-3 Types of Steamers.......................................................................... 8-3 Controls ........................................................................................... 8-5 Steamer Performance..................................................................... 8-6 Benchmark Energy Performance................................................... 8-11 Steamer Energy Consumption ....................................................... 8-13

Contents

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Ventilation Requirements ............................................................... 8-14 Research and Development........................................................... 8-14 Industry Market Focus .................................................................... 8-15 References...................................................................................... 8-17 9 Steam Kettles ...................................................................................... 9-1 Introduction...................................................................................... 9-1 Cooking Processes......................................................................... 9-1 Types of Kettles .............................................................................. 9-2 Controls ........................................................................................... 9-4 Advanced Steam Kettle Technologies........................................... 9-4 Steam Kettle Performance ............................................................. 9-5 Benchmark Energy Efficiency ........................................................ 9-6 Steam Kettle Energy Consumption................................................ 9-7 Ventilation Requirements ............................................................... 9-8 Research and Development........................................................... 9-8 Industry Market Focus .................................................................... 9-8 References...................................................................................... 9-9 10 Braising Pans ...................................................................................... 10-1 Introduction...................................................................................... 10-1 Braising Pan Performance.............................................................. 10-2 Benchmark Energy Efficiency ........................................................ 10-3 Braising Pan Energy Consumption ................................................ 10-3 Ventilation Requirements ............................................................... 10-4 Research and Development........................................................... 10-5 Industry Market Focus .................................................................... 10-6 References...................................................................................... 10-7 Appendix A: Glossary

List of Figures and Tables

5011.02.26 vii Food Service Technology Center

Page 1-1 Daily energy consumption profiles for a broiler and a fryer .......... 1-3 1-2 ASTM test method applied to a fryer ............................................. 1-6 1-3 Prescriptive code requirement for unlisted hood........................... 1-18 1-4 Engineered requirements for listed hood (with side panels)......... 1-19 1-5 Short-circuit hood illustrating potential for spillage........................ 1-20 1-6 CKV hood testing ............................................................................ 1-24 1-7 Schlieren example .......................................................................... 1-24 1-8 Thresholds of capture and containment for a 5-ft.

wall-canopy hood ............................................................................ 1-25 1-9 Impact of CKV research on design guidelines............................... 1-27 2-1 Standard open deep-fat fryer ......................................................... 2-1 2-2 An example of a console fryer........................................................ 2-2 2-3 Pressure fryer.................................................................................. 2-3 2-4 Donut fryer....................................................................................... 2-4 2-5 Fire tubes in the vat of a gas fryer.................................................. 2-5 2-6 Gas fryer idle rates.......................................................................... 2-9 2-7 Gas open deep-fat fryer cooking-energy efficiency....................... 2-10 2-8 Gas open deep-fat fryer production capacity................................. 2-11 2-9 Fryer oil temperature while cooking a heavy (3-pound)

load of fries...................................................................................... 2-12 2-10 Gas open deep-fat fryer cooking-energy efficiency

characteristics ................................................................................. 2-13 2-11 Electric open deep-fat fryer cooking-energy efficiency

characteristics ................................................................................. 2-14 2-12 Gas pressure fryer cooking-energy efficiency characteristics ...... 2-15 2-13 Electric pressure fryer cooking-energy efficiency characteristics. 2-15 2-14 Open deep-fat fryer cooking-energy efficiency bandwidths.......... 2-16 2-15 Pressure fryer cooking-energy efficiency bandwidths................... 2-16 2-16 Gas open deep-fat fryer energy consumption based on the

two-mode model.............................................................................. 2-17 2-17 Electric open deep-fat fryer energy consumption based on the

two-mode model.............................................................................. 2-18

Figures


5011.02.26 viii Food Service Technology Center

2-18 Gas pressure fryer energy consumption based on the two-mode model.............................................................................. 2-18

2-19 Electric pressure fryer energy consumption based on the two-mode model.............................................................................. 2-19

3-1 Countertop griddle .......................................................................... 3-1 3-2 Gas griddle with a grooved plate.................................................... 3-3 3-3 Duplex cooker ................................................................................. 3-3 3-4 Covered griddle surface.................................................................. 3-4 3-5 Standard efficiency thermostat-sensing bulb placement .............. 3-5 3-6 Bulb-type thermostat sensor .......................................................... 3-5 3-7 Comparison of griddle cooking profiles.......................................... 3-6 3-8 Welded thermocouples to a griddle surface .................................. 3-12 3-9 Griddle temperature uniformity plot................................................ 3-12 3-10 3-ft. gas griddle idle energy rates................................................... 3-14 3-11 3-ft. gas griddle cooking energy efficiencies.................................. 3-15 3-12 3-ft. gas griddle production capacity .............................................. 3-16 3-13 3-ft. griddle input rate vs. productivity ............................................ 3-16 3-14 Gas 3-ft. griddle cooking-energy efficiency characteristics........... 3-18 3-15 Electric 3-ft. griddle cooking-energy efficiency characteristics ..... 3-19 3-16 3-ft. griddle cooking-energy efficiency bandwidths ....................... 3-19 3-17 Gas 3-ft. griddle energy consumption based on the

two-mode model.............................................................................. 3-21 3-18 Electric 3-ft. griddle energy consumption based on the

two-mode model.............................................................................. 3-21 4-1 A gas underfired charbroiler with overfired broiler below.............. 4-1 4-2 Underfired broiler using rock to diffuse heat.................................. 4-3 4-3 Diagram of the “radiant” style of underfired charbroiler ................ 4-3 4-4 This broiler can be converted from ceramic stone to

steel radiants................................................................................... 4-4 4-5 Overfired upright broiler with two broiling decks............................ 4-6 4-6 A salamander broiler, mounted on a backshelf ............................. 4-6 4-7 A cheesemelter ............................................................................... 4-7 4-8 Broiler range battery ....................................................................... 4-7 4-9 Conveyor broiler.............................................................................. 4-8


5011.02.26 ix Food Service Technology Center

4-10 Gas combination griddle-broiler ..................................................... 4-8 4-11 Underfired Broiler with 9 control knobs.......................................... 4-9 4-12 Thermocoupled steel disks............................................................. 4-12 4-13 Underfired broiler temperature uniformity plot............................... 4-12 4-14 3-ft. gas underfired charbroiler cooking-energy efficiencies ......... 4-14 4-15 3-ft. gas underfired charbroilers production capacities ................. 4-15 4-16 Direct-fired broiler energy consumption profile before installation

of the Broil-Master control .............................................................. 4-18 4-17 Direct-fired broiler energy consumption profile after installation

of the Broil-Master control .............................................................. 4-19 5-1 Six-burner range top with range oven............................................ 5-1 5-2 Stock pot range............................................................................... 5-2 5-3 Ring burner...................................................................................... 5-4 5-4 Star burner ...................................................................................... 5-4 5-5 Electric speed coil ........................................................................... 5-5 5-6 French plate range top.................................................................... 5-5 6-1 Guangdong style Chinese range.................................................... 6-1 6-2 West-coast style Chinese range .................................................... 6-1 7-1 Double-stacked convection oven ................................................... 7-3 7-2 Six-burner range with range oven.................................................. 7-4 7-3 Deck oven ....................................................................................... 7-5 7-4 Full-size convection oven ............................................................... 7-7 7-5 Double-rack rack oven.................................................................... 7-7 7-6 Combination oven ........................................................................... 7-8 7-7 Cook-and-hold oven........................................................................ 7-9 7-8 Double-stacked conveyor oven...................................................... 7-10 7-9 Rotisserie oven ............................................................................... 7-12 7-10 Flashbake® oven............................................................................. 7-15 7-11 TurboChef® oven............................................................................. 7-15 7-12 Sheet cake uniformity ..................................................................... 7-25 7-13 Pinking of meat ............................................................................... 7-26 7-14 Uncured meat (left); cured meat (right).......................................... 7-27 7-15 Pink ring around meat cooked in direct-fired oven........................ 7-27


5011.02.26 x Food Service Technology Center

8-1 Two-compartment convection steamer on self-contained base ... 8-1 8-2 Two-compartment pressure steamer............................................. 8-4 8-3 Connectionless steamer ................................................................. 8-5 8-4 Normalized electric pressureless steamer idle energy rates ........ 8-8 8-5 Typical frozen green pea cooking-energy efficiencies of steamers 8-9 8-6 Typical red potato cooking-energy efficiencies of steamers......... 8-9 8-7 Normalized electric pressureless steamer production capacity.... 8-10 8-8 Electric pressureless steamer cooking-energy efficiency ............. 8-12 9-1 Floor-mounted tilting self-contained steam kettle.......................... 9-3 10-1 40-gallon braising pan .................................................................... 10-1 10-2 Braising pan with food receiving pan support mounts under

pouring lip........................................................................................ 10-2 10-3 Accu-Steam braising pan ............................................................... 10-5 10-4 Skittle® cooker................................................................................. 10-6


5011.02.26 xi Food Service Technology Center

Page 1-1 Appliance Categories and Types ................................................... 1-2 1-2 Benchmark Cooking-Energy Efficiency Summary......................... 1-10 1-3 AGA Published Gas/Electric Energy Ratios .................................. 1-11 1-4 Gas/Electric Energy Consumption Ratios...................................... 1-12 1-5 Typical Minimum Exhaust Flow Rates for Listed Hoods

by Cooking Equipment Type .......................................................... 1-22 1-6 Estimate of Ventilation Volumes by Facility Type in the U.S. ....... 1-26 2-1 Energy Efficiency for 14-inch Open Deep-Fat Fryers ................... 2-13 2-2 Energy Efficiency for 4-Head Pressure Fryers .............................. 2-14 2-3 Projected Energy Consumption for Gas Fryers............................. 2-20 2-4 Projected Energy Consumption for Electric Fryers ....................... 2-21 3-1 Energy Efficiency for 3-foot Griddles ............................................. 3-18 3-2 Projected Energy Consumption for Gas Griddles ......................... 3-22 3-3 Projected Energy Consumption for Electric Griddles.................... 3-22 4-1 Typical Grid Dimensions, Input Rates and Input Densities

for Underfired and Overfired Broilers ............................................. 4-5 4-2 Underfired Broiler Cooking-Energy Efficiency ............................... 4-10 4-3 Projected Energy Consumption for Gas Broilers........................... 4-16 4-4 Projected Energy Consumption for Electric Broilers ..................... 4-17 4-5 Summary of Broil-Master® Energy Saver Performance ................ 4-18 5-1 Comparison of ASTM and ANSI Range Top Efficiency Tests...... 5-11 5-2 Range Top Energy Efficiency......................................................... 5-12 5-3 Projected Energy Consumption for Gas Ranges .......................... 5-13 5-4 Projected Energy Consumption for Electric Ranges..................... 5-14 6-1 Summary of Chinese Range Types ............................................... 6-4 6-2 Chinese Range Energy Efficiency.................................................. 6-6 6-3 Projected Energy Consumption for Gas Chinese Ranges............ 6-7 7-1 Oven Energy Efficiency .................................................................. 7-20 7-2 Projected Energy Consumption for Gas Ovens ............................ 7-22 7-3 Projected Energy Consumption for Electric Ovens ....................... 7-23 8-1 Input Rate and Preheat Test Results for Different Steamers ....... 8-7

Tables


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8-2 Projected Energy Consumption for Gas Steamers ....................... 8-13 8-3 Projected Energy Consumption for Electric Steamers.................. 8-14 9-1 Steam Kettle Performance Comparison Based on Preliminary

Data for Three Steam Kettles......................................................... 9-6 9-2 Benchmark Steam Kettle Cooking-Energy Efficiency ................... 9-7 9-3 Projected Energy Consumption for Gas Steam Kettles ................ 9-7 9-4 Projected Energy Consumption for Electric Steam Kettles........... 9-8 10-1 Energy Efficiency for Braising Pans............................................... 10-3 10-2 Projected Energy Consumption for Gas Braising Pans ................ 10-4 10-3 Projected Energy Consumption for Electric Braising Pans........... 10-4

Executive Summary

5011.02.26 xiii Food Service Technology Center

This technology review presents a comprehensive description and energy performance assessment of commercial cooking equipment. In the absence of energy-efficiency standards and rating systems, all classes of commercial food service equipment have historically exhibited relatively poor energy performance. Possibly the greatest hurdle to improving the efficiency of commercial food service and refrigeration equipment is the lack of understanding (by both manufacturers and purchasers) of benchmark efficiency. If the buyer is not exposed to accurate efficiency data, there is less incentive on the part of the manufacturers to improve equipment performance. If the buyer does not realize that the most energy efficient appliance option may also be the best performer, the hurdle is even more difficult to knock down. Significant energy savings have been achieved in residential refrigeration equipment, yet proven energy savings technologies have not been implemented in the commercial markets.

In 1987, with co-funding by the Electric Power Research Institute (EPRI), the Gas Technology Institute (GTI), and the National Restaurant Association, the Pacific Gas and Electric Company undertook the development of uniform testing procedures to measure energy efficiency and evaluate the overall performance of gas and electric cooking equipment within the scope of the Food Service Technology Center project (FSTC), operating in San Ramon, California. At the end of 2001, the FSTC had developed 30 standard test methods for the performance of commercial food service equipment.

When the FSTC research team completes a uniform testing procedure for a particular appliance category, the document is submitted to the American Society for Testing and Materials (ASTM) F 26 Food Service Equipment Committee, where it is reviewed by a group of industry professionals, then ratified and published as an official ASTM Standard Test Method. These test methods produce unbiased energy performance data that can be used to help end users and designers specify energy efficient equipment, qualify Energy Star® candidates and help determine minimum mandated standards for

Executive Summary

5011.02.26 xiv Food Service Technology Center

energy efficiency. Manufacturers use these test methods to benchmark and improve the efficiency and performance of their equipment. End users have used the test methods in partnership with their equipment suppliers to improve the efficiency of specific appliances they purchase.

Although the application of advanced technologies could improve the performance and energy efficiency of the existing stock of food service equipment, the application of existing technologies, such as insulation, improved heat exchanger design, and enhanced controls, may provide the greatest return over the short term.

Overall recommendations of this study include:

• Continuing commercial appliance testing programs (e.g., FSTC) that can be used to further benchmark energy performance in direct support of R&D projects for commercial cooking equipment.

• Using benchmark performance data as justification, developing an industry strategy that will influence the purchase-decision criteria so that customers will specify more energy efficient equipment.

• Developing and sponsoring training courses and workshops for the food service and utility industries based on this appliance technology review.

• Initiating research and development projects that will deliver the greatest return for R&D dollars invested (i.e., that achieve the largest efficiency gain for the largest percentage of equipment installed in food service facilities). The R&D focus needs to be on improving part-load performance of gas cooking equipment and reducing the cost premium associated with producing more efficient equipment. New equipment needs to be compatible with the NAFEM Online Kitchen Protocol.

• Collaborating with European utilities and research groups (such as Gaz de France) on appliance R&D initiatives.

• Developing a web-based appliance efficiency directory reporting data acquired through testing in accordance with the ASTM Standard Test Methods for evaluating the performance of commercial cooking

Executive Summary

5011.02.26 xv Food Service Technology Center

equipment. Initially, such a directory would rely extensively on the efficiencies reported by FSTC and cover a fraction of the cooking equipment on the market. However, such an initiative would increase awareness in the industry, hence stimulate manufacturers to have their equipment tested in accordance with the ASTM test methods in other U.S. and Canadian laboratories. A natural extension is promoting Energy Star® as a voluntary labeling program.

1 Introduction

5011.02.26 1-1 Food Service Technology Center

This technology review presents a comprehensive description and energy performance assessment of commercial cooking equipment. The focus is on the potential for improving the energy efficiency and overall performance of both gas-fired and electric appliances in support of utilities' marketing and energy conservation initiatives for this end-use sector. The ultimate goal is to stimulate the development of more energy efficiency equipment through col-laborative efforts between utilities, research groups, end-users and manufac-turers.

This edition is an update of a technology assessment prepared by Fisher Con-sultants (now Fisher-Nickel, inc.) under contract with the Canadian Gas Re-search Institute (CGRI) published in 1996.1 Fisher-Nickel, inc. (www.fishnick.com) currently operates the Food Service Technology Center (FSTC) in San Ramon, California.

The glossary in Appendix A is provided so that the reader has a quick refer-ence to the terms used in this study.

Appliance Categories and Types

The categories and types of cooking equipment described in subsequent sec-tions of this report are listed in Table 1-1. Each section has been developed as a “textbook” style module complete with references. Subsequent to the 1996 edition of this report, the FSTC has expanded the performance database for several major categories of equipment including gas fryers, gas griddles, electric convection steamers, and underfired gas broilers.

Objective & Scope

Introduction


Table 1-1. Appliance Categories and Types.

Category Type

FRYER Open Deep Fat Open Kettle Pressure Flat Bottom: – chicken – fish – donut

GRIDDLE Single Sided: – flat – grooved Double Sided

BROILER Underfired (Charbroiler) Overfired: – upright – salamander – cheesemelter Conveyor (chain)

RANGE Range: – open burner/element – hot top

CHINESE RANGE Traditional Wok North American Wok OVEN Standard

Convection – full size – half size – rack ovens Combination Oven/Steamer Deck Conveyor Rotisserie – rotisserie oven – rotisserie broiler

STEAMER Compartment Pressureless – natural convection – boiler/steam generator based Compartment Pressurized

STEAM KETTLE Steam Kettle BRAISING PAN Braising Pan/Tilting Skillet

Introduction


Energy Performance

Although the nameplate energy input of an appliance (Btu/h for gas and kW for electric) reflects available cooking “horsepower,” it is more difficult to estimate actual energy consumption for specific cooking appliances in a spe-cific food service operation based on this rated input. While one understands that a cooking appliance may not draw power or consume gas at its peak in-put rate, it is not as easy to project the average rate of energy consumption for the various appliances that one might encounter in a restaurant kitchen. The amount of energy consumed by commercial cooking equipment is de-pendent on the operating time of an appliance, the cooking surface or cavity temperature (based on a selected thermostat setpoint) and/or heat-input set-ting (e.g., “high”, “medium” or “low” input energy control), the quantity of food being cooked and, for some appliances, the mode of operation. The rela-tive dependence of appliance energy consumption on each of these variables is a function of equipment type and design, as well as on the usage of an ap-pliance within a specific food service operation. For eight generic appliance types evaluated within the scope of an appliance energy end use monitoring project,2 a large variation in the characteristic energy demand and consump-tion was documented. This also was reflected by the reported range in the duty cycles (i.e., from 12 to 92%) of appliance burners or elements for each category of equipment. The duty cycle of an appliance is defined as the aver-age rate of energy consumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy. Figure 1-1 com-pares the daily energy profiles for two pieces of cooking equipment.

Thermostat vs. Non-Thermostat Control. Whether an appliance type in-corporates a thermostat can impact significantly on the characteristic energy consumption of that appliance. For example, a gas broiler consumes energy at a rate that is close to its input rate as thermostat control is not incorporated. Characteristically different from the broiler is an appliance such as the fryer, which is thermostatically controlled. The average rate of energy consumption required to maintain the frying oil at approximately 350°F (177°C) is 15 to 20% of the rated energy input for fryers.2

Background

Figure 1-1. Daily energy consump-tion profiles for a broiler and a fryer.

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Introduction


Situation Analysis

A study3 published by the U.S. Department of Energy titled Characterization of Commercial Building Appliances effectively summarizes the status of cooking technologies and foreshadows the importance of R&D initiatives designed to improve the performance of commercial cooking equipment:

All commercial food service equipment is represented in both gas-fired and electric models. The efficiency of commercially available gas-fired cooking equipment varies significantly depending on the specific manufacturer and model. There are no mandated minimum efficiency standards in this industry, and uniform test procedures for measuring actual cooking efficiencies are in the process of being developed (ref. Food Service Technology Center). The largest impact on the future efficiency of the installed base of cooking equipment will depend more on factors that influence the purchase decision criteria for the equipment than on technology developments. Quite simply, the installed base of commercial gas-fired cooking equipment efficiencies could be significantly increased if customers purchased more efficient mod-els. However, the cost premium associated with the high efficiency cooking equipment does not always justify the resultant savings.

As a result, projecting future efficiencies, we need to consider customer trends and driving forces behind the more energy efficient system. Often times, the higher efficiency systems also provide better cooking performance, which is extremely important to the fast food chains. Electric powered cook-ing equipment has not changed in efficiency as dramatically as gas-fired models.

In addition to the low-first-cost economic pressure on the food service opera-tor to purchase less efficient equipment, the general lack of objective per-formance data has slowed the development of energy efficient equipment. If the buyer is not exposed to accurate benchmark performance data, there is less incentive on the part of the manufacturers to improve equipment per-formance. As identified by the DOE study,3 the absence of government legis-lation specifying minimum efficiencies for cooking equipment is another factor in the slow-development equation for improving the energy perform-ance of cooking equipment.

In 1987, with co-funding by the Electric Power Research Institute (EPRI), the Gas Technology Institute (GTI), and the National Restaurant Association, the Pacific Gas and Electric Company undertook the development of uniform testing procedures to measure energy efficiency and evaluate the overall per-

Standard Test Method Development

Introduction


formance of gas and electric cooking equipment within the scope of the Food Service Technology Center project, operating in San Ramon, California.

When the FSTC research team completes a uniform testing procedure for a particular appliance category,4-11 the document is submitted to the ASTM F 26.06 Food Service Equipment Subcommittee on Productivity and Energy Protocols. The testing procedure is then reviewed by this group of industry professionals before it is balloted by the main F 26 Food Service Equipment Committee. Once approved by the main committee, the testing procedure is submitted for Society ballot and published as an official ASTM Standard Test Method.

ASTM Test Methods Benefit Food Service Industry

The application of an ASTM Standard Test Method (STM) to cooking equipment provides end-users with performance parameters that can be used to compare the energy efficiency, production capacity, cooking sur-face/cavity uniformity, etc. of one piece of equipment with another. A unique aspect of the test methods is that the productivity (i.e., production capacity) and energy efficiency are determined from the same test using standardized food product under tightly controlled conditions. Figure 1-2 illustrates an ASTM test method being applied to a fryer.

From the perspective of energy efficiency, it is important to compare a gas appliance with other gas appliances and an electric appliance with other elec-tric equipment. Since the energy efficiency of a gas appliance is inherently lower than it is for its electric counterpart, a purchaser must establish differ-ent minimums for gas and electric equipment. For example, an end-user might choose to specify a minimum full-load cooking-energy efficiency of 50% for gas fryers while requiring a minimum of 80% for electric fryers.

The specification of the production capacity (i.e., weight of food cooked per hour) should be the same for both gas and electric appliances, as the “work” that a cooking appliance is required to do for the end-user is the same. Simi-larly, performance parameters such as cooking surface/cavity temperature uniformity apply equally to gas and electric appliances. Idle energy rate is

Introduction


another important parameter in characterizing the energy performance, as appliances spend many hours in a ready-to-cook mode.

These test methods produce unbiased energy performance data that can be used to help end users and designers specify energy efficient equipment, qualify Energy Star® candidates and help determine minimum mandated standards for energy efficiency. Manufacturers use the test methods to benchmark and improve the efficiency and performance of their equipment. End users have used the test methods in partnership with their equipment suppliers to improve the efficiency of specific appliances they purchase.

Status of ASTM Test Methods

At the end of 2001, the FSTC had developed 30 standard test methods for the performance of commercial food service equipment. Standard test methods ratified by the ASTM F26 Committee on Food Service Equipment include:

Figure 1-2. ASTM test method applied to a fryer. Photo: Fisher-Nickel, inc.

Introduction


1. ASTM Standard Test Method for the Performance of Griddles, Designa-tion: F 1275-99

2. ASTM Standard Test Method for the Performance of Open Deep-Fat Fryers, Designation: F 1361-99

3. ASTM Standard Test Method for the Performance of Steam Cookers, Designation: F 1484-99

4. ASTM Standard Test Method for the Performance of Convection Ovens, Designation: F 1496-99

5. ASTM Standard Test Method for the Performance of Range Tops, Desig-nation: F 1521-96

6. ASTM Standard Test Method for the Performance of Double-Sided Griddles, Designation: F 1605-95

7. ASTM Standard Test Method for the Performance of Combination Ov-ens, Designation: F 1639-96

8. ASTM Standard Test Method for the Performance of Underfired Broil-ers, Designation: F 1695-96

9. ASTM Standard Test Method for the Performance of Single-Rack, Hot Water Sanitizing, Door-Type Commercial Dishwashing Machines, Des-ignation: F 1696-96

10. ASTM Standard Test Method for the Performance of Commercial Kitchen Ventilation Systems, Designation: F 1704-99

11. ASTM Standard Test Method for the Performance of a Pasta Cooker, Designation: F 1784-97

12. ASTM Standard Test Method for the Performance of Steam Kettles, Des-ignation: F 1785-97

13. ASTM Standard Test Method for the Performance of Braising Pans, Designation: F 1786-97

14. ASTM Standard Test Method for the Performance of Rotisserie Ovens, Designation: F1787-98

15. ASTM Standard Test Method for the Performance of Conveyor Ovens, Designation: F 1817-97

16. ASTM Standard Test Method for the Performance of Conveyor Dish-washing Machines, Designation: F 1920-98

17. ASTM Standard Test Method for the Performance of Pressure and Kettle Fryers, Designation: F 1964-99

18. ASTM Standard Test Method for the Performance of Deck Ovens, Desig-nation: F 1965-99

19. ASTM Standard Test Method for the Performance of Chinese Wok Ranges, Designation: F 1991-99

20. ASTM Standard Test Method for the Performance of Booster Heaters, Designation: F 2022-01

21. ASTM Standard Test Method for the Performance of Rack Ovens, Desig-nation: F2093-01

22. ASTM Standard Test Method for the Performance of Hot Food Holding Cabinets, Designation: F 2140-01

Introduction


23. ASTM Standard Test Method for the Performance of Hot Deli Cases, Designation: F2141-01

24. ASTM Standard Test Method for the Performance of Drawer Warmers, Designation: F2142-01

25. ASTM Standard Test Method for the Performance of Refrigerated Prepa-ration and Buffet Tables, Designation: F2143-01

26. ASTM Standard Test Method for the Performance of Large Fryers, Des-ignation: F2144-01

27. ASTM Standard Test Method for the Performance of Rapid Cook Ovens, Designation Pending.

28. ASTM Standard Test Method for the Performance of Conveyor Broilers, Designation Pending.

29. ASTM Standard Test Method for the Performance of Conveyor Toasters, Designation Pending.

30. ASTM Standard Test Method for the Performance of Blast Chillers, Des-ignation Pending.

Under development (or consideration) at the FSTC are test methods for over-fired broilers, salamanders, pre-rinse sprayers, powered pot washers, donut fryers, steam tables, food warmers, soft-serve ice cream machines, retherm ovens and a field test method for exhaust hoods.

Appliance cooking-energy efficiency is a measure of how much of the en-ergy that an appliance consumes is actually delivered to the food product during the cooking process. The ASTM test methods for measuring cooking appliance energy efficiency have been based on this fundamental definition and equations:

cooking-energy efficiency ⎯ quantity of energy imparted to the specified food product, expressed as a percentage of energy consumed by the appli-ance during the cooking event:

ηcookfood

appliance

EE

= × 100

where: ηcook = cooking-energy efficiency Eappliance = energy into the appliance Efood = energy to food = Esens + Ethaw + Eevap. where:

Appliance Energy Efficiency

Introduction


Esens = quantity of heat added to food product, which causes its temperature to increase from the starting temperature to the average bulk temperature of a “done” food product

= (Wi )(Cp )(Tf - Ti ) where:

Wi = initial weight of food product, lb (kg) Cp = specific heat of food product, Btu/lb, °F (kJ/kg, °C) Tf = final cooked temperature of food product, °F (°C) Ti = initial internal temperature of food product, °F (°C)

Ethaw = latent heat (of fusion) added to the food product, which causes the

moisture (in the form of ice) contained in the food product to melt when the temperature of the food product reaches 32°F (0°C)

= Wiw × Hf where: Wiw = initial weight of water in the food product, lb (kg), Hf = heat of fusion, Btu/lb (kJ/kg), and = 144 Btu/lb (336 kJ/kg) at 32°F (0°C).

Eevap = latent heat (of vaporization) added to the food product, which causes

some of the moisture contained in the food product to evaporate. = Wloss × Hv where:

Wloss = weight loss of water during cooking, lb (kg), Hv = heat of vaporization, Btu/lb (kJ/kg), = 970 Btu/lb (2256 kJ/kg) at 212°F (100°C)

Table 1-2 lists the benchmark cooking-energy efficiencies that were com-piled within the scope of this study. The cooking efficiencies are based on both measured and estimated performance of a cooking appliance under dis-crete full-load tests (e.g., oven) or full-load barreling tests (e.g., fryer) as de-scribed by the ASTM Test Methods. The source of the estimates are discussed in each appliance section. Of significance to this study's objective, are the relatively low efficiencies (e.g., 20 - 50%) for standard gas appli-ances. One would conclude that there is significant potential for raising the base efficiency of gas-fired cooking equipment.

It is important to recognize that cooking appliances are more efficient when they are cooking food at capacity (i.e., fully loaded). In the real world, appli-ances typically are not used to capacity for extended periods of time. Thus, part-load performance is an important parameter and has been incorporated within the ASTM testing procedures. Similar to other energy consuming equipment such as heat pumps or gas furnaces, the energy efficiency is re-duced under part-load operation. The amount of time that an appliance is left idling in a ready-to-cook mode also adds to the denominator of the real-

Introduction


kitchen energy efficiency equation. Neither the part-load performance nor the in-kitchen utilization are reflected by the efficiencies in Table 1-2. Alterna-tively stated, the real-world energy utilization efficiencies of gas cooking equipment are very low (e.g., 5 - 10%).

Table 1-2. Benchmark Cooking-Energy Efficiencya Summary.

Standard Gas High Efficiency Gas Electric

FRYER: Open Deep Fat 25 - 50 50 - 65 75 - 85 Pressure/Kettle 25 - 35 35 - 50 65 - 85 Flat Bottom 25 - 35 35 - 50 65 - 85

GRIDDLE 25 - 35 40 - 50 65 - 75

BROILER 15 - 30 35 - 65

RANGE TOP 25 - 30 45 - 60 65 - 85

WOK 15 - 30 50 - 70

OVEN: Std./Conv./Comb. 30 - 40 40 - 50 50 - 80 Deck 20 - 30 40 - 60 Conveyor 10 - 20 20 - 40 Rotisserie 20 - 30 50 - 60

COMPARTMENT STEAMER 30 - 40 60 - 80

STEAM KETTLE 40 - 60 80 - 95

BRAISING PAN 30 - 55 80 - 95 a Energy efficiencies are for full-load cooking scenarios

The ratio of energy consumption between a gas appliance and its electric counterpart is an energy performance parameter often used by the industry. Ratios of energy consumed by a gas appliance to its electric counterpart were reported by the Minnesota Study12 and subsequently reported by the Ameri-can Gas Association.13 However, these ratios were based on full-load cook-

Gas/Electric Consumption Ratios

Introduction


ing tests applied to one gas and one electric appliance in each equipment category. Table 1-3 presents the energy ratios published by AGA.

Table 1-3. AGA Published Gas/Electric Energy Ratios.13

Appliance

Energy Ratio Gas to Electric

Broiler 1.4 Braising pan 1.8 Fryer, standard 2.0 Fryer, pressure 2.3 Griddle, flat 1.4 Griddle, grooved 1.4 Oven, convection 1.5 Oven, deck 2.2 Range, hot top 2.0 Range, open burner 2.0 Steam kettle 1.7 Steamer, atmospheric 1.5 Steamer, pressure 2.1

Although this data provided an excellent tool for comparing gas and electric appliance energy consumption (and cost), the fact that the ratios were based on full-load testing generated an optimistic comparison for some of the equipment categories. This is because the efficiency of a gas appliance under part-load operation may be less than it is under full-load conditions. Fur-thermore, the AGA ratios do not consider the fact that an appliance in an ac-tual food service operation may spend much of its time idling or under light-duty operation.

The ratio of energy consumption between every gas and electric appliance combination in the same category is not a precise number⎯it can vary de-pending on the specific model of gas and electric appliance being compared and on the usage of the appliance in the commercial kitchen. It also is a func-

Introduction


tion of the technology incorporated in either the gas or electric unit (e.g., in-frared burners). For example, if one compares the least efficient electric grid-dle with the most efficient gas griddle, the energy consumption ratio will be lower (e.g., ratio = 1.5) than if one compares the most efficient electric grid-dle with the least efficient gas griddle (e.g., ratio = 2.5). However, a more representative ratio for all electric griddles compared to all gas griddles under typical real-world conditions may be somewhere in between (e.g., ratio = 2.0).

Estimates of real-world energy consumption ratios for gas and electric appli-ances are presented in Table 1-4 based on the average rate of energy con-sumption reported in the respective appliance sections. These average energy consumption rates were estimated using either an energy consumption model or typical appliance duty cycles estimated from available end-use monitoring data.

Table 1-4. Gas/Electric Energy Consumption Ratios.

Average Energy Consumption Energy Ratio Appliance Gas Electric a Gas/Electric

Deep-Fat Fryer 20 10 2.0 Griddle 23 10 2.3 Underfired Broiler 84 27 3.1 Range 48 17 2.8 Convection Oven 25 17 1.5 Compartment Steamer 32 17 1.9 Steam Kettle 50 27 1.9 Braising Pan 40 24 1.7

a Conversion Factor = 3.413 (kBtu/kWh)

Potential for Efficiency Improvements

Although the application of advanced technologies could improve the per-formance and energy efficiency of the existing stock of food service equip-ment, the application of existing technologies, such as insulation, improved

Higher Efficiency

Introduction


heat exchanger design, and enhanced control, may provide the greatest return over the short term.

Improved insulation. The addition of insulation around an appliance can reduce standby convective heat losses by as much as 25%. Some appliance groups such as ovens and steamers already incorporate some level of insula-tion, but many appliances do not. The addition of insulation is an inexpensive method for reducing stand-by losses and thereby improving light-load cook-ing-energy efficiency for appliances.

Improved heat exchanger design. The energy performance within each category or type of appliance varies significantly: first, depending on whether the appliance is gas or electric, and second, based on the applied heating technology. Due to the many possible arrangements of the combustion and heat exchanger systems, there are greater differences in efficiencies among gas appliances on the market than among electric appliances.

A major difference between high-efficiency and low-efficiency appliances is the effectiveness of their heat exchangers in transferring heat to the cooking surface, cavity or medium. This is especially pronounced in gas appliances that use indirect heating. It is estimated that improved heat exchanger designs could account for up to a 25% increase in cooking-energy efficiency for gas appliances. An example of this is the use of recirculation baffles on a gas fryer. Recirculation tubes, or recycle baffles, route the flue gasses through or around the sides of the frypot to provide a greater effective heat transfer sur-face for the hot gasses. More heat is transferred to the frying oil, yielding a 10% to 15% increase in efficiency.

Enhanced control. Appliances such as range tops and broilers are generally not amenable to timers or cooking computers, and therefore, controls for these appliances are typically simple. There is most often an infinite-control knob to regulate the input of each burner or element. The controls are cali-brated in terms of the percentage of input, as the burner does not generally sense the temperature of the cooking medium. “Smart controls” that sense the presence of cooking loads offer potential improvements to these types of appliances.

Introduction


Other appliances, such as fryers, griddles, and ovens, have the potential for more sophisticated controls. Quick service chains often specify elaborate “cooking computers” that sense time, temperature, and in some cases, rela-tive humidity. These computers give the user a high level of control over the cooking process by defining various temperature curves and different pro-grammable cooking cycles. The use of these controls allows for a more con-sistent food product and can reduce the energy consumption of the appliance. Another example is a control operation that provides a “soft landing” strat-egy. These controls reduce energy usage and improve cooking performance by minimizing overshoots of the desired temperature setpoint.

A commercial kitchen includes a great number of control systems, all operat-ing independently of each other, and with no oversight beyond the restaurant staff and management. This leads to increased energy consumption because appliances are often turned on when they are not being used and there is no feedback mechanism to alert the restaurant owner that energy is being wasted. The food service industry has been slow to adopt the types of centralized computer control systems typical in most other industrial processes because of the cost, complexity and lack of a standardized approach.

NAFEM Online Kitchen Protocol

In 1999, the National Association of Food Equipment Manufacturers (NAFEM) joined forces with a group of appliance manufacturers and the major chain restaurants to define an industry-wide approach to the imple-mentation of computer controls within the kitchen. The result of this on-line kitchen initiative was the publication of a standard data communications pro-tocol. This standard allows the appliance manufacturers to configure their individual control systems for easy communication with a centralized control program. The energy related benefits of the on-line kitchen include better documentation of energy consumption, real-time diagnostics of equipment energy performance, and hands-off appliance scheduling based on demand for the food product. Details are available on NAFEM’s web site at: www.nafem.org

Introduction


The next step in the industry-wide implementation of the on-line kitchen is industry education and promotion. This process includes working with the chain restaurants to quantify the energy benefits of the on-line kitchen so that they can justify the initial capital cost. It also involves educating the non-chain food service operators who have not been a part of this process to date. Both of these goals can be achieved through a process of seminars, presenta-tions, and demonstration projects. This protocol has major implications with respect to appliance R&D.

EPA Energy Star®

Possibly the greatest hurdle to improving the efficiency of commercial food service and refrigeration equipment is the lack of understanding (by both manufacturers and purchasers) of benchmark efficiency. If the buyer is not exposed to accurate efficiency data, there is less incentive on the part of the manufacturers to improve equipment performance. If the buyer does not real-ize that the most energy efficient appliance option may also be the best per-former, the hurdle is even more difficult to knock down. Significant energy savings have been achieved in residential refrigeration equipment, yet proven energy savings technologies have not been implemented in the commercial markets. The labeling of residential refrigeration equipment with its energy usage, utility incentive programs and the Energy Star® program has helped to promote the buying of energy efficiency residential refrigeration equipment. The goal is to parallel these accomplishments in the commercial food service sector.

The Food Service Technology Center has established a working relationship with the EPA team responsible for Energy Star® initiatives in commercial food service. Our role to date has been to provide “behind-the-scene” techni-cal support in establishing criteria to qualify commercial refrigerators and freezers for Energy Star®. Rachel Schmeltz, Energy Star® Program Manager was a speaker at the FSTC March 16 & 17, 1999 symposium on food service equipment⎯Investing in Performance⎯discussing EPA’s initial efforts with reach-in refrigerators and freezers. In September 2001, EPA announced En-ergy Star® for commercial refrigerators and freezers with seven participating

Introduction


manufacturers. This is the first appliance category within commercial food service to exhibit this distinction.

Strategies for expanding Energy Star® within commercial food service in-clude:

• Introducing Energy Star® for commercial food service equipment on an appliance-by-appliance basis, working with the proactive manufacturers (who have had equipment tested by the FSTC) within each category. The FSTC would facilitate kick-off meetings with manufacturers and stake-holders in each equipment category.

• Move strategically into commercial cooking equipment, utilizing the portfolio of ASTM Standard Test Methods developed by the FSTC. De-termine threshold efficiencies or energy saving criteria through the con-sensus of participating manufacturers. Start with appliances that the FSTC has a large database, manufacturer participation and/or energy sav-ing potential (e.g., gas fryers, insulated holding cabinets, compartment steamers, low-flow prerinse sprayers, exhaust hoods/fans). These effi-ciency criteria will provide a foundation for the EPA Energy Star® Pro-gram accelerating the development and purchase of energy efficient appliances and systems for commercial food service.

• On the whole-building concept, utilize FSTC benchmarking and energy efficient design experience (e.g., McDonald’s TEEM project) to establish criteria for Energy Star® labeling of restaurants.

Background

The need to exhaust heat and vapors associated with the operation of com-mercial cooking equipment directly impacts on the energy demand and con-sumption of food service facilities. It has been demonstrated that the HVAC load represents approximately 30% of the total energy consumed in a restau-rant.14 It has been further estimated15 that the kitchen ventilation system can account for up to 75% of the HVAC load and, as such, often represents the largest single-system, energy consumer in food service operations. However, commercial kitchen ventilation (CKV) systems are typically designed, in-

Ventilation Requirements

Introduction


stalled and operated with little consideration for energy efficiency. This can be attributed to the fact that designers are primarily concerned with the capa-bility of the CKV systems to capture, contain and remove cooking contami-nants, while the building owner’s goal is to minimize both the design and installed cost of the HVAC system.

The problem is compounded by the lack of comprehensive design informa-tion for commercial kitchens. Although the ASHRAE handbooks are recog-nized as a fundamental source of information for designing HVAC systems, these handbooks lacked any design information for ventilating commercial cooking equipment prior to 1995. Thus, many designers specified exhaust ventilation rates based on the more prescriptive code requirements or experi-ence. Although kitchen exhaust systems sized according to “rules-of-thumb” may be inadequate from the perspective of removing grease, odors and heat from the commercial kitchen⎯they may operate with a safety factor in ex-haust flow rate that significantly increases the energy burden and operating cost.

Influence of Model Codes

As discussed above, guidelines for kitchen ventilation systems have been influenced strongly by model codes such as the Uniform Mechanical Code, Uniform Building Code, and up to 1973, the National Fire Protection Asso-ciation (NFPA Standard No. 96), which list the required exhaust air quanti-ties according to the type, placement and face area of the exhaust hood (Figure 1-3). More recently, the International Mechanical Code (IMC) is having influence and is being adopted by more “authorities having jurisdic-tion” around the U.S. Fortunately, efforts of the CKV industry have success-fully impacted changes to the IMC that better reflect the results of recent research and consensus-based design practice. For example, the IMC now classifies cooking equipment as light duty, medium duty, heavy duty and extra-heavy duty from the perspective of exhaust requirements. The IMC also changed the prescriptive requirements from cfm/ft2 of open-hood area to cfm/linear foot of hood to be more consistent with manufacturers’ design guidelines and listings.

Introduction


�

Code Example: 4 ft. x 4 ft x 100 cfm/ft2 = 1600 cfm

Exahust ventilation rate based on 1per square foot of hood area. 1600 cfm

Listed Hoods It is important to recognize that a large percentage of the CKV systems being installed today are designed and operated below the code-specified ventila-tion rates for unlisted hoods. Many of the commercially available exhaust hoods have been listed in accordance with UL 71016 at airflow rates signifi-cantly below code (e.g., 300 cfm vs. 450 cfm per linear foot of hood for heavy-duty cooking) and are typically permitted by the “authority having jurisdiction.” The National Fire Protection Association's (NFPA) Standard 96 simply states, “exhaust air volumes for hoods shall be of sufficient level to provide for the capture and removal of grease laden vapors.”

An industry survey by the FSTC CKV research team suggests that 60 - 70% of the total installed base of kitchen hoods are listed hoods. Although there is general agreement within the industry that the exhaust rates dictated by code are excessive, there is no consensus regarding the potential for reduction in the design ventilation for UL-listed hoods. In fact, several manufacturers have suggested that their UL values may not be adequate for many applica-tions. However, based on actual performance data or experience, listed hoods can be applied at design levels that are above the listed capacity, but below the code specified capacity (Figure 1-4).

Figure 1-3. Prescriptive code re-quirement for unlisted hood.

Introduction


�

Example: 4 ft. x 200 cfm per linear ft. = 800 cfm

Exhaust ventilation rate based on labtory performance of custom hood desig800 cfm

Short-Circuit Hoods

A controversial issue relates to the performance of what are referred to as “short-circuit” exhaust hoods. Alternatively referred to as “compensating,” “no-heat,” or “cheater” exhaust hoods, such systems were developed in an attempt to reduce the amount of conditioned makeup air required by an ex-haust system designed to code. By introducing a portion of the required makeup air in an untempered condition directly into the exhaust hood itself, the net amount of conditioned air exhausted from the kitchen is reduced. Thus, the total exhaust capacity of the system will be able to meet conserva-tive design requirements while the actual quantity of makeup air that needs to be heated or cooled is minimized. But if less “net” exhaust air is adequate, why not simply design the exhaust system to ventilate the cooking equipment at a reduced rate in the first place. A good idea, but the short-circuit hood continues to propagate within the industry. And in actual installations, the amount of short-circuited air often reduces the net ventilation to the point where spillage of cooking effluent occurs (Figure 1-5), compromising the kitchen environment.

Figure 1-4. Engineered require-ments for listed hood (with side panels).

Introduction


Fortunately, one major proponent (manufacturer) of short-circuit hoods has redirected their marketing and design efforts towards exhaust-only systems over the last two years. The end of the short-circuit hood era is in sight!

ASHRAE Role

Technical issues and concerns related to kitchen ventilation have been dis-cussed at ASHRAE forums, seminars, symposia and technical sessions for a number of years. “Standing room only” attendance has been the experience at these kitchen ventilation programs. Although several technical committees (TC’s) have served as sponsors, the number of individuals on any TC with a major interest in kitchen ventilation has been limited, as is the scope of exist-ing TC's with respect to this topic. In an effort to focus ASHRAE's effort in this area, and to meet a perceived need of its membership, an ASHRAE tech-nical committee on kitchen ventilation (TC5.10) was finally established. The mission of this committee on kitchen ventilation is to address the needs of ASHRAE membership with respect to the energy efficient control, capture, and effective removal of airborne contaminants and heat resulting from the cooking processes. The technical scope includes the introduction of supply and makeup air as it influences the contaminant control process, and the thermal environment in the cooking space.

Figure 1-5. Short-circuit hood illus-trating potential for spillage.

Introduction


This committee recently developed a new handbook chapter on kitchen ventilation,17 a starting point for the designer of CKV systems. Unfortunately, there is still little guidance within the new handbook chapter with respect to the introduction of makeup air and the effect that a makeup air strategy will have on hood performance and/or energy consumption of the system⎯a subject of current research at the Wood Dale CKV lab funded by the California Energy Commission and coordinated by the FSTC.

There has been strong industry support of ASHRAE's involvement in kitchen ventilation, and a new Standard Project Committee, designated SPC 154P, is currently developing a Standard for Ventilation of Commercial Cooking Op-erations. The focus of the proposed ASHRAE standard will be towards opti-mizing the design and operation of the commercial kitchen ventilating systems with respect to system performance (e.g., capture and containment). Ultimately, the goal of the ASHRAE standard is to impact standardization of the mechanical codes across North America.

Exhaust Ventilation Rates

Exhaust flow rate requirements to capture, contain and remove the effluent vary considerably depending on the hood style, the amount of overhang, the distance from the hood to the cooking appliances, the presence and size of end panels, and the cooking equipment and food product involved. The hot cooking surfaces and product vapors create thermal air currents that are re-ceived or captured by the hood and then exhausted. The velocity of these cur-rents depends largely upon the surface temperature and tends to vary from 15 fpm (0.076 m/s) over steam equipment to 150 fpm (0.76 m/s) over charcoal broilers. The actual required flow rate is determined by these thermal cur-rents, a safety allowance to account for cross drafts and flare-ups, and a safety factor for the style of hood and configuration of makeup air system.

The approach ASHRAE takes is to categorize cooking equipment into four groups. While published equipment classification varies, and accurate docu-mentation does not exist, the following reflects the consensus opinion of the membership of ASHRAE TC 5.10 and is listed in Chapter 30 of the 1999 ASHRAE Applications Handbook17 as:

Introduction


1. Light duty, such as ovens, steamers, and small kettles (up to 400°F (204°C))

2. Medium duty, such as large kettles, ranges, griddles, and fryers (up to 400°F (204°C))

3. Heavy duty, such as upright broilers, charbroilers, and woks (up to 600°F (316°C))

4. Extra heavy duty, such as solid fuel-burning equipment (up to 700°F (370°C)).

Acknowledging that variance in product or volume could shift an appliance into another category, the exhaust flow rate requirement is based on the clas-sification of equipment under the hood. If there is more than one category, the flow rate is based on the heaviest-duty group, unless the hood design permits different volumes over different sections of the hood.

Listed hoods are allowed to operate at their listed exhaust flow rates by ex-ceptions in the model U.S. codes. Most manufacturers verify their listed flow rates by conducting tests per UL Standard 710.16 Minimum exhaust flow rates for listed hoods serving single categories of equipment vary from manu-facturer to manufacturer, but are typically as shown in Table 1-5.17 Actual exhaust flow rates for hoods with internal “short circuit” makeup air are typi-cally higher than those in Table 1-5, although the net exhaust (i.e., total ex-haust less short-circuit makeup air) may be similar.

Table 1-5. Typical Minimum Exhaust Flow Rates for Listed Hoods by Cooking Equipment Type.17

Type of Hood

Light Duty (cfm/linear ft)

Medium Duty (cfm/linear ft)

Heavy Duty (cfm/linear ft)

Extra Heavy Duty (cfm/linear ft)

Wall-Mounted Canopy

150 - 200 200 - 300 200 - 400 350 +

Single Island Canopy

250 - 300 300 - 400 300 - 600 550 +

Double Island Canopy (per side)

150 - 200 200 - 300 300 - 600 500 +

Eyebrow 150 - 250 150 - 250 --- --- Backshelf 100 - 200 200 -300 300 - 400 not recommended

Introduction


Radiant Heat Gain to Kitchen

Heat gain from commercial cooking appliances may have a major impact on the air conditioning load and thermal comfort of a commercial kitchen. To estimate heat gain for building design of a commercial kitchen, engineers currently use Table 8 in Chapter 26 of the ASHRAE Handbook of Funda-mentals.18

CKV Research

In parallel with the cooking appliance research conducted by the Food Ser-vice Technology Center, GRI and EPRI have funded separate commercial kitchen ventilation projects over the past decade. GRI’s project was centered at the AGA Research Commercial Kitchen Ventilation Research Laboratory in Cleveland, Ohio. EPRI’s Commercial Kitchen Ventilation Laboratory, formerly the McDonald’s Corporation Air Lab, is in Wood Dale, Illinois. In 1994 these two programs collaborated in a round of inter-lab testing to vali-date the standard test method that became ASTM F 1704-96, Standard Test Method for Performance of Commercial Kitchen Ventilation Systems.19 The FSTC coordinated the integration of research results from the two projects and the inclusion of new heat gain data in the ASHRAE handbook.20 The CKV facility, managed by Architectural Energy Corporation, is now under the umbrella of the Food Service Technology Center program. The AGA Re-search facility has been decommissioned.

The Wood Dale CKV Lab applied a focusing schlieren flow visualization system to assess the capture and containment performance of hoods and ap-pliances (Figure 1-6).21 The schlieren flow visualization system is a major breakthrough for visualizing thermal and effluent plumes from hot and cold processes, particularly in food service. The word “schlieren” means “smear” in German; the optical effect encompassed by the word is best illustrated by the wavy visual pattern that can be seen in the exhaust stream of jet aircraft or over a hot asphalt parking lot during the summer. The system at the CKV lab is sensitive enough to detect the warm air coming off a person’s body.

Introduction


The schlieren flow visualization system allows non-intrusive investigation of hot air flow in real-time based on the refractive index dependency of air on temperature. Air in and surrounding the thermal plume from a cooking appli-ance changes its mass density and thereby its dielectric constant with tem-perature. This change in dielectric constant results in a change in refractive index, causing schlieren effect. Figure 1-7 shows still photos of a test condi-tion. However, one of the real advantages of this flow visualization technique is the ability to document the dynamic flow patterns on videotape.

Hood

Range Top(side view)

Capture andContainmentat 220 cfm/lf

Hood

Range Top(side view)

Spillageof Plume

at 165cfm/lf

Figure 1-6. CKV hood testing. Photo: Architectural Energy Corp.

Figure 1-7. Schlieren example.

Introduction


Figure 1-8 presents thresholds of capture and containment (C&C) for differ-ent types of gas and electric cooking appliances determined using such flow visualization techniques in accordance with the new ASTM test method.21 Each appliance was individually operating under a 5-foot (wide) by 4-foot (deep) wall mounted canopy hood. Makeup air for this exhaust-only hood configuration was supplied in non-obtrusive fashion from the far side of the laboratory. The C&C threshold flow rate was determined for a heavy-load cooking condition and under an appliance “idle” or standby condition as re-ported by the CKV lab in an ASHRAE paper.22 As illustrated, there are sig-nificant differences between appliance types. In some cases, there are notable differences between fuel source and/or appliance usage (e.g., idle vs. cook-ing). It is important to note, however, that the comparison is based on one gas and one electric appliance in each category.

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Figure 1-8. Thresholds of capture and containment for a 5-ft wall-canopy hood.21

Introduction


Conservation Potential

Although the opportunities for energy conservation and load management in CKV are large, the lack of publicly documented lab and field data has made achieving savings difficult. The FSTC estimates the connected kitchen venti-lation exhaust capacity in the United States to be in the range of 2.5 to 3.0 billion cfm. Table 1-5 shows a summary by industry segment. Data published by Cahners Bureau of Foodservice Research shows that an estimated total of 737,000 food service facilities were in operation in 1992. The per unit ex-haust volumes are estimates based on collective design experience and knowledge of installed systems by the authors. Note that the Canadian con-nected capacity is approximately 10% of the U.S., or 300 million cfm.

Total savings should range between 30% and 40%, with some facilities as high as 60%. Total cost savings across the industry could range from $1.0 to $1.5 billion per year. A reduction in CKV rates will improve energy effi-ciency in restaurants, lower restaurant demands (often at system peak hours), reduce capital construction costs by decreasing the size of installed HVAC equipment, and have a positive impact on the environment by reducing utility loads at the source and reducing effluent discharged from CKV systems to the atmosphere.

Table 1-6. Estimate of Ventilation Volumes by Facility Type in the U.S.

Industry Segment

Number of Units

Estimated Exhaust Per Unit (cfm/unit)

Total Exhaust (Million cfm)

Fast Food 180,125 3,000 540 Full Service 196,250 6,000 1,177 Educational 92,460 3,500 319 Health Care 63,730 3,500 219 Grocery & Retail 106,425 600 67 Lodging, Rec. 64,875 4,300 281 Other 33,300 4,400 146 Grand Totals 737,165 3,700 2,749

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Introduction


For example, 100 to 150 fpm (0.51 m/s to 0.76 m/s) face velocity is usually required, but levels as low as 50 to 75 fpm (0.25 m/s to 0.38 m/s) have been shown to be satisfactory 22 An experimental study23 published by ASHRAE reported that for wall and island canopies, only 40 to 50% of the normal de-sign flow was required to provide satisfactory capture of smoke generated at any location on or beside the cooking surfaces (Figure 1-3). These studies are consistent with research and development conducted by the McDonald’s Corporation.24 In general, their laboratory-based hood design and sizing pro-cedures have allowed them to install exhaust systems that operate at an ex-haust ventilation rate that is significantly less (e.g., 50%) than specified by model codes such as the International Mechanical Code (IMC).

In addition to the energy/load management benefits that can be achieved through a direct cfm reduction in exhaust capacity, significant benefits can be realized through integrated HVAC design strategies, engineered equipment, and enhanced system control and operation. Optimizing systems and operat-ing strategies for foodservice facilities during retrofit and new construction will present additional opportunities that will not be at the expense of cus-tomer or employee comfort.

A simplified schematic of CKV system optimization is illustrated in Figure 1-9, where the target conservation and load management goals are realized through the development of new design guidelines and supporting changes to codes.

Commercial Kitchen

Ventilation (CKV)

Research & Testing

ASHRAE Standard 154P on the Ventilation of Commercial

Cooking Operations (1998)

Impact Model Mechanical Codes

(1998 - 2000)

Industry-Wide Application of

Optimized CKV Systems

Develop Comprehensive Design Guidelines for

CKV Systems Update Appliance Heat Gain

Data in ASHRAE Handbook

(1997)

Figure 1-9. Impact of CKV research on design guidelines.

Introduction


Kitchen Ventilation Research/Utility Market Needs

The optimum design and operation of kitchen ventilation systems presents a great opportunity for reducing energy consumption and improving the work-place environment within commercial food service operations. However, the development of comprehensive design guidelines for commercial kitchen exhaust ventilation systems that would complement the new ASHRAE Handbook chapter, but targeted towards geographical or regional areas in the U.S. and Canada, is needed. Utility industry R&D efforts should focus on optimizing appliance/hood systems that will reduce both ventilation require-ments and kitchen heat gain.

Clean Air Act

The Clean Air Act (CAA), first enacted by the U.S. Congress in 1967, over-sees and regulates the impact of environmental stresses imposed by indus-tries in the U.S. Most importantly, it facilitates the establishment and implementation of air pollution standards at federal and state levels. The En-vironmental Protection Agency (EPA) established the national ambient air quality standards (NAAQS) to define the specific levels of air quality that must be achieved for health reasons.

Air Quality Management Districts

The enforcement of the Clean Air Act in the U.S. has been delegated to local government regulatory agencies called Air Quality Management Districts (AQMD's). In areas of non-compliance with the CAA, the AQMD's were first created by state legislation. These local agencies were then mandated to develop strategies to control polluting sources and provide necessary re-sources to enforce the requirements of the CAA in daily industry operation.

The South Coast Air Quality Management District (SCAQMD) has jurisdic-tion over the four-county Los Angeles basin that is one of the most severe non-attainment areas in the United States for PM10 (particulate matter less than 10 microns in diameter) and ozone. The combination of severe air pollu-tion and earlier EPA concerns over charbroiling operations gave rise to the

Emissions from Commercial Cooking

Introduction


first local regulation of restaurant emissions through Rule 219—a regulation requiring permitting of underfired broilers by SCAQMD. This regulation regulated underfired broilers for smoke and odor. This legislation, although still in effect, will be displaced by the more comprehensive Rule 1138 when it is enacted.

Restaurant Emissions

The argument is not that commercial cooking processes contribute to urban air pollution. What is being debated is just how much of the pollution is actu-ally coming from restaurants and, furthermore, from which restaurants it is coming.

The variation in the types of restaurants, the diversity of menus and appli-ances, and the lack of consensus-based methods for measuring emissions from cooking processes

25 challenge the South Coast Air Quality Manage-

ment District (SCAQMD) as they try to implement legislation that will re-duce the contribution to air pollution from the food service industry in the Los Angeles basin. We can be assured that urban centers with increasing air pollution in both the U.S. and Canada are closely watching California.

A 1994 research report26 takes a macro look at the picture, concluding that meat cooking contributes to 17% of the total carbonaceous aerosol emissions in the Los Angeles basin. It also was reported27 that people in the United States consumed about 40% of their meat (including beef, port, lamb, poultry and seafood) in restaurants. If this ratio held true for California, a gross cal-culation would imply that 17% x 0.4 = 7% of the Los Angeles pollution was due to cooking meat in restaurants.

SCAQMD Restaurant Rule. RULE 1138. CONTROL OF EMISSIONS FROM RESTAURANT OP-ERATIONS http://www.aqmd.gov/rules/html/r1138.html

Applicability: This rule applies to owners and operators of commercial cooking operations preparing food for human consumption. The rule requirements currently ap-

Introduction


ply to chain-driven charbroilers used to cook meat. All other commercial res-taurant cooking equipment including, but not limited to, underfired char-broilers may be subject to future rule provisions.

Requirement: No person shall operate an existing chain-driven charbroiler on and after No-vember 14, 1999 unless it is equipped and operated with a catalytic oxidizer control device, and the combination charbroiler/catalyst has been tested in accordance with the test method specified in subdivision (g) and certified by the Executive Officer. Other control devices or methods may be used, if found, in accordance with the test method specified in subdivision (g), to be as or more effective than the catalytic oxidizer in reducing particulate matter (PM) and volatile organic compounds (VOC) (as defined in Rule 102) emis-sions and certified by the Executive Officer.

Exemption: • Exemption permit will be issued to those cooking less than 875 lb of

meat per week. • Demonstrate emissions from the automated charbroiler is less than 1

lb/day.

Emission Measurement. SCAQMD currently recognizes a modified EPA test method designated Method 5.1, Determination of Particulate Matter Emissions from Stationary Sources Using a Wet Impingement Train and a modified EPA test method designated Method 25.1, Determination of Total Gaseous Non-Methane Organic Emissions as Carbon.

Grease vapor and aerosols—the constant in restaurant emissions—represent a big part of the challenge as the standard industry test methods are applied to the restaurant exhaust stream. Of the two protocols, Method 5.1 for PM has demonstrated the best repeatability when emission measurements from the same cooking process are replicated. Method 25.1 continues to challenge researchers and source testing experts as they apply this test method to cook-ing effluent.

Introduction


Characteristics of Cooking Effluent. The composition of the effluent from different food products being cooked on different types of equipment varies significantly. Furthermore, the composition of a specific food product itself may impact the composition of emission (e.g., 20% versus 30% fat content hamburger patties). A primary component (particularly the visible part) may include fly ash and smoke from the combustion of grease and solid fuels. But grease, existing as both an ultra-fine aerosol and a vapor, is a major compo-nent of the emission plume from a meat cooking process.

Best Available Control Technology (BACT). Control strategies that are considered candidates for reducing restaurant emissions include:

• Electrostatic precipitators (ESPs) • High efficiency filtration/adsorption • Catalytic converters • Scrubbers • Afterburners • Any type of filtration equipment that reduces emissions • Change in the cooking process/equipment

The pollutant-removal efficiency of such devices and strategies, when ap-plied to restaurant exhaust, is not well documented. At this time, no consen-sus-based standard test methods exist for rating the performance of grease extraction or emission control equipment.

Depending on the design and size of the kitchen exhaust ventilation system, installed cost for the emission control package may range from $10,000 to $100,000, with little known about maintenance or durability. The more one pays for the equipment, the better one can expect it to work. But the cost of installing and maintaining an “industrial strength” air cleaning system that will do the job for the next 20 years may be much higher than the restaurant operator is prepared to spend. The food service consultant or engineer faced with specifying such equipment have their work cut out when they take on the design of a new facility where the “authority having jurisdiction” is de-manding emission control.

Introduction


Prognosis

The Restaurant Rule has become a reality in Southern California for restau-rants using chain (conveyor) charbroilers. AQMD's in other areas that are in non-compliance with EPA's threshold limits for emissions may adopt similar legislation. High-volume restaurants using underfired broilers will be the next target for legislation.

On the longer term, exhaust ventilation systems with integrated emission control may become standard equipment for restaurants doing business in urban areas in the U.S. and Canada. The reality is that ventilating and con-trolling emissions from cooking equipment will become an integral cost of doing business in what is becoming a much more technically sophisticated industry.

Appliance energy performance data, which can help a utility implement suc-cessful energy conservation initiatives, also can effectively serve a utility's interests as it pursues market retention or expansion in the restaurant sector. The better one understands “how” a cooking appliance or process “per-forms,” the better one's position with respect to marketing the “use” of that appliance or process.

Overall recommendations include:

• Continuing commercial appliance testing programs (e.g., FSTC) that can be used to further benchmark energy performance in direct support of R&D projects for commercial cooking equipment.

• Using benchmark performance data as justification, developing an indus-try strategy that will influence the purchase-decision criteria so that cus-tomers will specify more energy efficient equipment.

• Developing and sponsoring training courses and workshops for the food service and utility industries based on this appliance technology review.

• Initiating research and development projects that will deliver the greatest return for R&D dollars invested (i.e., that achieve the largest efficiency gain for the largest percentage of equipment installed in food service fa-cilities). The R&D focus needs to be on improving part-load perform-

Conclusions

Introduction


ance of gas cooking equipment and reducing the cost premium associated with producing more efficient equipment. New equipment needs to be compatible with the NAFEM Online Kitchen Protocol.

• Collaborating with European utilities and research groups (such as Gaz de France) on appliance R&D initiatives.

• Developing a web-based appliance efficiency directory reporting data acquired through testing in accordance with the ASTM Standard Test Methods for evaluating the performance of commercial cooking equip-ment. Initially, such a directory would rely extensively on the efficien-cies reported by FSTC and cover a fraction of the cooking equipment on the market. However, such an initiative would increase awareness in the industry, hence stimulate manufacturers to have their equipment tested in accordance with the ASTM test methods in other U.S. and Canadian laboratories. A natural extension is promoting Energy Star® as a volun-tary labeling program.

Introduction


1. Rahbar, S., Fisher D. et. al. 1996. Technology Review of Commercial Food Service Equipment. Final Report. May.

2. Pieretti, G., Blessent, J., Kaufman, D., Nickel, J., Fisher, D., 1990. Cooking Appliance Performance Report - Pacific Gas and Electric Company Production-Test Kitchen. Pacific Gas and Electric Company Department of Research and Development Report 008.1-90.8, May. This reference encompasses appliance performance reports subsequently published by Pacific Gas and Electric Company and the Food Service Technology Center (individual reports are cited in each appliance sec-tion of this report).

3. Arthur D. Little, Inc., 1993. Characterization of Commercial Building Appliances. Prepared for U.S. Department of Energy, ADL Reference No. 42520, June.

4. Kaufman, D.A., Fisher, D.R., Nickel, J. and Saltmarch M., 1989. Devel-opment and Application of a Uniform Testing Procedure for Griddles. Pacific Gas and Electric Company Department of Research and Devel-opment Report 008.1-89.2, March.

5. Conner, M. M., Young, R., Fisher, D.R. and Nickel, J., 1991. Develop-ment and Application of a Uniform Testing Procedure for Fryers. Pa-cific Gas and Electric Company Department of Research and Development Report 008.1.89.2, November.

6. Blessent, J., 1994. Development and Application of a Uniform Testing Procedure for Convection Ovens. Pacific Gas and Electric Company Department of Research and Development Report 008.1-94.12, May.

7. Young, R., 1994. Development and Application of a Uniform Testing Procedure for Range Tops. Food Service Technology Center Report 1022.95.20, October.

8. Selden, M., 1995. Development and Application of a Uniform Testing Procedure for Steam Cookers. Food Service Technology Center Report 1022.95.19, April.

9. Zabrowski, D., 1997. Development and Validation of a Standard Test Method for Underfired Broilers. Food Service Technology Center Re-port 5011.97.48, December.

10. Zabrowski, D., 1999. Development and Validation of a Standard Test Method for Rotisserie Ovens. Food Service Technology Center Report 5011.99.66, September.

11. Knapp, S., 1999. Development and Validation of a Standard Test Method for Pasta Cookers. Food Service Technology Center Report 5011.99.53, September.

12. Snyder, O.P., Thompson, D.R. and Norwig, J.F., 1983. Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study. University of Minnesota, March.

References

Introduction


13. American Gas Association, 1989. Commercial Kitchens.

14. Claar, C.N., Mazzucchi, R.P., Heidell, J.A., The Project on Restaurant Energy Performance (PREP) - End-Use Monitoring and Analysis, Pre-pared for the Office of Building Energy Research and Development, DOE, May 1985.

15. Fisher, D.R., Increasing Profits by Optimizing and Controlling Kitchen Exhaust Ventilation, a seminar program developed for Energy Mines, and Resources Canada, 1986.

16. UL. 1990. Standard for Safety Exhaust Hoods for Commercial Cooking Equipment, 4th ed. Standard 710-90. Underwriters laboratories, Northbrook, IL.

17. 1999 ASHRAE Applications Handbook. Chapter 30 on Kitchen Ventilation.

18. ASHRAE 1993. Handbook of Fundamentals, Chapter 26, Nonresiden-tial Air-Conditioning Cooling and Heating Load.

19. American Society for Testing and Materials, 1996. Standard Test Method for the Performance of Commercial Kitchen Exhaust Systems, ASTM Designation 1704-96. In Annual Book of ASTM Standards, West Conshohocken, PA.

20. Fisher, D.R. New Recommended Heat Gains for Commercial Cooking Equipment. ASHRAE Transactions. V. 104. Pt. 2.1998.

21. Swierczyna, R.T., Smith, V.A., Schmid, F.P. New Threshold Exhaust Flow Rates for Capture and Containment of Cooking Effluent. ASH-RAE Transactions 1997. V. 103. Pt. 2.

22. Giammer, R.D., Locklin, D.W., Talbert, S.G., Preliminary Study of Ven-tilation Requirements for Commercial Kitchens, ASHRAE Journal, 1971.

23. Talbert, S.G., Flanigan, L.B., Fibling, J.A., An Experimental Study of Ventilation Requirements of Commercial Electric Kitchens, ASHRAE Transactions, 1973.

24. Soling, S.P., and Knapp, J., Laboratory Design of Energy Efficient Ex-haust Hoods, ASHRAE Transactions, 1985.

25. Gordon, E., .Kam, V. and Parvin, F. Topical Paper: Emissions from Commercial Cooking Operations and Methods for Their Determination. American Gas Association Laboratories, December 1994.

26. Hildemann, L.M., Kilnedinst, D.B., et al., Cass, G.R. Sources of Urban Contemporary Carbon Aerosol. Environmental Science and Technol-ogy, Vol 28, N0. 9, 1994.

27. Raloff, J. Cholesterol: Up in Smoke; Cooking Meat Dirties the Air More Than Most People Realize. Science News, Vol 140, July 1991.

2 Fryers


Fried foods continue to be popular on the restaurant scene. French-fried pota-toes are still the most common deep-fried food, along with onion rings, chicken and seafood. The fryer menu has expanded to include various deep-fried snacks such as mushrooms, zucchini, peppers and mozzarella cheese. Equipment manufacturers have responded by designing fryers that operate more efficiently, quickly, safely and conveniently.

Fryers are available in a range of configurations. The kettle, or “frypot”, may be split into more than one vat, allowing the operator to prepare different foods without flavor transfer. Some fryers have automatic lifts that lower and raise food baskets. Fryers may have built-in filters that greatly reduce the labor and risk involved in filtering hot oil. Fryers may be countertop units, freestanding floor units, and in batteries of several fryers in one housing.

All fryers share a common basic design. The kettle contains a sufficient amount of oil so that the cooking food is essentially supported by displace-ment of the oil rather than by the bottom of the vessel (Figure 2-1). The oil is typically heated by atmospheric or infrared gas burners underneath the kettle or in “fire tubes” that pass through the kettle walls. Electric fryers use heat-ing elements immersed in the oil. Energy inputs range from 30-260 kBtu/h for gas fryers and 2-27 kW for electric fryers.

Fryers range in capacity from about 15 lb (7 kg) of oil for a small, countertop fryer to over 200 lb (90 kg) of fat for the largest floor-model fryers used for donuts and chicken. Most fryers have a “cold zone” at the bottom of the ket-tle where breadcrumbs and other food particles settle. The cold zone is in-tended to have no convection current and a relatively low temperature, so that food crumbs will not carbonize and create the breakdown products that limit oil life.

A console fryer is pictured in Figure 2-2. The fryer on the right has a split vat; both have automatic basket lifts. The center is a fry station, for holding

Introduction

Figure 2-1. Standard open deep- fat fryer. Photo: Pitco Frialator, Inc.

Fryers


cooked product. In the cabinet below the fry station there is a built-in oil fil-ter, which both fryers share.

Fryers are most often compared on the basis of width and energy-input rat-ing. Taken together, these two numbers suggest the approximate amount of food a fryer can prepare in a given time, which is one of the most important factors in choosing the proper fryer for a kitchen. The energy cost of operat-ing a fryer can be significant, and different fryers can have quite diverse pat-terns of energy use. However, fryer-energy use has not been documented until recently, and as a result, initial cost generally plays a more significant role in appliance purchasing than the operating cost.

Frying is a process of heating and dehydration. The food product is sub-merged in the oil, which transfers heat into the food. Moisture in the food is vaporized and forces its way to the food surface. The outside of the food, in addition to being browned by the heat of the oil, is puffed and crisped by this rapid moisture loss. Departing steam increases convection of the hot oil as it rises to the surface of the frypot; this convection and the high oil temperature cause the uniform and rapid cooking that is characteristic of frying.

Figure 2-2. An example of a console fryer. Photo: Vulcan-Hart Company

Cooking Processes

Fryers


Fryers may take as little as ten to fifteen minutes to preheat, but they are typically turned on in the morning and left on throughout the day. Some op-erators use a backup fryer that is turned on as needed to handle increased demand during busy periods. Even in a busy fast-food restaurant, fryers may be idle 75% of the time.

Open Deep-Fat Fryers

Open deep-fat fryers are by far the most common type. As distinguished from pressure fryers, open fryers do not have a sealed lid on the kettle and cook at atmospheric pressure. The frypot is not generally insulated, and can lose heat from both the surface of the oil and from the sides of the fryer cabi-net. Open fryers are used to prepare all types of fried food.

Pressure Fryers

Pressure fryers are less common. They are mainly used for cooking chicken, and are said to reduce moisture loss and oil uptake. The pressure fryer is similar to an open-kettle fryer, but with the addition of a heavy, gasketed lid and a pressure valve. As steam escapes from the food and builds up above the oil, the pressure inside the kettle rises. Moisture in the food reaches higher temperatures before escaping into the kettle, and the cook time is somewhat decreased. Most pressure fryers have a heavy top and a round flat-bottomed kettle, like the unit pictured in Figure 2-3.

Pressure fryers do incur some additional labor. Because of the locking lid, there are currently no pressure fryers with an automatic basket lift option. Opening and closing the lid adds extra steps to the cooking cycle and par-tially offsets the advantage of a shorter cook time. Product cannot be checked part way through the cycle, although this is not generally a problem with standardized recipes and procedures.

Specialty Fryers

Most specialty fryers have a rectangular or circular kettle with a deep cold zone at the bottom below the heat source. Specialty fryers include donut and

Types of Fryers

Figure 2-3. Pressure fryer. Photo: Ballantyne

Fryers


chicken fryers, which are generally wide and shallow to allow a layer of food to float as it cooks. Instead of a standard fry basket, chicken and fish are gen-erally lowered into the oil on a screen or shallow basket that is the same size as the top of the kettle. Donut fryers may have an upper “submerger” screen to immerse certain types of donuts during frying. A typical donut fryer is il-lustrated in Figure 2-4.

Fryers are thermostatically controlled, and generally have an over-limit switch to cut off energy to the burners or elements if the oil approaches its ignition point. Some fryers have a special “melt cycle”, which toggles the burners on and off to melt solid shortening without becoming hot enough to scorch and burn it.

Thermostats sense the oil temperature with either a bulb or a solid-state sen-sor. Bulb-type sensors use a working fluid, which expands when heated, closing a valve or electrical contact. Solid-state sensors use a thermocouple to detect oil temperature and are more durable and accurate, but more expen-sive than bulb-type sensors.

Frying computers, or compensating timers, adjust the cook times in response to average-oil temperature. They also have the potential to regulate fryer in-put to maintain a consistent “cooking curve” and provide more consistent product.

The energy performance within each category or type of fryer varies signifi-cantly; first, depending on whether the fryer is gas or electric, and second, based on the applied heating technology. Due to the many possible arrange-ments of the combustion and heat-exchanger systems, there are greater dif-ferences in performance among gas fryers on the market than among electric fryers.

The usage of a fryer from one food service operation to another also impacts its energy efficiency and consumption. Both gas and electric fryers are less efficient under part-load operation due to the increased effect that the heat loss from the fryer has on its efficiency. Gas fryers lose even more due to the part-load efficiency penalty that is characteristic of gas burners. Fryers also

Controls

Figure 2-4. Donut fryer. Photo: Pitco Frialator, Inc.

Heating Technologies

Fryers


spend a significant portion of their operating time in stand-by or idle mode. Under such conditions, the energy efficiency of a gas fryer drops even further due to the short duty cycle of the burners. Under idle conditions, the energy consumed by a gas fryer may exceed an electric fryer’s energy consumption by a factor of three or more.1

Gas

Gas fryers can be separated into three categories: standard, mid-range and high efficiency. Standard gas fryers (the more common of the three) are de-signed with atmospheric or “blue-flame” burners with simple heat exchang-ers that either run through the frypot or underneath it. Mid-range gas fryers are fryers that employ an atmospheric burner with a heat-exchanger design that allows more heat to be imparted to the oil than a typical straight-through design (Figure 2-5) by restricting the flow of the hot flue gasses. High-efficiency gas fryers take advantage of new developments in gas technology, such as infrared (IR) burners, heat pipes, pulse combustion, powered burners, and recirculation tubes.

Advanced Gas Fryer Technologies

A wide bandwidth exists among gas fryer efficiencies. Typically, burners fire into the tubes from the front towards the flue at the rear of the fryer. The tubes may contain catalysts or baffles to increase heat transfer. Infrared burn-ers also may be mounted inside fire tubes. At the high end, various new tech-nologies are incorporated into fryer design, yielding more efficient fryers with greater productivity. Among the new technologies already in place are infrared (IR) burners, powered burners, recirculation tubes, and frypot insula-tion.

Infrared Burners. Infrared burners employ a fine honeycomb matrix to evenly disperse the fuel/air mixture across the burner surface. Combustion takes place close to the burner surface, causing it to become red-hot (ap-proximately 1,800°F (980°C)) and emit infrared radiation to the surrounding heat-transfer-tube walls. In addition to the increased rate of heat transfer, IR burners operate with little excess air (less than 10%), allowing a greater per-

Figure 2-5. Fire tubes in the vat of a gas fryer. Photo: Fisher-Nickel, inc.

Fryers


centage of gas to be burned than in a conventional atmospheric burner. Due to their potentially high first cost and maintenance cost, IR burners represent only 5% to 10% of the gas fryers in the marketplace.

Powered Burners. Powered burners employ a blower to force the fuel/air mixture into the burner at the optimum ratio. Like infrared burners, powered burners operate with little or no excess air, allowing a greater percentage of the energy generated by combustion of gas to be transferred to the frypot.

Recirculation Tubes. Recirculation tubes, or recycle baffles, route the flue gasses through or around the sides of the frypot to provide a greater effective heat-transfer surface for the hot gasses. More heat is transferred to the frying oil, yielding a 10% to 15% increase in efficiency. More restrictive designs require a blower to pull the flue products through the heat exchangers.

Pulse Combustion. Pulse combustion is a technology adapted from high- efficiency boilers. The process is essentially a series of controlled explosions at a rate of 40 to 60 times a second. A forced-draft blower initially delivers the fuel/air mixture to the combustion chamber, where it is ignited by a spark plug or glow coil. Once the combustion chamber heats up, the process be-comes self-perpetuating and no longer requires the ignition device. The ad-vantage of this technology is that it allows the use of a compact, highly efficient heat exchanger to deliver heat to the frying oil. This technology was found to be too expensive to market successfully. Currently, no manufactur-ers are producing pulse combustion fryers.

Convection/Thermal Fluids. Thermal fluids enable the use of an enclosed, highly efficient burner, independent of fryer design. Specially formulated oil acts as a medium to transfer heat from the burner to the frypot. Inefficiencies in the heat transfer to the thermal fluid and the requirement of a specialized pump to circulate the fluid make this a less attractive possibility.

Heat Pipe. Heat pipes are enclosed tubes that connect the heat source to the frypot. The tubes are filled with a working fluid that vaporizes at the heat-source end and condenses at the end connected to the frypot. This technology requires extremely tight tolerances and was found to be too expensive to suc-cessfully market. As such, there are no heat-pipe gas fryers available on the market.

Fryers


Electric

Electric fryers typically use immersed elements in the frypot to provide heat to the frying oil. New developments in element design and controls are be-ginning to change the landscape of the electric fryer market.

Advanced Electric Fryer Technologies

Induction Heating. Induction fryers use electromagnetic coils inside stainless steel immersion tubes. The electromagnetic fields created by these coils induce eddy currents in the surrounding metal, causing it to heat up. The amount of heat generated is controlled by changing the frequency of the magnetic field in the coils. Although an induction-based fryer was introduced in the U.S. in the early nineties, the manufacturer has ceased production and there are currently no induction fryers on the market.

Frypot Insulation. Insulation around the frypot reduces standby convective heat losses by as much as 25%. Frypot insulation is currently being applied to a few high-end electric fryers. Apparently, manufacturers do not currently insulate their gas fryers due to safety limitations.

Low Watt-Density Elements. Low watt-density elements provide an even distribution of heat to the frying oil by spreading the power across a greater surface area than standard cal-rod elements. This enables the elements to provide quick temperature recovery without scorching the frying oil. Low watt-density elements are used in many electric fryer designs.

Triac Controls. TRIAC controls provide a high current electricity supply to the elements without the use of a mechanical contactor. The controller works in conjunction with a resistive thermal device (RTD) to modulate power to the elements during preheat and frying-oil recovery. The TRIAC controller provides an effective option for modulating power to the elements of a fryer.

The work of the fryer can be outlined as bringing the oil from room tempera-ture up to cooking temperature (preheating), holding the oil at cooking tem-perature until cooking begins (idling), and restoring heat to the oil when cold food is dropped into the fryer (recovery).

Fryer Performance

Fryers


An ASTM standard test method for fryers2 developed at the Food Service Technology Center in California now allows manufacturers and users to gauge fryers’ production directly, and to evaluate fryer-energy performance as well. As hard data on fryers becomes available, it is apparent that certain technologies and designs yield better performance.

Fryer performance is characterized by preheat time and energy consumption, idle energy consumption rate, pilot energy consumption rate, cooking-energy efficiency and production capacity.

Energy Input Rate

Energy input rate is one of the performance characteristics usually included in product literature. It is the maximum rate at which the fryer draws energy, expressed in kBtu/h or kW. Energy input rate is an important factor in pro-duction capacity. The more energy a fryer can deliver to the oil, the faster it can preheat and recover between loads. However, efficiency also plays an important part. A very efficient fryer may be able to supply more energy to the oil while requiring less input than an inefficient fryer with a higher en-ergy input rate.

Preheat

Preheat Time. Preheat time is the time required to raise the oil from room temperature to cooking temperature (typically 350°F (175°C)). Fryers are usually left on during the day, so preheat time may not be important to the operator. Preheat time is determined by energy input rate, oil capacity, heat-ing technology and control strategy.

Preheat Energy. The energy required to preheat a fryer is a function of the oil capacity of the fryer and its heat-up efficiency. However, preheat energy consumption represents less than 15% of the daily energy consumption for a fryer that was turned on twice over an 8-hour operating period.3 For longer fryer operations (e.g., 16 hours) with only one preheat, the energy perform-ance of the fryer during this phase of its operation becomes less important.

Fryers


Idle Energy Consumption

Both gas and electric fryers consume energy while maintaining the frying medium at the desired cooking temperature. This is due to the heat that is lost from the surface of the oil and through the sides and bottom of the frypot. The idle-energy consumption rate is a function of the thermostat setpoint and the effective resistance of the fryer to heat loss. Figure 2-6 illustrates more than a three-to-one range in idle energy rates for 14-inch (350 mm), open deep-fat gas fryers.3-13

0

2

4

6

8

10

12

14

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Monitoring the usage of fryers in commercial kitchens14 has demonstrated that fryers spend a significant proportion of their “on time” in idle mode and that the rate of idle energy consumption has a significant impact on total daily energy consumption.

Cooking Energy Rate and Efficiency

Cooking energy rate is the rate at which a fryer consumes energy while it cooks a load of food product. It is reported in kBtu/h or kW. Cooking-energy

Figure 2-6. Gas fryer idle rates.

Fryers


efficiency is the ratio of energy added to the food and total energy supplied to the appliance during cooking:

CookingEfficiency EE

Food

Appliance= × 100%

The ASTM standard test method defines cooking rates and efficiencies for heavy-load (3-pounds (1.4 kg)), medium-load (1 ½-pound (0.7 kg)) and light-load (¾-pound (350 g)) conditions. Due to variances in burner and heat-exchanger design, gas fryers demonstrate a dramatic difference in heavy-load cooking energy efficiencies (Figure 2-7). Electric fryers are much closer in performance since the elements are directly submerged in the frying me-dium.3-13

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Production Capacity

Production capacity is the amount of product that can be cooked in a fryer in a given time. For open fryers, this figure is typically given in product litera-ture and in the standard test method as the number of pounds of frozen French fries that can be cooked per hour. Production capacity is determined by the cook time and the recovery time of the fryer. These, in turn, depend

Figure 2-7. Gas open deep-fat fryer cooking-energy efficiency.

Fryers


strongly on energy input rate, heating technology and control strategy. Figure 2-8 shows the range in production capacity for gas fryers.3-13

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Recovery Time

Recovery time is the time it takes a fryer to return to within 10°F (5°C) of the thermostat setpoint after the food is removed from the oil. It is determined by energy input rate, control strategy and the heating technology, among other factors.

Water-Boil Versus Cooking-Energy Efficiency

Although a water-boil test has historically been used to determine fryer effi-ciency, it fails to accurately characterize fryer performance during cooking. A fryer’s job is to maintain a vat of oil at a relatively high temperature (e.g., 350°F (175°C)) while cooking food. During this time, the burners or ele-ments may cycle off as the thermostat is satisfied. But during a water-boil test the frypot temperatures cannot exceed 212°F (100°C). Furthermore, the thermostat is never satisfied during this test and the duty cycle of the ele-

Figure 2-8. Gas open deep-fat fryer production capacity.

Benchmark Energy Performance

Fryers


ments or burners remains at 100%. The fryer’s controls are effectively by-passed during a water-boil test. Thus, the ability of a water-boil efficiency test to reflect in-kitchen performance has been challenged by restaurant op-erators, and a new, standardized test method for the performance of fryers was developed (ASTM test method F1361). This test method uses the more representative “French fry test” for cooking-energy efficiency, along with a test for energy use in the idle (“ready”) mode.

Evaluating performance with real food allows both energy efficiency and productivity (production capacity) to be determined with the same test. Im-portant performance characteristics such as recovery time can also be evalu-ated. The cooking-cycle temperature illustrated in Figure 2-9 helps highlight why an efficient fryer is more desirable than a base-model fryer. In general, the higher the average oil temperature, the better the product quality. With shorter cooking and recovery times, the more efficient fryer is able to pro-duce nearly twice the amount of food as the base-model fryer.

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Figure 2-9. Fryer oil temperature while cooking a heavy (3-pound) load of fries.

Fryers


Table 2-1 summarizes the energy performance parameters for gas and elec-tric open deep-fat fryers. Figure 2-10 and 2-11 show the cooking-energy effi-ciency curves for gas and electric open deep-fat fryers. Under light-load testing (approximately 20 lb/h (9 kg/h)), the cooking energy efficiencies for these three fryers dropped further to 66%, 28% and 35%, respectively. Al-though the light-load efficiencies are dramatically lower than the respective water-boil efficiencies for these fryers, they better reflect real-world energy performance where the average rate of cooking is typically less than 20 lb/h (9kg/h).

Table 2-1. Energy Efficiency for 14-inch Open Deep-Fat Fryers.

Electric Std-Eff Gas Med-Eff Gas High-Eff Gas

Rated Energy Input (kBtu/h) 40 – 60 80 – 120 80 – 120 80 – 90 Idle Energy Rate (kBtu/h) 2.5 – 3.5 12 – 18 8 – 12 4 – 8 Cooking-energy efficiency (%) 75 – 85 25 – 35 35 – 50 50 – 65 Production Capacity (lb/h) 60 – 70 30 – 45 45 – 60 60 – 70

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Figure 2-10. Gas open deep-fat fryer cooking-energy effi-ciency characteristics.

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Pressure fryers require a large vat and typically use a “bottom-fired” design. The benchmark performance of pressure fryers is somewhat lower than that of open deep-fat fryers. In fact, the high-efficiency gas pressure fryers utilize atmospheric burners, as opposed to infrared burners in the open deep-fat fry-ers. Table 2-2 summarizes the energy performance parameters for gas and electric pressure fryers. Figure 2-12 and 2-13 illustrate the cooking-energy efficiency curves for gas and electric pressure fryers.15

Table 2-2. Energy Efficiency for 4-Head Pressure Fryers.

Electric Std. Gas High-Eff Gas

Rated Energy Input (kBtu/h) 30 - 50 55 - 80 40 - 60 Idle Energy Rate (kBtu/h) 1.5 - 4.0 10 - 15 4 - 10 Cooking-energy efficiency (%) 65 - 85 25 - 35 35 - 50 Production Capacity (lb/h) 30 40 25 - 30 30 – 40

Figure 2-11. Electric open deep-fat fryer cooking-energy efficiency characteris-tics.

Fryers


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Gas Versus Electric Fryer Performance

Electric fryers typically use immersed elements to impart heat to the frying medium. This heating technology exhibits higher energy efficiencies due to

Figure 2-12. Gas pressure fryer cook-ing-energy efficiency characteristics.

Figure 2-13. Electric pressure fryer cooking-energy effi-ciency characteristics.

Fryers


the absence of the flue losses associated with gas fryers. Figures 2-14 and 2-15 compare the gas and electric efficiency bandwidths for both open deep-fat fryers and pressure fryers.

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Figure 2-14. Open deep-fat fryer cooking-energy effi-ciency bandwidths.

Figure 2-15. Pressure fryer cooking-energy efficiency band-widths.

Fryers


Energy Consumption Model

In support of the development of standard test methods for cooking appli-ances, a model has been reported that simplifies cooking appliance energy analysis.16 This model, described as a two-mode model, is based on the as-sumption that any condition of appliance operation can be described as the sum of proportionate idle and heavy-load cooking operations, with preheat as an additional factor. The model, therefore, requires measurement of only preheat, idle and heavy-load cooking parameters. This model was based on work contained in U.S. Department of Energy regulations for hot water heat-ers and, with some limitations, is considered applicable to fryers. The model can be effectively applied to estimate part-load efficiencies for a fryer instal-lation where only the operating time (e.g., 12h/day) and quantity of food cooked (e.g., 100 lb/day (45 kg/day)) is known. Figures 2-16 through 2-19 show estimated energy consumption rates and typical operating ranges for gas and electric open deep-fat fryers and pressure fryers based on this model.

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Figure 2-16. Gas open deep-fat fryer energy consumption based on the two-mode model.

Fryers


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Figure 2-17. Electric open deep-fat fryer energy consump-tion based on the two-mode model.

Figure 2-18. Gas pressure fryer en-ergy consumption based on the two-mode model.

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A more robust energy model has been included in subsequent revisions of the ASTM Test Method for the Performance of Open Deep Fat Fryers. In this model, cooking-energy use is broken down between heavy-, medium-, and light-load conditions. Annual energy use is calculated based on preheat, idle, cooking energy rate, and production rate test results from applying ASTM F1361-99. The ASTM energy model also can be used to predict total daily energy consumption and/or the average rate of energy consumption for a given fryer.

Projected annual energy consumption for gas and electric fryers are pre-sented in Tables 2-3 and 2-4 based on the assumptions documented by the table footnotes. The information is based on test method development work for fryers at the Food Service Technology Center and proprietary end-use monitoring reports. The duty cycle is defined as the average rate of energy consumed expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy.

Typical fryer usage involves one or two preheats over an 8- to 12-hour oper-ating day. Figures 2-16 through 2-19 can be used to determine the average

Figure 2-19. Electric pressure fryer energy consumption based on the two-mode model.

Fryers


energy rate during operating hours for each type of fryer. Annual energy con-sumption ranges for gas and electric open deep-fat fryers and pressure fryers are summarized in Tables 2-3 and 2-4. These ranges can be applied to demo-graphic information to estimate the total annual fryer energy consumption for typical use in North America.

Table 2-3. Projected Energy Consumption for Gas Fryers.

Oil

Capacity

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (lb) (kBtu/h) (%) (kBtu/h) (h/d)a (kBtu)b

OPEN DEEP FAT: Open Deep Fat 35 - 50 80 - 120 (Median) 100 20 20c 12 74,900

PRESSURE/KETTLE: Pressure/Kettle 30 - 50 40 - 80 (Median) 60 30 18d 10 56,600

FLAT BOTTOM: Chicken/Fish 125 180 (Median) 180 30e 54 10 168,000

Donut 80 60 - 76 (Median) 68 20f 14 8 34,900

a Operating hours or appliance "on time" is the estimated period of time that an appliance is typically operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy use rate x the typical operating hours x 6 days per week x 52 weeks per year. c The average energy consumption rate is based on a median production rate of 10 lb/h generated from the two-mode energy model.16 An associated duty cycle of 22% was calculated. d The average energy consumption rate is based on a median-production rate of 10 lb/h generated from the two-mode energy model.16 An associated duty cycle of 30% was calculated for a pressure/kettle fryer. e A 30% duty cycle has been assumed for flat-bottom chicken/fish fryers based on the assumption that the us-age pattern is similar to pressure/ kettle operations. Based on the duty cycle and the median energy input rate, an average energy consumption rate of 54 kBtu/h was calculated. f A 20% duty cycle has been assumed for flat- bottom donut fryers based on the assumption that the usage pat-tern would be somewhat less than open deep-fat fryer operations. Based on the duty cycle and the median en-ergy input rate, an average energy consumption rate of 14 kBtu/h was calculated.

Fryers


Table 2-4. Projected Energy Consumption for Electric Fryers.

Oil

Capacity

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (lb) (kW) (%) (kW) (h/d)a (kWh)b (kBtu)c

OPEN DEEP FAT: Open Deep Fat 35-50 12 - 17 (Median) 15 20 3d 12 11,200 38,300

PRESSURE/KETTLE: Pressure/Kettle 30 - 50 9 -14 (Median) 12 33 2e 10 6,200 21,300

FLAT BOTTOM: Chicken/Fish 125 20 - 28 (Median) 24 20 5 10 15,600 53,200

Donut 80 10 - 18 (Median) 14 14 f 2 8 4,990 17,000

a Operating hours or appliance "on time" is the estimated period of time that an appliance is typically operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical op-erating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h d The average energy consumption rate is based on a median-production rate of 10 lb/h generated from the two-mode energy model.16 An associated duty cycle of 20% was calculated. e The average energy consumption rate is based on a median-production rate of 10 lb/h generated from the two-mode energy model.16 An associated duty cycle of 12% was calculated for a pressure/kettle fryer. f A 14% duty cycle has been assumed for flat-bottom donut fryers based on the assumption that the usage pat-tern would be somewhat less than open deep-fat fryer operations. Based on the duty cycle and the median-energy input rate, an average energy consumption rate of 2 kW was calculated.

Impact of Fryer Design on Oil Life

The type of energy and its method of delivery to the frying oil has some ef-fect on oil degradation; however, documented studies indicate that the effect is overshadowed by the degradation caused by the cooking process itstelf.17,18

Fryers generate moderate levels of effluent and, therefore, require moderate ventilation rates (200 to 300 cfm (95 to 140 L/s) per linear foot). Due to their relatively low idle energy rates and associated low surface temperatures, fry-ers introduce little radiant heat gain to the space.


Fryers


Gas fryers have a large energy performance bandwidth, due in part to the prevalence of inexpensive, low-efficiency burner designs. Additionally, a fryer exhibiting high heavy-load cooking-energy efficiency may still have significant idle losses. Since most fryers are operated in the 10 to 20 lb (4½ to 9 kg) per-hour range, improving the part-load efficiency of fryers will have the largest impact on reducing overall fryer energy usage. Fryer part-load performance is primarily affected by the fryer’s standby losses. Reduc-ing these losses with a minimal additional first cost will make a significant impact on total annual energy consumption.

Potential technologies or strategies that could be applied include: enhanced temperature control, frypot insulation, advanced atmospheric burners, pulse combustion, modulating burners, recirculation tubes, and/or flue dampers.

First cost is a major factor in food service equipment purchases. Many en-ergy efficient technologies (e.g., powered IR burners) have a high premium associated with them that deters many food service operators from purchas-ing the higher efficiency model. An attractive strategy for the gas industry involves the development of a lower first-cost, atmospheric-burner fryer with reduced standby losses and advanced performance by applying better heat transfer, control and insulation.

The performance and diversity advantages of split-vat fryers should be better documented and promoted, particularly to the independent operator. Interest-ingly, split-vat fryers typically are listed by fryer manufacturers.

Developing a higher efficiency donut fryer is another opportunity that, to date, has not experienced any end-user pull. A similar situation exists for many of the flat-bottom and kettle/pressure fryers. These specialty fryers tend to incorporate very low-cost burner components and controls.

Research and Development

Industry Market Focus

Fryers


1. Conner, M. M., Young, R., Fisher, D.R. and Nickel, J., 1991. Develop-ment and Application of a Uniform Testing Procedure for Fryers. Pa-cific Gas and Electric Company Department of Research and Development Report 008.1.89.2, November.

2. American Society for Testing and Materials, 1999. Standard Test Method for the Performance of Open, Deep Fat Fryers. ASTM Designation F 1361-99. In Annual Book of ASTM Standards, West Conshohocken, PA.

3. Holliday, J., Conner, M., 1993. Frymaster® Model H-17CSC Electric Fryer Performance Test: Application of ASTM Standard Test Method F 1361-91. Food Service Technology Center Report 5017.93.2, Novem-ber.

4. Zabrowski, D., Nickel, J., Holliday, J., 1994. TekmaStar Model FD-212 Electric Fryer Performance Test: Application of ASTM Standard Test Method F 1361-91. Food Service Technology Center Report 5011.94.2, June.

5. Zabrowski, D., Nickel, J., Knapp, S., 1995. Keating Model 14 IFM Gas Fryer Performance Test. Food Service Technology Center Report 5011.95.32, December.

6. Knapp, S., Zabrowski, D., 1996. Pitco Frialator® Model RPB14 Technofry 1™ Gas Fryer: Application of ASTM Standard Test Method F1361-95. Food Service Technology Center Report 5011.94.11, April.

7. Knapp, S., Zabrowski, D., 1996. Pitco Frialator® Model E14B Electric Fryer Performance Test. Food Service Technology Center Report 5011.95.12, March.

8. Zabrowski, D., Bell, T., 1999. Ultrafryer, Model PAR 3-14 Gas Fryer Performance Test. Food Service Technology Center Report 5011.99.78, September.

9. Cowen, D., Zabrowski, D., 2000. Vulcan 14-inch Fryer Performance Test: Application of ASTM Standard Test Method F1361-99. Food Ser-vice Technology Center Report 5011.00.87, December.

10. Cowen, D., Zabrowski, D. 2000. Vulcan High Capacity Fryer Perform-ance Test: Application of ASTM Standard Test Method F1361-99. Food Service Technology Center Report 5011.00.88, December.

11. Cowen, D., Zabrowski, D., Miner, S., 2001. Anets Fryer Performance Tests. Food Service Technology Center Report 5011.01.03, December.

12. Cowen, D., Zabrowski, D., Miner, S., 2001. Pitco AG14 Fryer Perform-ance Tests: Application of ASTM Standard Test Method F1361-99. Food Service Technology Center Report 5011.02.07, September.

13. Cowen, D., Zabrowski, D., Miner, S., 2001. Pitco SGH50 Fryer Per-formance Tests: Application of ASTM Standard Test Method F1361-99. Food Service Technology Center Report 5011.02.08, September.

References

Fryers


14. Pieretti, G., Blessent, J., Kaufman, D., Nickel, J., Fisher, D., 1990. Cooking Appliance Performance Report - PG&E Production-Test Kitchen. Pacific Gas and Electric Company Department of Research and Development Report 008.1-90.8. May.

15. Zabrowski, D., Young, R., Ardley, S., Knapp, S., Selden, S., 1995. Deli-catessen Appliance Performance Testing. Food Service Technology Center Report 5016.95.23. October.

16. Horton, D.J., Caron, R.N., 1994. Two-Mode Model for Appliance En-ergy Analysis. A presentation to the Society for the Advancement of Food Service Research, April.

17. Saltmarch, M., Conner, M., Fisher, D., 1992. Frying Medium Quality Life Determination. Pacific Gas and Electric Company Department of Research and Development Report 008.1-90.20, January.

18. Holiday, J., Conner, M., Fisher, D., 1993. In-Kitchen Frying Medium Life Study. Pacific Gas and Electric Company Department of Research and Development Report 008.1-92.16, May.

Information in this module also references Manufacturers Product Literature, catalogues, and appliance specification sheets.

3 Griddles


Griddles are used throughout the hospitality industry from the first order of bacon at breakfast to the last seared steak at dinner. The griddle is a work-horse that usually occupies a central position on the short-order line. Its ver-satility ranges from crisping and browning; for foods like hash brown potatoes, bacon and pancakes, to searing; for foods like hamburgers, chicken, steak and fish, and to warming or toasting; for bread and buns.

The relatively simple design of a griddle can have very different performance characteristics. Knowing the differences between griddles allows a food ser-vice operator to choose one that provides them with the best appliance for their kitchen. With increases in electric and gas rates, more kitchen operators are becoming aware that griddles with higher energy efficiency deliver high cooking performance and capacity.

Two factors are currently driving energy efficient griddle designs. First, quick service chains, now followed by casual dining chains, have stimulated research on energy efficient griddles because they recognize the possibility of increasing profits by specifying better equipment. Second, ASTM standard test methods developed by the Food Service Technology Center (FSTC) 1 have allowed testing facilities to produce griddle energy performance data that can be compared between labs. This allows both manufacturers and pur-chasers to calculate the cost of operating specific griddle models and tech-nologies. Published data shows that energy performance can vary significantly with griddle type and construction details.

Griddles vary in size, power input, heating method, griddle-plate construc-tion and control strategy. All designs cook via contact with a heated metal plate that has splashguards attached to the sides and rear and a shallow trough to guide grease and scraps into a holding tray. The griddle plate is heated from underneath by gas burners or electric elements, and controls are generally located on the front of the appliance.

Introduction

Figure 3-1. Countertop griddle. Photo: AccuTemp Products, Inc.

Griddles


A griddle’s low-profile design (Figure 3-1) enables manufacturers to offer them in a variety of configurations. The same griddle can be placed on a stand (freestanding floor model), a countertop, or be incorporated into a rangetop. Manufacturers also commonly offer griddles as a component of a restaurant range battery.

The cooking surface is commonly 24 inches (610 mm) from front to back, but may be as shallow as 15 inches (380 mm) or as deep as 32 inches (810 mm). Widths range from 1 foot (305 mm) to 7 feet (2130 mm), and the griddle plate may be ½ to 1¼-inches (15 to 30 mm) thick. Energy input rates vary from 20-180 kBtu/h for gas griddles and from 4-36 kW for electric griddles.

Griddles transfer heat to food by direct contact with the hot griddle plate. The desired characteristics of this style of cooking are crisping and browning, for foods like hash browns, bacon and pancakes; searing, for foods like ham-burgers, steak, and fish; toasting, for bread and buns. Griddle temperatures range from 200 to 450°F (95 to 230°C), depending on the food being cooked.

Because griddles can take as long as 25 minutes to preheat, they are routinely turned on at the beginning of the day and idled at cooking temperature. Some operators turn off sections of the griddle during slow periods to reduce idle energy use.

Single-sided Griddles

The most common type of griddle is a single-sided griddle with a flat, pol-ished steel griddle plate. Burners or electric elements are usually spaced 8-12 inches (200-300 mm) apart with one control per 12-inch (300 mm) section. This allows each section of the griddle to be maintained at a different tem-perature for different products, or turned off during slow periods.

Cooking Processes

Types of Griddles

Griddles


Grooved Griddles

Some manufacturers offer grooved griddles, typically with ½-inch (10 mm) grooved plates as an option (Figure 3-2). These allow the operator to serve products that have the characteristic striped sear mark of a charbroiler with-out the broiler’s high-energy cost or the increased ventilation requirements due to a broiler’s smoke and heat. The grooves also drain away some of the grease that forms during cooking. Less of a grooved griddle’s surface con-tacts the food and transfers heat, so operators may compensate by operating the griddle at a higher temperature. As the grooved surface is not appropriate for all food products (i.e., eggs, pancakes and sandwiches), some griddle plates are manufactured with both grooved and flat sections.

Chrome-Finished Griddles

Several manufacturers offer griddles with a chrome-finished cooking surface. Such a surface is easier to clean and radiates less heat towards the operator and the kitchen. In addition to being more comfortable for the user, this tech-nology exhibits lower heat loss during idle and cooking, offering an indirect savings in the cost of cooling the kitchen. In preliminary testing, a chrome surface reduced an electric griddle’s idle rate by a third (1.5 kW vs. 2.25 kW). Both flat and grooved griddles are available with a chrome finish.

Double-Sided Griddles and Duplex Cookers

Double-sided griddles were developed for fast food chains that wanted to shorten cook times and increase hamburger production. A two-sided griddle has a hinged upper griddle plate that swings down to contact the food so that it cooks from both sides at once. The upper section has a manual or auto-matic adjustment for the thickness of food being cooked. The upper griddle plates are most often electrically heated, even if the lower section uses gas.

Duplex cookers are similar to double-sided griddles, except that the top sec-tion incorporates a broiler and hood instead of a griddle plate (See Figure 3-3). When the upper platen is lowered, the broiler, which sits a few inches above the griddle surface, comes to full power and cooks with infrared heat.

Figure 3-2. Gas griddle with a grooved plate. Photo: Lang Mfg. Co.

Figure 3-3. Duplex cooker. Photo: Lang Mfg. Co.

Griddles


The radiants in the broiler may be either gas or electric. A variation on the duplex griddle being marketed by Thermodyne Food Service Products, Inc. uses a covered griddle surface with steam injection between the lid and the griddle surface to shorten cook times (Figure 3-4).

Both double-sided griddles and duplex griddles can cook hamburger patties twice as fast as a traditional single-sided griddle. This allows operators to fill orders faster and save labor involved in cooking the product, since no turning is required. In addition, these griddles are more energy efficient. A duplex cooker or double-sided griddle can produce the same amount of food per hour as a much larger conventional griddle. Its smaller surface area has lower radiant and convective energy losses during idle and cooking. The top sec-tions further reduce heat loss by acting as a cover when in the closed posi-tion.

Duplex and double-sided griddles have a high initial cost and require more maintenance. Energy savings alone will probably not make up for the price difference. However, for a high-volume operation the increased production capacity, reduced labor and shorter customer response times justify the higher initial cost.

Griddle controls are usually quite simple. The temperature of each section is controlled either manually or with a thermostat. Manual controls are analo-gous to the familiar controls on a gas broiler; the height of the flame is ad-justed directly to set the desired level of heat and there is no temperature measurement. The addition of thermostats improves the temperature control of the cooking surface and allows the griddle to be responsive to loads of raw (or frozen) food. This is especially valuable for operators interested in prod-uct consistency. The use of thermostats may also allow manufacturers to use lower-mass griddle plates in their construction, since stored heat is not as critical for temperature recovery as with manual controls.

Thermostats sense the plate temperature with either a fluid-filled bulb or a thermocouple. The sensor may be mounted to the underside of the griddle plate, as shown in Figure 3-5, or embedded into each section of the plate (preferred method for maximizing griddle performance). Bulb-type sensors

Figure 3-4. Covered griddle surface. Photo: Thermodyne.

Controls

Griddles


(Figure 3-6) use a working fluid that expands when heated, which closes a valve or electrical contact. Thermocouples generate a small voltage that changes with temperature. Thermocouples are more accurate than bulb-type sensors and are frequently embedded within the griddle plate (rather than positioned underneath), but they are more expensive and are typically used only on advanced-design griddles.

The two primary types of thermostat controls are modulating and snap-action. Modulating or throttled thermostats adjust the gas flow incrementally to achieve “soft landing” at the setpoint temperature without overshoot. These types of thermostats typically include a flame bypass, which maintains a minimum flame setting in the burner as long as the griddle is on. Snap-action thermostats are either fully open or fully closed, causing the griddle temperature to cycle around the setpoint. These thermostat valves can either be mechanically controlled by the working fluid from the sensing bulb or electrically controlled by a solenoid. The function of the two types of snap-action thermostats is essentially the same, with the electrically powered thermostats exhibiting a tighter bandwidth around the setpoint than the me-chanical variety.

Griddles equipped with modulating controls have historically exhibited slug-gish response to a load of product. The controls begin to throttle back the input to the griddle as low as 75°F (42°C) below the thermostat setpoint,

Figure 3-5. Standard efficiency thermostat-sensing bulb placement. Photo: Fisher-Nickel, inc

Figure 3-6. Bulb-type thermostat sensor. Photo: Fisher-Nickel, inc.

Griddles


causing longer preheats as well as longer cooking and recovery times, as il-lustrated in Figure 3-7. The longer cook and recovery times adversely impact the griddle’s efficiency and production capacity.2 Additionally, modulating thermostats can be the victim of “creeping,” where the griddle temperature slowly climbs over the course of the day. A griddle with a modulating ther-mostat may begin the day at 350°F (175°C) and end the day at 450°F (230°C), with no change in thermostat setting. However, modulating thermo-stats are less expensive than snap-action thermostats and are typically found in lower-efficiency griddles.

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Some high-end double-sided griddles incorporate elaborate “cooking com-puters” to automate the cooking process. These griddles use solid-state elec-tronic controls with a thermocouple to sense plate temperature and offer cooking computers that can be programmed with temperatures and times for several different food products. The computers may be programmed on site, or remotely through an optional modem in the griddle.

Figure 3-7. Comparison of griddle cooking profiles.

Griddles


All varieties of griddle (flat, grooved, double-sided, chromium-finished) are available in both gas and electric models. For each fuel source, there are dif-ferent strategies for applying heat to the griddle including open flame atmos-pheric burners, infrared burners and heat pipe technology for gas, and standard elements and induction heating for electricity. Even among appli-ances that use the same heating technology, there can be significant varia-tions in energy use due to appliance design.

Griddle usage, from one food service operation to another, also impacts its energy efficiency and consumption. Both gas and electric griddles are less efficient under part-load operation due to the increased effect that the heat loss from the cooking surface has on appliance efficiency. Gas griddles lose even more due to the part-load efficiency penalty that is characteristic of gas burners. Griddles also spend a significant portion of their operating time in stand-by or idle mode. Under such conditions, the energy efficiency of a gas griddle drops even further due to the short duty cycle of the burners.

Gas Griddles

Gas griddles can be separated into three categories: low, standard, and high-efficiency. Standard- and low-efficiency griddles are designed with atmos-pheric or “blue-flame” burners, located directly below the griddle plate. High-efficiency gas griddles take advantage of new developments in gas technology, such as infrared (IR) burners, heat pipes, and thermal fluid or steam.

The primary difference between standard- and low-efficiency griddles is the design of the temperature controls and the placement of the temperature sens-ing devices. Low-efficiency designs typically employ modulating thermo-stats and position the thermostat bulbs underneath the griddle plate, where they are secured by angle iron or metal clips (Figure 3-5). Heat from the burners interferes with the bulb’s ability to sense plate temperature, leading to “lazy” thermostat response. Standard-efficiency designs generally use snap-action style thermostats and secure the thermostat bulb in a groove along the underside of the griddle plate or embed the bulb within the plate itself. This creates more contact between the sensing bulb and the griddle


Griddles


plate, allowing for better temperature response. High-efficiency gas griddle designs employ solid-state controls with a thermocouple embedded within the griddle plate.

Advanced Gas Griddle Technologies

Gas griddles represent approximately 75% of the griddles on the market, based on a 1989 NAFEM study.3 There are several different burner types currently in use and under development.

Atmospheric burners. Atmospheric burner griddles represent the low end of the heavy-load cooking efficiency range for griddles. However, a high-end atmospheric gas griddle approaches the performance of an infrared griddle in heavy-load cooking efficiency and idle energy consumption rate.

Infrared burners. Infrared burners are more expensive and generally more efficient. Gas is forced through a ceramic block perforated with thousands of small holes. Combustion takes place close to the burner surface, causing it to become red-hot (approximately 1,800°F (980°C)) and emit infrared radiation to the underside of the griddle plate. Due to their potentially high initial cost and maintenance cost, IR burners represent only 5% to 10% of the gas grid-dles in the marketplace.

Thermal Fluid. The Gas Technology Institute (GTI) partnered with a manu-facturer to develop a double-sided griddle heated by circulation of hot oil. This technology makes gas heat easy to distribute across the griddle surface and to the upper plate of a double-sided griddle. It takes advantage of well-developed methods for applying gas heat to a liquid, which in devices such as boilers and booster heaters, has proven to be very cost effective. Addition-ally, thermal fluid technology allows for better distribution of heat across the griddle plate. However, the significant reduction in cook time of a double-sided griddle can amplify the effect of temperature differences across the plate and its impact on cooking uniformity. The cost of the thermal-fluid technology (including a specialized pump to circulate the fluid) is signifi-cantly higher than a conventional griddle and this product was not brought to market.

Griddles


Pulse Combustion. Pulse combustion is a technology adapted from high efficiency boilers. The process is essentially a series of controlled explosions at a rate of 40 to 60 times a second. A forced-draft blower initially delivers the fuel/air mixture to the combustion chamber, where it is ignited by a spark plug or glow coil. Once the combustion chamber heats up, the process be-comes self-perpetuating and no longer requires the ignition device. The ad-vantage of this technology is that it allows the use of a compact, highly efficient heat exchanger to deliver heat to the griddle plate. Griddles with pulse combustion were perceived as too expensive for the market place (at least when compared with IR burner griddles) and remain in the experimental stage.

Heat Pipe. Heat pipes are enclosed tubes that connect the heat source to the griddle plate. The tubes are filled with a working fluid that vaporizes at the heat-source end and condenses at the end connected to the griddle plate. Like the thermal-fluid griddle, heat-pipe technology has the potential to evenly distribute heat across the griddle plate, yielding good temperature uniformity. A version of this technology has successfully been introduced by AccuTemp Products, Inc.

Electric Griddles

Electric griddles use heating elements that are attached to the bottom of the griddle plate or embedded into it. Depending on the pattern of the elements, surface temperature uniformity can be very good from edge to edge. New technologies, such as the induction griddle, are highlighting temperature uni-formity as a desirable performance parameter. Electric griddles typically use solid-state thermostats with a thermocouple embedded within the griddle plate to control the temperature of the cooking surface.

Advanced Electric Griddle Technologies

Electric griddles are generally more efficient than gas griddles, but in most areas have higher energy costs.

Griddles


Standard Elements. Standard electric griddles use heating elements that are either attached to the bottom of the griddle plate or embedded into it. Place-ment of the elements affects surface temperature uniformity. One manufac-turer uses a loop element near the perimeter of the griddle to reclaim the area where temperature usually falls off due to radiant losses from the sides of the griddle plate.

Insulation. Insulation along the bottom of the griddle reduces standby con-vective heat losses by as much as 25%. Griddle insulation is currently being applied to a few high-end electric griddles. Apparently, manufacturers do not currently insulate their gas griddles due to safety limitations.

Infrared Heat Panels. Infrared heat panels have greater control over the dis-tribution of heat than standard elements. Electricity runs through a filament wound back and forth through a ceramic composite block. The block heats evenly, allowing for a uniform cooking surface.

Induction. Induction technology has been developed for griddles, but not successfully marketed. Induction griddles use an induction coil below the griddle plate to generate a magnetic field that induces a current in the plate itself. This current heats up the plate with little energy lost in the transmis-sion from coil to plate, and the griddle temperature can be regulated by ad-justing the current in the coil.

In a variation on this technology, the plate itself regulates the griddle tem-perature. The plate is built with a tri-metalic composite whose Curie point (temperature where a metal will transition from a magnetic to a non-magnetic state) is near the desired cooking temperature determined by the design of the metal composite plate. When the plate reaches its Curie point, it loses its magnetic properties and stops drawing energy from the induction coil below. This characteristic allows this induction-heated appliance to provide a con-stant temperature across the cooking surface. Also, when food draws heat from the griddle, the cooled plate can again gain energy from the magnetic field. The area of the griddle plate directly under the food falls below the Cu-rie point and becomes magnetic. The plate “senses” the food’s presence and generates an amount of heat sufficient to replace what it transfers to the food.

Griddles


Metcal, Inc. built a prototype induction griddle based on the temperature-limiting alloy plates. Each section of the griddle is a 12-inch (300 mm) wide removable plate with a fixed temperature setpoint. The operator selects and arranges plates to configure different temperature zones for the griddle. Met-cal reported a cooking-energy efficiency of 80%, well above the best-reported figure of 70% for a standard electric griddle. They also claimed ex-cellent surface temperature uniformity and a two minute preheat. Although induction technology holds promise for electric griddle performance and ef-ficiency, it is likely to remain a very expensive type of griddle due to the cost of the induction coils and, for some induction griddles, the cost of fabricating the griddle plate. Furthermore, Metcal, Inc. (with EPRI support) failed to license this technology and/or bring the product to market. However, more recently, Luxine, Inc., Malibu, California, has secured rights to the technol-ogy and is working with U.S. appliance manufacturers in an effort bring it to market.

The ASTM Standard Test Method for the Performance of Griddles1 quanti-fies energy use and efficiency, surface temperature uniformity and produc-tion capacity. Other factors that may affect the actual performance of a griddle include ergonomics, ease of cleaning and quality of construction.

Input Rating

Input rating is the performance characteristic usually included in product lit-erature. It is the maximum rate at which a griddle draws energy, expressed in kBtu/h or kW. Energy input rate varies from 20-180 kBtu/h for gas griddles, 4-36 kW for electric griddles.

Surface Temperature Uniformity

Surface temperature uniformity is the ability to maintain the desired tempera-ture across the entire surface of the griddle, without hot or cold spots that the operator must work around. Griddle surface temperature typically falls off along the perimeter, due to radiant losses from the sides and burner/element

Griddle Performance

Griddles


positioning. The ASTM test method measures uniformity by welding ther-mocouples directly to the griddle plate (Figure 3-8). The resulting plot pro-vides a visual reference to the hot and cool spots on the griddle surface during an idle state. Figure 3-9 presents a sample uniformity plot.

Figure 3-8. Welded thermocouples to a griddle surface.

Figure 3-9. Griddle temperature uni-formity plot.

Griddles


Temperature uniformity is affected by the type and placement of burners or elements, the thermostat and controls, and the thickness of the griddle plate. A thicker griddle plate will distribute heat more evenly, but has the disadvan-tages of additional cost and slower response.

Preheat Energy Consumption

The energy required to preheat a griddle is a function of the size of the grid-dle plate and its heat-up efficiency. However, preheat energy consumption represents less than 15% of the daily energy consumption for a griddle that was turned on twice over an 8-hour operating period.2 For longer griddle op-erations (e.g., 12 hours) with only one preheat, the energy performance of the griddle during this phase of its operation becomes less important.


Both gas and electric griddles consume energy while holding the griddle plate at the desired cooking temperature. This is due to the heat that is lost from the cooking surface or through the sides of the griddle. The idle energy consumption rate is a function of the thermostat setpoint and the effective resistance of the griddle to heat loss. Monitoring the usage of griddles in commercial kitchens has demonstrated that griddles spend a significant por-tion of their on time in idle mode and that the rate of idle energy consump-tion has a significant impact on total daily energy consumption.2 Figure 3-10 summarizes the idle rates for thirteen 3-ft gas griddles tested at the FSTC. Cooking-energy efficiency and production capacity data for the same thirteen griddles are presented in Figures 3-11 and 3-12, respectively. 4-11

Griddles


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Food

Appliance= × 100%

The ASTM standard test method (F1275-99) defines cooking rates and effi-ciencies for heavy-load (8 hamburger patties per foot (300 mm) of griddle width), medium-load (4 patties per foot (300 mm) of griddle width) and light-load (4 hamburger patties per load) conditions. Due to variances in burner and control design, gas griddles demonstrate a dramatic difference in heavy-load cooking energy efficiencies (Figure 3-11). Electric griddles are much closer in performance since the elements are typically embedded in the griddle plate.4-11

Figure 3-10. 3-ft. gas griddle idle en-ergy rates.

Griddles


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Production Capacity

Production capacity is the amount of food that can be cooked on a griddle in a given time. For griddles, this figure is commonly reported as the number of pounds of frozen hamburger patties that can be cooked per hour. For single-sided griddles, production capacity is most strongly linked to the size of the griddle plate. Figure 3-12 illustrates that the range in production capacities for the 3-ft. griddles can be as much as two-to-one.4-11 Figure 3-13 further examines griddle production capacity in relation to rated energy input. The lack of any correlation in the data points out that the difference between high and low-production models is more than sheer horsepower.

Figure 3-11. 3-ft. gas griddle cooking-energy efficiencies.

Griddles


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Figure 3-12. 3-ft. gas griddle produc-tion capacity.

Figure 3-13. 3-ft. griddle input rate vs. productivity.

Griddles


Recovery Time

Recovery time is the time it takes a griddle to come back up to 350°F (175°C) after the previous load has been cooked. Slow recovery time reduces the production capacity and cooking-energy efficiency of a griddle. Testing of multiple griddles from different manufacturers revealed that a griddle’s recovery temperature could be relaxed from 10°F (5°C) below the thermostat setpoint to 25°F (15°C) below the setpoint without adversely affecting grid-dle-cooking performance. High-performance griddles were unaffected by this change as they had recovered by the time the previous load had been re-moved and the cooking surface had been scraped.

Energy input rate, efficiency, control strategy and the thickness of the griddle plate are factors that directly affect recovery times. Reported recovery times range from less than one minute to over seven minutes.9-11

Water-Boil Versus Cooking-Energy Efficiency

In the body of published data on griddles, two different tests are commonly reported as “cooking efficiency” tests: a water-boil test, in which a dam is built on the griddle surface to contain a set quantity of water, which is weighed before and after boiling for a set period of time, and a test in which frozen hamburger patties are cooked.

Water-boil efficiencies of 88%, 44% and 51% have been reported for an electric, a gas atmospheric burner and a gas infrared (IR) burner 3-foot grid-dle, respectively, whereas cooking-energy efficiencies (cooking hamburgers under heavy-load conditions) for the same griddles were 65%, 31% and 42%.2 A water-boil test does not emulate the operation of a griddle in a real food service operation. A griddle’s job is to maintain a cooking surface at a relatively high temperature (e.g., 375°F (190 °C)) while cooking food prod-uct. During this time, the burners or elements may cycle off as the thermostat is satisfied. During a water-boil test the cooking surface temperatures cannot exceed 212°F (100°C). Furthermore, the thermostat is never satisfied during this test and the duty cycle of the elements or burners remains at 100%. The ASTM method specifies the more representative hamburger patty test, exclu-sively.


Griddles


Table 3-1 summarizes the energy performance parameters for gas and elec-tric griddles. Figure 3-14 and Figure 3-15 show the cooking-energy effi-ciency curves for gas and electric griddles.

Table 3-1. Energy Efficiency for 3-foot Griddles.

Electric Low-Eff Gas Std-Eff Gas High-Eff Gas

Rated Energy Input (kBtu/h) 25 - 60 40 - 80 40 - 80 60 - 80 Cooking-Energy Efficiency (%) 65 - 75 25 - 35 35 - 45 > 45 Idle Energy Rate (kBtu/h) 5 - 9 > 18 15 - 18 10 - 15

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Figure 3-14. Gas 3-ft. griddle cooking-energy effi-ciency characteristics.

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Gas Versus Electric Griddle Performance

Electric griddles typically use elements either located directly below or em-bedded in the griddle plate to impart heat to the cooking surface. This heating technology exhibits higher energy efficiencies due to the absence of the flue losses associated with gas griddles. Figure 3-16 compares the gas and electric efficiency bandwidths for 3-foot (910 mm) griddles.

Energy Use Models

In support of the development of standard test methods for cooking appli-ances, a model has been reported that simplifies cooking appliance energy analysis.12 This model, described as a two-mode model, is based on the as-sumption that any condition of appliance operation can be described as the sum of proportionate idle and heavy-load cooking operations, with preheat as an additional factor. The model, therefore, requires measurement of only

Figure 3-15. Electric 3-ft. griddle cooking-energy effi-ciency characteristics.

Griddle Energy Consumption

Griddles


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preheat, idle and heavy-load cooking parameters. This model was based on work contained in U.S. Department of Energy regulations for hot water heat-ers and, with some limitations, is considered applicable to griddles.

The model can be applied to estimate part-load efficiencies for a griddle in-stallation where only the operating time (e.g., 8h/day) and quantity of food cooked (e.g., 100 lb/day) is known, assuming that the entire griddle is left on during operating hours. Figure 3-17 and Figure 3-18 show estimated energy consumption rates and typical operating ranges for gas and electric 3-foot (910 mm) griddles based on this model.

A more robust energy model has been included in subsequent revisions of the ASTM Test Method for the Performance of Griddles.1 In this model, cook-ing-energy use is broken down between heavy-, medium-, and light-load conditions. Annual energy use is calculated based on preheat, idle, cooking energy rate, and production rate test results from applying ASTM F1275-99. The ASTM energy model also can be used to predict total daily energy con-sumption and/or the average rate of energy consumption for a given griddle.

Figure 3-16. 3-ft. griddle cooking-energy efficiency band-widths.

Griddles


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Figure 3-17. Gas 3-ft. griddle energy consumption based on the two-mode model.

Figure 3-18. Electric 3-ft. griddle en-ergy consumption based on the two-mode model.

Griddles


Projected annual energy consumption for gas and electric griddles is pre-sented in Table 3-2 and Table 3-3. Energy consumption was based on duty cycles of 34% for gas and 25% for electric as determined from Figure 3-17 and Figure 3-18. The duty cycle is defined as the average rate of energy con-sumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy.

Table 3-2. Projected Energy Consumption for Gas Griddles.

Nominal

Size

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Duty Cycle

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Consumption

Typical Operating

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Consumption (kBtu/h) (%) (kBtu/h) (h/d)a (kBtu)b

Single Sided

3-foot 60 - 80

(Median) 70 34 23c 12 86,100 a Operating hours or appliance "on time" is the estimated period of time that an appliance is typically operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy use rate x the typical operating hours x 6 days per week x 52 weeks per year. c The average energy consumption rate is based on a median production rate of 10 lb/h generated from the two-mode energy model.12 An associated duty cycle of 34% was calculated.

Table 3-3. Projected Energy Consumption for Electric Griddles.

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(kW) (%) (kW) (h/d)a (kWh)b (kBtu)c

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3-foot 8 - 16

(Median) 12 25 3d 12 11,232 38,300 a Operating hours or appliance "on time" is the estimated period of time that an appliance is typically operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical op-erating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h d The average energy consumption rate is based on a median production rate of 10 lb/h generated from the two-mode energy model.12 An associated duty cycle of 25% was calculated.

Griddles


The effluent generated by a griddle depends on the type of food being cooked. For example, hamburgers generate significantly more effluent than pancakes or hash brown potatoes. Since there is the potential for a high amount of grease-laden air, griddles can require ventilation rates in the range of 250 to 350 cfm (120 to 165 L/s) per linear foot of wall-mounted canopy.

The large cooking surface tends to be a good radiator of heat to the kitchen space. Typical griddles with polished steel griddle plates have a high emis-sivity and may represent a significant load on the ventilation system. Grid-dles are now being offered with chrome-finished cooking surfaces that have a low emissivity. Such a surface will reduce the thermal load to the kitchen space.

The most cost-effective method for improving griddle performance is im-proved temperature feedback. Traditional designs have focused on heavy-duty construction with inexpensive controls. If a thermostat is included (a significant number of griddles in the marketplace are manually controlled), the sensing device is generally attached to the bottom of the griddle plate. By improving the contact between the thermostat bulb and the griddle plate, it is possible to dramatically improve the griddle’s performance. With respect to Figure 3-11, the same manufacturer produces griddle #4 and #9. The only difference between the two griddles is the method of contact between the thermostat bulb and the griddle plate. Griddle #4 attached the bulb to the bot-tom of the plate, whereas Griddle #9 embedded the bulb within a groove in the plate. This simple design change yielded a 19% increase in cooking-energy efficiency (from 33.7% to 40.2%) and a 70% increase in production capacity (from 23 to 40 lb/h (from 10.5 to 18 kg/h)).

Gas griddles have a large energy performance bandwidth, due to the many different burner designs and control strategies. Griddles will continue to be burdened by a high idle rate as a result of keeping a large exposed plate at operating temperature (e.g., 375°F (190°C)). One of the more important as-pects of griddle performance is temperature uniformity. As the majority of griddles in the marketplace exhibit a difference of 50 to 100°F (28 to 56°C)


Improving Performance


Griddles


between the highest and the lowest temperature on the griddle plate, there is significant room for improvement.

Research issues related to developing an advanced gas griddle include:

Griddle Plate Temperature Measurement. Embedding the thermostat sen-sor into the griddle plate has been shown through FSTC testing to dramati-cally improve response. Although a long, narrow bulb running three quarters of the depth of the plate can improve response (over a short temperature bulb), the key is to measure plate temperature and not be affected by the burner below. Overall, different strategies for plate temperature sensing (and feedback) need to be investigated.

NAFEM Online Kitchen Protocol. An advanced-design griddle needs to comply with the NAFEM Online Kitchen Protocol, particularly with respect to griddle plate temperature feedback and recording. The introduction of mi-croprocessor based thermostat control using thermocouples to sense plate temperature would be a major step in this direction.

Improved Burner/Heat Exchanger Design. Assess the potential of differ-ent burner/heat exchanger designs to improve the cooking-energy efficiency, response and uniformity of the cooking surface. This includes looking into the potential of inshot or powered burners with an increased surface area for heat (which was successful in the Ultrafryer gas fryer13). Heat transfer fins along the underside of the griddle plate may assist with distributing the avail-able heat from the burners to the edges of the plate.

The effect of griddle plate thickness needs to be documented. If mass is not the critical issue for a fast response heating system, then alternative strategies could be used to achieve plate rigidity and prevent warping (e.g., fins beneath griddle plate could be both structural and enhance heat transfer).

Temperature Uniformity. Improving the temperature uniformity of conven-tional griddle designs goes hand-in-hand with increased heat transfer and overall efficiency. Again, finning may be an effective strategy.

Insulation. Incorporating a thin layer of high-tech insulation along the outer edges of the griddle plate could reduce temperature fall-off, as well as standby losses. For electric griddles, insulation could be applied below the plate and elements, significantly reducing idle energy consumption.

Griddles


Low-Emissivity Griddle Plate. Griddles lose a substantial amount of energy by radiating heat to the kitchen space, due to their large, hot cooking surface. Preliminary testing by the FSTC showed that a low-emissivity griddle plate (i.e., polished chrome surface) loses a third less energy in stand-by. Several griddle manufacturers offer this feature, however, better documentation of the benefits is needed—including reduced heat gain to space.

Lids. An optional lid could further energy reduction during idle, and poten-tially increase cooking performance. A lid could potentially enhance cooking performance, and most definitely, reduce idle energy requirements and heat gain to space. A lid is being marketed by one manufacturer, Thermodyne Food Service Products, Inc., as an integral compliment to steam injection within the cavity formed between the lid and the griddle plate.

Another variation could include a removable “dam” along the front edge of the griddle that could effectively convert the griddle into a shallow braising pan.

Deeper Griddle Plates. Simply extending the depth (front to back) of the cooking surface from 24 to 30 inches (610 to 760 mm) makes more use of the available heat from the burners and improves the griddle’s production potential. The high-efficiency griddles tested by the FSTC incorporated 30-inch deep (760 mm deep) cooking surfaces, allowing for an extra row of pat-ties to be cooked during the heavy-load cooking tests. 5-11

First cost is a major factor in food service equipment purchases. New, energy efficient technologies have a high premium associated with them, which de-ter many food service operators from purchasing these units. An attractive option for the gas industry involves developing a lower first-cost, advanced atmospheric-burner griddle with tighter control and reduced standby losses.

Better understanding and marketing of double-sided griddles or broiler-tops is needed to help independent operators understand the value of investing in an upper heating system.


Griddles


Revisions to the Standard Test Method

Temperature uniformity is a major aspect of griddle performance. While griddles have historically exhibited poor uniformity within a 3-inch bound-ary, the falloff near the edges was even more pronounced. New griddle de-signs, such as the Metcal induction griddle and AccuTemp steam griddle, exhibit little or no temperature falloff along the edges of the griddle plate. With manufacturers pushing the limits of griddle temperature uniformity, the test method needs to measure cooking surface temperatures along the edges to confirm manufacturer claims.

Griddles


1. American Society for Testing and Materials, 1999. Standard Test Method for the Performance of Griddles. ASTM Designation F 1275-99. In Annual Book of ASTM Standards, West Conshohocken, PA.

2. Kaufman, D.A., Fisher, D.R., Nickel, J. and Saltmarch M., 1989. Devel-opment and Application of a Uniform Testing Procedure for Griddles. Pacific Gas and Electric Company Department of Research and Devel-opment Report 008.1-89.2, March.

3. NAFEM 1989 Equipment & Supply Study, Volume C—Cooking and Reconstituting Equipment.

4. Zabrowski, D., Nickel, J., 1993. U.S. Range Model RGTA-2436-1 Gas Griddle Application of ASTM Standard Test Method. Food Service Technology Center Report 5017.93.1, September.

5. Zabrowski D., Nickel, J., 1993. Keating MIRACLEAN Model 36 x 30 IBLD Gas Griddle: Application of ASTM Standard Test Method F 1275-90. Food Service Technology Center Report 5017.93.3, September.

6. Zabrowski, D., Mogel, K., Weller, T., 1996. Toastmaster® Accu-Miser™, Model AM36SS Electric Griddle Performance Test. Food Ser-vice Technology Center Report 5011.96.34, January.

7. Zabrowski, D., Cadotte, R., Sorensen, G., 1998. AccuTemp, Model 2-3-14-208 Electric Griddle Performance Test. Food Service Technology Center Report 5011.98.55, February.

8. Zabrowski, D., Schmitz, M., Sorensen, G., 1999. Taylor, Model QS24-23 Electric Double-Sided Griddle Performance Test. Food Service Technology Center Report 5011.99.69, January.

9. Cowen, D., Zabrowski, D., Miner, S., 2001. Anets GoldenGRILL™ Gas Griddle Performance Test. Food Service Technology Center Report 5011.01.04, December.

10. Cowen, D., Zabrowski, D., Miner, S., 2001. AccuTemp Gas Griddle Performance Test: Application of ASTM Standard Test Method F1275-99. Food Service Technology Center Report 5011.02.04, January.

11. Cowen, D., Zabrowski, D., 2001. Garland Gas Griddle Performance Test: Application of ASTM Standard Test Method F1275-99. Food Ser-vice Technology Center Report 5011.02.05, December.

12. Horton, D.J., Caron, R.N., 1994. Two-Mode Model for Appliance En-ergy Analysis. A presentation to the Society for the Advancement of Food Research, April.

13. Zabrowski, D., Bell, T., 1999. Ultrafryer, Model PAR 3-14 Gas Fryer Performance Test. Food Service Technology Center Report 5011.99.78, September.


References

4 Broilers


Broilers are the central appliance in many food service operations, both large and small. Depending on size and design, broilers are used for anything from melting cheese to cranking out large cuts of meat in vast quantities.

Underfired charbroilers can cook high volumes of meat and seafood with the characteristic smoke and flame that make them a showpiece as well as a workhorse. They are similar to a barbecue in that food is cooked on a grid placed over a radiant heat source. Uprights, salamanders and cheesemelters are each categorized as overfired broilers; they apply heat to the food from above and produce much less smoke and flame. These broilers range in size and ability from those that are used to broil thick steaks in quantity to those intended for melting cheese and/or browning food. Conveyor broilers apply heat to both the top and bottom of the food as it travels through the appliance on a steel belt. These appliances can broil many different types of food prod-ucts in a quick, unattended cooking process. As well as incorporating differ-ent cooking methods, each type of broiler also varies in size and input rate to best suit its particular application in a given kitchen.

Figure 4-1 shows a typical 3-foot gas underfired charbroiler. This example features a grid below the burners that allows it to be used as a cheesemelter-type broiler as well.

By design, broilers are open to the kitchen and radiate a great deal of heat into the room. They tend to have high energy use and low efficiency, and represent one of the most expensive appliances to operate in a commercial kitchen. In addition, broiling—especially underfired broiling on a char-broiler—produces more smoke than comparable cooking methods by grid-dles. However, the flavor and appearance of broiled food is distinctive, and is often the selling point on the menu.

A significant innovation to come to market in recent years is the mechanized or conveyor broiler favored by high-volume fast-food chains for its high pro-duction capacity. Another innovation is the combination broiler/griddle such

Introduction

Figure 4-1. A gas underfired char-broiler with overfired broiler below. Photo: Magikitch'n

Broilers


as the Clamshell® that is well suited to operations with varied menus such as family-style and steak or seafood restaurants.

Broilers are used to cook steak, fish, chicken, shishkebab and seafood as well as to brown food such as casseroles, to finish au gratin dishes and meringues, to reheat plated food and to melt cheese toppings. The desirable characteris-tics of broiling are striping (the marks created by the hot grill or “grid”), browning, searing, charring, crisping, and with cheese, melting. Depending on the desired final product, some cooking applications are only appropriate for certain types of broilers. Construction details and specific applications for each type are discussed under Types of Broilers.

The terms “underfired” and “overfired” refer to the position of a broiler's heat source relative to the food. In both cases the food is cooked using radi-ant heat, although the heat source may vary. All broilers use a “grid”, which is the grill or grate on which the food is placed for cooking. When the broiler is standing by, the grid absorbs heat from the burners or elements, which is then conducted to the food placed on the cooking surface. In most types of broilers, the grid is hot enough to sear a pattern onto the product, and this is the most visually identifiable characteristic of broiling.

Gas is by far the most common fuel source. Some broilers use electric radi-ants or elements, and a few charbroilers use coal or wood for heat. Broilers are often idled throughout the day since they require preheating, which may take from 90 seconds to more than thirty minutes, depending on broiler type and design.

There are two major categories of broilers: underfired and overfired. Here the overfired category is further divided into uprights, salamanders and cheese-melters, following typical industry usage. Conveyorized broilers, character-ized by burners both above and below the food product simultaneously, are treated as a third category. Additional material describes a hybrid broiler/griddle combination.

Cooking Processes

Types of Broilers

Broilers


Underfired Broilers

Underfired broilers are commonly referred to as charbroilers and hearth broilers. They have the highest input rate and production capacity among broiler categories (with the possible exception of some conveyor broilers). They resemble the familiar barbecue, using a heat source below a sturdy metal grid to cook food with a combination of radiant heat, conduction and convection. Charbroilers are showy appliances that produce flames and smoke while cooking, and are often positioned in the kitchen so that these effects will be visible to patrons. The charbroiler marks food with distinctive striping, and the smoke that the broiler creates lends a particular flavor to food. They are widely used to prepare steaks, chops, hamburgers, chicken and fish.

In construction, underfired broilers share several common elements. Food is placed on a metal “grid”, a heavy-duty grill like that of a home barbecue. The grid commonly reaches temperatures of over 600°F (320°C) and conducts a significant amount of heat to the food. Below the grid, gas broilers have a set of atmospheric burners spaced every four to twelve inches along the width of the broiler. The flames are diffused by a bed of rock, ceramic briquettes, or a metal shield (“radiant”) just above the burners (Figures 4-2 and 4-3). This material between the flame and the food converts some of the flame's energy to radiant heat. Electric charbroilers may have elements interwoven with the bars of the grid, or the elements may be sheathed inside the grid itself, in which case, heat transfer is almost entirely by conduction. As food cooks on an underfired broiler, drippings burn on hot elements, coals or radiants to create the charbroiler's characteristic flame and smoke. Unincinerated drip-pings are collected in a grease tray.

The charbroiler's smoke and flame are both a selling point to patrons and an issue of concern for operators. Charbroilers require significant ventilation, and in some areas the effluent from charbroiling is a focus for Air Quality Management District (AQMD) regulations. The design of the grid may affect smoke and flare up. Several manufacturers produce a grid made of bars that, in cross section, resemble a check mark: √. Each bar is said to act like a small gutter for grease, carrying it away from the flames and directing it towards the grease pan.

Figure 4-2. Underfired broiler using rock to diffuse heat. Photo: Magikitch’n

Figure 4-3. Diagram of the “radiant” style of underfired char-broiler. Photo: Vulcan-Hart Company

Broilers


Grease also may be diverted by tilting the grid. Several broilers have a grid that slants toward the cook, or is adjustable between flat and tilted positions. This provides a temperature gradient from the front to the back of the broiler as it promotes grease runoff. One manufacturer uses a fan to blow air across the bed of ceramic coals to reduce flare up, and several more use water-filled grease pans.

Design of the heat source also may influence smoke and flare up. Gas char-broilers have traditionally diffused the burner's flames with a uniform layer of rock or ceramic coals that convert the flame's heat into radiant heat. A metal radiant directly over the burner and a reflector under it may allow more of the drippings to fall into the grease pan without burning, and shield the grease pan from the heat of the flame. This design has the additional benefits of eliminating the need to replace rock or coals periodically, while providing a faster preheat time. One manufacturer has addressed the situation by offer-ing a broiler that is able to convert from ceramic stone to steel radiants (or vice versa) depending on the chef’s preference (Figure 4-4). This conversion is in the form of a kit that can be installed by the operator.

Griddle manufacturers offer griddles with grooved plates as an alternative to charbroilers. These griddles sear food with the characteristic stripes of a broiler, but create no flame, produce far less smoke and use energy more ef-ficiently than a broiler does; additionally, they radiate less heat into the kitchen and require less ventilation.

Overfired Broilers

Overfired broilers differ according to their typical uses and energy inputs. The highest input overfired broilers may be used to broil inch-thick steaks in volume, while those with the lowest input are designed specifically to warm food, melt cheese toppings and finish dishes by browning the top. All over-fired broilers cook with a heat source that is positioned above the food, but there are three generally recognized categories delineated by the broiler's in-put rating and physical configuration. Upright broilers are high-input and generally freestanding. Cheesemelters are low-input broilers that may be countertop, wall mounted or installed above a rangetop. Salamander broilers

Figure 4-4. This broiler can be con-verted from ceramic stone to steel radiants. Photo: Magikitch’n

Broilers


span the input range between cheesemelters and uprights, and are usually mounted at eye level above a rangetop.

As is apparent from the data in Table 4-1, there is some overlap in the typical input ranges for the three categories of overfired broilers discussed below. In addition, manufacturers and operators may use several different terms to re-fer to the same category: “upright” broilers are also known as hotel broilers and floor broilers; “salamanders” are also called backshelf broilers.

Table 4-1. Typical Grid Dimensions, Input Rates and Input Densities for Under-fired and Overfired Broilers.

Type of Broiler

Fuel Grid Depth (in.)

Grid Width (in.)

Rated Input (kBtu/h)

Input Density (kBtu/h per ft2)

gas 14 – 35 13 – 122 30 – 240 16.7 – 28.8 Underfired

electric 18 18 – 30 21 – 46 3.0 – 6.6 gas 24 – 30 24 – 28 65 – 100 15.3 – 20.4

Upright electric 23 26 41 5.9 gas 12 – 14 21 – 28 30 – 66 12.0 – 19.6

Salamander electric 13 – 14 25 17 – 20 2.5 – 2.9 gas 13 – 15 24 – 70 18 – 60 7.8 – 10.1

Cheesemelter electric 13 20 – 42 8 – 16 1.2 – 2.4

Despite their differences, the three types of overfired broilers follow a similar plan. Food is cooked in a broiler cavity that resembles an oven without a door. The heat source may be gas radiants, infrared burners or electric ele-ments mounted in the top of the cavity. Food is placed on top of a grid, which can usually be adjusted to vary the distance between the food and the heat source. Cooking is accomplished by radiant heat from above the food and heat conducted from the grid to the food. Below the food there is a grease pan to catch drippings.

An overfired broiler typically has a lighter-weight grid than a charbroiler, and the grid is shielded from the elements or burners when it is covered with

Broilers


product. The grid may not receive and retain as much heat from the burners as a charbroiler grid does, making conductive heating less significant in an overfired broiler.

The radiant heat in an overfired broiler is generated with electric elements, gas infrared burners or gas radiants. Some manufacturers use powered burn-ers that force premixed gas and air through a ceramic infrared burner. The high heat generated by ceramic infrared burners may incinerate some of the smoke and grease that is formed during broiling and grease does not drip onto hot coals or radiants, thus overfired broilers produce less smoke than underfired broilers.

Upright Broilers. Upright broilers are heavy-duty freestanding overfired broilers. Their high input is in the same range as that of a charbroiler, and they can be used to prepare foods like steak and chicken quickly and in large quantities. They have the highest input rate and production capacity among overfired broilers. Manufacturers commonly offer two identical broiler cavi-ties or “decks” stacked vertically as one unit (Figure 4-5). The grids slide out for loading and unloading, and can be raised towards the infrared burners in the top of the cavity or lowered for slower cooking. Two knobs on the left of the cavity control input to the burners. Ovens may also be stacked with an upright broiler. Some manufacturers mount a finishing oven above an upright broiler so that the heat source at the top of the broiler cavity doubles as a heat source in the bottom of the oven cavity.

Uprights are constructed for heavy use. The grid is usually counterbalanced so that it can be easily raised and lowered to adjust cooking temperature. It also may pull out on slides against safety stops for loading and unloading. Uprights usually stand on a cabinet-style base, and some “modular” uprights can be placed on a stand or a countertop.

Salamanders. Salamanders are medium-duty overfired broilers. Their input range slightly overlaps that of both uprights and cheesemelters, but they are designed to fit above a rangetop on a backshelf. The broiling cavity is as wide as an upright's but not as deep, typically 12 inches (300 mm) instead of 24 inches (600 mm) deep. A typical salamander broiler is illustrated in Fig-ure 4-6. Salamanders generally have a lower input rate to match their smaller

Figure 4-5. Overfired upright broiler with two broiling decks. Photo: Vulcan-Hart Company

Figure 4-6. A salamander broiler, mounted on a backshelf. Photo: Garland

Broilers


size, and deliver slightly less energy to each square foot of the grid. They are intended to prepare the same range of foods as a high-input upright broiler, but at lower volume and without occupying floor or counter space.

In construction, the salamander closely resembles the upright broiler, but is often of lighter weight construction and materials. The grid is not as heavy, although it is usually counterbalanced and capable of sliding out for loading. Although salamanders are generally defined as medium-input broilers mounted on the backshelf of a range (as in Figure 4-6), some manufacturers advertise salamanders that also can be wall mounted or set on a countertop.

Cheesemelters. Cheesemelters have the lowest input rate among overfired broilers, and are generally used to melt the cheese on top of foods such as Mexican and Italian dishes, pie and French onion soup. They are usually in-capable of fully cooking food items like steak and chicken, and do not have grease pans to catch fat and drippings. In appearance they resemble salaman-ders, although they are generally smaller and have a more lightweight con-struction (Figure 4-7). This type of broiler is intended for a limited set of tasks, and so the grill adjustment is usually not as sophisticated as it is for other overfired broilers. The grid is a thin grill, which may not adjust to as many positions as a salamander's; in some cheesemelters it is fixed. It is not usually counterbalanced or mounted on slides, and typically does not have an external handle.

Cheesemelters may be mounted on a wall, a counter or on a backshelf like a salamander. Some cheesemelters are designed with the cavity open both front and back for use as a heated pass-through shelf. Some charbroilers include a cheesemelter underneath the burners to make use of the heat that is radiated downwards by the briquettes or rocks; cheesemelters may be incorporated in a similar fashion underneath the burners of a griddle in a restaurant range. Figure 4-8 shows a small griddle with an overfired broiler incorporated be-low it, as part of a range battery.

Conveyor Broilers

Conveyor or “chain” broilers employ both an overfired and an underfired heat source, cooking both sides of the food product at once. These broilers

Figure 4-7. A cheesmelter. Photo: U.S. Range

Figure 4-8. Broiler range battery. Photo: Vulcan-Hart Company

Broilers


are ideally suited to broiling hamburger patties in large quantities. Model sizes range from small, tabletop broilers favored by convenience stores to large-capacity broilers for fast-food operations. Conveyor broilers are avail-able with an additional section specifically for toasting buns. Multiple-chain models are available so that more than one size patty or meat product such as chicken, steaks or hamburgers can cook at the same time. Instead of a chain, some models use a Teflon belt; this requires an optional “marking platen” to sear broiling stripes onto the food product. Conveyor broilers are available in both gas and electric models. Figure 4-9 shows a typical gas conveyor broiler.

Broiler/Griddle Combination Hybrids

Like conveyor broilers, combination broiler/griddles function as two-sided cookers. The unique Clamshell® broiler features a 24-inch (600 mm) wide stainless steel, infrared broiler-hood mounted on the left end of a griddle. This combination allows the operator to simultaneously grill, poach, broil, and sauté a variety of foods, ranging from breakfast menus to dinner entrees: lobster, oysters, shrimp, sandwiches, egg dishes, steaks, chops, and ham-burgers.

Both gas and electric units are available in floor and countertop models. In addition to the flat-griddle plate, the manufacturer also offers a grooved-griddle plate and a combination grooved/flat plate.

The gas broiler hood features a single infrared burner rated at 35,000 Btu/h that covers approximately four square feet of surface area. This model has a “marking grid”, a thin grill that when contacting the food, sears broiler stripes onto the product. The electric version is similar to the gas model, but uses quartz-halogen tubes as a source of infrared heat.

Lowering the broiler hood activates the burners automatically. When the hood is lowered, it is “full” on. No preheat time is required. When the hood is in the raised position, the burner is off. In the lowered position, there is a 3-inch (75 mm) gap between the broiler hood and the griddle surface. The Clamshell griddle-broiler is shown in Figure 4-10.

Figure 4-9. Conveyor broiler. Photo: Nieco Corporation

Figure 4-10. Gas combination grid-dle-broiler. Photo: Lang Mfg. Co.

Broilers


Most broilers do not have thermostats or timers to control the cooking proc-ess, and so demand the attention and experience of the operator. The amount of heat transferred to the food is adjusted by regulating the energy input to the broiler and changing the placement of the grid, or the food on the grid. Operators become familiar with hot and cold areas on the grid through ex-perience, and these may be varied by adjusting the height of the grid in over-fired broilers and by slanting the grid in some underfired charbroilers. Input is regulated manually with one or two controls on overfired broilers and of-ten one control per burner on charbroilers (typically 2 burners per foot of broiler width).

The underfired gas charbroiler pictured in Figure 4-11 has one control for each burner; some charbroilers group burners into one or several zones. Total input for this 3-foot (900 mm) broiler is 126,000 Btu/h, a typical input rate for this type of broiler. Overfired broiler controls are simple, usually one or two knobs to adjust banks of elements or burners; like charbroilers, overfired broilers are not thermostatically controlled.

Conveyorized broilers are an exception in that they employ more sophisti-cated controls. With this type of broiler, the cook time and temperature are selected by the operator. Some conveyorized broilers have cooking com-puters that store time and temperature parameters for several products so that the operator need only load the broiler and press the appropriate button.

Energy conservation strategies

Broilers usually idle at full input so that they are ready to cook the instant they are needed. As a compromise between readiness and economy, some operators turn down the input to the broiler or turn off some sections alto-gether during slow periods; this can save significant amounts of energy. Some manufacturers have designed broilers with a weight-sensitive feature that turns the broiler down or off entirely until food is placed on the grid, when the broiler returns to full input. So far this strategy has been applied to a few of the smaller overfired broilers (salamanders and cheesemelters).

One manufacturer made an accessory for gas charbroilers that allowed broil-ers to idle at less than their full input rate without incurring a significant pre-

Controls

Figure 4-11. Underfired broiler with 9 control knobs. Photo: Baker’s Pride, Ltd.

Broilers


heat time.1 The “Broil-Master®” reduced gas flow when the broiler was on, but not cooking. When the operator was ready to cook, he pushed a button that restored full input to the broiler. The Broil-Master maintained this rate for a specified amount of time (e.g. 10 minutes) that covers most cooking events. If more food product was added to the grid, the operator pushed the button again to continue cooking. Results from in-kitchen testing of the Broil-Master control at Pacific Gas and Electric Company’s production test kitchen are presented in the Broiler Performance section of this chapter.

Since broilers are not thermostatically controlled and manufacturers have established input rates based on peak production (i.e., high broiling tempera-tures that minimize cook time), they typically consume energy throughout the day at a rate that is close to their maximum input (e.g. 90% duty cycle). The end of a cooking event does not automatically return the broiler to an “idle” state, unlike other appliances that consume less energy to maintain a set temperature once the food load is removed. Furthermore, a charbroiler's flame does not remind the operator to turn the broiler off between loads be-cause it is partially concealed beneath the grid and/or coals. Thus, a cooking-energy efficiency measured over the time span of the cooking event has less meaning for broilers than for other cooking appliances. However, measured discrete-load cooking energy efficiencies provide a benchmark as efforts are made to improve the performance of broilers.

The body of published information regarding broiler performance is rather thin, save for a 1983 University of Minnesota Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study.2 Partial results of this study, based on several gas and electric underfired charbroilers, is pre-sented in Table 4-2.

Table 4-2. Underfired Broiler Cooking-Energy Efficiency.

Gas Electric

Cooking-Energy Efficiency (U of M method, %)

15 - 30

35 - 65

Broiler Performance

Broilers


More recently, the Food Service Technology Center in San Ramon, Califor-nia has developed test methods for the performance of underfired, overfired and conveyor broilers. The underfired broiler test method has been adopted as an official ASTM Test Method.3 The test methods for overfired and con-veyor broilers are in the process of ratification by ASTM. These test methods quantify all aspects of broiler performance—energy input rate, preheat en-ergy consumption and time, idle energy rate (if applicable), cooking energy rate, cooking-energy efficiency, production capacity, temperature distribu-tion—even the pilot energy rate on gas broilers equipped with standing pi-lots.

The following sections give an overview of the different aspects of the un-derfired charbroiler test method, although most of the concepts apply to all broiler categories.

Energy Input Rate

As previously shown in Table 4-1, the energy input rate of a broiler varies with broiler width and burner (input) density. The ASTM test method meas-ures energy input rate to verify the manufacturer’s nameplate rating and con-firm that the broiler is operating properly.

Temperature Distribution

The ASTM test method measures the surface temperature distribution of an underfired broiler using ¼-inch thick carbon steel disks with thermocouple wires attached to their geometric centers (Figure 4-12). The broiler is oper-ated at its full input rate and the average temperature of each disk is reported. The data can then be presented in a uniformity plot, as shown in Figure 4-13.

The plot in Figure 4-13 shows a substantial temperature drop off towards the front of the cooking surface, which is not unusual for broilers. Where a grid-dle may see a maximum difference of 50°F across its entire surface, a tem-perature variation of 200°F or more across the cooking area of a broiler would be considered normal. While at first this may sound like a problem, this temperature difference is often used to the operator’s advantage. An ex-

Broilers


perienced cook will place more delicate items such as chicken or shrimp on the cooler areas of the broiler, and use the hottest spots for heavier items, such as steaks or chops.

Figure 4-12. Thermocoupled steel disks.

Figure 4-13. Underfired broiler tem-perature uniformity plot.

Broilers


On the other hand, this introduces a learning curve for the operator that may be undesirable in certain operations, such as those with high employee turn-over or operations utilizing entry-level cooks.

Preheat Energy Consumption and Time

While the energy used during preheat is relatively small when compared to the overall daily energy consumption of a broiler, the preheat time gives an accurate indication of how long the broiler needs to operate before it is ready for use. For gas underfired charbroilers, preheat times are typically 15 to 20 minutes.


At the present time, almost every broiler type operates at or near its maxi-mum input at all times. The exceptions, whose designs allow some type of energy rate reduction during periods of non-cooking, would be conveyor broilers and some of the lighter weight salamander/cheesemelters. So while most broilers would not need to have an idle energy rate test applied to them, the procedure is being incorporated into the ASTM Test Method in anticipa-tion of new designs that allow a lower idle energy rate.


The cooking energy rate indicates the rate of energy consumption during the cooking process. On an underfired broiler, this rate will be constant, since there is no cycling of the burners or heating elements as on most other appli-ances. To determine the energy efficiency of underfired broilers, the ASTM Test Method specifies cooking tests that use 1/3-pound hamburger patties as the food product. Cooking-energy efficiency is the ratio of energy added to the patties and the total energy supplied to the broiler during cooking:

× 100% E food

E appliance Cooking-energy efficiency % =

Broilers


Figure 4-14 shows the cooking energy efficiencies of several 3-ft gas under-fired charbroilers tested in accordance with the ASTM Test Method.4,5

20

25

30

35

40

45

1 2 3 4 5 6Test Broiler Number

Coo

king

-Ene

rgy

Effic

ienc

y (%

) .

These cooking-energy efficiencies were determined from cooking discrete loads of hamburger patties. However, the real-kitchen cooking-energy effi-ciency drops dramatically as the energy consumed by the broiler during peri-ods of non-cooking is factored into the denominator of the energy efficiency equation.

For example, Pacific Gas and Electric Company’s in-kitchen performance testing showed a gas underfired broiler used to cook 100 lb (45 kg) of food over an 8-hour period could consume 600 kBtu of energy.6 Estimating that 300 Btu was required to cook each lb (kg) of food,2 the total energy input to the food product over the eight-hour period would be only 30 kBtu. This translates to a real-world cooking-energy efficiency of only 5%, significantly less than the 25-35% efficiencies reported for discrete-load tests (Table 4-2

Figure 4-14. 3-ft. gas underfired char-broiler cooking-energy efficiencies.

Broilers


and Figure 4-14). Restated, only 5% of the energy consumed by an under-fired broiler in an actual kitchen is delivered to the food product. The poten-tial for energy-efficiency performance improvements in the design and usage of broilers is obvious.

Production Capacity

Production capacity indicates the amount of food (by weight) that can be cooked on a broiler in a given amount of time. Since the ASTM Test Method uses hamburger patties for the test product, production capacity is the weight, in pounds, of hamburger patties that can be cooked by the broiler in one hour (lb/h). This number is dependent on the size of the broiler and the length of the cook time. The production capacities of several gas underfired charbroil-ers are shown in Figure 4-15.4,5

20

30

40

50

60

70

80

1 2 3 4 5 6Test Broiler Number

Prod

uctio

n C

apac

ity (l

b/h)

.

Figure 4-15. 3-ft. gas underfired char-broiler production capacities.

Broilers


Projected energy consumption for gas and electric broilers are presented in Table 4-3 and 4-4. Based on Pacific Gas and Electric Company’s in-kitchen monitoring at its production test kitchen, average energy consumption rates for underfired gas and electric broilers reflect duty cycles of 90% and 82%, respectively.6-9 An appliance’s duty cycle can be defined as the average rate of energy consumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy. Daily energy consump-tion for broilers was calculated by multiplying the median rated input for each broiler category by the respective duty cycle and the hours of operation. Projected annual energy consumptions were determined by assuming 6-day operations for 52 weeks.

Table 4-3. Projected Energy Consumption for Gas Broilers.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (kBtu/h) (%) (kBtu/h) (h/d) a (kBtu) b

UNDERFIRED: Charbroiler 3 ft. 90-120 (Median) 105 80 c 84 8 210,000

OVERFIRED:

Upright 3 ft. 80-110 d Salamander 3 ft. 28-49 Cheesemelter 3 ft. 20-39 (Median) 65 e 70 f 46 8 115,000

a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c The average energy consumption rate and typical hours of operation are based on data from monitoring two 3-ft gas charbroilers in a real-world food service operation.6,7 An associated duty cycle of 80% was calculated . d Typical range for single-deck overfired broiler. eThe median energy input rate for overfired broilers is based on the ranges for upright broilers, salamanders and cheesemelters. f A 70% duty cycle has been assumed for overfired broilers based on the assumption that the usage pattern is some-what less than underfired (e.g., charcoal) broiler operations. Also, typical operating hours were assumed to be the same for both appliance types.

Broiler Energy Consumption

Broilers


Table 4-4. Projected Energy Consumption for Electric Broilers.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours



UNDERFIRED: Charbroiler 3 ft. 10 - 12 6 - 14 (Median) 11 70 d 8 10 24,960 85,200

OVERFIRED:

Upright 3 ft. 11 – 17 e Salamander 3 ft. 5 - 12 Cheesemelter 3 ft. 2 - 6 (Median) 10 f 70 g 7 10 21,840 74,500

a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h. d The average energy consumption rate and typical hours of operation are based on data from monitoring two 3-ft electric charbroilers in a real-world food service operation.8,9 An associated duty cycle of 70% was calculated . e Typical range for single-deck overfired broiler. f The median energy input rate for overfired broilers is based on the ranges for upright broilers, salamanders and cheesemelters. g An 70% duty cycle has been assumed for overfired broilers based on the assumption that the usage pattern is similar to underfired (e.g., charcoal) broiler operations. Also, typical operating hours were assumed to be the same for both appliance types.

Broil-Master® Control

The Broil-Master® control was evaluated over a 6-month period in a “before and after” installation on a 3-foot (900 mm) underfired charbroiler in Pacific Gas and Electric Company’s production-test kitchen.1 With the control set to reduce the energy rate by 65%, monitoring showed that average energy con-sumption was lowered from 112,000 Btu/h to 83,000 Btu/h. This reduced the broiler’s duty cycle from over 90% to 70%. Unfortunately, the Broil-Master is no longer available, but the results of its performance are encouraging when considering the design of a broiler with turndown technology. Results of the Broil-Master testing are presented in Table 4-5, Figure 4-16 and Figure 4-17.

Broilers


Table 4-5. Summary of Broil-Master® Energy Saver Performance.

Without Energy Saver With Energy Saver

Direct-fired Broiler a Data Collection Sept-Dec 1994 Jan-Mar 1995 Days in Data Set 39 22 Production Energy Use (kBtu/day) b,c 1,270 839 Appliance On-Time (h/day) 11.3 10.1 Average Production Energy Consumption Rate (kBtu/h) 112 83.2 Duty Cycle (%) 94 70

a 65% energy input reduction, 10-minute timer “on time.” b Energy consumption is based on an average gas heating value during the monitoring period. c Includes preheat and idle energy over the hours of operation when the broiler was in use.

0

20

40

60

80

100

120

140

5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9

Time of Day

Ener

gy C

onsu

mpt

ion

Rat

e (k

Btu/

h)

AM PM

Total Energy Consumption = 1,230 kBtu

Figure 4-16. Direct-fired broiler en-ergy consumption pro-file before installation of the Broil-Master control.

Broilers


0

20

40

60

80

100

120

140

5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9

Time of Day

Ener

gy C

onsu

mpt

ion

Rat

e (k

Btu/

h)

AM PM

Total Energy Consumption = 910 kBtu

The ventilation requirements for underfired broilers are greater than for other categories of cooking equipment, with the exception of woks and solid-fueled appliances. For example, typical ventilation rates for gas charbroilers operating under wall-mounted canopy hoods are in the range of 350-450 cfm (540-700 L/s) per linear foot of hood.

The radiant heat gain to the kitchen from broilers contributes significantly to the cooling load of a kitchen. Research has shown that an underfired broiler operating at an average energy rate of 78,000 Btu/h can radiate as much as 20,000 Btu/h to the surrounding space. This could represent several tons of additional cooling for a 3 to 4-ft (900 mm to 1220 mm) charbroiler.10

The high rate of energy consumption and associated low energy efficiency for gas broilers suggests that research and development efforts could quickly benefit the food service industry. The Food Service Technology Center was commissioned by Enbridge Gas Distribution to identify the elements of an advanced gas underfired charbroiler.5 The advanced broiler project, con-

Figure 4-17. Direct-fired broiler en-ergy consumption pro-file after installation of the Broil-Master control.



Broilers


ducted in collaboration with the Gas Technology Institute (GTI), will evalu-ate different technologies and designs in order to develop a gas underfired charbroiler that exhibits a marked increase in energy performance. While the goal of the project is to produce an advanced underfired (char) broiler, it is anticipated that the design of other broiler types may benefit from the re-search as well. Desirable characteristics of an advanced underfired broiler would include:

Improved Uniformity. Reduced variation in temperature across the cooking grid and more precise control over temperature in individual sections.

Reduced Energy Consumption. Allow the broiler to lower its energy input during idle periods and increase its energy efficiency during cooking.

Reduced Heat Gain. Increase operator comfort and potentially reduce the cooling load for the kitchen.

Lower Emissions. Reduce grease and smoke emitted by broiler.

Food Quality. Maintain the signature “charbroiled” food characteristics.

Research issues related to developing an advanced broiler include:

Grid/Burner/Heat Shield Design. Determine what characteristics allow op-timal combination for highest energy and cooking performance.

Temperature Feedback. Determination of type and location of temperature sensing to allow temperature feedback from broiler.

Load Sensing. Allow detection of cooking and non-cooking periods.

Gas Valves/Burners. Modulating gas valves to allow turn down during idle when coupled with load sensing.

Control. Allow temperature adjustment, broiler turn down and communica-tion compliant with NAFEM’s online kitchen protocol.

Lids. An optional lid to further energy reduction during idle, and potentially increase cooking performance. Explore the addition of forced convection or an air curtain for reduced cook times.

Integrated Ventilation. Develop a close-coupled integrated exhaust hood that can capitalize on reduced ventilation requirements during idle periods.

Broilers


Broilers represent a substantial load to gas utilities. In gas service territories, the electric broiler does not present a competitive advantage over gas equip-ment. However, the intense energy requirements of gas broilers and their po-tential (real or perceived) to contribute to urban air pollution could be considered a market threat. Conversely, the even more severe fuel costs and emissions from solid-fuel charbroilers present a marketing opportunity for gas broilers. In air-quality sensitive cities (e.g., Los Angeles), the future for solid-fueled appliances does not look good. Over the short term, gas broilers and rotisseries may represent a viable option to solid-fueled equipment (This is the strategy being adopted by The Keg and Swiss Chalet in Canada). How-ever, the long-term viability of gas-fired broilers may be dependent on the design of more environmentally friendly equipment.

There is a clear need for gas utilities to promote energy-efficient broiler technologies to keep high operating costs from impacting negatively on the economic viability of a customer. In this vein, the gas industry needs to sup-port development of broiler designs that are more environmentally friendly. With improved design, controls and operation, broilers could in fact, be more energy efficient than alternative appliances. Griddles, for example, will al-ways have significantly less stand-by energy requirements.


Broilers


1. Zabrowski, D., Conner, M., Mogel, K., 1995. Custom Electronics En-ergy Saver® Gas Control System for Commercial Broilers. Food Ser-vice Technology Center Report 5011.95.27, October.

2. Snyder, O. P., D. R. Thompson, J. F. Norwig., 1983. Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study. Final research report prepared by the University of Minnesota under contract with the American Gas Association.

3. American Society for Testing and Materials, 1996. Standard Test Method for the Performance of Underfired Broilers. ASTM Designation F 1695-96. In Annual Book of ASTM Standards, West Conshohocken, PA.

4. Zabrowski, D., Nickel, J., Weller, T., Mogel, K., 1997. Development and Validation of a Standard Test Method for Underfired Broilers. Food Service Technology Center Report 5011.97.48, December.

5. Sorensen, G., Fisher, D., 2002. Assessment of Technical Strategies for an Advanced Commercial Gas Charbroiler. Prepared for Enbridge Con-sumers Gas.

6. Geiger, T., 1993. Wolf Commander Range-Match SUPER Char-Broiler: Appliance Performance in Production. Pacific Gas and Electric Com-pany Department of Research and Development Report 008.1-91-28, February.

7. Pieretti, G., Blessent, J., Kaufman, D., Nickel, J., Fisher, D., 1990. Cooking Appliance Performance Report - PG&E Production-Test Kitchen. Pacific Gas and Electric Company Department of Research and Development Report 008.1-90.8, May.

8. Selden, M., 1992. Appliance Performance in Production: “Hobart” Electric Char Broiler Model CB51. 1992. Pacific Gas and Electric Com-pany Department of Research and Development Report 008.1-92-4, De-cember.

9. Zabrowski, D., 1994. Wells Model B-50 Electric Broiler: Appliance Performance in Production. Food Service Technology Center Report 5011.94.3, August.

10. American Society of Heating, Refrigerating and Air-Conditioning Engi-neers, Inc. 1993 ASHRAE Handbook: Fundamentals; I-P edition. 1993.


References

5 Range Tops


It can be said that the commercial range top is the most widely used piece of commercial cooking equipment. In addition to being widely used, the range top also is one of the most versatile cooking appliances, lending itself to nu-merous burner (element) configurations. Ranges are available with either gas or electric fuel sources, although gas dominates the market. Typically, a range-top configuration consists of six open gas burners with a standard oven incorporated underneath (see Figure 5-1). Though the commercial range top is similar to the residential stove, the major difference is durability; a food service range must withstand constant use and abuse while preparing tens or hundreds of meals a day.

The top section of the range is referred to as the “range top” and consists of burners or elements, which are used for cooking with pots and pans. The oven that is built into a range is called a "range oven". Range ovens are most often standard ovens sized to fit under the range top, though a growing num-ber of manufacturers offer convection range ovens. Ovens are discussed in detail in Section 7 of this report. Range-top configurations also may include griddles and broilers; these appliances are detailed in Section 3 and 4, respec-tively.

The configuration of a range is flexible by definition. The space underneath a range top that is usually devoted to a range oven may instead house a refrig-erated cabinet or storage space for pots and pans. Above and behind the range top is the backshelf, which can accommodate an overfired salamander- or cheesemelter-type broiler. Smaller ranges may include a narrow griddle and/or charbroiler on either side of the range top.

Ranges are often divided into three categories depending on their intended use: heavy-duty or hotel ranges, medium duty or restaurant ranges, and spe-cialty ranges such as stockpot and taco ranges. Heavy-duty ranges are built for continuous use in high-volume operations such as large restaurants, hos-pitals, and schools. They feature high-energy inputs and sturdy construction,

Introduction

Figure 5-1. Six-burner range top with range oven.

Range Tops


with range tops built to support the weight of large stockpots and enough power to heat such a vessel quickly. Restaurant ranges are more suited to a smaller operation, such as a lunch counter or smaller restaurant. Medium-duty ranges, although substantially built, are not as well suited for heavy use or abuse, and often have lower energy inputs (e.g., range top burners of 15-20 kBtu/h instead of a hotel range's 20-30 kBtu/h).

Induction range tops use electromagnetic energy to heat cookware made of magnetic material (steel, iron, nickel or various alloys). When the unit is turned on, the coils produce a high frequency alternating magnetic field, which ultimately flows through the cookware. Molecules in the cookware move back and forth rapidly, causing the cookware to become hot and cook the food.

Specialty ranges are built to perform a single function, as the name implies. Stockpot ranges consist of one or two high-input open burners with a very heavy-duty cast iron grate and are intended to cook large quantities of food in one cooking vessel. Chinese ranges are designed for wok cooking and are described in Section 6. An example of a specialty range is presented in Fig-ure 5-2.

Range tops vary with fuel source and heating technology. Both gas burners and electric elements can be built into restaurant range tops, although gas is by far the most common. In hotel range tops, gas is almost universal.

Two or more range tops joined side-by-side is called a battery, often with matching trim, countertop sections and possibly a front-mounted gas mani-fold; such a range battery may stretch the length of a kitchen wall.

All range tops provide heat to a pot or pan from below. The method of heat delivery to the pot may vary, but the cooking process is always a function of the heat being delivered from the bottom of the pot/pan. One way in which this cooking process may be affected is through the heated area, or size of the heating pattern. Some range-top heating strategies provide uniform heat over a larger area, while others concentrate it more in one spot. This becomes a significant performance factor if the range top is used in a process such as cooking pancakes, where surface uniformity is important; however, the

Figure 5-2. Stock pot range. Photo: Vulcan Hart

Cooking Processes

Range Tops


choice of pan construction and materials can be used to mitigate unevenness in the heating source.

Range tops are generally not amenable to timers or cooking computers, and most range top cooking demands the attention of the operator. Controls on the range top are typically very simple. There is most often an infinite-control knob to regulate the input of each burner or element. The controls are calibrated in terms of the percentage of input, as the burner does not gener-ally sense the temperature of the pot.

An exception to this rule is the induction ranges top, which has a tempera-ture-limiting switch to guard against the pot-melting temperatures that this type of unit can produce. In addition, induction range tops will often have a microprocessor for temperature control. Just beneath the glass cook top is a tiny temperature sensor that connects to the microprocessor. When the tem-perature control is set to a particular temperature, the microprocessor moni-tors the temperature and cycles the induction hob on and off to maintain the desired temperature.

Gas burners and electric elements can be described as "open" or "closed". The most common type of range top uses open burners, applying flame di-rectly to the bottom of the pot. Open tops generally offer fast heat-up, but can have slow cleanup, as spills can fall directly onto the burner or below. Cleanup may mean moving or removing parts of the range top to reach the mess. A closed burner or element seals the heat source under a ceramic, glass or metal cover, presenting a smooth surface to the bottom of the cooking ves-sel. This makes it easy to slide pots and pans on and off of the hot spots, and also eases cleanup.

Each heating technology described here comprises a different type of burner or element. Manufacturers commonly allow the user to specify a combination of burner or element configurations that will best suit their specific needs.

Controls


Range Tops


Open Burners and Discrete Elements

Open Gas Burners. Open gas burners remain the burner-of choice for most operators. They are inherently sturdy, inexpensive, and they respond in-stantly when the burner is turned on and adjusted. The visible flame provides direct feedback on the heat to the pan, enhancing the operator’s control, and can ignite spattered grease to “flash” flame inside the pan during display cooking.

The gas burner has two designs. The first is a hollow ring of cast iron or steel with holes that jet gas upwards towards the cooking vessel (Figure 5-3). A newer but similar design is the star burner, which has arms radiating from a central hub spreading its flame more evenly over the pot bottom (Figure 5-4). Each burner design has the gas mixed with primary air at an air shutter on the manifold. Secondary air provides most of the oxygen for combustion, com-bining with the gas as it jets from the burner. The flame is controlled with a gas valve mounted on the front of the range.

The burner is set into the surface of the range top and covered by a metal grate, which supports the cooking vessel. Grates are designed so that pots can be slid easily from burner to burner, and are stable in any position. Normally with this grate design, a spill tray will be underneath the burner to catch fal-ling particles and/or drips. The grates may be removable, and on some range tops the burner heads lift off for easy cleaning.

The typical input rating for an open gas burner is 20 to 25 kBtu/h, with manufacturers offering 30 kBtu/h burners as an option. Until recently, the higher-input burners only were used in the most demanding production ap-plications. However, they now are becoming the industry standard for heavy-duty ranges. Studies at the FSTC indicate that, under normal operating condi-tions, these higher input burners do not use significantly more energy to cook as one might intuitively think. Although the gas input is higher, the cook time is correspondingly shorter.1 However, the net effect of these more powerful burners could be an increase in energy consumption if the burners were left on between cooking events as sometimes happens in high profile display kitchens or on sauté lines.

Figure 5-3. Ring burner. Photo: Fisher-Nickel, inc.

Figure 5-4. Star burner. Photo: Fisher-Nickel, inc.

Range Tops


Electric Speed Coils. Sheathed electric coils, wound into a spiral element, are used on light- and medium-duty restaurant ranges. See Figure 5-5. These elements also are known as “speed coils.” Analogous to the elements on a residential electric range, they provide fast heat and response. They are rela-tively fragile though and not recommended for use with heavy stockpots.

Electric French Plates. (Also called round plates.) In a French plate ele-ment, the open electric coil is covered with a solid metal disk. They are gen-erally 6-10 inches (150-250 mm) in diameter, and protrude ¼ to ½ inch (6 to 12 mm) above the range top. By concentrating heat under the pot, they pre-heat faster than an electric hot top, and are more durable and easier to clean than an electric speed coil. Figure 5-6 shows an electric range with French plates.

Closed Burners and Elements

Gas Hot Tops. The hot top is a flat metal plate made of cast iron or steel, heated from underneath by atmospheric gas burners. The bottom of the plate may be flat, textured, or finned to distribute heat evenly. The surface of the hot top reaches temperatures of 800°F-1000°F (425°C to 540°C) at the maximum input. Some hot tops are constructed so that there is a temperature gradient from front to back, allowing different styles of cooking on the same section. The hot-top section is typically 24 inches (600 mm) deep and 12-18 inches (300-450 mm) wide. A range top may consist of several sections, each having its own burner and control knob.

Hot tops allow the entire surface of the range top to be used, instead of only the space directly over the burners. This allows an operation that prepares many small orders at once to fit more pans on the range top. Pots slide across the flat surface more easily than across the grids on an open-burner range top. This facilitates moving items such as soups or stews from a front hot- top section that is set at a high temperature (i.e., for boiling) to an alternate section that is set at a lower temperature (i.e., for continued simmering or holding). However, the hot top is slow to heat: it may take 30 to 60 minutes before the plate reaches its maximum temperature setting. Similarly, it is slow to respond to changes in the control setting.

Figure 5-5. Electric speed coil. Photo: Clarkenergy.com

Figure 5-6. French plate range top. Photo: Garland Range.

Range Tops


Hot tops are typically preheated in the morning and left on at maximum input throughout the day. They consume energy at a high rate, and radiate more heat into the kitchen than any other type of range top. The energy input rates are from 20-40 kBtu/h per section.

One alternative to the high energy consumption of the hot top is the open grate top. This range top has a continuous flat surface like a hot top but sur-face is comprised of a grate instead of a solid plate. This configuration re-duces the heat-up time of the top and allows the operator to see the burners and control them more accurately. Ultimately, the operator has the work sur-face associated with a hot top combined with the speed and flexibility of an open burner range top. This style of level-surface grate is becoming a stan-dard feature on most heavy-duty, open-burner ranges.

Gas Radiant Hot Top. (Also called French top or pot ranges) This is a spe-cialized hot top in which the metal plate is inset with removable concentric rings. The rings may be removed to expose more of the cooking vessel to the direct flame of the burners. This style of hot top uses very high-powered burners with inputs up to 45 kBtu/h. In this case, the controls on the range top allow the operator to adjust input to each ring separately.

Electric Hot Tops. Electric hot tops are not common. They are identical in construction and detail to the gas hot top, except the heat source is an electric element clamped to the bottom of the plate. Electric hot tops are rated from 5 kW to 7.5 kW per section.

Induction Cook Tops. The electric induction range is significantly different from other types of ranges. An induction cooktop by and large consists of a single hob (burner), but two-hob units are available, with the exception of Europe and Asia, where six-hob units are offered (note that a U.S. manufac-turer had a six-hob unit was on display at the 2002 National Restaurant As-sociation show in Chicago). The range surface is a smooth and continuous ceramic glass plate. Because it is not directly heated during operation, the surface remains relatively cool, gaining residual heat from the cooking con-tainer. These units offer precise temperature control and are more efficient because the cookware is heated directly, without the need to preheat heat the cooking surface.

Range Tops


A recent addition to the induction range family is the induction wok. These units offer high production capacity in a small package and without the need to water-cool the surrounding surface, as with traditional gas woks. They do employ a different control mechanism from traditional woks and may not be a direct replacement for gas-fired Chinese ranges in traditional Asian cook-ing. Induction units are by far the most energy efficient type of range avail-able.

Technologies developed for commercial use have focused on improving gas burner efficiencies, and on designing easy-to-clean closed range tops for both gas and electric ranges.

Power Burners

Power burners premix gas and air in stoichiometric proportions for efficient combustion. Because no secondary air needs to be drawn into the flame at the burner head, the grate can be constructed to form an almost airtight chamber beneath the pot. This eliminates the rapid convection that washes much of a conventional burner's heat up and around the cooking vessel. Thus, more of the hot-combustion products transfer heat to the bottom of the vessel. The intense heat of the power burner presented its own obstacle. The initial commercial release was halted because users complained about pots warping on the new burners, as a result of underestimating the cooking speed and allowing pots to boil dry.

Testing by the American Gas Association Laboratories (AGAL) showed a power burner to be 36% faster and use 34% less energy than a conventional 20 kBtu/h star burner.2 Although the initial cost of a power-burner is higher than a standard burner, AGAL estimated that energy savings would compen-sate for the cost difference in less than two years.

Sealed Combustion

The Canadian Gas Research Institute (CGRI) developed a prototype range top, which featured standard gas burners under a glass ceramic surface.3 Each

Advanced Technologies

Range Tops


burner is surrounded by a ceramic cup, which is heated to over 1200°F (650°C) during operation. Heat is supplied to the cooking vessel by conduc-tion through the glass ceramic surface and by radiation from the burner flame and ceramic enclosure. An over-limit switch shuts the burners off if the tem-perature of the ceramic glass top rises outside the operating range.

The burners are completely enclosed, and all combustion products are vented outdoors. This closed-burner design has the appeal of easy cleanup, a visible heat source and according to Gas Technology Institute (GTI), a higher effi-ciency than standard gas open burners.

The current sealed-combustion prototype is for residential applications. The unit's easy cleanup, speed and lower heat gain to the kitchen also would be valuable in a food-service setting.

Gaz de France, as part of their strategy to help the foodservice industry, and in concert with commercial cooking equipment manufacturers, has intro-duced a patented Vitrogaz ceramic hot plate. It features a smooth, flat, easy to clean cooking surface and is powered with two high-performance, 27 kBtu/h radiant burners. It can be used with an open flame or as a solid-top plate. Plate temperatures are adjustable between 140°F and 1112°F (60°C and 600°C).4

Infrared Burners

Infrared burners force gas and air through a ceramic burner. The surface of the burner, where combustion takes place, is perforated with thousands of pores. During operation the ceramic burner face reaches temperatures above 1600°F (870°C). Infrared burners are more efficient than the standard gas burner, but they have not yet been successfully applied to the commercial food service range top.

A setback lies in spilled food product clogging the burner holes. A solution is the infrared jet-impingement burner, which uses an infrared ceramic burner beneath a perforated glass-ceramic plate. The glowing ceramic burner trans-mits radiant heat to the cooking container, and the combustion products are propelled through the holes in the ceramic glass shield to impinge on the bot-tom of the pot. The shield prevents spillage from dripping onto the burner,

Range Tops


and what does flow through the holes is incinerated. The developer, Tecogen Inc., rates the ease of cleaning these burners as “somewhat better than con-ventional burners.” The developer reports a water boil efficiency of 66% as opposed to 40% for a regular burner.5

Halogen Range Tops

Halogen range tops share two of the major advantages of the induction range top—fast response to controls and a sealed cooking surface. In addition, the halogen elements glow red in proportion to the energy input, providing visual feedback of heat intensity. Unlike induction range tops, the cooking surface does heat up, and power does not instantly modulate to idle when the pot is removed.

The heat source for this range top is a set of halogen lamps beneath a glass ceramic cooktop. Pots and pans rest directly on the ceramic and are heated by radiant energy from the lamps. An over-limit switch monitors the glass ce-ramic material, cutting off the power when the temperature of the cooktop exceeds safe limits. The efficiency of a residential halogen cooktop has been reported at 52%-58%.6 Currently this technology is not available in commer-cial range units.

Automatic Burner Shut Off and Re-Ignition.

In catering kitchens it is often more practical to leave open-flame burners lit when not being used, rather than turning the gas off and re-lighting it each time when needed. Gaz de France, along with Madec-Mater Company, has patented the Top-Flam–an automatic shut-off and re-ignition device that is triggered by cookware detection. They proclaim energy savings around 50%.4

A similar burner control system was developed in the United States by Leo-nard Grech and documented by the U. S. Department of Energy’s Office of Industrial Technology. This system uses a small, vertically mounted, spring-loaded piston that controls a gas valve. When a pot is placed on the burner,

Range Tops


the piston is depressed and the gas valve is opened. When the pot is removed, the piston returns to its original position and the burner is turned off.

Performance Evaluation Criteria

ASTM Standard F 1521–96 Standard Test Methods for Performance of Range Tops 7, developed at the Food Service Technology Center, provides a means to compare performance and energy use of range tops 8.

The test method covers the performance of gas and electric range tops, in-cluding discreet burners and elements, as well as hot tops. The application of the test method provides results for maximum rate of energy input, tempera-ture uniformity of heating surface, cooking-energy efficiency and production capacity.

Measuring the temperature uniformity of a steel plate emulating the bottom of a frying pan can simulate the heat-transfer characteristics of a cooking unit. Applying this test procedure gives the temperature at several points across the area of a pot's bottom, indicating hot or cold spots.

Production capacity is the amount of food that a burner or element can cook in a given time, expressed as gallons of water that can be raised from 70°F to 200°F (21°C-93°C) in one hour. This provides an indication of the “speed” of a burner.

Maximum rate of energy input is a rough index of the “power” of a range top. The test method reports the total energy input rate for all the burners on a range top. It is more common in catalogs to see a rating for individual burners or elements. For a given type of burner or element, a higher rate of energy input generally indicates that the burner can supply more heat to the pan. This is only true when comparing similar burners; a high-efficiency burner can use less energy, but perform more work than a low-efficiency burner (i.e., cook the same quantity of food in less time).

The American National Standard Institute (ANSI) for Gas Food Service Equipment Ranges and Unit Broilers (Z83.11 –1989) section 2.12 9 also de-tails test criteria and methods for evaluating the efficiency of an open gas range top. ANSI’s test requirement is similar to ASTM with some minor dif-

Range Top Performance

Range Tops


ferences. Table 5-1 compares the test criteria between ASTM F1521-96 and ANSI Z83.11 – 1989.

Table 5-1. Comparison of ASTM and ANSI Range Top Efficiency Tests.

ASTM

F1521-96

ANSI Z83.11

Proposed Revisions to

ASTM F1521-96a

Stabilization Time (min.)

30

30

30

Temperature Rise (°F)

130°F

130°F

130°F

Control Setting Maximum Maximum Maximum

Pot Diameter

(inches)

12

<15,000 Btu

9.5”

15,000 to 25,999 Btu

13”

>26,000 Btu

16”

13”

Water Weight (lbs)

20

N/A (10) b

N/A (20) b

N/A (29) b

20

Water Depth (inches)

N/A (5) c

4

N/A (4) c

a Proposed change from 12-inch stockpot to 13-inch stockpot has been accepted by the F26 ASTM techni-cal committee. b Measured water weight with respect to 4-inches of water depth. Note: Water weight is not specified in ANSI Z83.11

c Measured water depth with respect to 20 pounds of water in the specified pot. Note: The ASTM test method specifies water weight instead of water depth since weight can be determined more accurately.

Table 5-1 shows that specified stabilization times, temperature rise, and power settings are identical for the two methods. The differences are the di-ameter of the pots and the weight and depth of water. Based on the outcome of investigating these latter differences, researchers at the Food Service Technology Center will initiate a proposal to revise ASTM F1521-96 to be consistent with ANSI Z83.11. The proposed changes are as follows:

1. Change the ASTM specification from a 12-inch diameter pot to a 13-inch

diameter pot to match ANSI’s requirement for a range top with an energy input rate between 15,000 – 25,999 Btu/h (Update: proposed change has been accepted by F26 ASTM Technical Committee; revision will be made to the current test method).

Range Tops


2. Adopt 13-inch diameter pot test for all burner types and input rates on standard range tops.

3. Add an extra-heavy load test using a 16-inch diameter pot.

4. Water weight will remain as the test criterion in the ASTM test, since weight is an accurate method of measuring water, and this value needs to be precise for the efficiency calculation.

Cooking-energy efficiency, as defined by the ASTM Standard Test Method for Performance of Range Tops,7 is the ratio of the amount of energy going into the food versus the amount of energy supplied to the burner:

%100×=Appliance

Food

EEiciencyCookingEff

Energy efficiency is determined by heating water from 70 to 200°F (21 to 93°C) at the full-energy input rate. Using FSTC data generated by the ASTM method 7, along with data from the Minnesota study10 and range top devel-opment and testing by AGAL, 11,12 benchmark energy efficiencies are pre-sented in Table 5-2.

The efficiency of gas range tops has received attention from both the manu-facturer and the end user. 13 Research organizations such as the GTI have been instrumental in attempting to develop and bring high-efficiency gas models to the US market. Standard electric range tops, at roughly 65-75%, are already quite efficient. With the introduction of induction technology, electric range top efficiencies are approaching 85%.

Table 5-2. Range Top Energy Efficiency. a

High Efficiency Gas (%) Standard Gas (%) Electric. (%) 30 - 40 25 - 30 65 - 85

a Energy efficiency numbers for range tops are best estimates based on FSTC test data from applying ASTM Stan-dard Test Methods to four different range tops1,14-16, on preliminary results from revising the existing ASTM Standard and applying it to three electric induction units18-19 and on data from both the Minnesota Study10 and AGAL test-ing9,11,12.

Benchmark Energy Efficiency

Range Tops


Projected energy consumption for gas and electric range tops are presented in Tables 5-3 and 5-4. The energy consumption rates for the range tops and range ovens are based on in-kitchen monitoring of gas and electric ranges, outfitted with either a standard or a convection oven, in the Pacific Gas and Electric Company production-test kitchen.20-26 The duty cycle was calculated by dividing the daily energy consumption rate by the appliance median en-ergy input rate. Typical operating hours were obtained from in-kitchen en-ergy-use monitoring experiences and observations as well as from the PREP study 27 and a proprietary end-use monitoring report. Projected annual energy consumption was determined by assuming a 6-day per week, 52-week per year operation.

Table 5-3. Projected Energy Consumption for Gas Ranges.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (kBtu/h) (%) (kBtu/h)a (h/d)b (kBtu)c

Range Top 6 Burners 120 - 210 (Median) 165 20 32 12 120,000 Range Oven 35 - 45 (Median) 40 40 16 8 39,900 Total Range 205 48 160,000 a Average energy consumption rates are based on monitoring five gas ranges in a real-world production kitchen.20-24

b Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". c The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year.

Range Top Energy Consumption

Range Tops


Table 5-4. Projected Energy Consumption for Electric Ranges.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating Hours


(kW) (%) (kW)a (h/d)b (kWh)c (kBtu)d

Range Top 6 elements 12 (Median) 12 25 3 12 11,200 38,300 Range Oven 8 (Median) 8 25 2 8 4,990 17,000 Total Range 5 16,200 55,300 aAverage energy consumption rates are based on monitoring two electric ranges in a real-world production kitchen.25,26

bOperating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". cThe annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. dConversion Factor: 1 kW = 3.413 kBtu/h.

Ranges are classified as medium duty from the perspective of exhaust venti-lation. For a sidewall canopy hood, the design ventilation rate for ranges would range from 200- 300 cfm (100-150 L/s) per linear foot of wall canopy hood.

Gas range tops have historically had several advantages over electric range tops. Gas is faster with no wait for preheating. Gas is more responsive: an adjustment to the controls changes the heat to the pan bottom immediately. Gas is more durable: heavy-duty construction and long life are hallmarks of gas-range construction. Gas is inexpensive: even though a gas range operates at a lower efficiency, the operating cost is often half that of an electric range top.

In turn, electric range tops have had the advantage of high efficiency and are easier to clean when closed burners are used. The induction range top com-bines these features with a serious challenge to the superiority of gas in speed and responsiveness. It is an easy to clean, fast heat source with a discrete-load cooking efficiency of over 80%, and it adds little heat to the kitchen. In real world cooking, induction saves even more energy by dropping to, effec-



Range Tops


tively, zero energy input the instant a pot is removed from the element, and coming back to full input when the pot is replaced. Although induction range tops have not yet been proven by years of use in the food service kitchen and the durability of the electronics and ceramic cooktop remains to be seen, they represent a credible challenge in a category that has historically been domi-nated by gas appliances.

In response, the gas industry initiated an advanced range top development project with the goal of modernizing the standard gas range and reinforcing its market dominance. Drawing on research performed by Arthur D. Little, the Food Service Technology Center, and Gaz de’ France, and with the addi-tional support of Enbridge Gas Distribution, the Southern California Gas Company, and the Gas Technology Institute, the Canadian Gas Research In-stitute (CGRI) published an Assessment of Technical Strategies for an Ad-vanced Commercial Gas-Fired Rangetop28. This report was further refined into a Summary Report on an Advanced Rangetop for Presentation to End-Users, Rangetop Manufacturers and Government Agencies29. The goals of this research were to create a gas range with:29

• Improved cooking efficiency/ productivity,

• Reduced energy consumption,

• Reduced maintenance/easy cleanabilitiy, and

• Improved food quality/consistency.

The assessment presented three advanced range top options29:

1. State-of-the-Art Rangetop with Atmospheric Burner – incorporating open top atmospheric burners with enhanced cleanability and boil booster and simmer capability.

2. Rangetop with Enhanced Output / Heat Transfer – incorporating power burner technologies and/or atmospheric pressurized burner concepts.

3. Smooth Top Rangetop – features a closed smooth top with high efficiency radiant burners.

Range Tops


All three of these options included improved burner technologies, incorpora-tion of an energy saving device/ burner control system, and elimination of standing pilots.

While there are technical issues that must be overcome before the advanced range is a market reality, the report’s conclusion was that it was possible to create an improved range top that met the expectations of end-users and in-dustry alike and that the payback would range from one to four years.29

With this in hand, the gas industry (with GTI’s lead) has continued work on the advanced gas range, focusing on developing commercial grade ceramic tops and sealed elements, and higher efficiency burners.

Future research should continue along these paths, with emphasis on the fol-lowing:

• Further development of the sealed combustion range top for commercial food service. This technology would allow ventilation at lower airflows and reduce kitchen heat gain, as well as provide a desirable closed cook-top.

• Development of a hot top using infrared burners. This technology is al-ready applied to analogous appliances such as griddles, and would re-duce energy costs for gas hot tops.

• Development of higher efficiency, low-first-cost open gas burners.

• Investigate the feasibility of the cooking vessel sensor. Open gas burners should take advantage of their traditional strength–instant heat–by turn-ing off when the pot is removed, and then back on when it is replaced. This can increase the cost advantage of gas, and provides a response to one of the strong features of the induction range top: zero idle energy us-age. This will also reduce heat gain to the kitchen.

• Development of cooking vessel temperature feedback. An over limit switch to cut input when a pot has heated to the point of warping would allow further marketing of the power burner. If sensitive enough, such a device could begin to automate cooking. For example, a stockpot could be brought to a boil and then held at simmer.

Range Tops


• Inclusion of the NAFEM Online Kitchen protocol compliant technology into the range control system.

Induction rangetops are rapidly gaining popularity within the commercial food service world. With recent improvements to the induction electronics and significant reductions in first cost, the induction rangetop will inevitably begin to impact the market share of the traditional gas range. The gas indus-try must continue to evolve the design and functionality of the gas range top if this appliance is to retain its current market dominance.

From a conservation perspective, gas utilities should promote the use of open burner or open-grate hot tops over full-hot tops. This can significantly reduce operating costs of ranges and heat gain to the kitchen.


Range Tops


1. Young, R., Cesio, C., 1995. Montague Model V136-5 Heavy-Duty 30,000 Btu/h Open Top Gas Range: Application of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.94.6, October.

2. American Gas Association, Food Facilities and Energy News: Advances in Gas Cooking Technology into the 1990s–an educational supplement published 13 times a year and bound into Restaurants and Institutions and Foodservice Equipment & Supplies Specialist magazines under the direction of AGA.

3. Canadian Gas Research Institute, 1992. Gas Technology Update: De-velopment of a Sealed Combustion Gas Range. Bulletin Number 2, Au-gust.

4. Gaz de France, 1992. Gas Utilization Research Centre, Research and Development Division CERUG Activities Report, pp.24.

5. Gas Research Institute. Advanced Residential and Light Commercial Cooktop Burner: a GRI Field Test Status Report.

6. Gas Research Institute, 1995. Project

7. American Society for Testing and Materials, 1996. Standard Test Method for Performance of Range Tops. ASTM Designation F1521-96. In Annual Book of ASTM Standards, West Conshohocken, PA.

8. Young, R., 1995. Development and Validation of a Uniform Testing Procedure for Range Tops. Food Service Technology Center Report 1022.95.20, October.

9. American Gas Association, July 1989. Gas Food Service Equipment Ranges and Unit Broilers. ANSI Z83.11 – 1989.

10. Snyder, O.P., and J.F. Norwig., March 1983. Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study. University of Minnesota.

11. American Gas Association, 1986. Performance Evaluation Methods: Convection, Deck, and Range Ovens. Prepared for the Gas Research In-stitute, GRI-87/0182, December.

12. Himmel, R.L. and Stack, R.E., 1981. Commercial Cooking Equipment Improvement, Volume I: Range Ovens. American Gas Association Laboratories report to the Gas Research Institute, GRI-80/0079.1, Octo-ber.

13. Little, Arthur D. Inc., August 1993. Characterization of Commercial Building Appliances: Final Report for Building Equipment Division Of-fice of Building Technologies U.S. Department of Energy, pp. 5-40.

14. Young, R., Cesio, C., 1995. Montague Model V136-5 Heavy-Duty Open Top Gas Range: Application of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.94.4, October.

References

Range Tops


15. Young, R., Cesio, C., 1995. Vulcan-Hart Model VR-4 Heavy-Duty Elec-tric Range: Application of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.94.7, October.

16. Young, R., Cesio, C., 1995. Toastmaster® Model RA36C1 Heavy-Duty Hot Top Electric Range: Application of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.94.8, October.

17. Cesio, C. and Young, R., 1996. Garland 2.5 kW Induction Range Top: Application of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.95.30, February.

18. Cesio, C. and Young, R., 1996. Vulcan-Hart Induction Range Top: Ap-plication of ASTM Standard Test Method F1521-94. Food Service Technology Center Report 5011.95.29, March.

19. Bohlig, C., 1999. Sunpentown, Model SR-1262F Induction Cooktop Performance Test: Application of ASTM Standard Test Method F1521-96. Food Service Technology Center Report 5011.99.77, November.


21. Young, R., 1993. Montague Model V136-5 Heavy-Duty Open Top Gas Range: Appliance Performance in Production. Food Service Technol-ogy Center Report 5011.93.7, December.

22. Young, R., 1993. Montague Model V136-5 Heavy-Duty Combination Open Top/Hot Top Gas Range: Appliance Performance in Production. Food Service Technology Center Report 5011.93.8, December.

23. Young, R., 1993. Montague Model V136-5 Heavy-Duty Hot Top Gas Range: Appliance Performance in Production. Food Service Technol-ogy Center Report 5011.93.13, June.

24. Yap, D., Chester, J., 1998. Montague Model V136-5 Heavy-Duty 30,000 Btu/h Open Top Gas Range: In-Kitchen Appliance Performance Report. Food Service Technology Center Report 5011.98.64, November.

25. Blessent, J., 1991. Appliance Performance Report: Vulcan-Hart Electric Range, Model VR-4. Pacific Gas and Electric Company Department of Research and Development Report 008.1-90.24, June.

26. Young, R., 1992. Toastmaster Model RA36C1: Electric Range Per-formance Report. Pacific Gas and Electric Company Department of Re-search and Development Report 008.1-92.10, September.

27. Claar, C.N., Mazzucchi, R.P., Heidell, J.A., 1985. The Project on Res-taurant Energy Performance (PREP) - End-Use Monitoring and Analy-sis. Prepared for the Office of Building Energy Research and Development, DOE, May.

28. Krsikapa, S., Joseph, A., Barker, R., 1998. Assessment of Technical Strategies for an Advanced Commercial Gas-Fired Rangetop Phase 1. Prepared for ENBRIDGE Consumers’ Gas, November.

Range Tops


29. Krsikapa, S., 1998. Summary Report on an Advanced Rangetop for Presentation to End-Users, Rangetop Manufacturers and Government Agencies. Prepared for ENBRIDGE Consumers’ Gas, October.


6 Chinese (Wok) Ranges


Ethnic menus are hot—Chinese, Vietnamese and Thai! As for equipment, the hottest thing—literally—is the Chinese range.1 Chinese ranges also are find-ing their way into more non-traditional kitchens from family-style restaurants to hotels, as the trend towards “healthy eating” continues. If using the smaller, single-countertop induction units offered by several manufacturers, the Chinese range is usually found in the middle of a regular cooking line or at a stir-fry or wok station at a catered event.

Although the majority of Chinese ranges are custom-made, they are generally classified as either traditional Oriental units (Figure 6-1) unique to different cooking styles (Guangdong, Shanghai, Chiu Chow and Chop Suey) or as North American units (Figure 6-2), which differ in construction only–East Coast style and West Coast style. The heat source can be natural gas, propane or butane gas, and in the case of induction units, electricity. Natural gas is by far the most common fuel source. A gas valve at knee-level allows the chef to adjust the heat while using both hands to cook. Energy input rates range from 50 kBtu/h to as high as 160 kBtu/h or more, depending on the type of burner. The purpose of the high input rates is to facilitate the short term, high temperature cooking process used in the preparation of Oriental-menu items.

The basic Chinese range is constructed of heavy-gauge steel and averages 30-45 inches (760-1150 mm) in depth and 34-36 inches (860-910 mm) in work height, and is often equipped with a high back shelf and rack for woks and utensils.1 Some ranges are insulated with fiberglass and feature flue ris-ers for ventilation (e.g., East Coast-style ranges) or use the flue gases to heat the soup wells (e.g., the Guangdon, Shanghai and Chiu Chow ranges). Units without insulation or flue risers feature perforated water lines to flush water across the range top for cooling. A built-in slop trough at the back of the range top allows drainage for the water and any splattered food (e.g., West Coast-style ranges).

Introduction

Figure 6-1. Guangdong style Chinese range. Photo: Montague Company

Figure 6-2. West-coast style Chinese range. Photo: Montague Company

Chinese (Wok) Ranges


Each range has one or more chambers or wells (openings) over which woks are placed for cooking. The overall width of the range is determined by the width required to accommodate the number and diameter of woks and bowls desired, allowing a 6-inch (150 mm) space between them.2 The number, di-ameter and heat inputs of these chambers are specific to the chef’s prefer-ences and cooking style. Woks are available in diameters of 12 to 32 inches (300-800 mm). What is important, however, is the relationship between the wok itself and the chamber. The chamber diameter must be 2 to 4 inches (50-100 mm) smaller than the wok diameter in order to ensure a proper wok fit. 1

Traditional type ranges may also include several 12-inch (300 mm) soup-pot holders and open-burner sections.

Chambers are available in 10-, 12-, 14-, 16-, 18-, and 20-inch (250 mm, 300 mm, 350 mm, 400 mm, 450 mm, and 500 mm) diameters, increasing in in-crements of 2 inches (50 mm), and can go up to 30 inches (760 mm). The smaller-chamber diameters are used for northern-style Hunan, Szechwan and Mandarin cooking; medium-sized chambers are used for southern-style Can-tonese cuisine. The large chambers are found in high-production kitchens. 1

The Chinese or wok range is a self-contained range, having one or more “wells” or chambers that are designed to use a wok as the cooking utensil. The primary cooking method is stir-frying. Stir-fried menu items require high cooking temperatures to quickly sear the exterior of the food, locking in the flavors while not destroying natural color and vitamins. A variety of foods cut into appropriate sizes and shapes, generally thin strips, may be combined in this technique (meat and vegetables, poultry and fish and so on). The food items are added to the hot cooking medium, traditionally peanut oil (used because of its flavor and its high smoking point) and stir-fried. That is, the food is kept in constant motion by stirring, lifting and tossing for a short amount of time over high heat. 3

Traditional Oriental Units

Guangdong. The Guangdong range features 18- to 20-inch (450 to 500 mm) diameter cooking or wok chambers and 12-inch (300 mm) soup chambers

Cooking Processes

Types of Chinese Ranges



that are heated by the flue gases from the rear of the range unit. Guangdong ranges are equipped with powered burners rated at 150 kBtu/h per burner.

Shanghai. This unit features 18- to 22-inch (450-500 mm) diameter cooking chambers and 12-inch (300 mm) soup chambers that are also heated by the range’s flue gases. This range is equipped with powered burners rated at 150 kBtu/h per burner for the woks and with open burners rated at 40 kBtu/h per burner, located towards the back of the range top.

Chiu Chow. The Chiu Chow range, similar to the Shanghai range, features 18-to 22-inch (450-500 mm) diameter cooking chambers and 12-inch (300 mm) soup chambers heated by its flue gases. This range has powered burners for the woks rated at 150 kBtu/h each. This style of range also may have an open burner with a grate, rated at 40 kBtu/h, towards the back and centered between the two soup chambers.

Chop Suey. The Chop Suey range features 16- to 24-inch (400-600 mm) diameter wok cooking chambers. This type of range comes with open or jet burners rated between 80 and 125 kBtu/h per burner. It does not have a flue riser. A Canadian manufacturer incorporates what it calls a “new concept in chop Suey range design and engineering.” The burners generate extremely high temperatures (2000°F (1100°C)) inside the chamber, without transfer-ring heat onto the range. The gas chamber is completely isolated. The heat is focused on the wok or pan by flame guide rings, and then conducted out of the gas chamber by three separate ventilation systems. 4

North American Units

East Coast Style. The East Coast-style range is insulated (front and sides) with fiberglass and features flue risers for ventilation. Some models also of-fer chambers lined with refractory brick for additional heat protection. Like traditional Oriental range styles, this unit’s cooking chambers are 16 to 24 inches (400-600 mm) in diameter; the soup chambers are 12 inches (300 mm) in diameter. Energy inputs range from 80 kBtu/h per burner to 125 kBtu/h per burner, depending upon burner configuration–open or jet. This type of Chinese range is characterized by a rear food trough with an external sink and food strainer.



West Coast Style. The West Coast-style range has neither insulation nor flues, but features perforated water lines to flush water across the range top for cooling. A built-in trough at the back of the range top allows drainage for the water. Steel cooking chambers measure from 16 to 24 inches (400 to 600 mm) in diameter. Energy input ranges between 50 kBtu/h and 160 kBtu/h. One manufacturer’s unit features a unique well-venting system that carries heat away from the kitchen and into a vent opening in the high shelf.

Table 6-1 compares the specifications for the different types of Chinese ranges.

Table 6-1. Summary of Chinese Range Types.

Range Type Cooking Chamber

Chamber Diameter (inch)

Burner Type

Input Rate per Burner (kBtu/h)

Traditional: Guangdong Wok 18 - 20 Powered 150

Soup 12 Open 40 Shanghai Wok 18 - 22 Powered 150

Soup 12 Open 40 Chiu Chow Wok 18 - 22 Powered 150

Soup 12 Open 40 Chop Suey Wok 16 - 24 Open or Jet 80 - 130

North American: East Coast Wok 16 - 24 Open or Jet 80 - 125

Soup 12 Open 40 - 80 West Coast Wok 16 – 24 Ring, or Jet 50 - 160

Although burners usually have modulating gas valves with adjustable inputs between on and off, they are typically operated at close to maximum input.

Controls



Gas

Ring burners, jet burners or powered burners provide heat to the woks, de-pending on the style of cooking and the level of heat required. Chinese ranges designed to work with woks up to 18 inches (450 mm) in diameter require 53-kBtu/h burners; woks with diameters greater than 20 inches (500 mm) generally require 110-kBtu/h burners. Standard models are available with up to as many as 8 to 10 burners. Ring-type burners are typically used in conventional Chinese cooking and can produce between 55 kBtu/h and 110 kBtu/h outputs. Jet burners, rated between 120 kBtu/h and 130 kBtu/h, pro-vide more intense heat and are used in Mandarin cooking. The jet burner is usually placed closer to the wok to create a faster, more intense heat and to decrease cooking time. Shielded-tip or duck-mouth burners, a variant of the jet burner, deliver the same intense heat, but have metal tips that prevent each port from becoming clogged with food.1 Powered burners, rated at 150 kBtu/h and higher, are used for larger wok stations in traditional Oriental units.

Electric

There are very few electric woks on the market. The induction wok uses an induction coil located beneath a ceramic cook top called an induction hob. As electric current flows through the coil, a corresponding field develops above the surface of the ceramic cook top. The field itself is not hot, and doesn't heat the ceramic: a hand placed on the range top will not be burned or heated. But the bottom of a metal pan set on the ceramic surface intersects the field, which induces a current in the pan. This current heats the pan bottom rapidly and the bottom becomes, in effect, an electric element. Because the field can only work on the metal (magnetic) wok, removing the wok automatically turns down the energy input to the appliance. Full input is restored instantly when a pot is placed on the hob. While idling without a wok on the induction hob, the induction element draws a small fraction of its full input energy, and adds no heat to the kitchen.

Changing the energy input to the induction coil can control heating. The re-sponse to change is rapid, comparable to a gas-open burner. Some induction




woks have electronic controls that allow patterns of heating appropriate to different styles of cooking, for example, a full-input heating period to raise soup to a boil followed by a reduced input for simmer. Induction woks also include temperature-limiting switches that sense the temperature of the ce-ramic surface and cut off input when it exceeds safety conditions (e.g., when a wok has boiled dry).

Induction woks have some practical limitations. Currently commercial mod-els exist, but mainly as single-unit hot plates.5 The coils are expensive and may prove too fragile for heavy-duty food service applications. Finally, the induction wok will only heat pots that are made of magnetic materials. At present, compatible cookware tends to be expensive and chefs may be reluc-tant to retool their kitchen for use with this new technology on a greater scale.

Energy Efficiency

The energy performance of Chinese ranges is not well documented. Re-cently, the Food Service Technology Center developed an efficiency test for Chinese ranges. The test method was subsequently approved and ratified by ASTM.6 Unfortunately, no reported energy efficiencies were identified by this study, although unpublished energy consumption data were available for estimating energy consumption (Table 6-2).

Table 6-2. Chinese Range Energy Efficiency.a

Gas Chinese Ranges 15 – 30% Electric Chinese Ranges 50 – 70% a Best estimate based on FSTC experience.

Projected energy consumption for gas Chinese ranges is presented in Table 6-3. An unpublished, proprietary end-use monitoring study showed that for all monitored equipment, woks consumed the largest measured daily energy consumption. Based on the median nominal chamber size of 20 inches (500

Chinese Range Performance

Chinese Range Energy Consumption



mm), a median energy input rate of 100 kBtu/h (an actual 20-inch diameter chamber is rated at 107 kBtu/h) and an estimated 10 hours of operation, an average energy consumption rate of 30 kBtu/h was calculated for Chinese ranges. This corresponds to a duty cycle of 30%. The projected annual en-ergy consumption was determined by assuming a 6-day, 52-week per year operation.

Table 6.3. Projected Energy Consumption for Gas Chinese Ranges.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy Consumption

Typical Operating

Hours


(kBtu/h) (%) (kBtu/h) (h/d)a (kBtu)b

2 Wok Range

100 - 320

(Median) 200 30 60 10 187,000 aOperating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". bThe annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year.

As for underfired broilers, the ventilation requirements for Chinese ranges are greater than for other categories of cooking equipment. Typical ventila-tion rates for a wall-mounted canopy hood over a Chinese range are between 350 and 450 cfm (175 and 225 L/s) per linear foot. The radiant heat gain from Chinese ranges contributes significantly to the heat gain of the kitchen. However, radiant factors have not been published.

The Chinese range is a very fundamental design, typically using low-cost components. Benchmark efficiencies are very low. Woks typically lack any end-user “pull” to raise the bar. However, consideration should be given to:

• End-use monitoring of Chinese ranges.

• Characterization of energy balance of wok-cooking process.





• Establishment of criteria for the development of a high-efficiency gas wok burner.

• Development of an energy efficient, advanced performance Chinese range in partnership with a North American manufacturer of tradi-tional Chinese ranges.

• Development of back-of-the house induction woks that can compete with traditional gas woks.



1. A Cahners Publication. 1992. Foodservice Equipment & Supplies Spe-cialist. Product Knowledge: Product Focus #109: Chinese Ranges, March, p.51.

2. Scriven, C. and Stevens, J., 1989. Food Equipment Facts: A Handbook for the Foodservice Industry. Van Nostrand Reinhold (NY), Revised Edition. pp. 123 - 124.

3. The Culinary Institute of America, 1991. The New Professional Chef™. Van Nostrand Reinhold (NY), Fifth Edition. pp. 393 - 394.

4. CP Publishing. Inc., 1995. Cooking for Profit. Buyer’s Guide, August 15, No. 531, p. 26.

5. Bohlig, C., Cesio, C., 1998. Glowmaster 5.0 kW Induction Wok Product Evaluation. Food Service Technology Center Report 5011.98.52, March.

6. American Society for Testing and Materials, 1999. Standard Test Method for the Performance of Chinese Ranges. ASTM Designation F1991-99. In Annual Book of ASTM Standards, West Conshohocken, PA.


References

7 Ovens


Many food service operations rely heavily on the versatility of ovens. Opera-tors can cook varieties of foods in large quantities with a single appliance. As a result of their versatility, ovens are the most widely used appliance in the food service industry. An oven can be simply described as a fully enclosed, insulated chamber used to heat food. But, there are many variations of the basic concept in the commercial kitchen. The most common types of com-mercial ovens include standard, or conventional ovens, convection ovens, combination oven/steamers (also known as combination or combi ovens), conveyor (pizza) ovens, and rotisseries. Additionally, an emerging group of high-performance hybrid ovens have been carving out a niche in today’s fast-paced culinary world. These rapid cook ovens are creating new food service opportunities for pubs, kiosks, quick-service restaurants, delicatessens, hotels and movie theaters.

Operators know that fresh-baked signature desserts, crusty breads, and famil-iar comfort foods, such as roasted meats and potatoes, are fundamental menu items. In addition to the traditional uses of ovens for roasting and baking, they may be used to cook a surprising range of foods usually associated with other appliances. For example, ovens in high-volume kitchens prepare large quantities of griddle standards such as bacon, eggs, sausages and French toast.1

Customized high-air velocity convection ovens using an “oil-less frying” technique can be used in place of a deep-fat fryer to cook French fries, onion rings, chicken nuggets, fish and other popular fried foods. In some cases, the cooked food produced using this technology contains less oil than food cooked using deep fat fryers.

Combination ovens are regularly used to proof dough, steam vegetables, cook and hold a wide variety of foods, rethermalize pre-plated meals and even broil steaks. The combination of a steam generator and a convection oven make these some of the most versatile ovens available.

Introduction

Ovens


Restaurant operators are increasingly cooking in plain view of their custom-ers. Exhibition baking and the popularity of several types of ovens have in-creased due to this style of operation. Rotisserie ovens offer food service operators a unique opportunity to simultaneously cook and merchandise a variety of popular foods such as chicken, ribs, lamb and duck. Pizza ovens, also commonly found in plain view of the customer in the more upscale op-erations, once again mix product visibility with production. Pizzerias and other restaurants that require high throughput and product consistency have enjoyed great success with conveyor ovens. For example, one large seafood restaurant chain employs conveyor ovens for their complete menu produc-tion.

A concept that is growing in popularity with large food service operations—such as hotels, school commissaries, groceries, correctional facilities and even quick-service chains—is use of a centralized kitchen. Huge quantities of food are produced in a large central cooking facility and then delivered to multiple satellite kitchens, which may serve the food hours or days later. The food is prepared and chilled at the main kitchen, and later reheated by the satellite location. Rack ovens, cook/chill systems and rethermalization ovens are becoming more prevalent in these operations due to the requirements of high production and food safety.2

Ovens represent the largest appliance category in terms of the types of units manufactured of any of the major cooking equipment categories.3 This versa-tility and diversity mean that they can be found in almost any type of food service operation.4 A recent US study showed that 95% of commercial (non-institutional) operations reported using at least one type of oven; 98% of noncommercial (institutional) operations reported the same. The percentage of operations, commercial and institutional, using general bake ovens was 52% and 56%, respectively. Fifty percent of the operations in the commercial sector reported using convection ovens as compared to 83% of noncommer-cial operations. Pizza ovens accounted for 19% and 12%, respectively. Mi-crowave ovens were popular in both sectors with installations in 71% of the noncommercial foodservice sector and 70% of the commercial operations. 1

Commercial ovens are available in various configurations using a variety of energy sources–electricity, natural gas or liquid propane, and in some cases,

Ovens


wood. Natural gas is the predominant fuel source for most commercial ovens, representing 55 to 60% of the installed base, but electric ovens are common and represent most of the remaining 40 to 45%.5 Because of the variety of potential installations, oven manufacturers strive to be space conscious and flexible in their designs. Ovens can be either freestanding or in a counter-top/stackable configuration, as illustrated in Figure 7-1. Even some of the largest conveyor ovens can be stacked, allowing for high output in a rela-tively small footprint and the same can be said for large rack ovens, which are tall but relatively narrow. Manufacturers are also making smaller ovens to fill niche markets and the needs of low volume food service operators. In order to facilitate consistent and energy efficient operation, manufacturers are beginning to introduce sophisticated control packages to their products, including temperature measurement and feedback loops, on board diagnos-tics, and external communications capabilities.

Ovens cook food products using all three fundamental heat transfer methods, convection, conduction, and radiation, both alone and in various combina-tions. The simplest model of an oven is a box that cooks the food by transfer-ring heat from the oven walls. The placing of air fans into ovens introduced forced convection into this process, which speeds up the cooking process and increases output. In early stone and brick ovens, food was placed directly on a hot slab or against the oven wall and the food was cooked primarily through conduction. This process has been updated and is the basis for mod-ern deck and wood fired ovens, many of which also include a convection component and in some cases even include strategically placed radiant heat sources. In most oven designs, a thermostat controls the oven cavity tempera-ture. In some cases, the oven humidity is also varied and controlled through the introduction of moisture in the form of steam into the cavity. Microwave and other rapid-cook ovens bombard the food product with waves of energy that agitate the molecules within the food product, causing the internal tem-perature to rise.

Figure 7-1. Double-stacked convec-tion oven. Photo: Blodgett Corp.

Cooking Processes

Ovens


Standard or Conventional Ovens

Standard or conventional ovens use natural convection and radiant heat to cook food products. In general, these ovens do not mechanically circulate the air within the cavity. The burner or elements heat the air within the oven cav-ity as well as the cavity walls, causing currents of hot air that transfer heat to the surface of the food. The arrangement of pans in the oven and the texture of the food can affect the circulation of air, changing the cooking speed and uniformity. Two familiar types of standard ovens are the range oven and the deck/pizza oven. The range oven is the most familiar, since it is the kind most often found in residential applications. These ovens can be used for nearly all types of food preparation including breads, pies, meats, fish, poul-try and baked potatoes. Standard ovens are ideal for precision baking because the natural flow of air within the oven cavity reduces the oven’s impact on delicate food products such as meringues, cream puffs, pastry shells and other products that require a dry atmosphere. Standard ovens are the least expensive to purchase, and their production capacity is typically not as high as forced convection ovens.

Range Ovens. The most common standard oven–the range oven, also known as the general-purpose oven, is heated with atmospheric gas burners located directly below the oven cavity. Flue gases are routed around and/or through the cavity. In electric ovens the elements are placed in the top and bottom of the oven cavity, where they add both radiant and convective heat; they also may be placed underneath the bottom deck.

Range ovens are part of a cooking unit or system (see Figure 7-2). The range oven forms the housing or base for the range top (i.e., burners, griddle, etc.), addressed in Section 5. The range/oven combination usually consists of the range system and only one oven cavity. Energy input ratings are often given for the complete range system. Typically, the energy input rate of a range oven will be between 35 kBtu/h to 45 kBtu/h for gas and 7 kW to 9 kW for electric.

Range ovens are normally specified for smaller operations. Their exterior dimensions are typically 36 inches (900 mm) wide by 30 inches (750 mm) deep by 30 inches (750 mm) high. They typically come equipped with a pan and support racks.

Types of Ovens

Figure 7-2. Six-burner range with range oven.

Ovens


Deck Ovens. Standard gas-fired deck ovens are similar to conventional roast or bake ovens except the inside cavity has a low height, ranging from 6 to 10 inches (150-250 mm). A typical deck oven is illustrated in Figure 7-3. The bottom of each compartment is called a deck and heat is typically supplied by burners or elements located beneath the deck. The oven ceiling, floor, and walls are designed to absorb heat quickly and radiate that heat back slowly and evenly. To accomplish this, the deck is often made of ceramic material, steel, brick, or some other composition material. Deck ovens with firebrick hearths are particularly good for bottom-crust baking and are widely used for cooking both bakery items and pizza. They also can be used to cook a wide variety of other foods fairly quickly including casseroles, meats, and fish. The limiting factor is the height or thickness of the food product.

Deck ovens can be found in both freestanding and stackable configurations. Stacked ovens are typically no more than three decks high. The differences between baking and pizza deck ovens are in size and energy input rates. Decks for baking ovens are commonly 33 to 42 inches (840-1070 mm) wide and 36 to 45 inches (915-1140 mm) deep. Pizza ovens range in width from 18 to 78¼ inches (460-1990 mm), in depth from 22 to 455/16 inches (560-1150 mm) and up to 67¾ inches (1720 mm) in height.

Baking Deck Ovens—Baking deck ovens are often categorized as one-pan or two-pan ovens, depending on their ability to hold one or two standard baking sheets (18 x 26 inches (460 x 660 mm) side by side. Each oven typically has one or two oven cavities, or compartments. Some baking deck ovens have optional steam injection to assist in finishing hard-crust breads. The com-partments are sized either for baking or roasting. Baking compartments are generally 7 inches (190 mm) high, whereas roasting compartments are typi-cally 15 inches (380 mm) high.

Pizza Deck Ovens—The most common deck/pizza oven will hold six 12-inch (300 mm) diameter pizzas. Small countertop ovens will hold one to four piz-zas. In many cases, pizza pans are placed directly on the oven deck. Some manufacturers recommend placing the pizza directly on the deck or hearth while others recommend using pizza screens or perforated pans. In fact, some manufacturers suggest that cook times can be reduced and product quality improved by using low, black aluminum, flat-bottomed pans rather than

Figure 7-3. Deck oven. Photo: Garland

Ovens


shiny or high-sided pans.6 Since the oven door is often opened to check doneness or break bubbles in the crust, at least one manufacturer offers an “air door” that retains oven heat with a vertical curtain of air inside the door opening.4 With a well-designed deck/pizza oven, a restaurant can not only satisfy its customer’s appetite for pizza, but also cook a variety of foods that might otherwise be cooked in a standard oven. Typically, deck ovens utilize conduction from the hot deck as a primary means of heat transfer to the food product but there is one manufacturer that utilizes forced convection as the primary means of heat transfer.

Convection Ovens

Reflecting years of technological refinements, today’s convection oven is one of the more significant developments in commercial cooking equipment. It originated as a modified conventional or standard oven developed to over-come the problem of uneven heat distribution in the cooking cavity and to provide more production capacity for a given size. Based on these attributes, the convection oven has naturally spawned a vast number of variations in terms of size, technology, capacity, and type. Almost all convection ovens are available in both gas and electric models. The concept behind the forced-air convection oven is a simple one. When food is cooking inside an oven, it is surrounded by an insulating layer of air that is cooler than the overall oven cavity temperature. A motorized fan (or blower) forces the heated air to move throughout the oven’s cavity, striping away the layer of cooler air next to the food. The result is a faster, more even cooking process than that pro-vided by standard, natural convection, radiant-heat ovens.7 Forced convec-tion can reduce the cook time significantly on long-to-cook items such as potatoes and can allow more food to be cooked in a period of time.

Most gas convection ovens use atmospheric rather than infrared (IR) burners although manufacturers have recently introduced several convection oven models featuring IR burners. Gas convection ovens are available with single or multiple burners. Historically, most gas convection ovens are indirectly fired. Burners are usually located at the bottom of the oven cavity, or be-tween the cavity and the insulated oven wall. The Blodgett Oven Company

Ovens


introduced a direct gas-fired heating system that places the burner in the oven cavity. This 38-kBtu/h burner has an electronic hot surface ignition system.

Manufacturers differ in how they route the flue gases and how they mix them with cavity air. Gas burners may be protected from air currents by an ar-rangement of baffles, and the flue gases directed around or through the cav-ity. Alternatively, the flames and flue gases may be directed into tubes that act as heat exchangers and vent into the flue. The oven walls are usually insulated by at least 4 inches (100 mm) of rock or mineral wool, marinite or pressed vitreous fiber to retain heat within the cooking cavity.

Forced convection ovens come in “full-size” (Figure 7-4) or “half-size” ca-pacities, depending on whether they can accept standard full-size (18 x 26 x 1 inch (460 x 660 x 25 mm)) or half-size (18 x 13 x 1 inch (460 x 330 x 25 mm)) sheet pans. Most half- and full-size ovens are capable of handling up to six sheet pans. Some of these ovens also include extra deep cavities, which allow a choice of pan direction placement. Convection countertop and range ovens are also available, as are high-capacity roll-in or rack ovens. The con-vection principle has also been applied to most conveyor and some rotisserie ovens.

Rack Ovens. Rack ovens are basically tall stainless steel boxes capable of high production in a relatively compact space. These large capacity, roll-in rack models fill the requirements of high-volume institutional operations. They are ideal for rethermalizing many products prepared in cook/chill sys-tems as well as baking and roasting. The rack oven is capable of producing thousands of identical products or many diverse menu items within the same cooking cavity.

The product is placed in pans that are loaded on mobile, stainless steel or aluminum racks. The loaded racks are rolled into the oven through a large vertical entrance door. The rack is then connected to a revolving mechanism that starts smoothly and rotates slowly in a carousel motion. This method of cooking contributes to the cooking speed and product consistency.

Rack ovens are available in a variety of sizes, the most common being single and double-rack (see Figure 7-5). The racks typically hold between 10 and 15 pans, depending on spacing and type of product being baked. Rack ovens are

Figure 7-4. Full-size convection oven. Photo: Southbend

Figure 7-5. Double-rack rack oven. Photo: Revent

Ovens


available in models requiring 16 to 20 square feet (1.5 - 1.9 square meters) of floor space and have rated inputs ranging from 125 kBtu/h to 375 kBtu/h. Mini-rack ovens offer the uniformity and production capacity benefits of rack oven design with the smaller footprint of a standard convection oven. These ovens use a fixed, non-removable rack and are available in 6, 8 and 10-pan models, with inputs ranging from 60 to 80 kBtu/h for gas-fired units and 14 to 25 kW for electric units.

Rack ovens have heat exchangers of various designs that utilize a power blower to circulate heat evenly throughout the cavity. Self-contained steam systems are available for injecting steam into the oven cavity at the appropri-ate time in the baking cycle.2

Combination Oven/Steamers. A combination oven/steamer, or combination oven, is a convection oven that includes the added capability to inject steam into the oven cavity and typically offers at least three distinct cooking modes. In the combination mode it provides a way to roast or bake with moist heat (hot air and steam); in the convection mode it operates as a purely convection oven providing dry heat; or it can serve as a straight pressureless steamer (discussed in Section 8). In addition, some manufacturers provide holding and proofing temperature settings. Others offer high-end temperatures ex-ceeding 550°F (290°C) to enable using the oven as a broiler. Figure 7-6 illus-trates a typical combination oven.

Initially, electric combination ovens dominated the market place but now most manufacturers also offer gas combination ovens. There are many differ-ent designs of combination ovens available – more than with any other spe-cific oven type. This is mainly due to the fact that this new oven technology has not existed long enough to settle on any one standard design, and is am-plified by the fact that many of these ovens are designed and manufactured in Europe. Each manufacturer has a different approach to the concept of the combination steamer. This includes multiple cavity sizes and shelf layouts as well as several different methods for generating and introducing steam to the oven cavity. Some ovens employ a traditional boiler-based steam generator design while others simply spray water on a heated metal mass within the oven or on the oven blower. Many of the combination ovens are available with complex and versatile controls systems that include programming func-

Figure 7-6. Combination oven. Photo: Rational

Ovens


tionality as well as a temperature sensor that feeds information to the controls system and varies the cooking cycle. These ovens might also include com-munications outputs that allow the operator to monitor and store food tem-perature information for HACCP record keeping. Some ovens utilize only a simple timer and three way switch which determines the cooking mode and duration.

Combination ovens are available in countertop sizes, which hold half-size (103/8 x 12¾ x 2½ inch (264 x 324 x 65 mm)) steam table pans. Full-size combination ovens are capable of loads of up to 12 full-size (12 x 20 x 2½ inch (300 x 510 x 65 mm)) steam table pans. They extend to large, floor-mounted, full-sized units that accept up to 20 standard (18 x 26 inch (460 x 660 mm)) sheet pans. Even large capacity, roll-in rack models are available in the combination oven format. One unifying factor in all combination oven designs is the ease of cleanability. The fact that these ovens typically include stainless steel interiors and spray heads as well as steam generators means that they are self cleaning—a feature that gives them a distinct maintenance advantage over the sometimes hard-to-clean convection ovens.

Cook-and-Hold Ovens. Some ovens are designed specifically for cooking and holding product while others (including combination and rotisserie ov-ens) offer low-temperature cooking options, or cook-and-hold modes. The primary use of the cook-and-hold is to roast and hold meats at lower temperature ranges, 175° to 250°F (80° to 120°C) vs. 275° to 400°F (135° to 200°C), than are typically used for conventional cooking methods in order to help retain product juiciness as well as tenderness.8 There are two standard types of cook-and-hold ovens. One uses natural convection with high humid-ity (90 - 95% humidity with minimal air movement) and slightly higher tem-peratures; the other uses forced convection with lower temperatures and lower humidity levels (between 30 - 60% humidity).4 A low-temperature cook-and-hold oven is presented in Figure 7-7.

The basic frame, housing and interior components are often the same as those in a forced convection oven—the main difference is that a cook-and-hold oven is able to produce relatively high humidity during the cooking process. This is usually accomplished through the use of a water reservoir within the oven cavity. The forced convection cook-and-hold ovens use a blower to

Figure 7-7. Cook-and-hold oven. Photo: Alto-Shaam

Ovens


evenly distribute the moist heat throughout the oven cavity. Cook-and-hold ovens are available in both gas and electric models, in the same general sizes and the same rated energy inputs as basic convection ovens.

Conveyor Ovens

Conveyor ovens are available using four different heating processes: infra-red, natural convection with a ceramic baking hearth, forced convection or air impingement, or a combination of infrared and forced convection. The air impingement ovens use a blower and baffles to intensify and focus the air movement within the oven cavity towards the food load. These high-velocity “fingers” of air impinge upon or blow away the layer of air and moisture that insulates the food, thus increasing the speed of the cooking process.4 Con-veyor ovens are generally used for producing a limited number of products with similar cooking requirements at high production rates. They are highly flexible and can be used to bake or roast a wide variety of products including pizza, casseroles, meats, breads, and pastries.

The ovens are available in many different sizes and configurations. They are available in sizes small enough to satisfy low-volume and niche operations, such as kiosks, that have limited production space, and large enough to meet the demands of high volume operations. Most conveyor ovens, both large and small, can be stacked up to three units high, significantly increasing pro-duction capacity without requiring increased floor space. Figure 7-8 presents a double-stacked conveyor oven.

Essentially, conveyor ovens are a rectangular housing unit containing a bak-ing cavity or chamber, which is open on two opposing sides. A conveyor sys-tem carries the food product through the baking chamber or tunnel on a wire rack. Most ovens can be outfitted with multiple conveyor belts, each of which may have a different operating speed. The typical counter-top unit has a conveyor width as small as 10 inches (250 mm) and a cavity length of 14 inches (350 mm). Freestanding units may have conveyor widths that range from 14 to 37 inches (350 mm-950 mm) and cavity lengths ranging from 20 to 75 inches (500-1900 mm). Oven controls adjust both the cavity tempera-ture and speed of the conveyor. In some models, the top and bottom heat in-

Figure 7-8. Double-stacked con-veyor oven. Photo: Middleby-Marshall

Ovens


put are independently adjustable. Many of the larger conveyor ovens have a hinged glass door along the front side of the tunnel to allow loading and un-loading of food that requires a shorter cook time.

One of the newer features included on some conveyor ovens is the option to have independently controlled cooking zones. The temperature within each zone may be independently adjusted. The first zone is very hot and as the product passes through it, it is quickly heated up to cooking temperature. Be-fore it starts to burn, the product is moved into the second zone, which is maintained at a considerably lower temperature. In this zone the product cooks at an even rate until it reaches the third zone, generally referred to as “the finishing” zone. Here the temperature is even lower, cooking the product to the desired degree of “doneness”. One manufacturer has expanded upon the multiple-zone concept by allowing each eight-inch length of tunnel to have a different operating temperature.4

A few manufacturers offer an air-curtain feature at either end of the cooking chamber that helps to keep the heated air inside the conveyor oven. The air curtain operates as a virtual oven wall and helps reduce both the idle energy of the oven and the resultant heat gain to the kitchen.4

Rotisseries

A rotisserie is fitted with one or more mechanically rotated spits that hold meat or poultry in position near a fixed heat source while the food is slowly being cooked on all sides. The heat source may be gas or electric and several models also offer an additional wood-fired option. Rotisseries can be sepa-rated into two main categories: rotisserie ovens and rotisserie broilers. Within these, many models are available.

Rotisserie Ovens. Rotisserie ovens are designed for batch cooking, with in-dividual spits arranged on a rotating wheel or drum within an enclosed cook-ing cavity. Figure 7-9 presents a typical electric rotisserie oven. The ovens can be equipped with either single action rotation cooking or a dual rotating action, planetary cooking system that incorporates convection, radiant, and air impingement cooking. Motors provide the labor saving power to rotate both types of cooking systems.

Ovens


For gas rotisserie ovens a number of burner systems are available. Single heat-source systems include atmospheric flame type, radiant and infrared. There are also dual burner systems that combine infrared with an open flame. Most gas models feature electronic ignition systems.

Rotisserie ovens range in size from high-volume floor models to space-saving countertop models. Most models are equipped with basic time and temperature controls, optional cook-and-hold controls, or more sophisticated control packages with programmable channels. Electric models may feature interior halogen merchandising lights.

Rotisserie Broilers. The rotisserie broiler is designed for continuous loading and cooking, with vertically stacked spits. Some models feature individual drive systems, which utilize a chain link from gear to gear to maintain the tension, allowing operation of one or more spits at any time. The rotisserie broiler employs super heated fire bricks strategically located over powerful pipe burners (e.g., 40 kBtu/h each with a total input rate between 105 kBtu/h to120 kBtu/h for a median of 112 kBtu/h, or roughly twice that of the rotisse-rie oven at 50 kBtu/h), which in turn, emit radiant heat. Unlike rotisserie ov-ens, rotisserie broilers have very rudimentary controls.

Standard Oven Controls

Standard ovens usually have simple controls, limited to a thermostat and a selector that allows the oven to bake or broil. Sensors may be electronic, but the more common ones are usually the mechanical bulb type (modulating thermostats), which adjust the burner incrementally and have a tendency to be somewhat uneven in temperature distribution. On/off snap action thermo-stats provide better temperature control, but add to the initial cost. Gas deck/pizza ovens use shut-off and adjustment valves for the gas control and usually feature automatic safety pilots and ignition. Vents get rid of the flue gases and generated steam, providing crisp crusts on the pizzas.

Figure 7-9. Rotisserie oven. Photo: Hobart

Controls

Ovens


Convection Oven Controls

In general, convection ovens, including conveyor ovens as well as convec-tion rotisseries, offer more control over the cooking process than standard ovens. Upgraded controls include more accurate electronic sensors and ther-mostats, electronic ignition controls (on gas models), and on many of the newer gas and electric models, programmable cooking computers which re-call several cooking sequences by the simple press of a button. Some of these ovens can be programmed to first cook and then hold food products. Food may be cooked at a high temperature with high convection and then held for an extended period at a lower temperature with the fan off.

Some ovens allow the user to control cooking by regulating fan speed, tem-perature, humidity and the cooking time. (The speed of the fan affects cook time and uniformity, as does the pattern of airflow through the interior.) In combination ovens, for example, a cook cycle may be programmed to begin with high steam and convection, then continue cooking with convection only, and hold the finished product at low temperature and moderate humidity. Other options included in many of these ovens are a low-speed fan setting to permit cooking of delicate items and a rapid cool down mode to facilitate going from oven to steaming quickly.

Microwave and many other rapid cook ovens control neither the temperature nor the humidity and instead base the cook cycle on a precisely timed pro-gram or algorithm that has been predetermined for the type of food being cooked.

Indirect-fired ovens have the gas burners and heat exchangers located outside the cooking cavity. The hot products of combustion heat the bottom, sides and top of the oven without entering the cooking cavity. Direct gas-fired ov-ens typically position the burners below the cooking cavity and allow the hot combustion products to route through the cooking cavity rather than around it. Heat is transferred directly from the hot gases to the food. If an oven sec-tion has two compartments, they may or may not be independently heated and controlled. Usually the cavity walls are insulated with 2 to 4-inch (50-


Ovens


100 mm) heat-stable fiberglass, vitreous fiber or rock wool on the sides and top with 2 inches (150 mm) of insulation in the door.

Advanced Oven Technologies

Recently, ovens have begun to evolve technically at an increased rate as new technologies have been introduced to the market. Manufacturers improved the standard or natural convection oven into the modern-day forced convec-tion oven simply by adding a fan but improvements in burner design and new heat transfer options are driving the modernization of the oven far beyond this simple improvement. More efficient infrared burners are replacing the traditional atmospheric burners in gas ovens; quartz halogen lamps cook food using a combination of infrared energy and visible light; circulating thermal fluids make conduction cooking and holding possible; and a combination of microwave and convection are playing a part in electric oven designs. Com-bining technologies such as infrared with forced convection or convection with steam injection, recirculating combustion gases via specially designed fans or venting tubes all add up to improved oven performance. Additionally, some oven manufacturers are coupling custom fitted ventilation hoods with their oven designs.

Infrared Burners. An infrared/forced convection oven combines the pene-trating heat of infrared radiation with the convective effect to reduce baking time as compared to natural convection ovens.

Air Impingement. Air impingement is a relatively new technology applied to conveyor and some rotisserie ovens. Air impingement typically uses a ported manifold to direct jets of air, or “fingers,” onto the product’s surfaces.

Quartz Halogen Lamps. Quadlux, Inc., the Northern California manufac-turer of the Flashbake® oven pioneered the use of quartz halogen lamps to cook food using a combination of infrared energy and visible light. The infra-red energy cooks from the outside in, browning and crisping the exterior, as would a conventional oven. The visible light penetrates into the food a short distance, with the depth varying depending on the color and composition of the food. The quartz lamps used in the oven design were first used to cure silicon chips for the microprocessor industry. The lamps start up instantly,

Ovens


thus have no preheat time, and remain off when idle. This oven however, typically uses as much or more energy than conventional ovens when cook-ing.9 This technology allows a substantial amount of energy to impinge on the food product and greatly reduces the cook time. Because of the speed of cooking and the use of a non-standard heat transfer technology, this hybrid oven falls into the category of “rapid cook” ovens. This technology has sub-sequently been licensed to other manufacturers (Figure 7-10) and has re-cently been applied to conveyor ovens.

Conduction. Heat is transferred to the foods via direct contact with a heated medium. For example, many pizza ovens incorporate a firebrick or compos-ite hearth with burners or elements underneath the hearth. The bottom of the pizza is cooked by direct contact with the hot hearthstone. This process of conduction, combined with the circulation of hot air above the pizza, allows good control of the cooking speed and texture of both the crust and toppings. Another recent entry into the market place is an electric cook-and-hold con-duction oven that circulates heat transfer fluids through the oven’s hollow shelves. The heat is conducted directly through the shelves to the pans and subsequently to the food. This method of heat transfer, according to the manufacturer, allows food to be brought evenly to a cooked state without burning or drying.

Combination Convection Microwave. Two ovens on the market10 combine convection with microwave for high-speed cooking. Like the quartz halogen ovens, this hybrid heat transfer combination falls into the rapid cook cate-gory. The TurboChef®, pictured in Figure 7-11, uses a modified high-velocity impingement system that propels hot air directly down onto the food, then pulls it around and underneath the product. This process is cou-pled with a microwave component to dramatically speed the cooking process. Amana’s Convection Express takes a similar approach to the TurboChef® and includes a single cooking chamber and a compact, stackable design. It includes 1000 watts of microwave energy and 2,700 watts of convection heating. With this cooking combination comes a host of usage options in-cluding the ability to program a multi-stage cooking sequence. For example, a frozen dish can be defrosted through the microwave-only function, then put through a fast-heating stage on a convection cycle, then baked by both mi-

Figure 7-10. Flashbake® oven. Photo: Vulcan-Hart

Figure 7-11. TurboChef® oven. Photo: TurboChef®

Ovens


crowave and convection heat and, finally, browned with a dose of convec-tion-only heat with single programmed recipe. While these ovens have typi-cally been electric only, a new gas convection microwave oven is in development and should be commercially available in the near future.

Combination Halogen Microwave. The latest hybrid or rapid cook oven on the market combines the quartz halogen cooking with microwave. As with the convection microwave, this oven offers a variety of cooking options and multi-stage cooking programs, all designed to produce consistent product while dramatically reducing product cook time.

The work of an oven can be outlined as bringing the cavity from room tem-perature up to cooking temperature (preheating), holding the cavity at cook-ing temperature until cooking begins (idling), and restoring heat to the cavity when cold food is placed into the oven (recovery).

The Food Service Technology Center has developed several Standard Test Methods for assessing the performance of ovens, which have been ratified by the American Society for Testing and Materials (ASTM).11-16

These test methods allow manufacturers and end users to accurately compare the performance and energy efficiencies of different models and configura-tions of ovens, and to evaluate oven-energy performance as well. As hard data on ovens becomes available, it is apparent that certain technologies and designs yield better performance.

Oven performance is characterized by energy input rate, preheat time and energy consumption, idle energy consumption rate, pilot energy consumption rate, cooking-energy efficiency, production capacity, and cooking uniform-ity.

Energy Input Rate

Energy input rate is one of the basic criteria for oven selection. It is the maximum rate at which an appliance draws energy, expressed in kBtu/h or kW. A well-designed, energy-efficient oven can operate with a lower input rate and still produce as much or more food product as an oven with a lower

Oven Performance

Ovens


quality design and a higher rated input. Initial cost of the energy-efficient oven may be higher, but the long-term operating costs will be lower.

Preheat Energy and Time

Preheat Time. Preheat time is the time required to raise the cavity from room temperature to cooking temperature (typically 350°F (175°C)). Ovens are usually left on during the day, so preheat time may not be important to the operator. Preheat time is determined by energy input rate, cavity size, heating technology and control strategy. Knowing the preheat time allows an operator to effectively schedule oven start-up and shutdown times, so that the oven does not need to be operated continuously from opening until closing.

Preheat Energy. The energy required to preheat a oven is a function of the cavity size of the oven and its heat-up efficiency. However, preheat energy consumption represents less than 15% of the daily energy consumption for a oven that was turned on once over an 8-hour operating period.4 For longer operations (e.g., 16 hours), the energy performance of the oven during this phase of its operation becomes less important.

Idle Energy Rate

The idle energy rate is the amount of energy consumed per hour when the oven is turned on and holding at operating temperature without a food load. The idle-energy consumption rate is a function of the thermostat set point and the effective resistance of the oven cavity to heat loss. Some ovens, es-pecially conveyor ovens, exhibit significant idle energy rates.

Monitoring the usage of ovens in commercial kitchens4 has demonstrated that they spend a significant proportion of their “on time” in idle mode and that the rate of idle energy consumption has a significant impact on total daily energy consumption.

Ovens



Cooking energy rate is the rate at which an oven consumes energy while it cooks a load of food. It is reported in kBtu/h or kW. Cooking-energy effi-ciency is the ratio of energy added to the food and total energy supplied to the appliance during cooking:


Food

Appliance= × 100%

The ASTM standard test methods define cooking rates and efficiencies for heavy-load (full-cavity), medium-load (half-capacity) and light-load (single-pan) conditions. Due to variances in burner and heat-exchanger design, gas ovens demonstrate a dramatic difference in heavy-load cooking energy effi-ciencies.

Production Capacity

Production capacity is the amount of food that can be prepared in an oven in a given time period and is directly related to the cook time. A shorter cook time for a given food product results in a higher production capacity. It is one of the most important factors in selecting the right oven for a kitchen because it allows an operator to match an oven to the anticipated production require-ments of a facility. An oversized oven, with an unnecessarily high production capacity, could cost the operator in up-front capital while an undersized oven could create a bottleneck that would impede the product output of the entire kitchen. Production capacity is typically reported in pounds per hour (lb/h) of food cooked although in some cases (deck ovens, conveyor ovens, and rapid cook ovens) the production capacity is also reported in pizzas cooked per hour. For convection ovens, the ASTM test method determines production capacity by cooking loads of potatoes and the result is reported in pounds of potatoes per hour. FSTC testing showed production rates of approximately 70 lb (32 Kg) per hour for both the gas and electric full-size convection ov-ens and around 40 lb (18 Kg) per hour for the half-size ovens tested.17

Ovens


Cooking Uniformity

Cooking uniformity is a measure of the ability of an oven to cook food evenly no matter where it is placed in the oven or how the oven is loaded. For example, the ASTM test method for convection ovens measures uniform-ity by baking a fully loaded oven of white sheet cakes and comparing the browning patterns. It is very difficult for an oven to display perfect uniform-ity without engineering the airflow within the oven cavity. Many of the cake-browning tests performed at the FSTC have reflected some level of uneven cooking, from front-to-back and from rack-to-rack.17 The testing effectively highlights the design differences between ovens. A poorly designed oven may burn food on the top rack before it finishes cooking the food on the cen-ter rack. Convection ovens with uneven airflow may burn the side of the food closest to the fan while the other side is barely browned.

Advanced burners are being developed by the gas industry to improve the uniformity in the burner section through the use of ported infrared burners and inconel wire mesh burners. These developments have the potential to improve cooking uniformity as well.18

The ASTM Standard Test Methods allow manufacturers and users to com-pare the cooking-energy efficiency of different ovens within comparable oven categories. For example, in the test method for convection ovens, en-ergy efficiency is determined by fully loading an oven with potatoes and then cooking them to a predetermined temperature of 205°F (96°C). Typical en-ergy efficiencies for convection ovens under these cooking scenarios, along with the other oven types are summarized in Table 7-1.

Gas ovens, by the very nature of their heat transfer from the combustion of gas are less efficient than their electric counterpart. In standard gas ovens, the combustion chamber and flue passages are located between the oven cavity and the exterior cabinet. The hot products of combustion indirectly heat the oven cavity by conduction through its walls. The hot flue passages also may be close to the exterior, causing heat losses to the environment. Modern con-vection ovens circulate flue gases through passages built into the oven cavity walls resulting in better thermal coupling and significantly improved effi-


Ovens


ciency.4 Two types of recirculation systems are currently available; one uses a specially designed fan, the other uses a recycling or “snorkel” tube. Both systems reuse the hot air, which would normally be vented.

Table 7-1. Oven Energy Efficiency. a

High-Efficiency Gas (%) Standard Gas (%) Electric (%)

Std/Conv/Comb 40 - 50 30 - 40 50 - 80 Deck 20 - 30 40 - 60 Conveyor 40 - 50 10 - 20 20 - 40 Rotisserie 20 - 30 50 - 60 a Energy efficiency numbers are based on FSTC test data from applying the ASTM Standard Test Methods to convection ovens, and on preliminary estimates for combination ovens, deck and conveyor pizza ovens, and rotis-series.

As pointed out by A.D. Little in their characterization of commercial ovens, efficiency improvements of gas-fired ovens has consisted mainly of control-ling burner excess air through the use of power burners.18 Convection oven technology can also be viewed as an energy conserving measure since the cooking time associated with convection cooking is shorter, thus reducing the overall energy consumption required during the cooking process. Direct-fired ovens, consequent to the gas flame being in direct contact with the oven cav-ity and food products being cooked, require less energy to do the same amount of work as indirect-fired ovens. A.D. Little projects energy efficien-cies associated with these ovens to be in the 45% range. They also speculate that the successful application of air impingement to conveyor ovens will drive the efficiency of these gas models into the 40% range versus the current 10% - 20% limits.

Projected energy consumption for gas and electric ovens are presented in Table 7-2 and 7-3. Based on Pacific Gas and Electric Company’s in-kitchen monitoring at its production-test kitchen, average energy consumption rates for convection ovens reflect duty cycles of 35% for a full-size gas convection

Oven Energy Consumption

Ovens


oven, 40% for a half-size gas oven and 25% for both electric full-size and half-size ovens.19-23 It was assumed that the usage patterns for countertop models would be similar to half-size convection ovens.

Duty cycles for deck ovens were assumed at 30% for gas ovens and 20% for electric ovens based on data from a proprietary unpublished end-use study. Similarly, a duty cycle of 50% was assumed for both gas and electric con-veyor ovens. Rotisserie duty cycles were based on data generated by the Food Service Technology Center.24 The duty cycle of an appliance is defined as the average rate of energy consumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy.

A study8 at the Food Service Technology Center showed that a fully loaded combination oven used to cook whole chickens could cost 30% more per load in the combination mode than in the convection mode with only a minimal reduction in cook times and little discernible difference in product quality or yield. This increase in energy consumption was driven by the en-ergy needed to create a constant supply of steam in combination mode and is illustrative of the need to use the combination mode sparingly and appropri-ately. Moderate use of the combination mode at the beginning of the cook cycle can reduce the product cook time without significantly impacting en-ergy consumption; however, indiscriminate use of the combination mode throughout the entire cook cycle, as per the example above, can lead to dra-matically increased operational costs for these appliances. Likewise, the cost to preheat an oven in the combination mode is about double that of convec-tion mode because the boiler must be preheated as well.

Daily energy consumption for ovens was calculated by multiplying the me-dian rated energy input for each oven category by the respective duty cycle and the hours of operation. Typical operating hours were gleaned from in-kitchen energy-use monitoring experiences and observations as well as on the PREP study25 and proprietary end-use monitoring reports. Projected an-nual energy consumption was determined by assuming a 6-day per week, 52-week per year operation.

Ovens


Table 7-2. Projected Energy Consumption for Gas Ovens.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (w x d) (kBtu/h) (%) (kBtu/h) (h/d)a (kBtu)b

STANDARD/CONVECTION/COMBINATION Full-Size 38" x 38" 40 - 100 (Median) 70 35d 25 8 62,400 Half-Size 30" x 26" 20 - 40 (Median) 30 40e 12 6 22,500 Countertop 20" x 22" 15 - 20 (Median) 18 40f 7 4 8,740

DECK g 20 - 120

(Median) 70 30h 21 10 65,500 CONVEYOR 120-150

(Median) 135 50i 68 10 212,000 ROTISSERIE 40 - 60

(Median) 50 60J 30 8 74,900 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c Includes cook & hold ovens. d The duty cycle is based on monitoring a full-size gas convection oven with an input rate of 72 kBtu/h in a real-world production kitchen.19 An associated average energy consumption rate of 25 kBtu/h was calculated. e The duty cycle is based on monitoring a half-size gas convection oven with a rated input of 35 kBtu/h in a real-world production kitchen.20 An associated average energy consumption rate of 12 kBtu/h was calculated. f A 40% duty cycle has been assumed for countertop ovens based on the assumption that the usage pattern is similar to half-size oven operations. g Includes bake, roast, combination and pizza ovens. h A 30% duty cycle has been assumed for deck ovens based on data from an unpublished proprietary end-use moni-toring study. I A 50% duty cycle has been assumed for conveyor ovens based on data from an unpublished proprietary end-use monitoring study. j A 60% duty cycle has been assumed based on Food Service Technology Center laboratory rotisserie testing.24

Ovens


Table 7-3. Projected Energy Consumption for Electric Ovens.

Nominal

Size

Rated Energy Input

Duty Cycle

Average Energy

Consumption

Typical Operating

Hours


(w x d) (kW) (%) (kW) (h/d)a (kWh)b (kBtu)c

STANDARD/CONVECTION/COMBINATIONd Full Size 38" x 38" 10 - 40 (Median) 25 253 5 8 12,500 42,600 Half Size 30" x 26" 6 - 10 (Median) 8 25f 2 6 3,740 12,800 Countertop 20" x 22" 2 - 6 (Median) 4 25g 1 4 1,250 4,260

DECKh 6 - 12

(Median) 9 20i 2 10 6,240 21,300 CONVEYOR 35 - 45

(Median) 40 50j 20 10 62,400 213,000 ROTISSERIE 4 - 12

(Median) 8 65k 5 8 12,500 42,600 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h. d Includes cook & hold ovens. e The duty cycle is based on monitoring a full-size electric convection oven with an input rate of 16 kW in a real-world production kitchen.21 An associated average energy consumption rate of 5 kW was calculated. f The duty cycle is based on monitoring two half-size electric convection ovens with a rated inputs of 5 kW each in a real- world production kitchen.22,23 An associated average energy consumption rate of 2 kW was calculated. g A 25% duty cycle has been assumed for countertop ovens based on the assumption that the usage pattern is similar to half-size oven operations. h Includes bake, roast, combination and pizza ovens. I A 20% duty cycle has been assumed for deck ovens based on data from an unpublished proprietary end-use moni-toring study. j A 50% duty cycle has been assumed for conveyor ovens based on data from an unpublished proprietary end-use monitoring study. k A 60% duty cycle has been assumed based on Food Service Technology Center laboratory rotisserie testing.24

Ovens


Some recent building codes and guidelines reflect the differences between gas and electric oven characteristics, while others do not. The 1995 ASHRAE Applications Handbook classifies both gas and electric ovens as light duty with respect to ventilation requirements. Typical ventilation rates for a listed (e.g., ULC), wall-mounted, canopy hood range from 150 to 200 cfm (75 to 100 L/s) per linear foot.26

Ovens may be equipped with a standard draft hood, which may be directly vented to a flue or chimney. This may eliminate the need for an exhaust hood for these ovens when used to prepare food product that does not produce grease.

Integrated Ventilation Systems. Several oven manufacturers have inte-grated appliance-specific ventilation hoods in their oven designs. Designing hoods for a given model eliminates the risk of mismatched or incompatible equipment. The In-Vent™ integrated ventilation hood for Blodgett’s Master-Therm conveyor oven is a revolutionary new vent system designed to mini-mize heat gain—both radiant and convective as well as the net exhaust re-quirement. Its unique configuration surrounds the majority of the oven’s exterior and makes optimum use of untempered make-up air. This, in turn, reduces the load on the restaurant’s HVAC system while providing increased operator comfort. Also, because of its enclosed nature, this system is quieter than canopy hood ventilation systems. Another company–Franklin/Southern Pride–has integrated a hood with their rotisserie system. Although the system is currently restricted to the rotisserie oven, Franklin plans to accommodate their other ovens in the near future.

Insulation. One of the key features of any piece of food service equipment is its energy efficiency. For cooking appliances such as ovens in particular, this number is an invaluable indicator of how much energy will be applied to-ward cooking the food and how much will be wasted or lost. Cooking-energy efficiency is controlled by two primary factors: how heat is imparted to the food and how heat loss is controlled. The first factor involves such concepts as effective air circulation within the cooking cavity and will be discussed later.



Ovens


Today, most oven manufacturers have realized that insulation is essential to minimizing heat loss in the cooking process⎯ appliances with effectively incorporated insulation perform better than those without. This can be easily determined by comparison of their cooking energy efficiencies. The proper amount or thickness and the proper R-value of insulation are critical in minimizing the amount of conductive heat transfer through oven cavity sur-faces. Studying insulation use in ovens is an effective way of promoting en-ergy efficiency and energy-conscious designing in the industry.

Air Circulation and Cooking Uniformity. Air circulation within an oven cavity is another basic concept behind convection ovens as well as other de-vices. It is the underlying principal of convective heat transfer cooking; without proper air circulation there would be little or no heat transfer. For appliances such as convection ovens, adequate hot air distribution promotes uniform cooking and high energy efficiencies. In order to achieve proper air circulation, several basic features need to be considered: fan speed and siz-ing, cooking cavity design and geometry, and location of flue gas inlet and exit (for direct-fired ovens). Existing standard test methods incorporate tech-niques to determine the effectiveness of air circulation components in ovens and challenge their cooking uniformity ability. For example, one test moni-tors an array of food temperatures that are distributed throughout the cooking compartment. Another example is the sheet cake browning uniformity test, which shows darker and lighter surface areas that produce qualitative results indicating how well heat is circulated and transferred to various sections of an oven (see Figure 7-12). Together these techniques are used to establish an oven's cooking uniformity profile.

As long as tests are conducted to measure cooking and heating inconsistency within ovens, designs will improve and energy efficiencies will follow ac-cordingly. Manufacturers are constantly refining oven design and geometries to optimize performance and heat transfer, yielding better cooking uniformity in the long run. As these oven technologies advance, testing of these appli-ances will ultimately be the deciding factor and basis for more and more of today's consumer decisions.

Moisture and Humidity. One of these advanced technologies that is used in many ovens today is moisture and humidity control. In proofing ovens,

Figure 7-12. Sheet cake uniformity.

Ovens


breads and similar items are held in an environment where the interior hu-midity is controlled; it is in this “proofing” stage that the moisture is utilized to increase the bread volume after the loaves have assumed their form. Simi-larly, combination ovens inject steam into the cooking cavity to induce vari-ous food qualities such as the crustiness and golden brown color in breads. In direct-fired ovens, hot combustion gases which contain water vapor are routed directly into the cooking cavity. Humidity control and moisture inter-action with foods are areas that deserve further research and testing of this cooking process will greatly improve consumer understanding and equip-ment selection.

Food Quality and Appearance. While much focus and emphasis in the re-search and testing of food service equipment is placed on energy use, effi-ciency and productivity, there is also a concern among manufacturers and end users about the quality and appearance of the foods that are cooked. Due to the varying technologies employed by the vast array of ovens in the food service industry, there are differences in the quality of their finished prod-ucts. More specifically, within the classification of direct and indirect-fired ovens, aside from the concept and design differences, other disparities can also exist with regards to the final food quality, depending on exactly what is being prepared.

One particular issue that warrants the need for further investigation is the undesired pinking of meats (see Figure 7-13), especially chicken, pork, and turkey, when cooked in direct-fired gas ovens. In the public eye, a pink col-oration in cooked meat products is normally considered an indication of the food being underdone, even if the meat has been properly cooked. The phe-nomenon of pinking in cooked meats can be attributed to the reaction of combustion gases or byproducts, which are forced into the cavity in direct-fired ovens, with the internal chemicals found in all meats. These cases have been studied and observed to occur even after various meats were cooked to temperatures in the range of 180°F. Researchers have found direct correla-tions between the presence of combustion byproducts such as carbon monox-ide and the occurrence of pinkness in the final food product.27 Their research associates this coloration with the interaction between oven flue gases and the water contained in the meats, which together yield higher acidity levels

Figure 7-13. Pinking of meat.27 Photo: Courtesy Cornforth, Utah State Uni-versity.

Ovens


that promote the ideal conditions for pinking. These resultant acidic chemi-cals disassociate into nitrites (chemical formula NO3-),27 which coinciden-tally, are used in the preparation of cured meat products to produce a desired pink color.28 In one scenario, these nitrites are what meat preparation compa-nies use to purposefully cure meats to a desired pink tone; however in an-other it is the same chemical that ultimately causes an undesired effect when meats are cooked in direct-fired ovens (see Figures 7-14 and 7-15). Thus far, this is an issue that greatly affects public opinion and end user satisfaction.

While direct-fired ovens have an advantage over indirect-fired gas convec-tion ovens in the areas of energy efficiency and cook time, the indirect-fired oven (by its very definition) and intrinsic nature (no combustion gases in the oven cavity) does not produce meats that experience the pinking effect. Al-though direct-fired ovens have created a niche for themselves as an effective kitchen appliance, this harmless pink coloration may cause adverse effects such as end users choosing to focus on or switch over to indirect-fired ovens. Perhaps the occurrence of the pink coloration needs to be addressed in the classification and performance testing of direct and indirect-fired gas convec-tion ovens. Tests would reflect the flue gas distribution design and indicate the tendency of meats cooked in tested ovens to experience this pinking ef-fect. Therefore, it stands to reason that further industry wide research needs to be conducted to solve or eliminate the pinking of meats in direct-fired ov-ens. More importantly, research and studies of this phenomenon need to be brought to the attention of manufacturers and end users in order for them to be educated about why this happens and what can be done to avoid it. Indus-try awareness of this problem has already prompted one manufacturer to ac-knowledge this phenomenon and emphasize the fact that they are able to avoid this issue, while maintaining performance with the use of indirect gas streams within heat exchangers in their indirect-fired gas convection ovens.

As with other classes of cooking equipment, the average efficiency of ovens is more dependent on tendencies of end users to purchase more efficient equipment than on any future technology developments.18 There is a need for the food service industry to better benchmark the energy performance for all types of ovens. An opportunity exists for the utilities to promote higher effi-

Figure 7-14. Uncured meat (left); cured meat (right).27

Photo: Courtesy Cornforth, Utah State Uni-versity.

Figure 7-15. Pink ring around meat cooked in direct-fired oven.29 Photo: Courtesy Cornforth, Utah State Uni-versity.


uncured cured

Ovens


ciency and production capacity ovens with the best cooking uniformity—but the database needs to be expanded.

Ovens


1. A supplement to Restaurant Business Inc., 1995. Foodservice Equipment 1000 for NAFEM. The Baking Boom, p.53-54.

2. CP Publishing. Inc. 1994. Cooking for Profit. Rack/Tray Ovens, Septem-ber 15, No. 520, p. 14 - 15.

3. Opportunities and Competition in the Food Service Equipment Industry: A presentation by R. Simek, Senior Consultant, Arthur D. Little to The New England Gas Association, 1995, February 10.

4. Architectural Energy Corporation, 1991. Foodservice Equipment Volume 2: Ovens, Prepared for Southern California Edison Technology Assess-ment, Volume 2, December.

5. National Association of Foodservice Equipment Manufacturers. 1989 Equipment and Supply Study.

6. CP Publishing. Inc. 1993. Cooking for Profit. Gas Deck/Pizza Ovens, July 15 - August 14, No. 506, p. 16 - 17.

7. CP Publishing, Inc., 1990. Cooking for Profit. Gas Convection Ovens, May 15, No. 468, p. 4-5.

8. Unpublished. Increasing Profits by Using Energy Efficient Food Prepa-ration Equipment, Processes and Procedures: a Cooking Equipment Module prepared by Fisher, D.R., The University of Manitoba for En-ergy, Mines & Resources Canada, March.

9. Esource Inc., 1995. Exclusive Reports on Energy End-Use Efficiency Product Profile: The FlashBake Oven. PP-95-1, February.

10. Binder, M. in Pizza Today., published monthly by ProTech Publishing and Communications (New Albany, IN), 1995. August, Volume 13, Number 8, pp. 44 - 48.

11. American Society for Testing and Materials, 1999. Standard Test Method for Performance of Convection Ovens. ASTM Designation F1496-99. In Annual Book of ASTM Standards, West Conshohocken, PA.

12. American Society for Testing and Materials, 2000. Standard Test Method for Performance of Combination Ovens. ASTM Designation F1639-95. In Annual Book of ASTM Standards, West Conshohocken, PA.

13. American Society for Testing and Materials, 1998. Standard Test Method for Performance of Rotisserie Ovens. ASTM Designation F1787-98. In Annual Book of ASTM Standards, West Conshohocken, PA.

14. American Society for Testing and Materials, 1997. Standard Test Method for Performance of Conveyor Ovens. ASTM Designation F1817-97. In Annual Book of ASTM Standards, West Conshohocken, PA.

References

Ovens


15. American Society for Testing and Materials, 1999. Standard Test Method for Performance of Deck Ovens. ASTM Designation F1965-99. In Annual Book of ASTM Standards, West Conshohocken, PA.

16. American Society for Testing and Materials, 2001. Standard Test Method for Performance of Rack Ovens. ASTM Designation F2093-01. In Annual Book of ASTM Standards, West Conshohocken, PA.

17. Blessent, J., 1994. Development and Application of a Uniform Testing Procedure for Convection Ovens. Pacific Gas and Electric Company De-partment of Research and Development Report 008.1-94-12, October.

18. Little, Arthur D. Inc., 1993. Characterization of Commercial Building Appliances: Final Report for Building Equipment Division Office of Building Technologies U.S. Department of Energy, August, pp. 5-38.

19. Nickel, J., Conner, M., Cesio, C., 1996. Montague Model SE70AH Gas Full-Size Convection Oven: In-Kitchen Appliance Performance. Food Service Technology Center Report 5011.95.22, June.

20. Blessent, J., 1992. Appliance Performance in Production Blodgett Model DFG-60 Gas Half-Size Convection Oven. Pacific Gas and Electric Com-pany Department of Research and Development Report 008.1-9.11, De-cember.

21. Blessent, J., 1996. Montague Model SEK15AH Electric Full-Size Con-vection Oven: In-Kitchen Appliance Performance. Food Service Tech-nology Center Report 5011.95.21, June.

22. Nickel, J., Conner, M., Cesio, C., 1996. Blodgett Model CTB-1 Electric Half-Size Convection Oven: Appliance Performance in Production. Food Service Technology Center Report 5011.95.17, June.

23. Pieretti, G., Blessent, J., Kaufman, D., Nickel, J., Fisher, D., 1990. Cook-ing Appliance Performance Report - PG&E Production-Test Kitchen. Pacific Gas and Electric Company Department of Research and Devel-opment Report 008.1-90.8. May.

24. Zabrowski, D., Young, R., Ardley, S., Knapp, S., Selden, S., 1995. Deli-catessen Appliance Performance Testing. Food Service Technology Cen-ter Report 5016.95.23, October.

25. Claar, C.N., Mazzucchi, R.P., Heidell, J.A., 1985. The Project on Res-taurant Energy Performance (PREP)–End-Use Monitoring and Analysis. Prepared for the Office of Building Energy Research and Development, DOE, May.

26. ASHRAE, 1995. Applications Handbook, Kitchen Ventilation, Chapter 28, pp. 28.1-28.20.

27. Pinking in Cooked Poultry: Current Situation and General Theories. Webpage by Darren Cornforth, Utah State University. http://www.usu.edu/familylife/nfs/foodscience/faculty/pinking.htm

28. Bennion, Marion, 1980. The Science of Food. Chapter 25, sections 6 and 7.

Ovens


29. Meat Color. Webpage by Jane Ann Boles and Ronald Pegg. Animal and Range Sciences, Montana State University, and Saskatchewan Food Product Innovation Program,University of Saskatchewan. http://animalrange.montana.edu/Docs/meat_color.htm


8 Steamers


Commercial steamers provide an easy, fast way to prepare large quantities of food. Steaming offers good nutrient retention, short cook times, and ease of preparation; little attention is needed from the chef, food can be cooked and served in the same pan, and cleanup is simple. Steamers are versatile appli-ances that can be used to prepare almost any food that does not require a crust. Delicate vegetables such as asparagus and broccoli are cooked without damage, frozen foods are defrosted and cooked in one step, and hard-to-cook meats such as beef ribs can be par-cooked more quickly and with less weight loss than oven roasting.

In appearance, the compartment steamer resembles an oven. The cavity is typically rectangular on atmospheric steamers, and may be oval or round on pressure steamers. The door is “gasketed” and windowless. Controls are front-mounted. Figure 8-1 shows a typical two-compartment steamer atop a boiler base.

Steamers come in a variety of configurations, including countertop models, wall-mounted models and floor models mounted on a stand, pedestal or cabi-net-style base. A steamer may consist of one to four stacked cavities. The cavity is usually designed to accommodate a standard 12 by 20-inch (300 mm x 500 mm) hotel pan. Smaller steamers may be designed for use with one-third size pans, and some large steamers can hold several 18 by 26-inch (460 mm x 660 mm) baking trays.

The steam itself can be produced several ways. Many compartment steamers have an external (with respect to the cooking compartment) electric, gas, or service-steam powered boiler that produces potable steam under pressure. This pressurized steam is delivered to the cooking compartment as demanded by the control settings. However, in the case of a pressureless steamer (see Figure 8-1), the compartment is openly connected to a condensate drain and the steam environment within the compartment cannot sustain a pressure above atmospheric (both raw steam and condensate exit the cooking cavity

Introduction

Figure 8-1. Two-compartment convection steamer on self-contained base. Photo: Fisher-Nickel, inc.

Steamers


through this drain). In the case of a pressure steamer, only condensate is al-lowed to drain. Thus the cooking cavity is allowed to build up to the operat-ing pressure of the boiler. In the larger boiler-based designs, there may be additional steam capacity (referred to as a power-take-off or PTO) to power other appliances such as a steam-jacketed kettles installed along side the steamer.

Steam also may be produced by a steam generator located within (or directly connected to) the cooking cavity. This method differs from the boiler-based steamers in that the steam is produced at (or slightly above) the compartment operating pressure (i.e., atmospheric pressure). This strategy is not used for pressure steamers.

A steamer may produce steam by boiling water poured directly into the cook-ing compartment prior to operation (this is the simplest form of an internal steam generator, typically referred to as a “connectionless” steamer). Heating elements are located either beneath the compartment’s floor or placed di-rectly in the bottom of the compartment. Gas burners, placed below the com-partment, may produce steam in the same fashion.

Steam may be supplied from an external source (e.g., centralized building steam). If this steam is clean, it can be routed directly to the steamer com-partments. Otherwise, it can be run through a heat exchanger and used to generate potable steam from clean water.

Boiler-based and conventional steam-generator type steamers require a drain line, water line, and a connection to an energy source—typically gas or elec-tricity. Self-contained units typically have boilers that fill automatically. Condensate from the cavity is directed to a drain tube, where it is cooled by a stream of water before flowing into the sewer (In many areas it is against code to drain water above 140°F). The new generation of “connectionless” steamers require no such connections beyond the electrical (or gas) hook up. Water is poured into the bottom of the cooking compartment and periodically refilled during the course of operation. When operation is suspended, the wa-ter is drained from the cavity into a pan or bucket.

Steamers


Steam cooking exploits the latent energy that steam at 212°F (100°C) carries, which is six times greater than water at the same temperature. When steam condenses on the surface of cold food, it transfers this latent energy to the food. If the pressure inside the steamer compartment rises, the steam can reach higher temperatures and deliver more energy to the food. This is the mechanism behind pressurized steamers, which may cook food faster than pressureless (atmospheric) steamers.

As with baking, a layer of insulating vapor can form around food in a still steamer cavity. The natural convection inside the cavity tends to strip away this insulating layer of air, but it has a limited ability to do so. If food is tightly packed, or if the steamer is fully loaded with pans, convection is im-peded and cooking slows down. The last few years have seen the addition of a fan to some steamers. Forced convection in a steamer (e.g., via steam being injected from the boiler) has the same effect as it does in a convection oven, namely stripping away the insulating layer of vapor around the food to speed cooking and provide even heat throughout the steamer cavity.

There are two basic categories of steamers on the market, pressureless (at-mospheric) and pressurized. Each type is available in gas, electric and direct-steam models.

Pressureless Steamer

Pressureless steamers, also commonly referred to as "atmospheric" steamers, maintain the cooking compartment at close to atmospheric pressure (between 0 and 2.9 psig (0 and 20 kPa)). They generally employ a large cooking cavity to facilitate the circulation of steam around the food product. Because these steamers operate at or near atmospheric pressure, the door may be safely opened at any point during the cooking cycle to check the product. Many atmospheric steamers employ a fan for forced convection steaming, to pro-duce shorter cook times and even cooking throughout the compartment under full-load conditions.

Cooking Process

Types of Steamers

Steamers


Pressure Steamer

Pressure steamers employ a closed system to allow the steam to build pres-sure inside the cooking compartment. These steamers are easily identifiable by their smaller compartments and heavy locking doors (see Figure 8-2). Al-though these steamers may cook smaller batches of food than pressureless steamers, cook times can be shorter, and energy efficiency higher, depending on the food product.

Low-pressure steamers typically operate between 3 and 9 psig (20 and 62 kPa). These are high-volume steamers that are often used in schools and hos-pitals. High-pressure steamers generally have smaller compartments and op-erate at 10-15psig (70-105 kPa). Although they hold less food, they may cook up to twice as fast as a low-pressure steamer. Pressure steamers require precise cook times because the food product cannot be checked while the steamer is operating.

Advanced Steamer Technologies

Pressureless steamers vary in their technological complexity. In addition to the three primary designs (boiler, steam-generator, and connectionless), manufacturers have employed different strategies for improving performance and reducing energy consumption. These emerging technologies include convection, vacuum pumps, close-system design, connectionless designs, compartment insulation and a stand-by mode.

Convection. Turbulent steam strips away the insulating layer next to the food, for faster cooking that is more even throughout the cavity. There are two basic methods of producing this forced convection. Some manufacturers inject steam into the cavity through jets in the cavity wall, while others use a fan to circulate the steam within the compartment.

Vacuum Pumps. Vacuum pumps have been used to reduce the pressure within the cooking compartment and lower the cooking temperature. This technology is promoted to reduce cook times and be gentler on delicate food products.

Figure 8-2. Two-compartment pressure steamer. Photo: Fisher-Nickel, inc.

Steamers


Closed System. One manufacturer employs a unique steam-control system that monitors pressure fluctuations within the cooking compartment, which reflects how much steam is being condensed on the food during the cooking process. As pressure builds in the compartment and less steam condenses, the unit’s steam generator will suspend steam production. Only when the com-partment pressure lowers, indicating that the food has absorbed heat from the steam, will the steam-generator reactivate.

Connectionless Design. “Connectionless” steamers have a water reservoir in the bottom of the cooking compartment in lieu of a water connection. The reservoir is manually filled and drained. Connectionless steamers have an advantage in that no steam leaves the cooking cavity during operation (ex-cept through a compartment vent). Thus, steam that does not condense on the food remains within the cavity, thereby significantly improving the steamer’s energy performance. This strategy also mitigates some of the difficulties as-sociated with boiler maintenance, and allows easier access for cleaning. Fig-ure 8-3 shows a typical connectionless steamer. One manufacturer of a connectionless steamer incorporates a vacuum that reduces the temperature of steam (below 212°F) to provide a more “gentle” cooking event.

Compartment Insulation. Improved insulation around the cooking com-partment reduces heat loss to the kitchen and can have a significant effect on standby (idle) energy consumption.

Standby Mode. Some manufacturers maintain a steam generator stand-by temperature just below boiling (typically, 180 to 200°F). This allows the ap-pliance to produce steam 10-30 seconds after the steamer is loaded with food product and is a practical alternative to turning the steamer off between uses. Cook times may be slightly longer than if the steamer had been held at full input, as the cavity also absorbs heat. The increase in cook time depends on when the steamer was last used (leaving residual heat in the walls of the cavity.)

Steamer manufacturers offer a wide range of control packages. Some units are equipped with only the necessary controls for operation: an on/off switch, water-refill light, and simple timer. Others have an array of features such as

Figure 8-3. Connectionless steamer. Photo: Stellar Steam.

Controls

Steamers


boiler temperature, high- and low-power modes, idle/hold modes and other energy-saving settings. Timers can also terminate the cooking process to en-sure that food product is not over cooked. Boiler-based units may also incor-porate maintenance-indicator lights and an automated boiler blow-down mechanism to cleanse the heating elements or burner tubes of scale and sediment.

Some steamers use compensating timers, which automate defrosting and cooking. As an example, consider a load of frozen fish being cooked in a steamer with a compensating timer. Cavity temperature is monitored, and the timer does not begin to count down until the compartment nears 212°F (100°C), a temperature that corresponds to the frozen food having mostly thawed. At this point, the timer-preset with the desired cook time for a thawed food product has "compensated" for the food's initial condition, whether it was frozen or thawed (as well as the cavity’s initial condition, cold or preheated). In a pressure steamer, the drain valve would close at this point and pressurized cooking would begin. 1

An ASTM Standard Test Method for Performance of Steam Cookers2 devel-oped by the Food Service Technology Center (FSTC) allows manufacturers and users to gauge steamer-cooking performance directly, and to evaluate steamer energy consumption as well. As hard data on steamers has expanded, it is apparent that certain technologies and designs yield better performance.

The ASTM method reports several parameters of steamer performance, in-cluding preheat energy and time, idle energy rate, and cooking-energy effi-ciency and production capacity under heavy- (full-load) and light-loading (single-pan) conditions with both green peas and red potatoes.

Preheat Energy and Time

Preheat energy and duration can be useful to food service operators for man-aging power demands, and knowing how quickly the steamer can be ready for operation.

Steamer Performance

Steamers


Typical preheat times can be between 5 and 20 minutes. Longer preheat times can discourage operators from turning units off between loads. Cook times can also be adversely affected by the unit’s need to reheat the cavity walls as well as cook the food product. Some boiler-based units utilize com-pensating timers to address the challenge of reheating the cold compartment. Connectionless steamers, however, do not suffer this dilemma as the com-partment is continually exposed to steam produced by the boiling water in the cooking compartment. Table 8-1 summarizes typical preheat time and energy consumption for various types of steamers.

Table 8-1. Input Rate and Preheat Test Results for Different Steamers.3

Elec 1 Elec 2 Gas 1 Gas 2

Energy Input Rate 26.3 kW 19.1 kW 254 kBtu/h 199 kBtu/h Preheat Time

Heat-Up Time (min) 12.8 6.3 6.7 6.9 Fill Time (min) 4.2 0.5 3.9 3.6

Preheat Energy Consumption 5.3 kWh 1.0 kWh 28.1 kBtu 22.8 kBtu

Idle Energy Rate

Steamers spend the majority of the operating time in an idle, or stand-by condition. The idle energy rate of a steamer provides a good indication of its overall energy consumption use. Even in a busy restaurant, steamers may be idle 75% of the time. Figure 8-4 illustrates the range of normalized idle rates for three-pan, single-compartment steamers.3-14

Frozen Green Pea Cooking-energy efficiency

Frozen green pea cooking-energy efficiency is determined by cooking a full load of frozen peas (8 pounds (3.6 kg) of peas per pan) from a temperature of 0 ± 5°F to 180°F. Frozen green peas are representative of a typical frozen food product found on restaurant menus. As a test product, green peas are consistent in quality and readily available. More importantly, they yield con-sistent testing results that in turn provide reliable energy efficiency data.

Steamers


0.0

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*Idle rates are normalized for 3-pan steamers.

Red Potato Cooking-Energy Efficiency

Red potato cooking-energy efficiency is determined by cooking a full load of red potatoes (8 pounds (3.6 kg) per pan) from room temperature (75 ± 5°F) to 195°F. As a tough-to-cook food product, red potatoes challenge the produc-tion capacity of a steamer more so than frozen green peas. With a low surface to volume ratio and a slower rate of condensation, potato-cooking tests can reveal far greater differences in cooking-energy efficiency between one steamer and another. In particular, the benefit of pressure steaming over at-mospheric steaming becomes quite apparent when comparing red potato cooking energy efficiencies. Figures 8-5 and 8-6 compare the green pea and red potato cooking energy efficiencies for different types of steamers.12-17

Figure 8-4. Normalized electric pressureless steamer idle energy rates.

Steamers


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Figure 8-5. Typical frozen green pea cooking-energy efficien-cies of steamers.

Figure 8-6. Typical red potato cook-ing-energy efficiencies of steamers.

Steamers


Frozen Green Pea and Whole Potato Production Capacities

Production capacity is the amount of food that can be cooked in a steamer in a given time. This figure is typically presented in product literature as the number of pounds of frozen vegetables that can be cooked per hour. Potatoes are a more stubborn food product and tend towards longer cook times than frozen peas. Figure 8-7 compares the frozen green pea production capacity for various electric pressureless steamers.3-14

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*Production capacity is normalized for 3-pan steamers.

Water Consumption and Condensate Temperature

Water consumption is monitored during both green pea and red potato cook-ing-energy efficiency tests to determine the rate of water usage. Water con-sumption characterization is useful for estimating water and sewage costs associated with appliance operation.3

Figure 8-7. Normalized electric pressureless steamer production capacity.

Steamers


Condensate temperature is monitored during both cooking-energy efficiency tests. Measurement of condensate temperature is useful to verify that the temperature does not exceed regional building code limits.3

Heavy-Load vs. Light-Load Efficiencies

The ASTM test method specifies different loading scenarios for heavy-load (full-compartment) and light-load (single-pan) tests. The heavy-load tests represent a steamer’s maximum performance. The cooking compartment is filled to capacity with food product and the steamer exhibits its peak effi-ciency during these tests.

Light-load cooking-energy efficiency serves to ease comparisons between units of differing maximum compartment capacities. The cooking scenario also illuminates the wide disparity between steamers of differing cooking technologies. For example, boiler-based atmospheric steamers tasked with cooking a single pan of red potatoes can exhibit cooking energy efficiencies as low as 3%. Connectionless units typically exhibit cooking energy efficien-cies of 30% or more under similar loading conditions.

Pressureless steamers exhibit dramatic differences in energy-efficiency, pri-marily depending on how the steam is produced and/or introduced and then maintained within the cooking compartment. The first-generation boiler-based steamers continually forced steam into the cooking compartment, whether or not the unit was cooking. Additionally, the boilers themselves rarely incorporated any insulation. This led to cooking energy efficiencies in the 25 to 30% range (determined under the full-load potato testing conditions of ASTM F1484-99). Second-generation steamers employed an insulated compact steam-generator, which had significantly less heat loss than tradi-tional boiler systems. The performance of these second-generation steamers still suffered from continuously supplying steam to the cooking compart-ment, leading to high idle energy consumption.

Both of these approaches use an open-system design in which any steam in-jected into the compartment that does not condense on the food escapes down the drain as unused steam. Cooling water is injected into the steamer


Steamers


drain line to condense the wasted steam before it is expelled to the main sewer line. This continuous flow of steam down the drain places a continuous demand on the boiler as cold water (to replenish the wasted steam) is added to the boiler.

Connectionless steamers do not need the water and drain connections typi-cally associated with steam cookers. Water is manually poured into a reser-voir at the bottom of the cooking compartment at the beginning of each day and as needed. Heating elements inside or underneath the reservoir create steam by simply boiling the water, which then fills the compartment during the cooking process. Connectionless steamers are inherently more energy efficient than boiler-based or conventional steam-generator type steamers since any steam that does not condense on the food remains in the cooking compartment. Connectionless steamers typically exhibit cooking energy effi-ciencies that exceed 50% (ASTM full-load potato test). Figure 8-8 compares the cooking-energy efficiency for several types of electric pressureless steamers. Note that steamers numbered 4 through 12 are connectionless.3-14

20

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Figure 8-8. Electric pressureless steamer cooking-energy efficiency.

Steamers


Projected energy consumption for gas and electric steamers are presented in Table 8-2 and 8-3. Based on in-kitchen monitoring at the Pacific Gas and Electric Company Production-Test Kitchen in San Ramon, California, aver-age energy consumption rates for steamers reflect a duty cycle of 15% for gas units and 20% for electric units.18-22 Daily energy consumption for steam-ers was calculated by multiplying the median rated energy input for each steamer category by the respective duty cycle and the hours of operation. Duty cycle is defined as the average rate of energy consumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy. Typical operating hours were gleaned from in-kitchen en-ergy-use monitoring experiences and observations as well as on the PREP study23 and a proprietary end-use monitoring report. Projected annual energy consumption was determined by assuming a 6-day per week, 52-week per year operation.

Table 8-2. Projected Energy Consumption for Gas Steamers.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy

Consumption (kBtu/h) (%) (kBtu/h) (h/d) a (kBtu) b

PRESSURE: Boiler-Based 6 pan 170 - 250

(Median) 210 15 c 32 14 140,000

PRESSURELESS: Boiler-Based 6 pan 170 - 250

(Median) 210 15 c 32 14 140,000 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy use rate x the typical operating hours x 6 days per week x 52 weeks per year. c The duty cycle is based on monitoring two gas convection steamers with input rates of 250 kBtu/h and 200 kBtu/h in a real-world production kitchen. An associated average energy consumption rate of 32 kBtu/h was calculated. 18,19

Steamer Energy Consumption

Steamers


Table 8-3. Projected Energy Consumption for Electric Steamers.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours



PRESSURE: Boiler-Based 6 pan 36 - 48

(Median) 42 12 d 5 14 21,800 74,500

PRESSURELESS: Boiler-Based 6 pan 18 - 36

(Median) 27 20 d 5 14 21,800 74,500

Connectionless 6 pan 12 - 24 (Median) 18 14 e 2.5 14 10,920 37,300

a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy use rate x the typical operating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1kW = 3.413 kBtu/h. d The duty cycle is based on monitoring two steamers in a real-world operation. 20,21

d The duty cycle for connectionless steamers is based on monitoring two steamers in a real-world operation.22

A more robust energy model will be incorporated into subsequent revisions of the ASTM Test Method for the Performance of Steam Cookers (F1484). In this model, cooking energy use is broken down between heavy-and light-load conditions. Annual energy use is calculated based on preheat, idle, cooking energy rate, and production rate test results from applying ASTM F1484-99.

Steamers are classified as light duty from the perspective of exhaust ventila-tion. For a sidewall-canopy hood, the design ventilation rate for steam equipment would range from 150 to 200 cfm (75 to 100 L/s) per linear foot of hood.

Pressureless steamers have a large energy performance bandwidth, due to the inherent inefficiency of traditional boiler-based models and the efficient self-contained design of the new generation of connectionless steamers (Figure



Steamers


8-7). Additionally, some of the electric connectionless steamers with high heavy-load cooking energy efficiencies demonstrate relatively high idle en-ergy rates (steamer 10 in Figure 8-4). Since most steamers spend a significant amount of their operating time in idle, or stand-by mode, reducing idle losses would be a cost-effective way to reduce daily energy consumption. The op-tion of a stand-by switch, where the temperature of the compartment “idles” below 212°F is one strategy. Increasing the level of insulation is another.

While steamers are seldom used for cook-to-order in most food service op-erations, the shorter cook times associated with boiler-based models gives them a perceived advantage over their connectionless counterparts. One strategy for reducing connectionless steamer cook times is to add a fan that circulates the steam throughout the compartment. By adding a convection component, these manufacturers hope to not only increase the production capacity of their models, but also hope to improve the cooking uniformity. However, more development is needed in this area to optimize the design and truly compete with the boiler-based models.

Manufacturers of compartment steamers have applied dramatic development efforts since the 1996 edition of this technology assessment, particularly in the area of electric counter-top models. However, there is distinct need for the development of gas-fired “connectionless” steamers that can raise the efficiency bar over conventional gas-fired boiler-based steamers.

The latest generation of countertop-pressureless (atmospheric) steamers offer a significant improvement in energy efficiency and cooking performance, resulting in a lower operating cost. Pressureless steamers are available in compartment sizes ranging from 3 to 6 pans and may be stacked.

There are currently two types of high-efficiency pressureless steamers: con-nectionless and steam-generator. With respect to the connectionless variety, the absence of water and drain connections makes installation simple and lowers maintenance costs. The compartment is simply drained at the end of the day—no periodic de-liming is required. However, some connectionless steamers exhibit somewhat longer cook times than their steam-generator counterparts.


Steamers


New steam-generator designs employ more of a closed system, which strive to provide steam to the cavity only as it is needed. One advantage of steam-generator type steamers is faster cook times and higher production rates—although steamer cook times are seldom a critical-path issue for most com-mercial kitchens. The latest generation of steam-generator type steamers uses less water and offers lower idle energy rates than their predecessors, allowing them to reasonably compete with their connectionless counterparts (Steamer number 3 in Figure 8-7).

Steamers


1. Avery, A.C., 1980. A Modern Guide to Foodservice Equipment. CBI Publishing Company, Inc. Boston.

2. American Society for Testing and Materials, 1999. Standard Test Method for the Performance of Steam Cookers. ASTM Designation F 1484–99. In annual book of ASTM Standards, West Conshohocken, PA.

3. Selden, M., 1995. Development and Validation of a Uniform Testing Procedure for Steam Cookers. Food Service Technology Center Report 1022.95.19, April.

4. Yap, D., Bell, T., Knapp, S., 1999. AccuTemp Steam ‘n’ Hold, Model 208-D8-300 Electric Steamer Performance Test: Application of ASTM Test Method F1484-99. Food Service Technology Center Report 5011.99.75, September.

5. Bell, T., Yap, D., 1999. Southbend Simple Steam, Model EZ-3 Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Technology Center Report 5011.99.83, December.

6. Bell, T., Miner, S., Nickel, J., Zabrowski, D., 2001. Stellar Steam CAPELLA Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Technology Report 5011.01.94, January.

7. Bell, T., Miner, S., 2001. Vulcan VPX3 Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Tech-nology Center Report 5011.01.01, May.

8. Bell, T., Miner, S., 2001. Vulcan VPX5 Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Tech-nology Center Report 5011.01.02, May.

9. Knapp, S., Nickel, J., 2001. AccuTemp Steam “n” Hold, Model 208-D8-300 and 400 Electric Steamers In-Kitchen Appliance Performance. Food Service Technology Center Report 5011.01.90, October.

10. Bell, T., Nickel, J., 2001. Cleveland Range Inc., Electric Steamer Per-formance Test: Application of ASTM Test Method F 1484-99. Food Ser-vice Technology Center Report 5011.00.84, November.

11. Bell, T., Miner, S., Nickel, J., Zabrowski, D., 2001. Market Forge, ET-3E Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Technology Center Report 5011.01.99, April.

12. Bell, T., Miner, S., Nickel, J., Zabrowski, D., 2001. Market Forge, ET-5E Electric Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Technology Center Report 5011.01.98, April.

References

Steamers


13. Yap, D., Ardley, S., 1998. Groen HyperSteam, Model HY-3E Electric Steamer Performance Test: Application of ASTM Standard Test Method F1484-93. Food Service Technology Center Report 5011.98.54, May.

14. Bell, T., Nickel, J., 2001. Market Forge STP-6E Electric Steamer Per-formance Test: Application of ASTM Test Method F 1484-99. Food Ser-vice Technology Center Report 5011.01.05, December.

15. Bell, T., Nickel, J., 2001. Market Forge STP-6E Electric Steamer Per-formance Test: Application of ASTM Test Method F 1484-99. Food Ser-vice Technology Center Report 5011.01.05, December.

16. Bell, T., Miner, S., Nickel, J., Zabrowski, D., 2000. Vulcan-Hart Gas Steamer Performance Test, Model VL2GSS (Pressure) and Model VS3616G (Atmospheric) Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Technology Report 5011.00.85, December.

17. Bell, T., Miner, S., Nickel, J., Zabrowski, D., 2001. Vulcan-Hart Gas Steamer Performance Test, Model VHX24G-3 Steamer Performance Test: Application of ASTM Test Method F 1484-99. Food Service Tech-nology Report 5011.01.97, January.


19. Food Service Technology Center. Cleveland Model 42-CKGM-250 Gas Pressureless Steamer: Appliance Performance in Production. Publica-tion Pending.

20. Selden, M., 1991. Production-Test Kitchen Appliance Performance Re-port: Cleveland Electric Pressureless Steamer. Pacific Gas and Electric Department of Research and Development Report 008.1-90.30, June.

21. Cesio, C., Nickel, J., Conner, M., 1997. Groen Model HY-6E Hyper-Steam Electric Pressureless Steamer In-Kitchen Appliance Performance Report. Food Service Technology Center Report 5011.95.23, August.

22. Knapp, S., Nickel, J., Bell, T., 2001. AccuTemp Steam “n” Hold, Model 208-D8-300 and 400 Electric Steamers: In-Kitchen Appliance Perform-ance Report. Food Service Technology Center Report 5011.01.90, De-cember.

23. Claar, C.N., Mazzucchi, R.P., Heidell, J.A., 1985. The Project on Res-taurant Energy Performance (PREP) –End-Use Monitoring and Analy-sis. Prepared for the Office of Building Energy Research and Development, DOE, May.


9 Steam Kettles


Steam kettles are an improved, self-contained version of the large stockpot used for range top cooking. And they are put to many of the same tasks. Steam kettles are often used to boil pasta, simmer sauces, stocks and stews. But, steam kettles offer a huge increase in productivity, convenience and en-ergy efficiency. Steam-kettle cooking can be partially automated and closely controlled, far more so than cooking on a range top.

Steam kettles are enclosed by an outer wall, or jacket, containing raw steam. This steam jacket typically extends from the bottom of the kettle to between half and two-thirds of the distance to the rim. The circulation of steam inside the jacket provides even heating to the contents of the kettle. The pressure of the steam, which may be from 1 to 50 psig (7 to 345 kPa), determines the maximum temperature of the kettle.

Steam kettles cook by conduction: heat passes directly from the wall of the kettle into the food. This is the most common mode used for tasks like boil-ing and simmering large quantities of food product. Depending on the pres-sure of the steam in the jacket, the maximum temperature of the kettle may be 212-300°F (100-150°C). Some kettles have additional connections to the jacket for cold water, which allows the kettle to first cook the food and then chill the food.

Because kettles heat evenly, they need less supervision than a pot on the stove. A variety of controls allow the cooking process to be further simplified and automated. Manufacturers offer devices to measure the amount of water flowing into the kettle, timers to start cooking unattended and signal the end of the cook time, automatic valves to control cooking and chilling, and mix-ers to eliminate the need to check or stir the food.

Operators also use steam kettles for heating food up (e.g., rethermalizing precooked food and heating prepared sauces), boiling bagels and spaghetti, and for simmering long-cooking items such as chili. Cooking events may last

Introduction

Cooking Process

Steam Kettles


from a few minutes to several hours, and take place at temperatures from 150°F to 300°F (70 to 150°C). Reliance on steam kettles in institutional op-erations such as hotels and university kitchens is diminishing as menu prepa-ration changes from batch cooking to accommodate the “fresh” concept so popular in today’s market. Many are moving towards cooking food items in other pieces of equipment such as combis and steamers, as batch cooking smaller quantities defines production. However, this trend is offset by the fact that the kettle is one of the primary appliances used within cook-chill systems for rethermalizing food received from a central commissary.

Manufacturers offer a variety of steam kettles for commercial food service: direct steam and self-contained, tilting and stationary, floor-, wall- and coun-tertop-mounted. All are available in gas and electric models. Many have a building service steam option for institutional facilities.

Capacity ranges from 1 quart to 200 gallons (1 to 760 liters). The source of steam may be a boiler built into the housing or base of a "self-contained" type kettle, or an external steam supply for "direct-steam connect" type ket-tles. Many smaller capacity (i.e. less than 60 gal (230 L)) steam kettles are mounted on pivots so that they may be tilted for pouring. Some manufactur-ers offer accessories such as timers and mixer attachments to automate steam kettle cooking. Kettles may be mounted on the wall, on a cabinet, pedestal or open-style base, or on a countertop.

Direct Steam Kettles

In all kettles, steam enters the jacket and condenses on the kettle wall, trans-ferring heat into the kettle and condensing back into water. The source of steam varies. Direct steam kettles are supplied with steam from an external boiler. While this makes the design of the kettle itself simpler, it incurs some additional maintenance. The kettle may need to be “blown down” once a day or more to eliminate condensate build-up in the steam supply line. This proc-ess is usually manual, although some kettles offer systems that take care of the condensate automatically.

Types of Kettles

Steam Kettles


Self-Contained Kettles

Self-contained kettles have a closed steam system. The jacket is filled with distilled water and steam is supplied by a gas or electric boiler contained in a housing on the kettle's stand. This complicates design and increases the price of the kettle, but makes steam kettles available to kitchens of any size and with any configuration of gas and electrical plumbing. Maintenance of the steam jacket is simple. There is generally a sight glass to inspect water level, and the jacket occasionally requires manual venting or refilling.

Tilting and Stationary Kettles

Tilting kettles simplify the task of decanting a large volume of food product. Tilting kettles range in size up to 100 gal (380 L), and are available in all configurations of steam source and mounting style. The kettle is generally tilted with a hand-operated wheel (Figure 9-1), but in some cases an electric motor is used. The kettle is counterbalanced so that it may stop and remain in any position as it tilts. Tilting kettles are also provided with a pouring lip to guide the food into steamer pans or other serving dishes. Additionally, larger units may have a tangent draw-off valve at the bottom of the kettle. This al-lows food such as spaghetti to be drained before decanting.

Stationary kettles do not tilt, but are usually equipped with a draw-off tangent valve at the bottom of the kettle. The largest steam kettles, those between 100 and 200 gal (380 and 760 L) capacity, are available only as stationary mod-els.

Mounting Style

Smaller steam kettles, generally less than 10 gal (40 L) capacity, may be available in countertop models. Countertop kettles are available in gas heated-, electric-heated and direct-steam configurations, and are generally tilting-type kettles.

Wall-mounted kettles may be stationary or mounted on trunnions for tilting. They are generally direct steam kettles, and often are installed as part of a

Figure 9-1. Floor-mounted tilting self-contained steam kettle. Photo: Southbend

Steam Kettles


battery of appliances. Kettles of one-quart to 100-gallons (1-400 L) capacity are available in wall-mounted configurations.

Floor-mounted models may be from 10-200 gal (40-800 L), direct or self contained, tilting or stationary. The kettle may be mounted on a pedestal or on an open or cabinet-style base.

Steam-kettle controls are generally simple, consisting typically of a power switch and a pressure dial. Smaller kettles may use thermostats to control cycling, while larger kettles use a pressure sensor in the jacket.

Some manufacturers offer optional lines of accessories including electronic controls that start and stop kettle cooking and/or chilling operations auto-matically. Systems are also available to automate boiler maintenance opera-tions.

Insulated Steam Kettles

One manufacturer has introduced a line of insulated steam kettles. The insu-lated jacket will reduce heat losses from the bottom and sides of the kettle, which in turn increases efficiency, lowers energy consumption and reduces heat flow into the kitchen.

Thermal Fluid Kettles

This type of kettle circulates a thermal fluid through the jacket instead of steam. This increases the temperature range of kettles significantly, with the manufacturer reporting cooking temperatures of up to 360°F (182°C) versus a more typical peak of 300°F (150°C) with high-pressure steam. This may make it possible to cook additional items such as braised meats in a steam kettle.

Controls

Advanced Steam Kettle Technologies

Steam Kettles


There is little published data for this category of appliances. An ASTM stan-dard test method for steam kettles was developed by the Food Service Tech-nology Center (F1785-97).1 The ASTM method reports several parameters of steamer performance including maximum input rate, production capacity, cooking-energy efficiency and rate of energy use while simmering.

Other factors that affect the actual performance of the steamer include ergo-nomics, ease of use and maintenance, and quality of construction.

Maximum Energy Input Rate

Maximum energy input rate is determined for kettles while the controls are set for maximum heating and the burners are on. Maximum input rate can be useful to food service operators for managing power demands and estimating a kettle's energy cost.

Production Capacity

Production capacity is determined during a heat-up test that brings water from 70°F to 160°F (20°C to 70°C). It is a close indicator of how fast the kettle can bring soups, sauces, or other liquids up to temperature. Production capacity can be used by food service operators to choose a steam kettle to match their particular food output requirements.

Heat-up Energy Efficiency

The heat-up test is used to determine both production capacity and efficiency of the steam kettle. Efficiency of the steam kettle during heat up enables the food service operator to consider energy performance when choosing a steam kettle.

Simmer Energy Rate

The simmer test determines the energy rate while simmering foods. Simmer rate is an indicator of kettle performance while cooking foods that demand long cook times, such as soups and chili. This information also allows the

Steam Kettle Performance

Steam Kettles


food service operator to consider energy performance when choosing a steam kettle. Table 9-1 presents performance characteristics for three different ket-tles based on data generated by the Food Service Technology Center from its development of the ASTM Standard Test Method for the Performance of Steam Kettles.

Table 9-1. Steam Kettle Performance Comparison Based on Preliminary Data for Three Steam Kettles.2

Elec 10 Gas 10 Gas 40

Maximum Energy Input Rate (kBtu) 35 55 203 Heatup Energy Efficiency (%) 87 39 54 Production Capacity (gal/h) 41 29 131 Simmer Energy Rate (kBtu/h) 3 7 9 Note: Electric 10 and Gas 10 are a matched pair of 10-gal (40 L) tilting, tabletop kettles. Gas 40 is a tilting 40-gal (150 L) kettle.

The heat-up energy efficiencies in Table 9-1 are derived from a period when the burners or elements of the steam kettle boiler are at full input and have been running for several minutes. At this point, the kettle walls are stabilized and most of the available energy is being transferred into the water inside the boiler. Therefore, heat-up efficiency is a close indicator of boiler efficiency. Gas 10's lower efficiency, 39% vs. 54%, is probably not due to a smaller ket-tle or more surface area to volume, but to a less efficient boiler design. Oper-ating within the manufacturer’s specifications, Gas 10's exhaust temperature was over 800°F (425°C).

Table 9-2 summarizes the range of efficiency for steam kettles. Benchmark energy efficiencies for steam kettles were based on the personal experience of the authors from work associated with test method development for steam kettles at Pacific Gas and Electric Company2 and on data conducted by the University of Minnesota.3


Steam Kettles


Table 9-2. Benchmark Steam Kettle Cooking-Energy Efficiency.

Gas Steam Kettles 40 – 60% Electric Steam Kettles 80 – 95%

Projected energy consumption for gas and electric steam kettles is presented in Table 9-3 and Table 9-4. The information is based on test method devel-opment work for steam kettles at the Food Service Technology Center, on data from the University of Minnesota Study,3 and from an unpublished pro-prietary end-use monitoring study. Daily energy consumption for kettles was calculated by multiplying the median rated energy input for each kettle type by the respective duty cycle and the hours of operation. The duty cycle for the gas kettle is based on data from proprietary end-use monitoring reports; the duty cycle for the electric kettle is based on an energy consumption ratio of 1.8 for tilting skillets and assumes that kettles and skillets have similar energy use patterns. The duty cycle is defined as the average rate of energy consumption expressed as a percentage of the rated energy input or the peak rate at which an appliance can use energy. Typical operating hours were gleaned from the PREP study.4 The projected annual energy consumption was determined by assuming a 6-day per week, 52-week per year operation.

Table 9-3. Projected Energy Consumption for Gas Steam Kettles.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy Consumption


Annual Energy


Steam Kettle

10-100 gal 50 - 125

(Median) 60 125 40c 50 4 62,400 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c The duty cycle of 40% is based on data from unpublished proprietary end-use monitoring studies An associated average energy consumption rate of 50 kBtu/h was calculated.

Steam Kettle Energy Consumption

Steam Kettles


Table 9-4. Projected Energy Consumption for Electric Steam Kettles.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption




Steam Kettle

10-100 gal 6 - 36

(Median) 60 21 40d 8 4 9,980 34,000 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h. d The duty cycle of 40% is based on an energy consumption ratio of 1.8 for tilting skillets with an assumption that energy usage is similar for the two appliance types. An associated average energy consumption rate of 8 kW was calculated.

Steam kettles are classified as light-duty equipment from the perspective of exhaust ventilation. For a wall-mounted canopy hood, the design ventilation rate for steam equipment would range from 150 to 200cfm (75 to 100 L/s) per linear foot of hood.

Consideration for R&D projects include:

• Evaluate the benefit of upgraded kettle insulation.

• Development/application of high-efficiency boilers.

• Evaluate thermal fluid kettle.

• Support benchmarking of steam kettle energy efficiency.

• Encourage the use of lids for steam kettles (60% simmer energy use reduction).




Steam Kettles


1. American Society for Testing and Materials, 1997. Standard Test Method for the Performance of Steam Kettles. ASTM Designation F1785-97. In Annual Book of ASTM standards, West Conshohocken, PA.

2. Unpublished experience of FSTC from developing and applying the standard test method to three steam kettles.

3. Snyder, O.P., and J.F. Norwig., March 1983. Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study. University of Minnesota.

4. Claar, C.N., Mazzucchi, R.P., Heidell, J.A., 1985. The Project on Res-taurant Energy Performance (PREP) –End-Use Monitoring and Analy-sis. Prepared for the Office of Building Energy Research and Development, DOE, May.

5. Reed Business Information [Oak Brook, Illinois], 2002. Foodservice Equipment and Supplies, pp 86-87, May.


References

10 Braising Pans


Braising pans, also known as tilting skillets or tilting-frying pans are among the most versatile appliances found in the commercial kitchen. They are used to braise, sauté, broil, roast, boil, fry, griddle, proof, hold, simmer, melt and steam. They can also be used as a steam table to hold warm foods.

In appearance, a braising pan resembles a flat-bottomed kettle. In practice, it combines the characteristics of a steam kettle and a griddle. The cooking sur-face is like a griddle plate, heated from beneath by atmospheric gas burners or electric elements. But this “griddle” plate has walls on all four sides so as to form a shallow rectangular pan. Energy input ranges from 6 to 18 kW for electric appliances and 6 to 120 kBtu/h for gas units. Capacities vary from 10-50 gal (38-190 L).

Braising pans are commonly freestanding, on an open stationary frame of tubular steel (Figure 10-1) or equipped with casters. They also may be on a cabinet-style base, wall-mounted on trunnions, with smaller braising pans as tabletop configurations. Since they are often used for simmering, braising pans are typically equipped with a lid, which is usually mounted on the frame and counterbalanced.

One characteristic feature of braising pans is the ability to tilt forward be-tween 10 and 110° for pouring and cleaning. A lever or hand wheel, or more rarely an electric motor, brings the pan forward and holds it in a tilted posi-tion. A safety switch cuts off power to the burner or elements when the tilt exceeds a certain angle. Some cooking is done at a slight incline: grease from bacon and ground beef can be drained forward as it forms.

The front rim of the pan has a lip or spout to guide food into serving pans when the skillet is tilted for pouring, and a common feature of many tilting skillets is a rack positioned to hold steam table trays just below this spout for filling as seen in Figure 10-2. Some braising pans are also equipped with a draw-off valve, so that food can be decanted from the bottom of the pan while it is horizontal.

Introduction

Figure 10-1. 40-gallon braising pan. Photo: Groen Inc.

Braising Pans


The braising pan can save time, money and line space in a commercial kitchen by performing the jobs of several different appliances. Throughout the day, the braising pan may provide extra griddle space for breakfast or lunch; be used as a kettle to prepare rice or pasta; be rolled to the serving line and used as a holding cabinet; be fitted with steamer baskets to prepare vege-tables or rethermalizing frozen food, with a rack to wet-roast meat, or with fry baskets to prepare French fried potatoes and other foods typically pre-pared in a deep fat fryer.

This appliance is particularly well suited to moving from one mode of cook-ing to another. The procedure for making stew provides a distinctive exam-ple. A cook can braise the meat in the hot pan, allowing the juices to remain in the bottom. When the meat is cooked, he adds water, vegetables and spices into the pan. With the lid down, the stew is left to simmer for several hours. When it is done, the cook tilts the skillet to fill pans for the serving line and keeps the rest warm through mealtime.

One manufacturer is about to launch its steam skillet. The 40-gallan capacity Accu-Steam Skillet™ uses AccuTemp griddle technology to steam heat the pan bottom, providing uniform heating and gentle no-scorch “kettle” cooking and near instant recovery for high volume braising of meats and griddle cooking applications.

The Food Service Technology Center (FSTC) developed an ASTM standard test method1 for braising pans. Performance parameters include maximum input rate, production capacity, cooking-energy efficiency and rate of energy use while simmering. The test method allows manufacturers and users to ob-jectively evaluate energy performance and production capacity from different labs.

A skillet that is the right size for the kitchen will be used more often. A study by Pacific Gas and Electric Company at their production test kitchen1 showed that the foodservice staff began to use the braising pan regularly only after a 32-gallon braising pan was replaced with a smaller 18-gallon braising pan.

Figure 10-2. Braising pan with food receiving pan support mounts under pouring lip. Photo: Vulcan-Hart

Braising Pan Performance

Braising Pans


An ASTM standard test method for braising pans was developed by the Food Service Technology Center (F1786-97).1 The ASTM method reports several parameters of steamer performance including maximum input rate, produc-tion capacity, cooking-energy efficiency and rate of energy use while sim-mering. Based on the Food Service Technology Center’s work associated with developing the standard test method and on data from the University of Minnesota,3 a range of energy efficiencies for both gas and electric skillets are presented in Table 10-1.

Table 10-1. Energy Efficiency for Braising Pans.

Gas Braising Pans 30 – 50% Electric Braising Pans 80 – 95%

The Minnesota study compared two 18-gal (68 L) braising pans, one electric and one gas. They found a cooking efficiency of 52% for the gas-powered braising pan and 79% for the electric. The gas unit heated water much faster than the electric unit, but consumed 1.8 times more energy.

The gap between gas and electric performance should narrow as better tech-nology is applied to gas braising pans. Most skillets in use are older models that don’t take advantage of standard efficiency measures such as insulation or advanced burner/heat exchanger design.

Projected energy consumption for gas and electric braising pans are pre-sented in Table 10-2 and Table 10-3. Daily energy consumption for braising pans was calculated by multiplying the median rated energy input for each skillet by its duty cycle and the hours of operation. The duty cycles are based on monitoring two gas and two electric tilting skillets in Pacific Gas and Electric Company’s Production Test Kitchen.1 The duty cycle of an appli-ance is defined as the average rate of energy consumption expressed as a per-centage of the rated energy input or the peak rate at which an appliance can use energy. Typical operating hours were gleaned from in-kitchen observa-


Braising Pan Energy Consumption

Braising Pans


tions along with data from an unpublished proprietary end-use monitoring study. Projected annual energy consumption was determined by assuming a 6-day per week, 52-week per year operation.

Table 10-2. Projected Energy Consumption for Gas Braising Pans.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours

Annual Energy


Braising Pan

10-50 gal 60 - 120

(Median) 30 90 45c 40 4 49,900 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c The duty cycle is based on monitoring two gas braising pans with input rates of 85 kBtu/h and 62 kBtu/h in a real-world production kitchen (FSTC unpublished data). An associated average energy consumption rate of 40 kBtu/h was calculated.

Table 10-3. Projected Energy Consumption for Electric Braising Pans.

Nominal

Size

Rated Energy Input

Duty Cycle

Avg. Energy

Consumption

Typical Operating

Hours.



Braising Pan

10-50 gal 6 - 18

(Median) 30 12 60d 7 4 8,730 29,800 a Operating hours or appliance "on time" is the total period of time that an appliance is operated from the time it is turned "on" to the time it is turned "off". b The annual energy consumption calculation is based on the average energy consumption rate x the typical operating hours x 6 days per week x 52 weeks per year. c Conversion Factor: 1 kW = 3.413 kBtu/h. d The duty cycle is based on monitoring two electric tilting skillets with input rates of 9 kW and 11 kW in a real-world production kitchen.1 An associated average energy consumption rate of 7 kW was calculated.

Braising Pans


Braising pans are classified as light-duty equipment from the perspective of exhaust ventilation. For a wall-mounted canopy hood, the design ventilation rate for this equipment would range from 150 to 200 cfm (75 to 100 L/s) per linear foot of hood.

Atmospheric Burners

All braising pans now on the market use atmospheric burners. These are the simplest and least expensive type of burner, and using them helps keep the initial cost of the appliance low. Design of the burners and the heat transfer system can have a significant impact on appliance efficiency. In studies of deep-fat fryers, well-designed atmospheric burners demonstrated cooking energy efficiencies that approached those of infrared-burner fryers. However, the same studies show that fryers with poorly designed atmospheric burners have the lowest cooking efficiencies tested.

One manufacturer of braising pans, Groen, uses a heat transfer system that incorporates heat exchanger fins on the bottom of the pan and an insulated combustion chamber. All of these are simple, reliable and inexpensive to im-plement with a relatively good increase in cooking efficiency.

Infrared Burners

Braising pans with high efficiency infrared burners are not yet on the market, but they have been associated with high overall efficiency in appliances such as fryers and griddles. Griddles using infrared burners show higher cooking efficiencies than griddles using atmospheric combustion burners. However, the new Accu-Steam Skillet™ , shown in Figure 10-3, will incorporate the same IR burner design as the AccuTemp griddle. A braising pan heated with infrared burners should enjoy a similar increase in efficiency.

Thermal Fluid

Lang, Inc. developed a prototype thermal fluid griddle in conjunction with GTI, using gas burners to heat oil that is circulated through pipes to heat the griddle plate. It may prove more efficient to transfer heat into a thermal fluid



Figure 10-3. Accu-Steam braising pan. Photo: AccuTemp

Braising Pans


than to use burners under the griddle plate. This system also promises better temperature uniformity on the bottom of the pan, which would be an advan-tage for those operators who use the braising pan as a backup griddle. Essen-tially, the new Accu-steam Skillet operates with the simplest working fluid – water and steam.

Insulation

Appliances like braising pans spend much of their duty cycle holding food at temperature, as in proofing and simmering. If the lid is open and the food is losing moisture freely, as much as half the energy into the appliance is work-ing to evaporate water. Closing the lid can reduce energy use by 40% to 60%. With the lid down, the major energy loss from the appliance is radiant heat lost to the room. Insulation could further reduce this loss, but insulation is rarely used in braising pans.

Currently, only Legion Industries, Inc. makes a braising pan with insulated sides and under body. The outside of the pan is only warm to the touch when it is filled with 320°F (160°C) oil, demonstrating reduced radiant heat losses due to insulation. The manufacturer also offers a model with a tall, capsule lid that is fully insulated (the Skittle™, Figure 10-4).

This manufacturer contends their Skittle works well as a steamer, utilizing gentle closed-cycle steaming and is just as fast as conventional steamers, but with the added plus that there is no boiler. As a griddle surface, it is as hot at the very edges as it is in the center. It also can be used as a deep fat fryer; and when not it use, the capsule lid can be lowered and the insulation will mini-mize heat gain to the kitchen.4

• Support benchmarking of braising pan energy efficiency. Apply the ASTM Standard Test Method to the Accu-Steam Skillet™.

• Support development of advanced burner options for gas braising pans.

• Encourage insulating pan body and lid.

Figure 10-4. Skittle® cooker. Photo: Legion Ind.


Braising Pans



2. American Society for Testing and Materials, 1997. Standard Test Method for the Performance of Braising Pans. ASTM Designation F1786-97. In Annual Book of ASTM Standards, West Conshohocken, PA.

3. Snyder, O.P., and Norwig, J.F., March 1983. Comparative Gas/Electric Food Service Equipment Energy Consumption Ratio Study. University of Minnesota.

4. Legion Industries, Inc., Pennsylvania. “The Legion Line”, Newsletter, Special Edition, Vol. 1 No. 5.


References

A Glossary

5011.02.26 A-1 Food Service Technology Center

Cooking Energy (kWh or kBtu) The total energy consumed by an appliance as it is used to cook a specified food product. Cooking Energy Consumption Rate (kW or kBtu/h) The average rate of energy consumption dur-ing the cooking period. Cooking Energy Efficiency (%) The quantity of energy input to the food prod-ucts; expressed as a percentage of the quantity of energy input to the appliance during the heavy-, medium-, and light-load tests. Duty Cycle (%) Load Factor The average energy consumption rate (based on a specified operating period for the appli-ance) expressed as a percentage of the measured energy input rate.

Duty Cycle = RateInput Energy Measured

Rate nConsumptioEnergy Average x 100

Energy Input Rate (kW or kBtu/h) Energy Consumption Rate Energy Rate The peak rate at which an appliance will con-sume energy, typically reflected during preheat. Heating Value (Btu/ft3) Heating Content The quantity of heat (energy) generated by the combustion of fuel. For natural gas, this quantity varies depending on the constituents of the gas.

Idle Energy Rate (kW or Btu/h) Idle Energy Input Rate Idle Rate The rate of appliance energy consumption while it is holding or maintaining a stabilized operating condition or temperature. Idle Temperature (°F, Setting) The temperature of the cooking cavity/surface (selected by the appliance operator or speci-fied for a controlled test) that is maintained by the appliance under an idle condition. Idle Duty Cycle (%) Idle Energy Factor The idle energy consumption rate expressed as a percentage of the measured energy input rate.

Idle Duty Cycle = RateInput Energy MeasuredRate nConsumptioEnergy Idle x 100

Measured Input Rate (kW or Btu/h) Measured Energy Input Rate Measured Peak Energy Input Rate The maximum or peak rate at which an appli-ance consumes energy, typically reflected during appliance preheat (i.e., the period of operation when all burners or elements are “on”). Pilot Energy Rate (kBtu/h) Pilot Energy Consumption Rate The rate of energy consumption by the stand-ing or constant pilot while the appliance is not being operated (i.e., when the thermostats or control knobs have been turned off by the food service operator).

Glossary

5011.02.26 A-2 Food Service Technology Center

Preheat Energy (kWh or Btu) Preheat Energy Consumption The total amount of energy consumed by an appliance during the preheat period. Preheat Rate (°F/min) The rate at which the cook zone heats during a preheat. Preheat Time (minute) Preheat Period The time required for an appliance to “pre-heat” from the ambient room temperature (75 ± 5°F) to a specified (and calibrated) operating temperature or thermostat set point. Production Capacity (lb/h) The maximum production rate of an appliance while cooking a specified food product in accordance with the heavy-load cooking test. Production Rate (lb/h) Productivity The average rate at which an appliance brings a specified food product to a specified “cooked” condition.

Rated Energy Input Rate (kW, W or Btu/h, Btu/h) Input Rating (ANSI definition) Nameplate Energy Input Rate Rated Input The maximum or peak rate at which an appli-ance consumes energy as rated by the manufacturer and specified on the nameplate. Recovery Time (minute, second) The average time from the removal of the cooked food product until the appliance has returned to a specified ready-to-cook condition. Test Method A definitive procedure for the identification, measurement, and evaluation of one or more qualities, characteristics, or properties of a material, product, system, or service that pro-duces a test result. Typical Day A sampled day of average appliance usage based on observations and/or operator inter-views, used to develop an energy cost model for the appliance.

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