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Combined Cooling, Heating, Power, and Ventilation(CCHP/V) Systems Integration

Fred BetzPhD. Dissertation

Center for Building Performance and DiagnosticsSchool of ArchitectureCollege of Fine Arts

Carnegie Mellon UniversityPittsburgh, Pennsylvania

May 11, 2009

Copyright Frederik Betz, 2009. All rights reserved.


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Copyright Declaration

I hereby declare that I am the sole author of this thesis.

I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to lend this thesis to

other institutions or individuals for the purpose of scholarly research.

I authorize Carnegie Mellon University, Pittsburgh, Pennsylvania to reproduce this thesisby photocopying or by other means, in total or in part, at the request of other institutionsor individuals for the purpose of scholarly research.

Copyright Frederik Betz, 2009. All rights reserved.


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Acknowledgements

I would like to thank Dr. Volker Hartkopf for chairing my thesis committee and for

bringing me to the Center for Building Performance and Diagnostics four years ago. He

helped me gain a new perspective and appreciation for the built environment. His never

ending supply of energy and optimism is truly inspiring.

Dr. David Archer has guided my day to day tasks since my arrival in the Intelligent

Workplace four years ago. Through his tireless efforts he inspired me to persevere

through my entire project from preliminary design ideas all the way through construction

and evaluation of a complex system.

Prof. John Wiss provided me with invaluable insight into engine technology and always

helped me stay grounded with his years of practical experience. I would especially like to

thank Sharilynn and Jim Jarrett who provide support services in the Intelligent Workplace,

which allowed all of the faculty and staff to function as a team.

Flore Marion generously spent months of her time assisting me with her fantastic

TRNSYS programming skills without which an entire chapter of my thesis would never

have existed. I am truly thankful to have had her assistance on this thesis.

I would like to thank all of the students working in the IW for their support and

encouragement over the years. In particular I would like to thank Philip Kwok, Bing


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Dong, Joonho Choi, and Viraj Srivastava. Their advice and attitude made working long

hours enjoyable.

I would like to thank my parents Karin and Al Betz for helping me develop and maintain

a work ethic that has made all of my success to date possible. Finally, I would like to

thank my brother Ingo, whose sense of humor helped me keep a smile on my face for the

last four years in the face of some tough challenges.


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Dedication

I would like to dedicate this dissertation to my wife Victoria. Without her love and

support everyday for the last four years this dissertation would not have been possible.


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Abstract

Combined heat and power (CHP) systems are frequently used to reduce energy

consumption in a facility due to the increased energy efficiency. System efficiencies

range between 65% and 85%, whereas the average utility efficiency for electric power

supply is 31% and for heating from a natural gas supply is around 80%, which yields a

combined efficiency of approximately 50% for all energy supplied in the United States of

America. Buildings use 70% of all electricity generated in the U.S., 40% of all U.S.

primary energy to heat, light, ventilate and cool facilities. Therefore, it makes sense to

site power plants near both the electrical and thermal loads to make use of the nearly 70%

of energy that is annually wasted by large central power plants.

CHP systems are frequently reserved for larger facilities due to high first costs and

complex operations, however 75% of all buildings in the U.S. have an area of less than

10,000 ft2 (929 m2). There have been several attempts made by various corporations to

break into the micro CHP market with limited success. Studies commissioned by the

Department of Energy show that two of the key barriers to the adoption of CHP systems

in smaller facilities is the high first cost and the lack of packaged plug-and-play systems.

To address this challenge, the Center for Building Performance and Diagnostics (CBPD)

has designed, installed, operated and evaluated a 25 kWe biodiesel fueled CHP system

that is integrated with an absorption chiller system and an enthalpy recovery ventilation

system with solid desiccant dehumidification in a single system that provides all of the

electric, cooling, heating, and ventilation needs of the Intelligent Workplace, IW. The


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chiller and ventilation systems are well understood with three published dissertations in

the last four years.

This dissertation integrates elements of each subsystem through the use of calibrated

simulations to determine the effectiveness of operating such a system in a commercial

office building as well as potentially in a data center.

Key contributions of this work include:

A complete accounting of how the CHP system is setup and how it operates with

both Diesel and biodiesel fuel.

A generic preliminary design procedure for the CHP system of a building as well

as the specific design procedures for the biodiesel fueled CHP system.

A simplified TRNSYS CHP system performance model that can be easily

adjusted to be used for different buildings and/or for different prime movers.

A conceptual systems integration model, which identifies how components and

sub-systems may fit together.

Key results in this dissertation include:

The results show that for efficient and effective performance of a CHP system in a

high performance building it is essential to have electrical and thermal grids

available to export and/or import CHP energy. The grids allow the CHP system to

operate continuously at the design load. The grids also provide back up in case of

system outage.


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The results of operating the biodiesel fueled CHP system in the IW yields an

average annual efficiency of about 66% and a peak of 78%.

A scaled up system for the Building As Power Plant (BAPP) will achieve similar

efficiencies unless a larger load for the coolant energy can be found.

Data centers offer an ideal location for CHP systems as they do not have such

highly variable loads such as office buildings. Furthermore, data centers do not

have latent cooling or heating loads, which simplifies systems integration, as the

only components required for the system are an engine or turbine, heat recovery

equipment, and absorption chillers. A CHP system with absorption chillers has

been calculated in this dissertation to achieve an average efficiency of 78% in

data centers.

There are many possible next steps; however the three most important steps in the

development of the CCHP/V technology are to complete the automation and integration

of the CHP system with the rest of the IW.

Second, to refine the BAPP data for the TRNSYS simulation and to create a modular

CHP system in TRNSYS so the development of BAPP mechanical system can proceed

and provide a future testing ground for packaged CCHP/V systems.

Third, to conceive and develop the means for reducing equipment and installation costs

by a factor of 10 to 20 must be developed.


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Table of Contents

Copyright Declaration......................................................................................................... 2Acknowledgements............................................................................................................. 3Dedication...........................................................................................................................5Abstract............................................................................................................................... 6Table of Contents................................................................................................................9List of Figures................................................................................................................... 12List of Tables....................................................................................................................14Nomenclature.................................................................................................................... 151.0 Introduction.................................................................................................................16

1.1 Rationale.................................................................................................................161.2 Market Size............................................................................................................. 181.3 Why not CHP?........................................................................................................18

2.0 Background................................................................................................................. 202.1 DG & CHP Principles............................................................................................. 202.2 Fuels........................................................................................................................ 222.3 Energy Grids...........................................................................................................252.4 Prime Movers.......................................................................................................... 26

2.4.1 Central Power Plants........................................................................................ 262.4.2 Boilers and Steam Turbines............................................................................. 272.4.3 Gas Turbine...................................................................................................... 272.4.4 Internal Combustion Engines........................................................................... 282.4.5 Fuel Cells.........................................................................................................282.4.6 Prime Mover Summary.................................................................................... 28

2.5 Heat Loads..............................................................................................................29

2.5.1 Space Heating..................................................................................................302.5.2 Absorption Cooling.......................................................................................... 302.5.3 Desiccant Regeneration...................................................................................312.5.4 Other Heat Loads............................................................................................. 312.5.5 Storage............................................................................................................. 322.5.6 Heat Loads Summary....................................................................................... 32

2.6 Existing Packaged Systems.................................................................................... 332.7 Case Studies............................................................................................................34

3.0 IWESS Components and Subsystems......................................................................... 373.1 Biodiesel Fueled Engine Generator with Heat Recovery....................................... 37

3.1.1 System Components......................................................................................... 37

3.1.2 Input / Output................................................................................................... 473.1.3 Operating Description and Results.................................................................. 48

3.1.3.1 Engine: Measured Data versus Manufacturers Specifications................ 513.1.3.1 Pressure Time Crank Angle Measurements........................................533.1.3.2 Turbocharger Analysis.............................................................................. 553.1.3.3 Combustion Gas and Emissions Analysis.................................................563.1.3.4 Heat Recovery Analysis............................................................................ 60

3.1.4 Systems Integration Potential ..........................................................................63


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3.2 Steam Driven Double Effect Absorption Chiller.................................................... 653.2.1 System Components......................................................................................... 653.2.2 Input / Output................................................................................................... 663.2.3 Operating Description and Results.................................................................. 683.2.4 Systems Integration Potential ..........................................................................70

3.3 Ventilation System with Enthalpy Recovery and Solid Desiccant Dehumidification....................................................................................................................................... 713.3.1 System Components......................................................................................... 713.3.2 Input / Output................................................................................................... 723.3.3 Operating Description and Results.................................................................. 733.3.4 Systems Integration Potential ..........................................................................77

4.0 Preliminary Design Guide........................................................................................... 794.1 Generic Design Steps.............................................................................................. 79

4.1.1 Loads................................................................................................................ 804.1.2 Fuel Selection................................................................................................... 814.1.3 Energy Grids.................................................................................................... 82

4.1.4 Prime Movers................................................................................................... 834.1.5 Auxiliary and Heat Recovery Equipment........................................................844.1.6 Operating Strategy........................................................................................... 854.1.7 CHP System Evaluation................................................................................... 86

4.2 Design of Biodiesel Fueled CHP System...............................................................874.2.1 Load Profiles.................................................................................................... 874.2.2 Fuel Selection................................................................................................... 884.2.3 Energy Grids.................................................................................................... 894.2.4 Prime Movers................................................................................................... 904.2.5 Auxiliary and Heat Recovery Equipment........................................................914.2.6 Operations........................................................................................................ 94

4.2.7 Evaluation........................................................................................................ 944.2.8 Submittals........................................................................................................955.0 TRNSYS Modeling.....................................................................................................96

5.1 IWESS Model .........................................................................................................965.1.1 Biodiesel Fueled Engine Generator with Heat Recovery Modeling................965.1.2 Double Effect Steam Driven Absorption Chiller............................................. 975.1.3 Ventilation Unit with enthalpy recovery and solid desiccant wheel................ 985.1.4 Computational Model Issues............................................................................ 985.1.5 Combined IWESS Model .............................................................................. 1005.1.6 IWESS Simulations....................................................................................... 103

5.1.6.1 Mode Zero: Design Operation................................................................ 1045.1.6.2 Mode One: Thermal Load Follow..........................................................1045.1.6.3 Mode Two: Regeneration Load Follow.................................................. 1065.1.6.4 IWESS Simulation Discussion............................................................... 108

5.2 BAPP Model ......................................................................................................... 1085.2.1 Engine Modification...................................................................................... 1085.2.2 BAPP Simulations......................................................................................... 112

5.2.2.1 Mode Zero: Design Operation................................................................ 1125.2.2.2 Mode One: Thermal Load Follow.......................................................... 113


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5.2.2.3 Mode Two: Regeneration Load Follow.................................................. 1135.2.2.4 BAPP Simulation Discussion.................................................................114

5.3 Data Center CHP Operation.................................................................................. 1166.0 Systems Integration................................................................................................... 119

6.1 Individual Systems Integration............................................................................. 120

6.2 Packaged Systems Integration.............................................................................. 1267.0 Contributions, Conclusions, and Future Work......................................................... 1307.1 Contributions......................................................................................................... 1307.2 Conclusions........................................................................................................... 1327.3 Future Work.......................................................................................................... 134

References.......................................................................................................................140Appendix ..143


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List of Figures

Figure 1: U.S. Electrical Energy Flow for Large Central Plants (Quadrillion BTUs) [2] 21Figure 2: Energy Flow for Distributed Generation with Heat Recovery (QuadrillionBTUs) (Adapted from Reference 2) ................................................................................. 22Figure 3: Basic CHP Flow Diagram................................................................................. 38Figure 4: CHP System Components................................................................................. 39Figure 5: Baldor Engine Generator................................................................................... 39Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe.........40Figure 7: Assembled Components: Engine Generator (Left), Steam Generator (Right).. 41Figure 8: Steam - Hot Water Converter............................................................................42Figure 9: Coolant Heat Exchanger with Piping before Insulation.................................... 43Figure 10: Remote Mounted Radiator.............................................................................. 44

Figure 11: Engine Generator Onboard Interface.............................................................. 44Figure 12: Engine Generator Onboard Interface.............................................................. 45Figure 13: Automated Logic CHP User Interface for the Heat Recovery/Rejection System........................................................................................................................................... 48Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel........................................................................................................................................... 53Figure 15: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel........................................................................................................................................... 54Figure 16: Turbocharger Compressor Map []...................................................................55Figure 17: Summer Operation of the Steam Generator T-Q Diagram.............................. 61Figure 18: T-Q Diagram for Coolant Heat Exchanger at 25 kWe.................................... 63

Figure 19: Steam Driven Absorption Chiller Flow Diagram []........................................ 66Figure 20: Absorption Chiller Process and Instrumentation Diagram [31]......................67Figure 21: Automated Logic Absorption Chiller User Interface...................................... 68Figure 22: Absorption Chiller Component Heat Transfers vs. Cooling Load [31]..........69Figure 23: Plan View of Ventilation Unit [] ..................................................................... 71Figure 24: Interior View of the Ventilation Unit [33] ...................................................... 73Figure 25: Ventilation Unit Flow Diagram [33]...............................................................74Figure 26: Psychrometric Chart for Ventilation System Operation [33].......................... 74Figure 27: Enthalpy Removal Breakdown by Component [33] ....................................... 75Figure 28: Moisture Removal Breakdown by Component [33] ....................................... 75Figure 29: Operating Cost Breakdown by Component [33]............................................. 76

Figure 30: IW Heating and Cooling System Flow Diagram\ ........................................... 92Figure 31: CHP system input / output module.................................................................. 97Figure 32: Double effect absorption chiller input / output module..................................98Figure 33: Ventilation system input / output module....................................................... 98Figure 34: Combined TRNSYS Model........................................................................... 100Figure 35: Combined/Simplified IWESS TRNSYS Model............................................ 101Figure 36: BAPP TRNSYS Simulation.......................................................................... 111Figure 37: CHP Major Component Diagram.................................................................. 121


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Figure 38: Absorption Chiller Major Component Diagram........................................... 121Figure 39: Ventilation System Major Component Diagram...........................................122Figure 40: CCHP/V Energy Cascade..............................................................................123Figure 41: Major Component Piece-wise Systems Integration...................................... 125Figure 42: Packaged CCHP/V System........................................................................... 126

Figure 43: CCHP/V Summer Operation Flow Diagram................................................. 128Figure 44: CCHP/V Winter Operation Flow Diagram...................................................129Figure 45: Cost Breakdown of CHP System.................................................................. 138


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List of Tables

Table 1: Prime Mover Performance Summary.................................................................29Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results......49Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results........49Table 4: Averaged Winter Biodiesel Experimental Results.............................................50Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications.......51Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications...................52Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel .................56Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel ........................56Table 9: Absorption Chiller Test Program and Results [31] ............................................69Table 10: Typical U.S. Commercial Building Loads.......................................................80Table 11: Prime Mover Performance Summary...............................................................83Table 12: IWESS Design Operation Simulation Results................................................104Table 13: IWESS Thermal Load Follow Simulation Results.........................................105Table 14: IWESS Regeneration Load Follow Simulation Results.................................107Table 15: IWESS 25 kWe CHP Coolant Heat Exchanger Results vs. Power Level ......110Table 16: Estimated BAPP 200 kWe CHP Coolant Heat Exchanger Results vs. PowerLevel ............................................................................................................................... 110Table 17: IWESS 25kWe CHP Air Flow Rate vs. Power Level ....................................111Table 18: Estimated BAPP 200 kWe CHP Air Flow Rate vs. Power Level ..................111Table 19: BAPP Design Operation Simulation Results..................................................112Table 20: BAPP Thermal Load Follow Simulation Results...........................................113Table 21: BAPP Regeneration Load Follow Simulation Results...................................114Table 22: IWESS Input / Output Table...........................................................................124Table 23: IWESS Component List .................................................................................125

Table 24: Packaged System Component List.................................................................127


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NomenclatureBAPP: Building As Power Plant

CHP: Combined Heat and Power, also known as cogeneration

CCHP: Combined Cooling Heat and Power, also known as trigeneration

CMU: Carnegie Mellon University

CBPD: Center for Building Performance and Diagnostics

DG: Distributed Generation

IC: Internal Combustion

IW: Intelligent Workplace

IWESS: Intelligent Workplace Energy Supply System

kW: kilowatt

kWc: kilowatt chemical (fuel energy)

kWe: kilowatt electric

kWt: kilowatt thermal


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1.0 Introduction

The work described in this dissertation covers the preliminary design, procurement,

detailed design, installation, operation, and evaluation of a 25 kWe combined heat and

power subsystem as well as the future integration with installed absorption chillers and an

enthalpy recovery ventilation system with solid desiccant dehumidification as a combined

energy supply system.

The goals of the integration is to show how the three subsystems operate together as a

system by combining three validated simulation models and to show how the first and

operating costs can be reduced through systems integration.

1.1 Rationale

While the cost of energy has dropped substantially in the last year, experts agree that the

price will rebound to historic highs as the world economy recovers [1]. Due to the double

threat of high energy cost and global climate change there is increased interest in the use

of combined heat and power systems, which can reduce the primary energy consumption

of power and heat by up to 50% for building and plant operations.

Currently the U.S. average efficiency for producing electricity is 32% including

transmission and distribution losses [2]. If heating efficiencies are considered, then

standard practice efficiency is around 50% for heating and electricity. Typical CHP

system efficiencies range from 65% to 90% efficiency, including the Intelligent


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Workplace Energy Supply System (IWESS) CHP system which has achieved 76%

efficiency.

Studies commissioned by the Department of Energy [3, 4, 5] show that one of the key

barriers to the use of CHP systems is the high first cost and the availability of packaged

systems. This PhD. dissertation attempts to address these two issues by providing a first

step in the creation of a packaged plug-and-play system that can be delivered to a facility

and be connected rapidly. Furthermore, the packaged system will have reduced overall

costs of design, engineering, and field assembly as compared to a system purchased

piecewise.

One of the key problems when using a CHP system is to find a sufficient heat load that

matches the heat output of the CHP system. CMUs Intelligent Workplace (IW) offers

two thermal loads during the summer; the regeneration of a desiccant wheel in the

ventilation system and the operation of absorption chillers. During the winter, the IW has

a space heating load. These loads allows the CHP system to operate year round, with the

possible exception of the intermediate seasons, spring and fall, where a properly designed

building should have little need for air conditioning (heating, cooling, or

dehumidification). However, because there are Carnegie Mellon campus electrical, steam,

and chilled water grids, year round export of energy is possible from the IWs CHP

system.


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1.2 Market Size

Several studies commissioned by the Department of Energy in 2002 have looked into the

market size of CHP systems using current technology [3, 4, 5]. Between 2003 and 2017:

7% of hospitals plan to install CHP systems within 2 years, starting in 2003,

3% of supermarkets plan to install CHP systems within 2 years, starting in 2003,

4% of hotels plan to install CHP systems within 2 years, starting in 2003,

2% of big-box retailers plan to install CHP systems within 2 years, starting in

2003 [4].

Institutions construct new buildings every year, which require power for lighting

and ventilation as well as thermal energy for heating and cooling.

Approximately 42,000 new commercial buildings are built every year; 75% of the

buildings have peak loads below 200 kWe [6].

Several markets would be impacted by improvements in CHP systems most notably

hospitals, supermarkets, and hotels [5]. A total of 3,075 sites were identified for 300-600

kWe CCHP retrofits. For new construction through 2020, 2,464 CHP sites were

identified [5]. It should be noted that this study was conducted in 2002 and 2003, and the

market will have shifted somewhat as fuel and electricity prices have increased several

fold since the publication of this report. Also, the study did not include large institutional

complexes such as universities, in the market sizing.

1.3 Why not CHP?

The advantage of standard electrical and natural gas utilities, boilers and chillers that

provide energy to buildings inefficiently over CHP systems is that it is simple for the


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building owner and/or occupant. The job of keeping the power on falls to the utility

company and chillers and boilers may include warranties and service contracts in addition

to being mature technologies. Furthermore, the first cost is low for the builder. In essence,

the risk for the consumer is low, while the energy and associated environmental and

economic impacts are large even though CHP systems have existed as long as utilities

have existed.

Currently, CCHP/V systems have a greater perceived risk to the owner or occupant

versus a conventional energy supply system. A buyer would choose a CCHP technology

based on first cost, operating cost, and maintenance cost and reliability.

A major objective of this project is to reduce the first cost by working on systems

integration strategies that reduce the number and complexity of components in the CCHP

system. Reduced first cost would make an owner/occupant more likely to purchase a

CCHP system, which would help refine the technology to the level of relatively simple

boilers and chillers and make it more robust.

An additional objective is the reduction of operating costs by making maximum use of

the fuel energy going into the prime mover (engine, microturbine, etc.). This would

include the electrical energy for office equipment and lighting, high temperature heat for

absorption chillers to make cooling, and low temperature heat for space heating,

dehumidification, and domestic hot water.


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2.0 Background

Buildings account for approximately 40% of all primary energy consumption in the

United States, and consume about 70% of the electricity [6]. Furthermore, approximately

57% of that electricity is generated using coal [7]. These coal power plants use what is

called a Rankine cycle process which entails burning coal in a boiler, to generate steam.

That steam passes through a turbine, which turns a generator. The first steam power

plants in the 1880s had an efficiency of approximately 8%, or in other words 8% of the

heat of combustion of the coal was converted to electrical energy, the rest was rejected as

heat to the surroundings [7]. Steady increases in conversion efficiency occured through

the 1960s, but have peaked at about 35%; the other 65% of the energy is still lost as heat

[8].

In the early 1880s, Thomas Edison realized this large inefficiency and sold the heat to

neighboring buildings in a successful effort to increase his bottom line [8]. In a sense, the

first Edison steam plants were combined heat and power (CHP) plants. The same is true

today of CHP plants. Heat that is normally rejected can be recovered from exhaust gases

and coolant and applied in a useful way. This can improve the efficiency of power

generation facilities from 35% to over 80% [9,10,11,12,13]. This improvement in

efficiency reduces the overall demand for fuel and green house gas emissions.

2.1 DG & CHP Principles

Distributed generation (DG) is simply defined as any electrical generating source with a

capacity of less than five megawatts. Combined heat and power (CHP) is defined as the


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simultaneous production and use of electricity and heat from a single fuel source. This

concept can be applied to large and small generating facilities. Another term used for

CHP is cogeneration. Also, sometimes cooling is added to the acronym resulting in

combined cooling heating and power (CCHP), or trigeneration.

Figures 1 and 2 show how electrical power is typically generated in the U.S. As shown in

Figure 1, the largest energy flow is the conversion losses seen at the top.

Figure 1: U.S. Electrical Energy Flow for L arge Central Plants (Quadrillion BTUs) [2]

In Figure 2, the recoverable conversion losses are highlighted along with the transmission

and distribution losses which are avoided by producing electricity locally.


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Figure 2: Energy Flow for Distributed Generation with Heat Recovery (Quadrillion BTUs) (Adapted

from Reference 2)

The amount of heat recoverable heat varies depending on the building loads; however the

goal of CHP systems is well described.

2.2 Fuels

There are many fuels available for the operation of CHP systems including: natural gas,

petroleum products (gasoline, Diesel, etc.), biomass (biogas, biodiesel, ethanol, solids),

coal, and waste fuels (waste coal, garbage, etc.). Many of these fuels are associated with a

particular type of prime mover and vary in energy content, cost, availability, and

emissions.

Natural gas is by far the most common fuel type accounting for about 75% of all CHP

systems in operation in the U.S. [14]. The reason for this is that the fuel is readily

available with a nationwide distribution network, the cost per unit of energy is relatively


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low, and the emissions are relatively clean. However, it should be noted that while the

cost of natural gas is relatively low as compared to many other common fuels, the price is

very volatile making operating costs projections problematic.

Diesel fuel is the most common petroleum product used for CHP systems as Diesel

engines provide a high electrical efficiency. Furthermore, Diesel fuels can be stored

relatively easily adding a margin of security in case of a power outage, which may also

affect the flow of natural gas. The cost is relatively high as Diesel fuel for CHP

applications must still compete with Diesel fuel used for transportation, which is on

average three times as expensive as natural gas per unit energy.

Renewable fuels such as biomass are gaining market share due to their emissions

characteristics and public appeal. Biomass can come in a gaseous, liquid or solid form.

Biogas often comes from landfills and waste water treatment facilities. The first cost of

treatment systems for the fuel is high; however operational costs are very low. Biogas is

typically difficult to distribute, therefore it is often used on site or in nearby locations.

Biodiesel on the other hand has a growing distribution network yet is being primarily

used for transportation rather than power and heat generation. Biodiesel is typically made

from soybean oil in the U.S., but can be made from many different plant oils and animal

fats. The cost is relatively high as biodiesel is primarily used as a transportation fuel and

does divert feed stocks from the food supply.


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Ethanol, which is typically made from corn is the most common liquid biofuel in the U.S.

and is typically used for transportation, but would work in gasoline fueled engine

generators that have been modified to operate with E85, or a gasoline-ethanol mixture

that is 85% ethanol. Corn based ethanol is a controversial fuel, which may or may not

provide energy independence or a net energy gain, as well as diverting a food source to

fuel production. Ethanol from cellulose (corn husks, grass clippings, etc.) may solve the

issue of diverting food production to fuel production and would be relatively inexpensive,

however cellulosic ethanol is not commercially available yet. Finally, ethanol is a

problematic fuel from an engineering point of view. Ethanol is hygroscopic, meaning it

absorbs water, it has a relatively low energy density, and requires the modification of

engines to run on E85. Cellulosic butanol may be the best of both worlds providing a fuel

that is very similar to gasoline in energy density and performance, while not requiring

engines to be significantly altered [15]. Cellulosic butanol is still in the laboratory scale

development and will not be commercially available for several years.

Solid fuels, referred to as biomass include wood chips, saw dust, grass clippings and any

other solid biological material can be burned in an incinerator to generate steam and drive

a turbine to generate electricity. Biomass is considered a relatively crude fuel and is

somewhat difficult to distribute, however it is usually inexpensive. The emissions vary,

and care must be taken when using biomass to fuel a CHP system, but it can be clean.

Coal is typically used in larger CHP systems and carries with it negative emissions

characteristics including high CO2, particulates, SO2, NOX, heavy metals, etc.. However,


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the distribution system is relatively good and the cost is relatively low and steady. The

emissions characteristics of coal systems are highly regulated by the EPA and getting

permits may be difficult, especially in urban environments.

Finally, waste fuels such as waste coal, garbage and heavy oils can be used in CHP

systems; however such systems typically require significant emissions controls. Garbage

presents an interesting challenge as the actual fuel composition on site is unknown;

however it can be successfully implemented in a CHP system. For example, the

Hennepin Energy Recovery Center in downtown Minneapolis, MN burns garbage

providing electricity and heat to the downtown area [16].

2.3 Energy Grids

There are several types of energy grids, most commonly the electric utility grid. This grid

is nationwide and offers some flexibility to operators of CHP systems. Each utility grid

operator has different sets of rules and regulations; therefore it is important to contact the

utility when considering the installation of a CHP system. Thermal grids are sometimes

available for CHP operators such as steam, hot water and chilled water. These grids can

provide sources and sinks for thermal energy.

Energy grids enable CHP operators to manage both excess and shortages of energy.

Buildings typically have varying loads over the course of a day as occupants come and go

and as the weather changes. Furthermore, various energy loads may not be coincident.

There may be a large electrical load and a low heating load during the day as the sun is


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shining and people are present on a fall day. However at night, the temperature drops and

additional heating is required but there is little demand for electricity.

CHP systems tend to operate better with steady conditions simultaneously generating

electricity and heating that should be used. Some energy grids allow CHP systems to

operate flexibly giving and taking a variety of forms of energy as they are needed or not

needed depending on the regulations set by the primary grid operator. Furthermore,

energy grids provide a great backup source of energy in case the CHP system fails.

Energy grids found on college campuses are particularly effective, providing electricity,

heating, and cooling to a mix of institutional and residential applications. As students are

preparing for the day they are using energy in their dormitories, then they move to

laboratories, classrooms, and offices and continue to use energy. In the evening they

return to their dormitories to study, eat dinner, and enjoy recreation, all of which can use

the same CHP system.

2.4 Prime Movers

Prime movers are defined as the device that consumes the fuel, delivers power, and

rejects heat; such as a boiler with a steam turbine, a Diesel engine, or a gas turbine.

2.4.1 Central Power Plants

Many central power plants are of the boiler steam turbine type and burn coal to

generate steam in a boiler, and then send that high pressure steam through a turbine to

generate electricity. Furthermore, these central power plants typically have very large


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generating capacity, in excess of 500 MW and sometimes greater than 1,000 MW. The

efficiency of these plants appears to have reached a maximum at about 35%, although

38% efficiency is possible with very sophisticated and expensive equipment [8]. Nuclear

power plants operate in a similar way with the exception of using enriched uranium as a

fuel to provide heat rather than coal. Note, a combination of boiler and steam turbine can

be used on a smaller scale, and are often used with low grade fuels making them cheap to

operate.

2.4.2 Boilers and Steam Turbines

The combination of a boilers and steam turbines is an effective way of using low quality,

inexpensive fuels such as biomass and waste fuels to generate electricity and heat. The

electrical efficiency of these systems is relatively low, 10% to 15%; however a lot of low

quality steam is available for a variety of applications. The emissions generated from this

type of system vary, and will require detailed study for permitting. These systems come

in a variety of sizes, typically 100 kWe and up.

2.4.3 Gas Turbine

Gas turbines for power generation typically use natural gas, however examples of

turbines using kerosene, jet fuel, biogas, and biodiesel among others can be found. Gas

turbines come in a variety of sizes from 30 kW up to 50 MW. The efficiencies of gas

turbines can vary based on the technology used. A simple gas turbine can have an

electrical efficiency as low as 15%, but as high as 45% [8]. This difference is primarily

based on the use of a regenerator to preheat incoming air or the use of a combined cycle


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process that captures waste heat to generate steam and drive an additional turbine.

Distributed Generation systems typical operate around 15-25% electrical efficiency.

2.4.4 Internal Combustion Engines

Internal combustion (IC) engines can use multiple types of fuel but typically use natural

gas, Diesel, or gasoline for operation. Biodiesel and biogas have also been frequently

used, but are much less common. Efficiencies also vary for reciprocating engines based

on the technology but a natural gas fired IC engine would have a high efficiency of 25%,

whereas a very efficient Diesel engine can reach an efficiency of 40%.

2.4.5 Fuel Cells

Fuel cells have taken on a variety of forms, fuel types, and efficiencies. While fuel cells

are arguably the most efficient form of generating electricity, the high cost both in raw

materials and manufacturing has not allowed them to become a mainstream prime mover

in the last century. Therefore, fuel cells will not be considered in this paper as possible

DG source, although the future potential of this technology is considerable.

2.4.6 Prime Mover Summary

In a CHP system it should be noted that none of these prime movers is inherently better

than another on an energy basis. If each CHP system achieves an efficiency of 80%, then

the factors that vary are the proportion of electricity to heat, and the ability to use the

various fuels effectively. As the goal is to use as much reject heat as possible, a CHP

operator will have to be aware of many issues, including how much heat and electricity

are demanded by the building and its surrounding facilities and how much is available

and in what forms. First costs, cost of fuel, cost of heat and electricity, and maintenance


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costs will all vary and need to be accounted for. Also, while there isnt necessarily a cost

associated with emissions, this too may be regulated in the future. Furthermore, the EPA

has designated some locations as non-attainment zones for sulfur oxides, nitrogen oxides,

and particulates, etc. that may have a mitigation cost associated with it. A summary of

prime movers, fuels, and performance is shown in Table 1.

Prime Mover FuelsElectricalEfficiency

Recoverable HeatCHP

Efficiency

Heat toPowerRatio

Boiler +SteamTurbine

Nat. gas, coal, wastefuels, biomass 10 - 15 %

45 - 65 % low qualitysteam 65 - 80 % 4.3

Gas Turbine Natural gas, biogas 15 - 25 % 45 - 55 % 600oF exhaust 60 - 80 % 2.8

IC Engine

-Diesel Diesel, biodiesel 30 - 40 % 15 - 20 % 190

o

F coolant,15 - 20 % 900oF exhaust 60 - 80 % 1.6

-SparkGasoline, E85,natural gas 20 - 30 %

15 - 30 % 190oF coolant,15 - 20 % 900oF exhaust 50 - 80 % 2.0

Fuel Cell

-SOFC Natural gas 35 - 45 % 25 - 35 % 500oF exhaust 60 - 80 % 0.8

-PEM Hydrogen 35 - 45 % 25 - 35 % 300oF exhaust 60 - 80 % 0.8Table 1: Prime Mover Performance Summary

2.5 Heat Loads

The earliest use for reject heat from power generation facilities was in the 1880s with

Thomas Edisons Pearl street power plant in New York [8]. The plant was only about 8%

efficient and Edison recognized that he could improve his bottom line by selling the

excess heat to neighboring buildings in the winter for space heating [8].

Over the last century additional uses for reject have been found and implemented to

varying degrees around the world, many of which are found in the Intelligent Workplace.

Reject heat temperatures vary greatly depending on the type of prime mover; however

ball park temperatures are available. A Diesel engine would supply exhaust at


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temperatures in excess of 900oF (482oC) and coolant at 195oF (91oC). A microturbine

might provide exhaust around 600oF (316oC). All of these heat sources provide a high

enough temperature for many applications, which will be discussed below.

2.5.1 Space Heating

Space heating is probably the most common application for reject heat utilization. This

heat can be utilized using radiant and convective systems typically found in many

buildings. Space heat is particularly effective as the temperature is relatively low with a

wide range of useful temperature possible. Operating temperatures range between 90oF

(32oC) for the radiant surfaces in the Intelligent Workplace to 120oF (49oC) common for

air handling units.

2.5.2 Absorption Cool ing

A heat pump is a technology that enables the transfer of heat from a low temperature to a

high temperature [17]. Heat pumps can be mechanical driven using electricity and a

motor or by heat. Absorption chillers are heat driven heat pumps [17].

Absorption chillers come in three common types based on the type of refrigerant that they

use; ammonia and water, lithium-bromide and water, and lithium-bromide, water, and

hydrogen [17]. The types of chillers used as part of IWESS are both lithium-bromide and

water. Furthermore, different configurations of absorption chillers are available; single

effect, double effect and triple effect [17]. The higher the number of chiller stages, the

higher the overall efficiency [17]. However, the control system becomes more expensive

and there is an increased cost per unit of cooling. A typical single effect chiller will have


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a coefficient of performance (COP) of around 0.5 to 0.7, whereas a double effect chiller

can reach a COP of 1.2. It should be noted that normal chillers have a COP of 3.2 on

average or greater [18]. However, the electricity used to drive the chiller must be paid for,

whereas the heat used to drive the absorption chiller is nearly free in the form of solar

energy or engine exhaust as demonstrated in the IWESS project.

2.5.3 Desiccant Regeneration

A common method of humidity control in buildings is to cool incoming outside air to a

temperature at which the water vapor in the air condenses and is removed from the air

stream, and then to reheat the air to the desired set point temperature. Needless to say this

is an energy intensive process that can be accomplished more efficiently using a

desiccant to absorb moisture [19].

As the desiccant absorbs water from the incoming air it becomes saturated overtime.

Therefore, the desiccant needs to be regenerated using a hot air stream, which could come

from a natural gas burner as is presently the case in IWESS or from a hot water heating

coil in the future [19].

2.5.4 Other Heat Loads

There are many other places to utilize waste heat such as domestic hot water, which is

found in almost every building. Additional heat demands include, but are not limited to;

heating pools, drying laundry, process energy, and thawing sidewalks and streets as is

done at Sierra Nevada College in Incline Village, Nevada. Research is being conducted


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into additional usages of reject heat; however the ones stated above are currently

employed.

2.5.5 Storage

As discussed in section 2.3 CHP systems tend to operate best in steady modes while

buildings operate in dynamic modes. When an energy grid is not available to import and

export energy, storage is an option to be considered by the engineer. While the electric

grid is almost always available, banks of batteries have been used for electrical storage as

well as using electrical resistance heaters to generate hot water or vapor compression

chillers to generate chilled water.

Thermal storage is most commonly used for domestic hot water in most businesses and

homes. The same concept can be used for chilled and hot water, which can provide a

buffer between the CHP systems outputs and the buildings demands. Based on the loads

an engineer must decide if storage should last for an hour or a day or longer. Ice storage

is a common way of storing large amounts of cooling energy. An absorption chiller can

be used to generate ice, however it must be an ammonia water chiller as lithium-bromide

absorption chillers can only achieve a minimum of 3oC, which is insufficient to create ice.

2.5.6 Heat Loads Summary

As stated in the previous section that there are a number of possible heat sinks that can

provide a use for reject heat from a CHP system. The overall goal is to have a steady

demand for heat year round, which improves the economics of the CHP system. Some

technologies are applied year round, some in a heating season and some in the cooling


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season; it is up to the CHP system designer to use the given building and site loads to find

the proper balance.

2.6 Existing Packaged Systems

There are a number of packaged units with varying degrees of integration. Some

manufacturers only provide a packaged generator set (prime mover plus generator with

controls). Additional equipment such as automatic transfer switches and soft load

controllers allow the engine generator to provide backup power and/or operate in parallel

with the utility electric supply. Soft load controllers are rarely included in the packaged

engine generator sets.

Integrated heat recovery is found in some 60 and 65 kWe Capstone microturbines as well

as many Schmitt Enertec units [20, 21]. Capstone has the majority of the microturbine

market in the U.S. as they offer a compact, low maintenance system with a small enough

electrical output to open a large market. The Capstone units have a sophisticated onboard

diagnostic system that enables remote diagnosis of faults and speeds repairs.

United Technologies Carrier has put together a CCHP system with grid paralleling

capabilities. This system can combine four to six 60 kW Capstone microturbines with a

direct fired absorption chiller. The system can be shipped loose or as a skid mounted

package. Furthermore, parallel grid connection control capabilities exist [22].

A search of Ingersoll Rands website yielded little in the way of packaged systems. It

does mention that Ingersoll Rand microturbines have been used in CHP systems.


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Furthermore, Trane, recently acquired by Ingersoll Rand, makes mention of possible

CHP applications for their packaged absorption chiller units yet there is no combination

available at this time [23].

The Baldor unit installed at CMU uses a John Deere Diesel engine, a Stamford generator

and an Intelligen controller. All of these pieces were purchased by Baldor, assembled on

a skid and shipped to CMU. Typically the unit also includes a radiator from ITT for

rejection of heat from the engine coolant; however, a special request was made to

separate the unit from the engine [13].

Units similar to the Baldor package are available from several integrators, including

Kohler Power Systems, Cummins, Caterpillar, Kato, and Generac to name a few. Some

of these companies develop and use their own engines in their generator sets, while

others select engines from the dozens of Diesel, gasoline, and natural gas engine

available on the open market.

2.7 Case Studies

There are literally thousands of DG, CHP and CCHP systems installed throughout the

U.S. varying in size from a few kilowatts to multi-megawatt systems. Many of these

systems are registered in the U.S. CHP database, which outlines location, owner/operator,

installation year, prime mover, capacity, and fuel type [24].

The database was searched for units with a capacity of less than one megawatt and fueled

with biomass (biogas, biodiesel, ethanol, etc.). Sixty-six systems have been identified.


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Most of these systems use waste from food processing, waste water treatment, or other

agriculture processes that is generated and used on site in reciprocating engines. This is

logical as the fuel for the prime mover would be free other than the fuel treatment costs.

There are only three examples of biomass fueled units being operated on non-locally

sourced fuel, two of which are on the campuses of the University of Montana in Missoula

and California Polytechnic State University in San Luis Obispo and one at a local utility

in Perry, New York.

Two biogas units, one a 30 kW microturbine and one a 30 kW reciprocating unit, both

with a custom heat recovery system are installed and are being operated in Sun Prairie,

Wisconsin at a waste water treatment facility [25]. These units have operated for several

years and have different operating characteristics. The reciprocating unit needs more

maintenance in the form of oil changes, general inspections, and requires a complete

rebuild after 8,000 operating hours. The microturbine has an onboard diagnostic system,

which detects faults and has a lifetime of 40,000 hours before needing replacement.

Furthermore, the first cost of the microturbine is about 20-50% higher than the

reciprocating unit. Both operate with a plant efficiency of about 80%, yet the proportion

of electricity generated by the reciprocating engine is higher than for the microturbine.

The majority of DG, CHP, and CCHP units are natural gas fired as there is little that has

to be done to provide fuel for the prime mover other than piping, which simplifies the

work for the operator of the system. A 60 kW microturbine was installed by the City of

Milwaukee, Department of Public Works to examine the potential economic benefits of


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CHP systems. At the time of the installation an integrated heat recovery system was not

available, which led to difficulties in the controls of the system. The heat recovery unit

suggested by the manufacturer of the microturbine did not communicate using the same

protocol, making analysis and more importantly control of the heat recovery unit difficult.

A custom solution had to be developed by the engineering staff to rectify this issue,

which the manufacturer has now solved by offering a unit with integrated heat recovery.

In 2007, a 240 kWe CCHP system was installed at the University of Toronto at

Mississauga, Canada and has been operated for nearly two years [26]. The system studied

was a four microturbine system with a double effect absorption chiller system designed

by United Technologies Carrier as mentioned in section 2.6. The system was a turn-key

contract in which the manufacturer provided all the parts, services, and installation

required to operate the system. It is not explicitly stated in the case study how the

components of the system were delivered or assembled, however, based on the provided

images; the major components (microturbines and chiller) are mounted on a concrete pad

and not on a single skid. This implies that each piece was shipped loose and mounted on

site. Furthermore, the case study does not state whether or not a grid interconnection

system was included or if that had to be purchased separately.


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3.0 IWESS Components and Subsystems

Three components of the IWESS will be integrated in this dissertation including the

biodiesel fueled engine generator with heat recovery, the steam driven double effect

absorption chiller, and the ventilation system with enthalpy recovery and solid desiccant

dehumidification. Each piece of the system will be assessed in the following sections

with the goals of:

describing the components of the system,

noting the inputs and outputs,

describing the operation of the system, and

describing how these three systems could be integrated.

3.1 Biodiesel Fueled Engine Generator with Heat Recovery

The biodiesel fueled engine generator with heat recovery system has been operating for

over a year achieving a maximum efficiency of 76%, and efficiency comparable to other

CHP systems.

3.1.1 System Components

There are four major components in the biodiesel CHP system:

engine generator,

steam generator,

coolant heat exchanger, and

automatic transfer switch (ATS) / soft load controller (SLC)

shown in Figure 3.


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Figure 3: Basic CHP Flow Diagram

Expanding upon Figure 3, Figure 4 shows the complexity of the CHP system with parts

from no less than twenty-three direct suppliers, manufacturers, and integrators.

Furthermore, this list does not include the installers for the piping, placing the equipment,

masonry work, electrical connections, instrumentation, and programming.


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Steam Generator

Engine-Generator

Intelligent Workplace

Baldor

Supplier/Manf/Integrator

Stamford

J ohn Deere

ASCO

Intelligen

Kickham

Vaporphase

Engine Generator

Turbo-charger

Controler

AutomaticTransfer

Switch

Day Tank 1

Day Tank 2

Fuel Tank

1

Fuel Tank

2

FillStation 1

FillStation 2

SteamGenerator

SteamConverter

AbsorptionChiller

Condensate

Receiver w/Controller

CondensatePumps (2)

Fuel Pump 1

Fuel Pump 2

Broad

Pryco

ITT

BorgWarner

Magnetek

Bell & Gossett

Belimo

CoolantHeat

Exchanger

Pump

Valve 3

Valve 4

Radiator

VFD Motor

Fan

FeedWaterValve

Air

DieselBiodiesel

ControlColumn

Mullion

Fan Coil

Cool Wave

RadiantPanel

Electric Grid

CampusSteam Grid

Motor

Motor

BackPressure

Valve

Motor (2)

Valve 5Motor

Valve 6

MotorMarathon

Highland Tank

Thermoflo

Penn Separator Corp.

BypassTee

BlowdownSeparator

Siemens

General Electric

Nelson

MufflerPomeco OPW

Motor

Marathon Electric

Starter

Valve 1

Motor

Valve 2

Motor

Figure 4: CHP System Components

The engine generator is a standard engine generator assembled by Baldor Electric

Company shown in Figure 5. It uses a 43 hp (33kW) four cylinder, 2.4 L John Deere

Diesel Engine and a Stamford, Inc. generator. It includes a standard engine generator

controller made by Intelligen, Inc.

Figure 5: Baldor Engine Generator


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The engine generator is connected to the grid via an ASCO 7000 automatic transfer

switch (ATS) and soft load controller (SLC) shown in Figure 6. The ATS/SLC allows the

engine generator system delivers excess power to the grid during operation, while

allowing the grid to power the mechanical room when the system is offline. The

operation of the ATS/SLC is fully automated, and once a power level is set and the start

command given, the engine generator is started and paralleled to the utility in less than

five seconds.

Figure 6: ATS/SLC with Screen Shot Operating at 18kWe and exporting 12 kWe.


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The steam generator made by Vaporphase, Inc. shown in Figure 7 is essentially a double

pass fire tube boiler without a burner. In lieu of a burner, the high temperature exhaust is

routed from the engine to the steam generator. The steam generator also acts as an

exhaust silencer, however the silencing effects are lost if the exhaust is bypassed;

therefore an extra muffler has been installed. Steam is generated at 87 psig (6 bar) in the

summer at 68 pounds per hour (31 kg/hr) for the absorption chiller and at 30 psig (2 bar)

and 65 pounds per hour (29 kg/hr) in the winter, spring, and fall for space heating the IW

and exporting the campus steam grid.

Figure 7: Assembled Components: Engine Generator (L eft), Steam Generator (Right)

It should be noted that while there is about 18 kWt of heat recovered from the exhaust,

the system is greatly oversized and can handle up to 250 kWt of heat transfer. This unit

was selected because it is the smallest commercially available exhaust heat recovery


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steam generator. A steam generator was required for this project as the absorption chiller

used in this project is steam driven. For new systems, direct firing of an absorption chiller

and high pressure hot water heat recovery can be considered to achieve space and cost

savings.

To deliver hot water to the IW, a steam hot water converter is used that can use steam

from the steam generator or the campus grid. The converter is shown in Figure 8.

Figure 8: Steam - Hot Water Converter

The coolant heat exchanger shown in Figure 9 is a standard plate and frame heat

exchanger made by ITT, Inc. The heat exchanger operates in parallel with a standard


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engine generator radiator, which has been removed and sits outside of the mechanical

room shown in Figure 10.

Figure 9: Coolant Heat Exchanger with Piping before Insulation


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Figure 10: Remote Mounted Radiator

There are several control loops within this CHP system that allow for robust control of

the system while also assuring safe operations. The engine controller monitors status,

power level, oil pressure, coolant temperature and level, battery conditions, etc. on an

engine mounted interface shown Figures 10 and 11.

Figure 11: Engine Generator Onboard Interface


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Figure 12: Engine Generator Onboard Interface

The Soft Load Controller (SLC) and the Automatic Transfer Switch (ATS) takes over

control of the governor in the engine, which was initially controlled by the Intelligen

controller to vary the speed to aid in paralleling the engine to the grid. The SLC/ATS

monitors the grids voltage and phase so that the generator output frequency, phase, and

voltage match the grid. The SLC/ATS monitors any disruptions in the grid or the engine

and protect either the grid or the generator from severe damage. If there is a failure the

ATS/SLC will separate the engine generator from the grid and will send a shutdown

order to the engine. The engine will continue to operate for five minutes powering lights,

ventilation, etc. so that occupants have enough time to vacate the lab. Then the engine

will go into its standard shutdown procedure, which includes a five minute cool down.

The steam generator has its own stand alone pneumatic control system that has three

principal tasks. First, it makes sure that the steam generator does not run dry as hot

exhaust gases can warp the coils if the heat is not dissipated. It can call for makeup water


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based on the output of a low level alarm and if makeup water is not available, it will

bypass the exhaust around the steam generator.

The second task for the pneumatic controller is to maintain the set point pressure inside

the steam generator using a back pressure control valve. The steam pressure is measured

inside the steam generator and downstream from the back pressure valve. If the pressure

inside the steam generator drops below the set point, the back pressure control valve will

restrict the flow of steam until the pressure rises again. The purpose of this controller is to

prevent a sudden drop in steam pressure, which can cause the steam generator to implode.

The third task is to match heat input to the output steam flow. The exhaust gas flow to the

steam generator is modulated by the bypass control valve to maintain a set point pressure

of the output steam flow. This arrangement allows the steam generator to operate at

partial loads, while the engine operates at full power.

The control of the steam is accomplished through a series of two position valves and

pressure reduction valves. During the summer, two two-position valves block flow to the

grid/hot water converter and route the steam flow to the absorption chiller. During the

rest of the year the flow to the chiller is blocked and directed towards the grid and hot

water converter. A pressure reduction valve reduces the steam supply pressure to the hot

water converter to 9 psig (0.6 bar) and the steam from the grid is reduced to 7 psig (0.5

bar) with another pressure reduction valve. The steam from the CHP system is prioritized

over the steam from the grid because the 9 psig steam will prevent the 7 psig pressure


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reduction valve from opening as the pressure on the outlet side is too high. If there is a

short fall of pressure from the CHP system, the steam grid will start to makeup the

difference once the pressure falls below 7 psig (0.5 bar). Schematics from the steam

system are shown in Appendix A.

The coolant system controller is designed to prevent the engine from over-heating. This is

accomplished by removing heat either through a plate and frame heat recovery exchanger

or a remotely mounted radiator with a fan. The coolant controller has two modulating

valves which allow the controller to proportion flows to control the amount of heat

removed. This arrangement allows the engine to operate at full power, while only

recovering a portion of the coolant energy. This controller is a part of the overall Web-

based building automation system (BAS). The BAS operates the overall dispatch of the

CHP system and logs all of the sensor data. The previously mentioned controllers all

function together to allow the system to address varying thermal and electrical energy

demands.

3.1.2 Input / Output

The Inputs for this system include:

fuel (Diesel or biodiesel)

air (fresh air for combustion)

condensate

hot water return


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The outputs for this system include:

electricity (208 V, 3 phase)

exhaust

steam

hot water

data (Modbus, 4-20mA, 0-5 V converted to BACNET and available on the web)

Data inputs and outputs from sensors and actuators in the heat recovery system are

compiled in the Automated Logic web based user interface shown in Figure 13.

Figure 13: Automated Logic CHP User I nterface for the Heat Recovery/Rejection System

3.1.3 Operating Descr iption and Results

The core of the biodiesel fueled engine generator with heat recovery is the engine

generator, which burns fuel in order to generate electricity which is sent to the grid, and


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generates heat in the forms of high temperature exhaust at 160oC (360oF) and lower

temperature engine coolant at 90oC (190oF). The high temperature exhaust can be

rejected to atmosphere or recovered using a steam generator, which can generate steam at

varying pressure levels. The steam can be used to heat the IW in the winter or drive an

absorption chiller in the summer. Furthermore, the steam system is connected to a

campus grid system, which allows for excess steam to be exported to the grid. The

coolant energy is recovered through another heat exchanger to heat water or rejected

through a radiator. The hot water is used in the winter for space heating in the IW.

Tables 2 through 4 show the compiled commissioning and experimental results, from the

operation of the engine generator, the heat recovery systems (exhaust and coolant), and

the integration with the Intelligent Workplace and campus systems. The engine was

operated at various loads and conditions for over 400 hours as shown in Appendix B.

Summer CHP Diesel Results

Power Output(kWe)

Fuel Input(kWc)

Plant Power(kWe)

Coolant HeatRecovered (kWt)

Exhaust HeatRecovered (kWt)

CHPEfficiency

6 25 3 6 3 47%

12 43 3 9 7 59%

18 57 3 12 12 68%

25 76 3 18 18 76%

Table 2: Averaged Summer Diesel Commissioning and Experimental CHP Results

Winter CHP Diesel Results

Power Output(kWe)

Fuel Input(kWc)

Plant Power(kWe)



CHPEfficiency

6 25 4 6 4 49%

12 43 4 11 7 61%

18 57 4 14 12 70%

25 76 4 18 17 74%

Table 3: Averaged Winter Diesel Commissioning and Experimental CHP Results


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Winter CHP Biod iesel Results

Power Output(kWe)

Fuel Input(kWc)

Plant Power(kWe)



CHPEfficiency

6 26 4 8 4 54%

12 42 4 10 9 65%

18 59 4 14 13 68%

25 76 4 18 18 76%

Table 4: Averaged Winter Biodiesel Experimental Results

The results shown in Tables 2 through 4 show average plant efficiency between 47% and

76%, consistent with typical CHP efficiencies. There is a substantial fall off in efficiency

as the power level drops, which indicates that the system operates more efficiently at full

load than part load. This is not surprising as engine efficiency usually peaks at about 80%

of the maximum engine rating, or 25 kWe of 33kWe. Furthermore, the power required to

operate pumps and fans, plant power, remains constant, and becomes a larger percentage

of the total power at the lower loads.


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3.1.3.1 Engine: Measured Data versus Manufacturers Specifications

It has been difficult to precisely compare all of the engines specifications with the

measured data as the manufacturers specifications are written for operation at 32 kWe,

whereas the engine has been operated at part loads from 6 kWe to 25 kWe electrical.

Note, the specification column is written for the maximum engine rating of 32kWe using

No.2 low sulfur Diesel fuel.

System Specification Data Notes

Air SystemMax. temp. rise, amb. to inlet 15 F (8C) ~15 F Varies due to room air temperature

Engine Air Flow 99 CFM (2.8 m3/min) 83 CFM at 25 kWeSteady increase in flow rate withpower (6 kW =64 CFM, 12kW =68CFM, 18kW =74 CFM)

Intake Manifold Pressure 9 psig (64 kPa) 0.4psi (6kWe), 0.9psi (12kWe), 1.6psi (18kWe), 2.3psi (25kWe)

Fuel System

Total Fuel Flow 185 lb/hr (84 kg/hr) NAThe individual fuel flow meters do notprovide independent outputs.

Fuel Consumption (6 kWe) 4.7 lb/hr (2.1 kg/hr) 4.6 lb/hr (2.1 kg/hr)Verified with weigh tankmeasurement

Fuel Consumption (12 kWe) 7.0 lb/hr (3.2 kg/hr) 7.9 lb/hr (3.6 kg/hr)Verified with weigh tankmeasurement

Fuel Consumption (18 kWe) 9.8 lb/hr (4.4 kg/hr)10.6 lb/hr (4.8kg/hr)

Verified with weigh tankmeasurement

Fuel Consumption (25 kWe) 13.3 lb/hr (6.1 kg/hr) 14.1 lb/hr (6.4kg/hr) Verified with weigh tankmeasurement

Fuel Consumption (32 kWb) 17.9 lb/hr (8.1 kg/hr) NASoft load controller will allow amaximum power of 25 kW

Cooling System

Engine Heat Rejection1303 BTU/min (23kW)

18 kW at 25 kWe

Coolant Flow 24 GPM (91 L/min) 10.2 GPMSpec assumes radiator attached toengine

Thermostatic Valve start toopen

185 F (82 C)Verified by comparing start of coolantflow and coolant temperature

Thermostatic Valve fully open 201 F (94 C)Verified by comparing by observingsteady flow above 201 F

Exhaust

Exhaust Temperature 963 F (517 C) 930 F (499 C) at 25kWe

Max allowable back pressure 30 in-H2O (7.5 kPa)14 in-H2O at 25kWe

Used a pressure gauge mountedbetween the engine exhaust andsteam generator

Table 5: Diesel Engine Generator Measured Data vs. Manufacturer Specifications


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Table 5 shows that the measured data corresponds well to the manufacturers

specifications; however, there is a small margin of error. This margin of error probably

comes from minor differences between engines during manufacturing and the sensors

used by the manufacturer and the IWESS team during testing. Table 6 shows similar

results to Table 5 for biodiesel fuel.

System Specification Data Notes

Air System

Max. temp. rise,amb. to inlet

15 F (8C)

Engine Air Flow99 CFM (2.8m3/min)

79 CFM at 25kWe

Steady increase in flow rate with power (6 kW =64CFM, 12kW =68 CFM, 18kW =74 CFM)

Intake ManifoldPressure

9 psig (64 kPa) 1.7psi (6kWe), 2.15psi (12kWe), 2.84psi (18kWe), 3.67psi (25kWe)

Fuel SystemTotal Fuel Flow 185 lb/hr (84 kg/hr) No Measurement Available

Fuel Consumption(6 kW)

4.7 lb/hr (2.1 kg/hr) Verified with weigh tank measurement


7.0 lb/hr (3.2 kg/hr)8.8 lb/hr (4.0kg/hr)

Verified with weigh tank measurement


9.8 lb/hr (4.4 kg/hr)12.6 lb/hr (5.7kg/hr)



13.3 lb/hr (6.1kg/hr)

16.1 lb/hr (7.3kg/hr)



17.9 lb/hr (8.1kg/hr)

NASoft load controller will allow a maximum power of25 kW

Cooling System

Engine HeatRejection

1303 BTU/min (23kW)

16 kW at 25 kWe

Coolant Flow 24 GPM (91 L/min) 10.2 GPM Spec assumes radiator attached to engine

Thermostatic Valvestart to open

185 F (82 C)Verified by comparing start of coolant flow andcoolant temperature

Thermostatic Valvefully open

201 F (94 C)Verified by comparing by observing steady flowabove 201 F

Exhaust

ExhaustTemperature

963 F (517 C)890 F (477 C) at25 kWe

Biodiesel experiments only conducted during winterat this time, may cause low temp.

Max allowable backpressure

30 in-H2O (7.5kPa)

14 in-H2O at 25kWe

Used a pressure gauge mounted between theengine exhaust and steam generator

Table 6: Biodiesel Engine Generator Data vs. Manufacturer Specifications

As shown in Tables 5 and 6, the primary difference between Diesel fuel and biodiesel

fuel is that the fuel flow rate is greater for biodiesel fuel. The reason for this is that the

energy density of biodiesel is lower than Diesel fuel, thus the engine controller naturally


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increases the fuel demand to meet power demand. As the engine operates below its

maximum, prime power operation, the fuel pump has no problem meeting this challenge.

3.1.3.1 Pressure Time Crank Angle Measurements

Pressure sensors have been installed in each engine cylinder to obtain information on

how the combustion process changes when using different fuels. In combination with a

crank angle encoder, the pressure measurements are collected using a high speed data

acquisition system, and plotted as shown in Figure 14.

Figure 14: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel


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Figure 14 shows the pressure vs. crank angle curve, and shows injection combustion

taking place around top dead center (TDC).

Figure 15: Pressure vs. Time for One Cylinder at 12 kWe using Low Sulfur Diesel Fuel

As can be observed in Figure 15, the wave forms shifts from injection and combustion at

TDC to a delayed combustion of about 15 degrees after TDC. The effect of a delayed

combustion is that the peak combustion temperature is reduced. The purpose of reducing

the peak temperature is to reduce NOX formation to meet U.S. Environmental Protection

Agency regulations. An additional effect of this control strategy is the reduction of engine

capacity and efficiency. Further analysis on these wave forms is under way to compare

the performance of the various fuels.


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3.1.3.2 Turbocharger Analysis

The engines turbocharger was completely instrumented with temperature, pressure and

flow sensors. The data collected from the turbocharger indicates a mass flow rate of

0.053 kg/sec and a maximum compression ratio of 1.25 at 25kWe. These data are plotted

in Figure 16, the compressor map provided in by the turbocharger manufacturer. They

show that this turbocharger is not suited for this engine operating under the specified

conditions.

Figure 16: Turbocharger Compressor Map [27]

It should be noted, that while the turbocharger is not effective for the duty cycle of this

engine, it may operate more efficiently at 33 kWe, the power level for which the


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turbocharger was designed. CHP system designers should be aware of this fact and

request a turbocharger that will operate more efficiently in the appropriate range.

3.1.3.3 Combustion Gas and Emissions Analysis

Emissions of gas-phase pollutants [carbon dioxide (CO2), carbon monoxide (CO),

nitrogen dioxide (NO2), nitrogen oxide (NO), unburned hydrocarbons (UHC), and

oxygen (O2)] have been measured over four loads using both low sulfur Diesel fuel and

soy based biodiesel fuel.

Load

(kWe)

%

O2

%

CO

%

CO2

UHC

(PPM)

NO

(PPM)

NO2

(PPM)6 16.1 0.0 3.7 4 251 412 13.9 0.1 5.2 9 424 618 11.6 0.1 6.8 11 466 525 9.6 0.1 8.2 12 502 4

Table 7: Average Gaseous Emissions vs. Load with Low Sulfur Diesel Fuel

Table 8: Average Gaseous Emissions vs. Load with Soy Biodiesel Fuel

The data in Tables 7 and 8 agree with published results [28, 29, 30] with significant

reductions in CO, and UHC. However, typically soy based biodiesel generates more NOX,

and the averaged data does not reflect that. The NOX emissions for this engine are

reduced due to the engine timing adjustments to meet emissions requirements, which may

account for the similar levels of NOX. Further research into the emissions is warranted if

Load(kWe)

%O2

%CO

%CO2

UHC(PPM)

NO(PPM)

NO2(PPM)

6 16.3 0.0 3.8 0 224 512 13.9 0.0 5.4 1 357 818 11.5 0.0 7.1 2 450 1025 9.7 0.0 8.4 3 498 9


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large scale use of biodiesel in CHP systems is to be achieved as emissions must be

understood to meet EPA regulations.

A combustion analysis has been conducted for the engine generator operating at 25 kWe

using Diesel fuel.

The stoichiometric material balance for Diesel fuel.

222222312 76.3 dNOcHbCONOaHC

C: 12 =b(1) b =12

H: 23 =c(2) c =11.5

O: a(2) =b(2) +c(1)

2a =2x12 +11.5 =35.5

a =17.75

N: a(3.76)(2) =d(2) d =66.7

222222312 7.665.111276.375.17 NOHCONOHC

Determine the molar air to fuel ratio.

5.84

1

76.375.1775.17

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(cchpv) systems integration betz

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