hvac design&implementation

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THIS HANDBOOK PROVIDES COMPREHENSIVE TECHNICAL INFORMATION TO HEATING, VENTILATING, AND AIR CONDITIONING ENGINEERS, DESIGNERS AND PRACTITIONERS HVAC: Handbook of Heating, Ventilation and Air Conditioning for Design and Implementation BY ALI VEDAVARZ, PH.D., PE Deputy Director of Engineering, New York City Capital Projects, New York City Housing Authority and Industry Professor, Polytechnic University, Brooklyn, NY SUNIL KUMAR, PH.D. Professor of Mechanical Engineering and Dean of Graduate School Polytechnic University, Brooklyn, NY MUHAMMED IQBAL HUSSAIN, PE Mechanical Engineer, Department of Citywide Administrative Services New York City, NY 2007 INDUSTRIAL PRESS INC. NEW YORK HVAC: Handbook of Heating, Ventilation and Air Conditioning Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

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Page 1: HVAC Design&Implementation

THIS HANDBOOK PROVIDES COMPREHENSIVE TECHNICAL INFORMATION TO HEATING,VENTILATING, AND AIR CONDITIONING

ENGINEERS, DESIGNERS AND PRACTITIONERS

HVAC:Handbook of Heating,

Ventilation andAir Conditioning for

Design and Implementation

BY

ALI VEDAVARZ, PH.D., PEDeputy Director of Engineering, New York City Capital Projects,

New York City Housing Authority andIndustry Professor, Polytechnic University, Brooklyn, NY

SUNIL KUMAR, PH.D.Professor of Mechanical Engineering and Dean of Graduate School

Polytechnic University, Brooklyn, NY

MUHAMMED IQBAL HUSSAIN, PEMechanical Engineer, Department of Citywide Administrative Services

New York City, NY

2007

INDUSTRIAL PRESS INC.

NEW YORK

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 2: HVAC Design&Implementation

COPYRIGHT © 2007 by Industrial Press Inc., New York, NY.

Library of Congress Cataloging-in-Publication Data

Vedavarz, Ali.

HVAC: handbook of heating ventilation and air conditioning / Ali Vedavarz, Sunil Kumar, MuhammedHussain.

p. cm.

ISBN 0-8311-3163-2

ISBN13 978-0-8311-3163-0

I. Heating--Handbooks, manuals, etc. 2. Ventilation--Handbooks, manuals, etc. 3. Air conditioning--Handbooks, manuals, etc. 4. Buildings--Environmental engineering--Handbooks, manuals, etc. I. Kumar, Sunil.II. Hussain, Muhammed Iqbal. III. Title.

Printed and bound in the United States of America

All rights reserved. This book or parts thereof may not be reproduced, stored in a retrieval system,or transmitted in any form without permission of the publishers.

TH7011.V46 2006697--dc22

2006041837

Cover Photo: Image published with kind permission of CVRD and Bluhm Engineering.

INDUSTRIAL PRESS, INC.

989 Avenue of the Americas

New York, New York 10018 -5410

1st Edition

First Printing

10 9 8 7 6 5 4 3 2 1

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 3: HVAC Design&Implementation

TABLE OF CONTENTS

iii

1. FUNDAMENTALS

1–1 Fundamentals of Thermodynamics1–3 Conservation of Mass1–3 First Law of Thermodynamics1–4 Second Law, Reversibility, and Possible Processes1–4 Thermodynamic Cycles1–6 Fundamentals of Fluid Flow1–6 Flow in Pipes and Ducts1–11 Noise from Fluid Flow1–11 Fundamentals of Heat Transfer1–14 Overall Heat Transfer1–15 Fins and Extended Surfaces1–18 Some Details of Heat Exchange1–19 Augmentation of Heat Transfer

2. PSYCHROMETRY

2–1 Psychrometrics2–1 Ideal Gas Approximation2–1 Equation of State2–2 Humidity Ratio2–2 Relative Humidity 2–2 Degree of Saturation2–2 Wet Bulb Temperature2–3 Partial Pressure of Water Vapor2–4 Dew Point Temperature2–4 Saturation2–4 Enthalpy2–5 Wet Bulb Temperature2–6 Properties of Moist Air2–7 Psychrometric Chart Presentation2–12 Thermodynamic Properties of Water at Saturation2–18 Thermodynamic Properties of Moist Air

3. AIR CONDITIONING PROCESSES

3–1 Introduction3–1 Heating and Cooling Process3–2 Cooling with Dehumidification3–3 Heating with Humidification3–3 Adiabatic Mixing of Two Air Streams3–5 Evaporative Cooling3–5 Heating and Air Conditioning System Cycles

4. INDOOR AIR QUALITY AND VENTILATION

4–1 Indoor Air Quality4–1 Ventilation Procedure4–5 Concentration of Air Pollutants4–6 Indoor Air Quality Procedure4–8 Filters4–10 Hepa Filters4–10 Carbon Media Filters4–10 Fiber and Foam Filters4–10 Ozone4–10 Ultraviolet Light

5. LOAD ESTIMATING FUNDAMENTALS

5–1 Conduction5–1 Thermal Conductivities of Materials5–2 Convection5–4 Thermal Radiation5–4 Emissivities of Some Materials5–6 Overall Heat Transfer Coefficient5–8 Parallel Arrangement5–11 Coefficient of Transmission

(Continued)5. LOAD ESTIMATING FUNDAMENTALS

5–17 Relative Thermal Resistances of Building Materials5–18 Surface Conductances and Resistances5–18 Emittance Values of Various Surafces5–19 Thermal Resistances of Plane Airspaces5–21 Thermal Properties of Building and Insulating Materials5–27 Coefficients of Heat Transmission of Various Fenestrations5–28 Transmission Coefficients for Wood and Steel Doors5–29 Outdoor Air Load Components

6. HEATING LOAD CALCULATIONS

6–1 Introduction 6–1 Calculating Design Heating Loads6–2 Heat loss Through Walls, Roofs, and Glass Area6–2 Heat Loss from Walls below Grade6–3 Below-Grade Wall U-Factors6–3 Heat Loss from Basement Floor Below Grade6–4 Heat Loss Coefficients 6–4 Heat Loss from Floor Slab On Grade6–6 Ventilation and Infiltration Heat Loss

7. COOLING LOAD CALCULATIONS

7–1 Transfer Function Method (TFM)7–1 Heat Source in Conditioned Space7–2 Heat Gain from Occupants7–3 Heat Gain from Cooking Appliances7–6 Heat Gain from Medical Equipments7–6 Heat Gain from Computer 7–6 Heat Gain from Office Equipments7–6 CLTD/SCL/CLF Calculation Procedure7–7 Cooling Load by CLTD/SCL/CLF Method7–8 Roof Numbers7–9 CLTD for Roofs7–11 CLTD for Walls7–27 Code Number for Wall and Roof7–28 Wall Types7–31 CLTD for Glass7–31 Zone Types for CLF Tables7–31 Zone Types for SCL and CLF Tables7–35 Residential Cooling Load Procedure7–36 SCL for Glass7–44 CLF for People and Unhooded Equipments7–46 CLF for Hooded Equipments7–47 Window GLF for Residences7–49 CLTD for Residences7–50 SC for Windows7–50 SLF for Windows7–50 Air Exchange Rates

8. DUCT DESIGN

8–1 Introduction8–1 Pressure Head and Energy Equation8–2 Friction Loss Analysis8–7 Dynamic Losses8–7 Ductwork Sectional Losses8–8 Fan System Interface8–8 Pressure Changes System8–9 Duct System Design8–9 Design Considerations8–12 Duct Design Methods8–13 Duct Design Procedures8–13 Automated Duct Design8–14 Duct Fitting Friction Loss Example8–14 Equal Friction Method Example8–15 Resistance in Low Pressure Duct System Example8–15 Static Regain Method Example8–17 Fitting Loss Coefficients

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 4: HVAC Design&Implementation

TABLE OF CONTENTSiv

9. PIPE SIZING

9–1 Pressure Drop Equations9–1 Valve and Fitting Losses9–3 Water Piping9–3 Flow Rate Limitations9–3 Noise Generation9–3 Erosion9–3 Allowances for Aging9–4 Water Hammer9–4 Hydronic System Piping9–6 Valve and Fitting Pressure Drop9–28 Service Water Piping9–29 Plastic Pipe9–29 Cold Water Pipe Sizing9–31 Steam Flow in Pipes9–31 Steam Flow Formulas9–32 Vertical Pipes9–32 Steam Piping9–59 Gas Piping For Buildings9–59 Residential Piping9–61 Commercial-Industrial Piping9–72 Compressed Air Systems9–72 Compressed Air9–78 Viscosity of Liquids9–80 Piping9–80 Types of Materials9–91 Plastics Pipe9–91 Joining Techniques9–93 Standards for Specification and Identification9–93 Design Parameters9–96 Installation9–97 Codes and Regulations9–97 Pipe Fittings9–97 Taper Pipe Thread9–132 Laying Lengths of Pipe with Screwed Fittings9–134 Allowable Spaces for Pipes9–134 Expansion of Pipe9–136 Corrosion Resistance9–136 Pipe Support Spacing9–139 Gate, Globe, and Check Valves9–139 Operation9–141 Maintenance Methods9–142 Formulas for Sizing Control Valves9–142 To Determine Valve Size9–142 To Determine Valve Capacity9–142 For Vapors Other Than Steam9–143 Identification of Piping Systems9–143 Dangerous Materials9–143 Fire Protection Materials and Equipment9–144 Safe Materials9–144 Protective Materials9–144 Method of Identification9–144 Heat Losses in Piping9–144 Heat Losses from Bare Pipe9–145 Heat Losses from Steam Piping9–157 Heat Loss from Insulated Pipe9–158 Cold Surface Temperature

10. HYDRONIC HEATING AND COOLING SYSTEM

10–1 Basic System10–4 Temperature Classifications10–4 Closed Hydronic System Components Design10–4 Convectors or Terminal Units10–4 Boiler10–4 Air Eliminations Methods10–6 Pressure Increase Due to Change in Temperature10–6 Expansion Tank10–7 Expansion Tank Sizing

(Continued)10. HYDRONIC HEATING AND COOLING SYSTEM

10–8 Characteristics of Centrifugal Pumps10–8 Operating Characteristics10–9 Pump Laws10–9 Change of Performance10–10 Centrifugal Pump Selection10–10 Total Dynamic Head10–11 Net Positive Suction Head (NPSH)10–11 Pumping System10–16 Parallel Pumping10–17 Series Pumping10–18 Design Procedures10–18 Preliminary Equipment Layout10–19 Final Pipe Sizing and Pressure Drop Determination10–19 Final Pressure Drop10–19 Final Pump Selection10–19 Freeze Prevention

11. ENERGY CALCULATION

11–1 Degree Day11–1 65°F as the Base11–2 Application of Degree Days11–4 Predicting Fuel Consumption11–5 Predicting Future Needs11–7 Empirical Constants11–7 Load Factor and Operating Hours11–7 Limitations11–8 Degree-Days Abroad11–9 Degree Days for Various US Locations

12. COMBUSTION

12–1 Combustion Basics12–3 Efficiency Calculations12–7 Saving Fuel with Combustion Controls12–11 Combustion Considerations12–11 Pressure and Flow Basic Principles12–12 Atomizing Media Considerations12–12 Combustion Air Considerations12–13 Flue Gas Considerations12–14 Gas Fuel Firing Considerations12–14 Fuel Oil Firing Considerations12–15 Operational Rules of Thumb12–16 Common Application12–20 Combustion Control Strategies12–20 Control System Errors12–20 Combustion Control Strategies12–21 Parallel Positioning Systems12–22 Fully Metered Control12–23 Feedwater Control Systems12–24 Draft Control12–26 Oxygen Trim12–27 Combustion Air Flow Control Techniques12–28 Flue Gas Recirculation (FGR)12–33 Fuel Oil Handling System Design12–33 Determination of Required Flow Rate12–34 Stand by Generator Loop Systems12–34 Multiple Pumps12–34 Burner Loop Systems12–36 Maximum Inlet Suction12–37 Pump Discharge Pressure12–37 Piping System Design12–37 Pump Set Control System Strategies

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 5: HVAC Design&Implementation

TABLE OF CONTENTS v

13. AIR CONDITIONING SYSTEMS

13–1 Air Conditioning Systems13–1 Single Package Units13–5 Single Package Installations13–7 Installation of Split Systems13–8 Zoning Unitary Installations13–10 Selection Procedure13–14 Evaporative Air Conditioning13–14 Permissible Air Motion13–17 Variable Volume AC System13–18 Initial Costs13–20 Cooling Considerations13–21 Overlapping13–22 Heat Recovery13–22 Heating Cooling Systems13–23 Air Systems13–26 Controls13–27 Air Water Systems13–30 Sources of Internal Heat13–31 Heat from Service Refrigeration13–31 Exhaust Air Heat Recovery Systems13–36 Heat Pumps13–36 Reverse-Cycle Principle13–36 Coefficient of Performance13–37 Heating Season Performance Factor13–37 Types of Heat Pumps13–38 Air-to-Air Heat Pumps13–39 Water-to-Water Heat Pumps13–40 Water-to-Air Heat Pumps13–40 Air-to-Water Heat Pumps13–41 Ground Source Heat Pumps13–41 Special Heat Sources13–42 Operating and Installation Factors13–42 Outdoor Temperature Effects13–43 Thermostats13–43 Heat Anticipators13–44 Equipment Arrangement13–44 Electrohydronic Heat Recovery13–45 Cooling Cycle13–47 System Design13–47 Supplementary Heat13–47 Optimized Data for Heat Pump13–48 Development of Equations13–48 Development of Tables13–49 Selecting Air Handling Units13–54 Well Water Air Conditioning13–54 Heat Pump/Solar Energy Application13–54 System Description and Operation13–60 High Velocity Dual Duct Systems13–60 Advantages and Disadvantages13–60 Dual Duct Cycles13–65 Duct Sizing Technique13–65 Large vs. Small Ducts13–66 Design Velocity13–66 Maximum Velocity13–67 Sizing High Pressure Ducts13–68 Return Air Ducts13–68 Low Pressure Ductwork13–69 Basic Arrangement13–69 Zoning13–70 Ceiling Plenum13–73 Modular Type Office Buildings13–76 Constant Volume Mixing Units13–77 Apparatus Floor Area13–80 Construction Details13–81 Automatic Control Applications13–81 Rooftop Multizone Units13–84 Multizone Unit Control13–88 Damper Control13–88 Economizer Control Cycle13–88 Unit Ventilator Control

(Continued)13. AIR CONDITIONING SYSTEMS

13–91 Hot Water System Control13–94 Mixing Box Control13–95 Rotary Air-to-Air Heat Exchanger Control13–95 Automatic Control for Dual Duct System13–97 Winterizing Chilled Water System13–97 Water Circulation to Prevent Freeze-Up13–99 Mechanical Draft Cooling Towers13–102 Atmospheric Cooling Towers13–104 Quantity of Cooling Water Required13–105 Roof is a Location for AC Equipment13–105 Advantages of Roof13–106 Disadvantages of Roof13–107 Servicing Cooling Plant13–107 Servicing Cooling Plant for Summer Use13–107 Water System13–107 Air Handling System13–107 Compressor Oil13–107 Condenser13–108 Refrigeration Unit13–108 Check Oil13–108 Compressor 13–108 Air Conditioning Equipment Maintenance13–108 Air Handling Equipment13–108 Air Distribution Equipment13–108 Water-Using Equipment13–108 Cooling Equipment13–110 Air Conditioning Maintenance Schedule13–111 Unit Air Conditioners13–111 Central Systems13–111 Condensing Water Circuit13–112 Cooling Water System13–112 Filters and Ducts13–112 Air Conditioning Maintenance Procedure13–112 Refrigerant Circuit and Controls13–113 Condensing Water Circuit13–113 Cooling Water System13–113 Filters and Ducts13–114 Rotating Apparatus13–114 Unit Air Conditioners13–114 Checklist for Air Conditioning Surveys

14. AIR HANDLING AND VENTILATION

14–1 Terminology, Abbreviations, and Definitions14–3 Fan Laws14–11 Fan Performance Curves14–16 Class Limits for Fans14–21 Fan Selection14–26 Fan Inlet Connections14–27 Fan Discharge Conditions14–31 Useful Fan Formulas14–32 Nomographs for Fan Horsepower14–32 Monographs for Fan Horsepower and Actual Capacity14–34 Fan Selection Questionnaire14–37 Air Flow in Ducts14–40 Pitot Traverse14–40 Friction Losses14–40 Correction for Roughness14–40 Rectangular Duct14–52 Air Balancing and Air Turning Hardware14–56 Air Distribution14–56 Fire Dampers and Fire Protection14–56 Duct System Design14–59 High Velocity System Design14–68 Step by Step Design14–68 Main Duct14–70 Branch Trunk Ducts14–71 Single Branch Lines14–72 Duct Design by Computer14–73 Fibrous Glass Duct Construction

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

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TABLE OF CONTENTSvi

(Continued)14. AIR HANDLING AND VENTILATION

14–75 Determining Required Air Volume14–75 Estimating Weight of Metal 14–77 Apparatus Casing Construction14–77 Condensate Drains for Air Conditioning Units14–78 Air Filters and Dust Collectors14–78 Air Filters14–79 Dust Collectors14–82 Dry Centrifugal Collectors14–82 Wet Collectors14–82 Fabric Collectors14–83 Electrostatic Precipitators14–83 Breeching Design and Construction14–83 Expansion14–84 Aerodynamics14–85 Access14–85 Round Breeching Construction14–85 Rectangular Breeching Construction14–90 Chimney Draft and Velocities14–92 Forced Draft and Draft Control14–94 Sizing of Large Chimneys14–95 Chimney Design and Construction14–96 Balancing Small Air Conditioning Systems14–97 Balancing Medium and Large Systems14–98 Balancing Duct Distribution14–98 Balancing Systems Using Booster Fans14–99 Air Balancing by Balancing and Testing Engineers

15. STEAM HEATING SYSTEM DESIGN

15–1 Large Systems15–1 Equivalent Direct Radiation15–1 Piping Connections to Boilers15–3 Direct Return Connection15–3 Common Return Header15–3 Two Boilers with Common Return Header and Hartford

Connection15–4 Two Boilers with Separate Direct Return Connections from

Below15–4 Separate Direct Return Connections15–4 Connections to Steam Using Equipment15–26 Piping Application15–30 Industrial and Commercial Steam Requirements15–39 Flash Steam Calculations15–40 Sizing of Vertical Flash Tanks15–40 To Size Flash Tank15–41 To Size Float Trap15–41 Airbinding15–46 Estimating Friction in Hot Water Piping15–49 Hot Water Heating Systems15–49 Service Water Heating15–49 Operating Water Temperature15–49 Air Removal from System15–49 Water Flow Velocity15–49 Prevention of Freezing15–49 Water Circulation below Mains15–49 Limitation of Pressure15–50 System Adaptability15–50 Use of Waste Steam Heat15–50 Heat from District Steam System15–50 Summer Cooling15–50 Types of Water Heating Systems15–52 Design Recommendations for Hot Water Systems15–52 Water Velocity15–52 Pump Location15–52 Air Venting15–53 Balancing Circuits15–53 Filling Pressure15–53 Preventing Backflow15–53 Connecting Returns to Boiler15–53 Locating the Circulating Pump

(Continued)15. STEAM HEATING SYSTEM DESIGN

15–53 Sizing the Expansion Tank15–54 Compressed Air to Reduce Tank Size15–54 Piping Details15–55 Design of Piping Systems15–58 Design of Two Pipe Reversed Return System15–58 Final Check of Pipe Sizes15–58 Design of Two Pipe Direct Return System15–59 Piping for One-Pipe Diversion System15–59 Sizing Piping for Main15–59 Sizing Piping for Branches15–59 Pipe Size Check15–60 Piping for One-pipe Series System15–60 Combination of Piping Systems15–60 Sizing Hot Water Expansion Tanks15–60 Conditions Affecting Design15–61 Sizing Hot Water Expansion Tanks15–61 High Temperature Water Systems15–63 High Temperature Drop15–63 Heat Storage15–63 Limitation of Corrosion15–63 Pressurization of HTW System15–63 Steam Pressurization15–64 Gas Pressurization15–64 Air Pressurization15–64 Nitrogen Pressurization15–65 Expansion Tanks15–65 Expansion Conditions15–65 Determining Expansion Tank Size15–65 Location of Steam Pressurizing Tank15–66 Nitrogen Pressurizing Tanks15–66 Application of HTW for Process Steam15–66 Circulating Pumps15–67 Pumps for HTW Systems15–67 Manufacturer’s Information15–67 Pump Specifications15–68 Net Positive Suction Head15–68 Effect of Cavitation Within Pump15–68 Pump Construction for HTW Systems15–68 Circulating Pump Seals15–69 Boiler Recirculating Pump15–69 Boilers for HTW Systems15–69 Boiler Emergency Protection15–69 Pipe, Valves, and Fittings for HTW Systems15–69 Valve Installation15–70 Welded Joints15–70 Venting of Piping15–70 Effect of Load Variation on Operation15–71 Pipe Sizing for HTW Systems15–73 Ratings of Steel Boilers15–73 Ratings15–74 Ratings for Steel Boilers15–76 Stack Dimensions15–81 Heating and Cooling Media15–81 Brine15–81 Glycerine15–81 Glycol15–81 Other Media15–82 Warm Air Heating15–82 Early Types15–83 Current Types15–85 Furnace Performance15–85 Testing and Rating of Furnaces15–86 Acceptable Limits15–87 Selection of Furnace15–87 Rule for Selection15–87 Blower Characteristics15–88 Blower Sizes15–88 Duct System Characteristics15–88 Trends15–89 Warm Air Registers15–90 Return Air Intakes

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

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TABLE OF CONTENTS vii

(Continued)15. STEAM HEATING SYSTEM DESIGN

15–91 Arrangement of Furnace and Ducts15–94 Basic Thermostatic Controls15–94 Continuous Air Circulation15–95 Continuous Blower Operation15–95 Intermittent Blower Operation15–109 Steam Supplied Unit Heater15–109 Gas Fired Radiant Heaters15–112 Sizing of Steam Traps15–117 Unit Heaters15–124 Checklist for Heating System Servicing

16. NOISE AND VIBRATION CONTROL

16–1 Noise and Vibration16–1 Definitions and Terminology16–2 Noise Criteria16–2 Speech Interference Criteria16–2 Sound Levels of Sources16–7 Ratings and Standards16–7 Airborne Sound Transmission16–7 Vibration Isolation16–9 Isolation Mount Selection16–13 Airborne Noise Through Ducts16–13 Regenerated Noise16–13 Other Mechanical Noise Sources16–14 Calculation of Sound Levels from HVAC Systems16–14 Description of Decibels16–14 Addition of Decibels16–15 The Sabin16–17 Determination of Sound Pressure Level16–20 Noise in Ducted Systems16–23 Fan Noise Generation16–23 Estimating Fan Noise16–24 Distribution of Sound Power at Branch Takeoffs16–24 Attenuation of Untreated Duct16–24 Duct Lining Attenuation16–25 Sound Attenuation of Plenums16–26 Duct Lining and Elbows16–27 Open End Reflection Loss16–27 Air Flow Noise16–31 Flow Noise Generation of Silencers16–31 Sound Transmission Through Duct Walls16–32 Calculation of Sound Levels in Ducted Systems16–36 Control of Cooling Tower Noise16–36 Fan Noise16–37 Water Noise16–37 Drive Components16–37 External Noise Sources16–38 Configuration Factors16–39 Location16–39 Reducing Sound Generated16–39 Half-Speed Operation16–39 Oversizing of the Tower16–39 Changing Leaving Conditions16–40 Sound Absorbers16–40 Obtaining Desired Sound Levels16–40 Acoustical Problems in High Velocity Air Distribution16–40 System Noise 16–42 Air Handling Apparatus Rooms16–42 Selection of Fan Isolation Bases16–42 Apparatus Casings16–42 Dampers and Air Valves16–43 Flexible Connectors16–43 Air Distributing Systems16–43 Duct Velocities16–43 Choice of Duct Design Method16–43 Ductwork Adjacent to Apparatus Room16–44 Duct Connections to Apparatus Casings16–44 Type Duct Construction16–44 Fittings for High Velocity Ductwork

(Continued)16. NOISE AND VIBRATION CONTROL

16–45 Take-off Fittings16–45 Dual Duct Area Ratio16–46 Dampers as a Noise Generating Source16–46 Sound Barrier for High Velocity Ductwork16–46 Sound Traps16–46 Cross Over of Horizontal Dual Duct Mains16–47 Testing of High Pressure Ductwork16–47 Terminal Devices16–48 Radiation Protection at Wall Openings for Duct or Pipe16–49 Medical Installations

17. MOTORS AND STARTERS

17–1 NEMA Motor Classifications17–1 Locked Rotor Torque17–2 Classification of Single-Phase, Induction Motors by Design

Letter17–2 Torque, Speed, and Horsepower Ratings for Single-Phase

Induction Motors17–3 Classification by Environmental Protection and Method of

Cooling17–3 Standard Voltages and Frequencies for Motors17–6 The National Electrical Code17–6 Grounding17–8 Motor and Load Dynamics, and Motor Heating17–8 Torque Speed Relationships17–9 Torque, Inertia, and Acceleration Time17–10 Dynamics of the Motor and the Load17–11 Motor Heating and Motor Life17–12 Rotor Heating During Starting17–12 Single Phase Motors17–12 Types of Motors17–15 Repulsion-Induction17–15 Large Single-Phase Motors17–16 Application17–17 Loading17–18 Motor Protection17–18 Motor Selection17–18 Analysis of Application17–19 Polyphase Motors17–19 Enclosure17–20 Bearings17–20 Quietness17–20 Polyphase, Squirrel Cage Induction Motors17–21 Speed Control17–21 Two-Speed Polyphase, Squirrel Cage Induction Motors17–21 Two Speed Motors Come in Two Types17–23 Wound-Rotor Polyphase Induction Motors17–24 Variable Speed17–24 Synchronous Motors17–25 Hermetic Type Motor Compressors17–25 Hermetic Compressors to 5 hp17–29 Starters17–29 Motor Controllers17–29 Overcurrent Protection17–30 Overload Protection17–31 Starters for Large AC Motors17–33 Winding and Reduced-voltage Starting17–33 Electric Utility Limitations17–33 Minimizing Mechanical Shocks17–33 Application17–36 Types of Starters17–36 Open Circuit Transition17–37 Advantages and Disadvantages17–39 Useful Formulas17–39 Electric Motor Maintenance

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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18. DESIGN PROCEDURE, ABBREVIATIONS, SYMBOLS

18–1 Design Procedure18–1 Contract and Mechanical Drawings18–1 HVAC Drawings18–1 Floor Plans18–5 Valve Symbols18–6 Piping Symbols18–7 Pipe Fittings Symbols18–8 Abbreviations for Scientific and Engineering Terms18–9 Lists of Abbreviations and Symbols

19. CLIMATIC DESIGN INFORMATION

19–1 Climatic Design Conditions19–1 Applicability and Characteristics of the Design Conditions19–27 Dry Bulb and Wet Bulb Temperature for US Locations

20. UNITS AND CONVERSIONS

20–1 U.S. Customary Unit System20–1 Linear Measures20–1 Surveyor's Measure20–1 Nautical Measure20–1 Square Measure20–1 Cubic Measure20–1 Shipping Measure20–2 Dry Measure20–2 Liquid Measure20–2 Old Liquid Measure20–2 Apothecaries' Fluid Measure20–2 Avoirdupois or Commercial Weight20–2 Troy Weight, Used for Weighing Gold and Silver20–2 Apothecaries' Weight20–2 Measures of Pressure20–3 Miscellaneous

(Continued)20. UNITS AND CONVERSIONS

20–4 U.S. System And Metric System Conversion20–4 Length and Area20–4 Mass and Density20–5 Volume and Flow20–6 Force, Energy, Work, Torque and Power Conversion20–7 Velocity and Acceleration20–8 Metric Systems Of Measurement20–8 Measures of Length20–8 Square Measure20–8 Surveyors Square Measure20–8 Cubic Measure20–8 Dry and Liquid Measure20–8 Measures of Weight20–10 Binary Multiples20–10 Terminology of Sheet Metal

21. INDEX

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 9: HVAC Design&Implementation

PREFACE ix

This Handbook provides comprehensive technical information in a modular form to heating, venti-lating, and air conditioning (HVAC) designers and practitioners, namely engineers, architects, con-tractors, and plant engineers. It is also a handy reference for students mastering the intricacies of the HVAC rudiments. Each chapter is self-contained to the extent possible and emphasis is placed on graphical and tabular presentations of data that are useful for easy understanding of fundamentals and solving problems of design, installation, and operation.

This Handbook draws upon the material presented in the Handbook of Air Conditioning, Heating,and Ventilating, Third Edition, Industrial Press, which forms the basis of the presentation. New top-ics and chapters have been introduced and previous information updated or rewritten. Examplesusing software solution tools have been added alongside traditional solutions using formulae fromthe handbook. The organization, however, remains, in the literal sense, a handbook.

We gratefully acknowledge the contributors and editors of the aforementioned Handbook of AirConditioning, Heating, and Ventilating, whose knowledge is embedded throughout the presentbook. We did not have the opportunity to meet any of them, but their written legacy has left an indel-ible imprint on the present work.

An important source of information is the ASHRAE (American Society of Heating, Refrigerating,and Air-Conditioning Engineers) repertoire of publications. ASHRAE serves as the authoritative,and occasionally the sole, source of up-to-date HVAC related data and analysis. We acknowledgetheir permission to use material from various publications, especially the latest ASHRAE Handbookseries.

ASHRAE Publications1791 Tullie Circle, NEAtlanta, GA 30329Web Site: www.ashrae.org

We also acknowledge three corporations for supplying us with material for inclusion in the Hand-book. We profusely thank Mr. Michael White of Bell & Gossett (an ITT Division), Mr. Kent Silveriaand Mr. Thomas Gorman of Trane Corporation, and Mr. Steven Boediarto of Preferred Utilities, forfacilitating the acquisition of these materials.

The Bell & Gossett corporation has graciously provided the ESP-PLUS software package toaccompany the Handbook. This software, a $100 value, permits users to select components based ondesign or operating conditions.

Bell & Gossett (ITT Fluid Handling)8200 N. Austin AveMorton Grove, IL 60053 Web Site: www.bellgossett.com

The Trane corporation has generously allowed us to include their Trace Load 700 load calculationlimited capability demonstration version software with the Handbook.

Trane C.D.S. Department3600 Pammel Creek RoadLa Crosse, WI 54601Web Site: www.trane.com

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

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PREFACEx

We are also grateful to the Preferred Utilities corporation for making available their publication onthe topic of combustion analysis, and consenting to let us base our combustion chapter on it.

Preferred Utilities Mfg. Corp31-35 South StreetDanbury, CT 06810Web Site: www.preferred-mfg.com

We acknowledge the input of our good friend, colleague, and HVAC critic, Mr. Naji Raad, whoseexperience in the profession provided a critical review of the manuscript. We thank our editors atIndustrial Press, Mr. Christopher McCauley and Mr. Riccardo Heald, for their editorial input andsuggestions, for reading the manuscript as it developed, and keeping the project on track; and JanetRomano for her cover design and production assistance. We acknowledge the effort of the many stu-dents at Polytechnic University who helped in researching for material, proofreading the manu-script, checking examples, and drawing figures. Those who deserve special recognition are Mr.Saurabh Shah and Mr. Christopher Bodenmiller for the graphics, Mr. Nayan Patel, Mr. Pranav Patel,and Mr. Prabodh Panindre for research, calculations, and proofing. Finally, we thank KathleenMcKenzie, freelance book editor, for her considerable contribution to this Handbook’s style, formatand readability.

Every effort has been made to prevent errors, but in a work of this scope it is inevitable that somemay creep in. We request your forgiveness and will be grateful if you call any such errors to ourattention by emailing them to [email protected].

Ali Vedavarz, Sunil Kumar, Muhammed Iqbal Hussain

New York CityDecember 2006

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ABOUT THE AUTHORS xi

Ali Vedavarz received his master of science degree in mechanical engineering from the University of Bridgeport in Connecticut and Ph.D. in mechanical engineering from Polytechnic University in Brooklyn, New York. Dr. Vedavarz is a member of ASME and ASHRAE and has published techni-cal papers in ASME journals. Dr. Vedavarz is a licensed Professional Engineer in the State of New York and is currently the Deputy Director of Engineering (for Design) in the Office of Capital Projects at New York City Housing Authority. He is also an adjunct Industry Professor at Polytech-nic University, Brooklyn, New York, where he teaches courses in HVAC design and energy sys-tems.

Sunil Kumar received his bachelor’s degree in mechanical engineering from the Indian Institute of Technology, Kharagpur, India, master’s degrees in mechanical engineering and mathematics from the State University of New York at Buffalo, and a doctoral degree in mechanical engineering from the University of California at Berkeley. He is presently a Professor of Mechanical Engineering and the Dean of Graduate School and Associate Provost at Polytechnic University in Brooklyn, New York. Dr. Kumar has authored over 100 journal and conference papers in the area of thermal-fluid sciences and has extensive consulting and research experience in this subject area.

Muhammed Hussain received his bachelor’s degree from Bangladesh University of Engineering and Technology, Dhaka, Bangladesh, and master’s degree in mechanical engineering from Poly-technic University in Brooklyn, New York. He is a licensed Professional Engineer in the State of New York. Mr. Hussain is presently working as a mechanical design engineer in the Department of Citywide Administrative Services in New York City. Mr. Hussain is also a contributor to, and asso-ciate editor of, Machinery’s Handbook.

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PSYCHROMETRY

2–1

PSYCHROMETRY

Psychrometrics.—Psychrometrics is the study of themeasurement of the moisture content of atmospheric air(moist air). Atmospheric air, or moist air is a mixture ofmany gases and pollutants plus water vapor. The watervapor (moisture) in atmospheric air exists in a super-heated state at a very low pressure, usually less than 1psia. One can also define atmospheric air as a mixture ofdry air and water vapor (moisture). In 1949, a standardcomposition of dry air was defined by the InternationalJoint Committee on Psychrometric Data as shown inTable 2-1.

Table 2-1. Composition of Dry Air

In HVAC study, psychrometry is commonly taken tomean the study of atmospheric moisture and its effect onbuildings and building systems.

Ideal Gas Approximation.—Atmospheric air pres-sure of 14.7 psi obeys the ideal gas law with sufficientaccuracy for most engineering applications. Errors in cal-culating the fundamental psychrometric parameters, suchas enthalpy, specific volume, and humidity ratio of satu-rated air at 14.7 psi are less than 0.7% for a temperaturerange of 60°F to 120°F when ideal gas relationships areused. Accordingly, we will assume that atmospheric airbehaves as ideal gases with constant specific heat. Table2-2 gives the properties of some ideal gases.

Table 2-2. Properties of Gases

Fundamental Parameters.—Atmospheric pressure ormoist air pressure: Dalton’s law for a mixture of idealgases states that the mixture pressure is equal to the sumof the partial pressures of the constituents:

(1)

For atmospheric or moist air

(2)

Equation (2) can be written as

(3)

where Pa =partial pressure of dry air (mixture of N2, O2,CO2, Ar); and

Pv =partial pressure of water vapor

Equation of State.—The ideal gas for dry air andwater vapor is as follows:

1. For dry air:

(4)

2. For water vapor:

(5)

where Pa =partial pressure of dry air;Pv =partial pressure of water vapor;V =total volume of mixture;v =specific volume;

na =number of moles of dry air;nv =number of moles of water vapor;R =universal gas constant;1545 .32 f t - lb f / lb -mol -°R, or 8314 .41J/kg-mol-°K;

T =absolute temperatureThe mixture also obeys the perfect gas equations:

(6)

where P =Pa + Pv is the total pressure of mixture; and

n =na + nv is the total number of moles in the mix-ture.

To compare values for moist air assuming ideal gasbehavior with actual table values, consider a saturatedmixture of air and water vapor at 75°F. Table 2-3 gives thesaturation pressure Ps of water as 0.43 lbf/ft2. For satu-rated air this is the partial pressure (Pv) of the vapor. Themass density is 1/v = 1/739.42 or 0.001352 lbm/ft3. ByEquation (5) we get

Constituent Molecular Mass Volume Fraction

Oxygen 32.000 0.2095Nitrogen 28.016 0.7809Argon 39.944 0.0093Carbon dioxide 44.010 0.0003

Gas

Sym

bol

Rel

ativ

eM

olec

ular

Mas

s R Cp Cv K

ft -

lbf /

lbm

-R

Btu

/lbm

- R

kJ/k

g-°K

Btu

/lbm

-R

kJ/k

g-K

Air … 28.97 53.34 0.240 1.00 0.171 0.716 1.400Argon Ar 39.94 38.66 0.125 0.523 0.075 0.316 1.667Carbon dioxide

CO2 44.01 35.10 0.203 0.85 0.158 0.661 1.285

Carbon monoxide CO 28.01 55.16 0.249 1.04 0.178 0.715 1.399

Helium He 4.003 386.0 1.250 5.23 0.753 3.153 1.667Hydrogen H2 2.016 766.4 3.430 14.36 2.44 10.22 1.404

Methane CH4 16.04 96.35 0.532 2.23 0.403 1.690 1.320

Nitrogen N2 28.016 55.15 0.248 1.04 0.177 0.741 1.400

Oxygen O2 32.000 48.28 0.219 0.917 0.157 0.657 1.395

Steam H2O 18.016 85.76 0.445 1.863 0.335 1.402 1.329

P P1 P2 P3+ +=

P PN2PO2

PCO2P Ar Pv+ + + +=

P Pa Pv+=

PaV naRT maRaT= =

or Pa ρaRaT=

or Paνa RaT=

PvV nvRT mvRvT= =

or Pv ρvRvT=

or Pvνv RvT=

PV nRT= or

Pa Pv+( )V na nv+( )RT=

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PSYCHROMETRY2–2

This result is accurate within about 0.2 percent. For non-saturated conditions water vapor is superheated and theagreement is generally better.

Humidity Ratio W.— The humidity ratio W is the ratioof the mass of the water vapor mv to the mass of the dryair ma in the mixture.

(7)

Relative Humidity φ.— The relative humidity is theratio of the mole fraction of the water vapor xv in a mixtureto the mole fraction xs of the water vapor in a saturatedmixture at the same temperature and pressure:

(8)

For a mixture of ideal gases, the mole fraction is equal tothe partial pressure ratio of each constituent:

(9)

since the temperature of the dry air and the water vaporare assumed to be the same in the mixture. SubstitutingEquation (9) in Equation (8) we find

(10)

where Pv =partial pressure of water vapor at temperatureT ; and

Ps =saturation pressure of water vapor at tempera-ture T and pressure P (Values of Ps may beobtained from Table 2-3).

Using the ideal gas law we can derive a relation betweenthe relative humidity φ and the humidity ratio W:

(11)

(12)

For the air-water vapor mixture, Equation (12) reduces to

(13)

Combining Equation (10) and Equation (13) gives

(14)

Degree of Saturation.—The degree of saturation µ isthe ratio of the humidity ratio W to the humidity ratio Ws

of a saturated mixture at the same temperature and pres-sure:

(15)

Wet Bulb Temperature (Tw).—Fig. 2-1 is a schematicdrawing of a device that measures wet and dry-bulb tem-peratures. The various instruments used to take thesemeasurements are called psychrometers.

When unsaturated air is passed over a wetted thermom-eter bulb, water evaporates from the wetted surface andlatent heat absorbed by the vaporizing water causes thetemperature of the wetted surface and the enclosed ther-mometer bulb to fall. As soon as the wetted surface tem-perature drops below that of the surrounding atmosphere,heat begins to flow from the warmer air to the cooler sur-face, and the quantity of heat transferred in this mannerincreases with an increasing drop in temperature. On theother hand, as the surface temperature drops, the vaporpressure of the water becomes lower, and, hence, the rateof evaporation decreases. Eventually, a temperature isreached where the rate at which heat is transferred fromthe air to the wetted surface by convection and conductionis equal to the rate at which the wetted surface loses heatin the form of latent heat of vaporization. Thus, no furtherdrop in temperature can occur. This temperature is knownas the wet-bulb temperature (Tw).

1ν--- ρ

Pv

RvT--------- 0.43 144×

85.78 460 75+( )×----------------------------------------------= = =

0.001349 lbm /ft3

=

Wmv

ma------=

Φxv

xs-----

T P,=

xv

Pv

P------= and xs

Ps

P-----=

ΦPv P⁄Ps P⁄-------------

Pv

Ps------

T P,= =

Wmv

ma------=

mv

PvV

RvT----------= and ma

PaV

RaT----------=

WPvRa

PaRv------------=

W18.015Pv

28.965Pa----------------------- 0.6219

Pv

Pa------= =

0.6219Pv

P Pv–----------------------=

ΦWPa

0.6219Ps----------------------=

µ WWs-------

T P,=

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PSYCHROMETRY 2–3

Fig 2-1. Psychrometry apparatus for measuring wet and dry- bulb temperatures

As moisture evaporates from the wetted bulb, the airsurrounding the bulb becomes more humid. Therefore, inorder to measure the wet-bulb temperature of the air in agiven space, a continuous sample of the air must passaround the bulb. The purpose of the fan in Fig. 2-1 is tocause the air to be drawn across the wetted bulb. Conven-tional air velocities used are between 500 and 1000 fpmfor normal size thermometer bulbs. Soft, fine-meshedcotton tubing is recommended for the wick; it shouldcover the bulb plus about an inch of the thermometerstem. The wick should be watched and replaced before itbecomes dirty or crusty. Distilled water is recommendedto give greater accuracy for a longer period of time.

Fig. 2-2 shows a device called a sling psychrometer. Itis commonly used especially for checking conditions on ajob. The instrument is rotated by hand to obtain the airmovement across the bulbs. The instrument is rotateduntil no further change is indicated on the wet bulb. Thereading taken at that time is the air wet-bulb temperature.

Thermodynamic wet-bulb temperature (T*), some-times called adiabatic saturation temperature, is dis-cussed later.

Partial Pressure of Water Vapor (Pv).—S e v e r a lequations for calculating this partial pressure have beenproposed and used. Carrier’s equation, first presented in1911, has been frequently used with a high degree ofaccuracy. The equation makes use of the easily obtainablewet and dry-bulb temperatures, and its present form is

(16)

where Pw =partial pressure of water vapor saturated atwet-bulb temperature Tw;

P =barometric pressure; and

T, Tw = dry and wet-bulb temperatures, respectively, in°F

Pv, P, and Pw must have consistent units, either in Hg orpsia.

At temperatures below 32°F, Equation (16) appliesonly to temperatures of air and water vapor over super-cooled water. For partial pressures of water vapor overice, the denominator becomes 3160 − 0.09Tw, and Pwmust be the partial pressure of water vapor over ice at Tw,the temperature of an iced wet bulb.

Example 1:A sample of moist air has a dry-bulb temper-ature of 80°F and a wet-bulb temperature of 70°F. Thebarometric pressure is 29.90 in. Hg. Determine the partialpressure of the water vapor and of the dry air in the sampleof moist air.

Solution: From Table 2-3 at 70°F wet-bulb tempera-ture, find Pw = 0.3632 psia. The barometric pressure of29.90 in. Hg is converted by (29.90) (0.491) = 14.681psia. By Equation (16)

Since P = Pa+ Pv

Fig 2-2. Sling psychrometer device for conveniently measuring wet and dry bulb temperatures

Pv Pw

P Pw–( ) T Tw–( )2831 1.43Tw–

------------------------------------------–=

Pv Pw

P Pw–( ) T Tw–( )2831 1.43Tw–

------------------------------------------–=

0.3632 14.681 0.3632–( ) 80 70–( )2831 1.43( ) 70( )–

-------------------------------------------------------------------–=

0.3107 psia=

Pa P Pv–=

14.681 0.3107–=

14.37 psia=

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PSYCHROMETRY2–4

Dew Point Temperature (Td).—During the variousseasons of the year, especially during the summermonths, in localities where the water supply is cool, it iscommon to see the outside surface of bare cold waterpipes covered with moisture. Another common sight isthat of a glass of ice water with its outside surface coveredwith a film of moisture. The term often used to describethe appearance of moisture on cold surfaces is sweating,as though the moisture came through the walls of the pipeor the glass.

What is actually happening is that the outside of thepipe or the glass is at or below the saturation temperaturecorresponding to the partial pressure of the water vapor inthe surrounding air. This saturation temperature is knownas the dew-point (Td) temperature, the temperature atwhich condensation first starts to appear on the cold sur-face as the moist air is cooled at constant pressure.

Example 1, we calculated the partial pressure of thewater vapor in the air to be 0.3107 psia. Referring to Table2-3, we find that the saturation temperature correspond-ing to a pressure of 0.3107 psia is 65.5°F by interpolation.Therefore, 65.5°F is the dew-point temperature of the airsample. If any surface located in this air sample were atthat temperature, moisture would start to condense on thesurface.

Air itself does not condense nor does it have anythingto do with the cooling and condensation of the watervapor. Actually, the same cooling and condensation of thewater vapor would take place if no air were present andthe entire process were carried out in a closed vessel undervacuum. Since this definition of the dew point tempera-ture is in common use, however, we will use it in our dis-cussion.

At the dew-point temperature and below, the air is saidto be saturated because the air is mixed with the maximumpossible weight of water vapor. If the mixture of air andwater vapor is cooled at constant pressure, but remainsabove the dew-point temperature, there will be no con-densation. However, as the mixture of air and water vaporis cooled, the volume of each component will contract inthe same proportion because both are cooled through thesame temperature range. In other words, if a mixture con-sisting of 1 pound of dry air and 0.15 pound of water vaporis cooled, the resulting smaller volume will still contain 1pound of dry air and 0.15 pound of water vapor as bothgases will contract in the same proportion. Changes in thetemperature of an air-water vapor mixture do not affectthe amount of water vapor mixed with each pound of airas long as the mixture is not cooled down to the dew-pointtemperature. Under these conditions, the mass of watervapor per pound of dry air will remain the same regardlessof the temperature changes. An air-water vapor mixture ata dry-bulb temperature higher than its dew-point temper-ature is said to be unsaturated and the water vapor in themixture is superheated.

At a given total pressure, the dew-point of a mixture isfixed by the humidity ratio W or by the partial pressure ofthe water vapor. Thus Td, W, and Pv are not independentproperties.

Saturation.—The term "saturation" denotes the maxi-mum amount of water vapor that can exist in one cubicfoot of space at a given temperature and is essentiallyindependent of the mass and pressure of the air that maysimultaneously exist in the same space. Frequently, wespeak of "saturated air". However, it must be rememberedthat the air is not saturated; it is the contained water vaporthat may be saturated at the air temperature.

Enthalpy.—The enthalpy of a mixture of ideal gases isequal to the sum of the enthalpies of each component:

(17)

Atmospheric air and water vapor mixture is usually ref-erenced to the mass of dry air. This is because the amountof water vapor may vary during some processes but theamount of dry air typically remains constant. Each term inEquation (17) has units of energy per unit mass of dry air.With the assumption of ideal gas behavior, the enthalpy isa function of temperature only. If zero Fahrenheit or Cel-sius is selected as the reference state where the enthalpy ofdry air is zero, and if the specific heats Cpa and Cpv areassumed to be constant, simple relations result:

(18)

where hg =enthalpy of saturated vapor at that tempera-ture, at 0°F is 1061.5 Btu/lbm and 2501.2kJ/kg at 0°C

Cpa, Cpv = specific heat of air and vapor, respectively.Using Equation (17) and (18) with Cpa and Cpv taken as

0.240 and 0.444 Btu/lbm-°F, respectively, we have

(19)

(20)

where Cpa, Cpv = 1.0 and 1.86 kJ/(kg°C), respectively.Example 2:What is the enthalpy of saturated air at 70°F

at standard atmospheric pressure?Solution: As per Equation (13)

h ha Whs+=

ha CpaT=

hs hg CpvT+=

h 0.24T W 1061.2 0.444T+( )+( ) Btu/lbma=

h 1.0T W 2501.3 1.86T+( )+( ) kJ/kg=

W 0.6219Ps

Pa------ 0.6219

Ps

P Ps–---------------= =

0.62190.3633

14.696 0.3633–---------------------------------------⎝ ⎠⎛ ⎞=

0.62190.3633

14.3327-------------------×=

0.015764=

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PSYCHROMETRY 2–5

As per Equation (19)

Thermodynamic Wet-bulb Temperature (T*).—Fig. 2-3 represents an idealized, fully insulated flow

device where unsaturated moist air enters at dry-bulbtemperature T1 enthalpy h1, and humidity ratio W1. When

this air is brought into contact with the water at a lowertemperature, the air is both cooled and humidified. If thesystem is fully insulated so that no heat is transferred intoor out of the system, the process is adiabatic and if thewater is at a constant temperature, the latent heat of evap-oration can come only from the sensible heat given up bythe air in cooling. The quantity of water present isassumed to be large (large surface area and quantity) com-pared to the amount evaporated into the air. We assumethat there is no temperature gradient in the body of water.

Fig 2-3. Adiabatic saturation of air

If the temperature reached by the air as it leaves thedevice where it is saturated is identical to the temperatureof the water, this temperature is called the adiabatic satu-ration temperature or, more commonly, the thermody-namic wet-bulb temperature (T*).

Thus, in Fig. 2-3, the saturated air leaving the devicewill have properties T2*, h2*, and W2*. Liquid water mustbe supplied to the device having an enthalpy hf2 at T2* forthe process to be steady-flow. Assuming steady-flowconditions exist, the energy equation for the process is

(21)

The asterisk is used to denote properties at the thermo-dynamic wet-bulb temperature. The temperature corre-sponding to h2 for the given values of h1 and W1 is thedefined thermodynamic wet-bulb temperature.

Equation (21) is exact since it defines the thermody-namic wet-bulb temperature T*. Substituting the approxi-mate ideal gas relationship for h from Equation (19), thecorresponding expression for h* and the approximaterelationship hf2 at T2* into Equation (21) and then solv-ing for the humidity ratio W1 gives

(22)

where T1 and T* are in °F.

The corresponding equation in SI units is

(23)

where T1 and T* are in °C.

Example 3:In an adiabatic saturator, the entering andleaving air pressure is 14.696 lbf/in2, the entering temper-ature is 70°F, and the leaving temperature is 60°F. Calcu-late the humidity ratio W and the relative humidity Φ?

Solution: After the adiabatic saturator, the relativehumidity is 100% absorbing the water, so Pv2 = Ps2. W2can be calculated by Equation (13)

W1 can be calculated by Equation (22)

By applying Equation (13)

h 0.24T W 1061.2 0.444T+( )+=

0.24 70× 0.015764 1061.2 0.444 70×+( )+( )=

34.01 Btu/lbma=

h1 W2∗ W1–( )hf2

∗+ h2∗=

W1

1093 0.556T∗–( )W2∗ 0.240 T1 T∗–( )–

1093 0.444T1 T∗–+-------------------------------------------------------------------------------------------------=

W1

2501 2.381T∗–( )W2∗ T1 T∗–( )–

2501 1.805T1 4.186T∗–+-----------------------------------------------------------------------------------=

W2 0.6219Pv

Pa------ 0.6219

Pv

P Pv–---------------= =

0.62190.2563

14.696 0.2563–---------------------------------------⎝ ⎠⎛ ⎞=

0.01104 lbv/lba=

W1

1093 0.556T∗–( )W2∗ 0.240 T1 T∗–( )–

1093 0.444T1 T∗–+-------------------------------------------------------------------------------------------------=

1093 0.556 60×–( )0.01104 0.24 70 60–( )–1093 0.444 70× 60–+

------------------------------------------------------------------------------------------------------------=

11.698 2.4–1064.08

------------------------------=

0.008738=

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PSYCHROMETRY2–6

By applying Equation (14)

The process discussed in this section is called the adia-batic saturation process. The usefulness of the foregoingdiscussion lies in the fact that the temperature of the satu-rated air-water-vapor mixture leaving the system is afunction of the temperature, pressure, and relative humid-ity of the entering mixture and the exit pressure. Addition-ally, knowing the entering and exit pressures andtemperatures, we may determine the relative humidityand humidity ratio of the entering mixture, as shown inExample 3.

In principle, there is a difference between the wet-bulbtemperature Tw, and the temperature of adiabatic satura-tion T*. The wet-bulb temperature is a function of bothheat and mass transfer rates, while the adiabatic saturationtemperature is a function of a thermodynamic equilibriumprocess. However, in practice, it has been found that forair-water-vapor mixtures at atmospheric pressures andtemperatures, the wet-bulb and adiabatic saturation tem-peratures are essentially equal numerically.

Thermodynamic Properties of Moist Air.—Table 2-4 shows values of thermodynamic properties, for stan-dard atmospheric pressure 14.696 psia or 29.92 in. Hg.The properties in this table are based on the thermody-namic temperature scale. This ideal scale differs onlyslightly from the practical temperature scales used foractual physical measurements.

Symbols used in Table 2-4 are:

T = Fahrenheit temperature;

Ws = humidity ratio at saturation, the condition atwhich the gaseous phase (moist air) exists inequilibrium with a condensed phase (liquid orsolid) at the given temperature and pressure(standard atmospheric pressure). At given val-

ues of temperature and pressure, the humidityratio W can have any value from zero and Ws.

vas =vs − va, the difference between the volume ofmoist air at saturation per lb of dry air, and thespecific volume of the dry air itself, ft3/lbda, atthe same pressure and temperature.

vs = volume of moist air at saturation per lb of dryair, ft3/lbma.

ha = specific enthalpy of dry air, Btu/lbda. The spe-cific enthalpy of dry air has been assigned thevalue of zero at 0°F and standard atmosphericpressure.

has = hs − ha, the difference between the enthalpy ofmoist air at saturation, per lb of dry air, and thespecific enthalpy of the dry air itself, Btu/lbda, atthe same pressure and temperature.

sa = specific entropy of dry air, Btu/lb-°F (abs). Thespecific entropy of dry air has been assigned thevalue of zero at 0°F and standard atmosphericpressure.

ss = specific entropy of moist air at saturation per lbof dry air, Btu/lbda-°F (abs).

hw =hs= specific enthalpy of condensed water (liquidor solid) in equilibrium with saturated air at aspecified temperature and pressure, Btu/lbwater.Specific enthalpy of liquid water has beenassigned the value of zero at its triple point(32.018°F) and saturation pressure.

Note: hw is greater than the steam table enthalpy ofsaturated pure condensed phase by the amount ofthe enthalpy increase governed by the pressureincrease from saturation pressure to one atmo-sphere, plus influence from the presence of air.

Pv = vapor pressure of water in saturated moist air,psia or in. Hg. Pv differs negligibly from the sat-uration vapor pressure of pure water Ps, at leastfor the conditions shown.

Example 4:What is the relative humidity of moist airthat has a dry-bulb temperature of 70°F and a wet-bulbtemperature of 60°F? The barometric pressure is 29.92 in.Hg.

Solution: Refer to Table 2-4, At 60°F wet-bulb, find hs =26.467 Btu/lbda. At 70°F dry-bulb, find ha =16.818Btu/lbda. Then,

This is the heat of the vapor. Using Table 2-4, the valueof has = 9.649 with corresponding value Pv of 0.4205 in.Hg. At 70°F dry-bulb, Ps= 0.73966 in. Hg. So, by Equa-tion (10)

W1 0.6219Pv

Pa------=

0.008738 0.6219Pv

P Pv–---------------=

0.0087380.6219 Pv×14.696 Pv–----------------------------=

Pv 0.2036=

ΦPv

Ps------ 100×=

0.20360.36328------------------- 100×=

56.04=

has 26.467 16.818– 9.649 Btu/lbda= =

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PSYCHROMETRY 2–7

Example 5:Moist air exists at 70°F dry-bulb and 60°Fdew-point when the barometric pressure is 29.92 in. Hg.What is the relative humidity of the moist air?

Solution: By definition, the 60°F dew-point temperatureis the saturation temperature corresponding to the actualpartial pressure of the water vapor in the air. From Table2-4 at 60°F, find Pv = Ps = 0.521930 in. Hg. At 70°F, findPvs = Ps = 0.739660 in. Hg. The relative humidity is

Example 6:What is the enthalpy of moist air at 80°F dry-bulb temperature and 40% relative humidity? Barometricpressure is 29.92 in. Hg.

Solution: By Equation (19), h = 0.240T + W(1061 +0.444T). From Table 2-4 at 80°F, find Pvs = Ps = 1.033020in. Hg. Relative humidity φ = Pv/Ps; then, Pv = φPvs =0.40(1.033020) = 0.413208 in. Hg. By Equation (13)

Example 7:Moist air exists at 70°F dry-bulb and 60°Fdew-point when the barometric pressure is 29.92 in. Hg.Determine (1) humidity ratio, (2) saturation ratio, (3) rel-ative humidity, (4) enthalpy, and (5) specific volume ofdry air.

Solution: From Table 2-4 at dew-point temperature of60°F, find Pv = Ps = 0.52193 in. Hg. By Equation (13),

From Table 2-4 at T= 70°F, find Ws = 0.0158320lbv/lbda, find Ws. By Equation (15),

From Table 2-4 at 70°F, find Pv = Ps = 0.739660 in. Hg.By Equation (21),

By Equation (21)

By Equation (5), PaVa=RaT, where Pa is the partialpressure of the dry air in the moist air, may be used to findVa. By Equation (3) Pa= P−Pv = 29.92−.52193=29.3981in. Hg.=14.434 psia. By Equation (5)

Graphical Representation of Psychrometric Chart.—To facilitate engineering computations, agraphical representation of the properties of moist air hasbeen developed and is known as a psychrometric chart.Richard Mollier was the first to use such a chart withenthalpy as a coordinate. Modern day charts are some-what different but still retain the enthalpy coordinate.ASHRAE has developed Mollier-type charts Figs. 2-5and 2-6 the necessary range of variables. These chartscontain all the necessary variables for carrying out HVACcomputations. Because the chart is complex in design this

ΦPv

Ps------ 100×=

0.42050.73966------------------- 100×=

56.11=

ΦPv

Ps------ 100×=

0.5219300.739660---------------------- 100×=

70.56 %=

W 0.6219Pv

P Pv–---------------=

0.62190.413208

29.92 0.413208–------------------------------------------⎝ ⎠⎛ ⎞=

0.00871 lbv/lbda=

h 0.24T W 1061 0.444T+( )+=

0.24 80 0.00871 1061 0.444 80×+( )+×=

28.75 Btu/lbda=

W 0.6219Pv

P Pv–---------------=

0.62190.52193

29.92 0.52193–---------------------------------------⎝ ⎠⎛ ⎞=

0.011 lb v/lb da=

µ WWs------- 0.0110

0.0158320------------------------- 0.694795= = =

ΦPv

Pvs-------- 100× 0.52193

0.739660---------------------- 100× 70.56 %= = =

h 0.240T W 1061 0.444T+( )+=

0.240 70 0.0110 1061 0.444 70( )+( )+×=

28.8129 Btu/lbda=

PaVa RaT=

Va

RaT

Pa---------=

53.352 460 70+( )×144 14.434×

-------------------------------------------------=

13.6043 ft3

lb⁄=

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PSYCHROMETRY2–8

section describes how each variable’s curves appear sothe user will see to which curves the examples refer.

Fig. 2-5 is the psychrometric chart for use at and abovesea level. Fig. 2-6 is the psychrometric chart for use at andabove 5000 ft. Dry bulb temperature is plotted along thehorizontal axis. The dry bulb temperature lines arestraight but not exactly parallel and incline slightly to theleft. Humidity ratio is plotted along the vertical axis on theright hand side of the chart. The scale is uniform with hor-izontal lines parallel. The saturation curve slopes upwardfrom left to right.

Dew point temperatures is also horizontal. Dry-bulb,wet-bulb, and dew point temperatures all coincide on thesaturation curve.Relative humidity lines with shapes sim-ilar to the saturation curve appear at regular intervals.

The enthalpy scale is drawn obliquely on the left of thechart. Enthalpy lines inclined downward left to right.Although the wet bulb temperature lines appear to coin-cide with the enthalpy lines, they gradually diverge withrespect to one another (i.e. they are not parallel). Thespacing of the wet bulb lines is not uniform. Finally wenote that specific volume lines also appear inclined fromthe upper left to the lower right, similar to enthalpy andwet bulb temperature lines they are not parallel.Theenthalpy, specific volume, and humidity ratio scales areall based on unit mass of dry air, not unit mass of moist air.

A protractor with two scales appears at the upper left ofCharts 1 and 2 of Figs. 2-5, and 2-6 respectively. Onescale gives the sensible heat ratio and the other the ratio ofenthalpy difference to humidity ratio difference.

Construction of the Psychrometric Chart: The charts ofFigs. 2-5, and 2-6 are slightly different organizations.The ones here should be studied before any other psychro-metric chart is used. To help the reader understand thesecharts, examples follow. But first, simplified versions ofthe chart is shown in Figs. 2-4a to 2-4g.

Fig 2-4a. Lines of constant dry bulb temperature td on the psychrometric chart

The location and positioning of the scales of the vari-ous properties as well as the constant value lines for theseproperties are shown in these simple charts which are notdrawn to the actual scale. When you read the values ordraw lines, always use a sharp drafting-type pencil andstraight edge.

Fig 2-4b. Lines of constant humidity ratio (W)

Fig 2-4c. Lines of constant specific volume v on the psychrometric chart

Fig 2-4d. Lines of constant wet bulb temperature Tw on the psychrometric chart

80Dry bulb temperature

W

Td

T d=

80

W

= 0.010

Hum

idity

rat

io

Td

W

Td

v = 13.5 ft /lb 3

WW

Td

T w

Tw = 70 F

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PSYCHROMETRY 2–9

Fig 2-4e. Lines of constant relative humidity φ on the psychrometric chart

Fig 2-4f. Lines of constant enthalpy h on the psychrometric chart

Fig 2-4g. Lines of constant dew point temperature Tdp on the psychrometric chart

Example 8:The air leaves a cooling coil is at 70°F Td and60°F Tw. What is its humidity ratio φ and specificenthalpy?

Solution: The intersection of the 70°F Td and 60°F Twlines defines the given state. This point on the chart is thereference from which all the other properties are deter-mined.

Humidity Ratio W: Move horizontally to the right andread W = 0.008778 lbmv/ lbma on the vertical scale.

Relative Humidity φ: Interpolate between the 50 and60% percent relative humidity lines and read 56.11%.

Enthalpy h: Follow a line of constant enthalpy upwardto the left and read h = 26.38 Btu/lbma on the oblique scale.

Specific Volume v: Interpolate between the 13.5 and14.0 specific volume lines and read v = 13.65 ft3/lbma.

Dew Point Tdp: Move horizontally to the left from thereference point and read Tdp = 53.7 F on the saturationcurve.

Solution of Example 8

Enthalpy h (alternate method): The nomograph in theupper left hand corner of Fig. 2-4g gives the difference Dbetween the enthalpy of unsaturated moist air and theenthalpy of saturated air at the same wet-bulb tempera-ture. Then h = hs + D. For this example hs = 26.5 Btu/lbma,D = −0.1 Btu/lbma, and h = 26.5− 0.1 = 26.4 Btu/lbma.

Although psychrometric charts are useful in severalaspects of HVAC design, the availability of computerprograms to determine moist air properties has madesome of these steps easier to carry out. These programsmay be easily constructed from the basic equations of thischapter. Computer programs give the additional conve-nience of choice of units and arbitrary (atmospheric) pres-sures.

Saturation Line(O = 100%)

O = 80%

Td

WW

=35 Btu/lb

h

dah

Td

Td

W

Tdp= 70Tdp

W

=70

O = 56.11

Tw = 60

dp = 53.7

h = 26.38 Btu/lb W = 0.008778

Td

T

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PSYCHROMETRY2–22

163 0.3333600 15.699 24.040 39.197 416.175 0.07298 0.71623 131.03 0.2362 10.377600

164 0.3457200 15.724 24.388 39.438 430.533 0.07337 0.73959 132.03 0.2378 10.625000

165 0.3586500 15.749 24.750 39.679 445.544 0.07375 0.76397 133.03 0.2394 10.877100

166 0.3722000 15.774 25.129 39.920 461.271 0.07414 0.78949 134.03 0.2410 11.134300

167 0.3863900 15.800 25.526 40.161 477.739 0.07452 0.81617 135.03 0.2426 11.396500

168 0.4013100 15.825 25.942 40.402 495.032 0.07491 0.84415 136.03 0.2442 11.664100

169 0.4169800 15.850 26.377 40.643 513.197 0.07529 0.87350 137.04 0.2458 11.937000

170 0.4334300 15.875 26.834 40.884 532.256 0.07567 0.90425 138.04 0.2474 12.214900

171 0.4507900 15.901 27.315 41.125 552.356 0.07606 0.93664 139.04 0.2490 12.498800

172 0.4690500 15.926 27.820 41.366 573.504 0.07644 0.97067 140.04 0.2506 12.788000

173 0.4882900 15.951 28.352 41.607 595.767 0.07682 1.00644 141.04 0.2521 13.082300

174 0.5086700 15.976 28.913 41.848 619.337 0.07720 1.04427 142.04 0.2537 13.383100

175 0.5301900 16.002 29.505 42.089 644.229 0.07758 1.08416 143.05 0.2553 13.689400

176 0.5529400 16.027 30.130 42.331 670.528 0.07796 1.12624 144.05 0.2569 14.001000

177 0.5771000 16.052 30.793 42.572 698.448 0.07834 1.17087 145.05 0.2585 14.319100

178 0.6027400 16.078 31.496 42.813 728.073 0.07872 1.21815 146.05 0.2600 14.643000

179 0.6300200 16.103 32.242 43.054 759.579 0.07910 1.26837 147.06 0.2616 14.973100

180 0.6591100 16.128 33.037 43.295 793.166 0.07947 1.32183 148.06 0.2632 15.309700

181 0.6901200 16.153 33.883 43.536 828.962 0.07985 1.37873 149.06 0.2647 15.652200

182 0.7233100 16.178 34.787 43.778 867.265 0.08023 1.43954 150.06 0.2663 16.001400

183 0.7588500 16.204 35.755 44.019 908.278 0.08060 1.50457 151.07 0.2679 16.356900

184 0.7970300 16.229 36.793 44.260 952.321 0.08098 1.57430 152.07 0.2694 16.719000

185 0.8381700 16.254 37.910 44.501 999.763 0.08135 1.64932 153.07 0.2710 17.088000

186 0.8825100 16.280 39.113 44.742 1050.892 0.08172 1.73006 154.08 0.2725 17.463400

187 0.9305700 16.305 40.416 44.984 1106.298 0.08210 1.81744 155.08 0.2741 17.846200

188 0.9827200 16.330 41.828 45.225 1166.399 0.08247 1.91210 156.08 0.2756 18.235700

189 1.0395100 16.355 43.365 45.466 1231.848 0.08284 2.01505 157.09 0.2772 18.632300

190 1.1015400 16.381 45.042 45.707 1303.321 0.08321 2.12733 158.09 0.2787 19.035800

191 1.1696500 16.406 46.882 45.949 1381.783 0.08359 2.25043 159.09 0.2803 19.446800

192 1.2447100 16.431 48.908 46.190 1468.237 0.08396 2.38589 160.10 0.2818 19.865200

193 1.3278800 16.456 51.151 46.431 1564.012 0.08433 2.53576 161.10 0.2834 20.291300

194 1.4202900 16.481 53.642 46.673 1670.431 0.08470 2.70208 162.11 0.2849 20.724400

195 1.5239600 16.507 56.435 46.914 1789.793 0.08506 2.88838 163.11 0.2864 21.166100

196 1.6407000 16.532 59.578 47.155 1924.187 0.08543 3.09787 164.12 0.2880 21.615200

197 1.7729900 16.557 63.137 47.397 2076.466 0.08580 3.33494 165.12 0.2895 22.071400

198 1.9247200 16.583 67.218 47.638 2251.102 0.08617 3.60647 166.13 0.2910 22.536700

199 2.0997500 16.608 71.923 47.879 2452.343 0.08653 3.91929 167.13 0.2926 23.009200

200 2.3045400 16.633 77.426 48.121 2688.205 0.08690 4.28477 168.13 0.2941 23.490600

a Extrapolated to represent metastable equilibrium with under cooled liquid.

Table 2-4. (Continued) Thermodynamic Properties of Moist Air at Standard Pressure

Temp Humidity Ratio Volume Enthalpy Entropy

Condensate Water

Enthalpy Entropy Vapor Press.

T lbw/lbda ft3/lbda Btu/lbda Btu/lbda-°F Btu/lb Btu/lb-°F in. Hg

°F Ws va vs ha hs sa ss hw sw ps

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AIR CONDITIONING PROCESSES

3–1

AIR CONDITIONING PROCESSES

Introduction.—The conservation of mass and energyis used in the study of air conditioning processes. Analy-sis of air conditioning processes is required for maintain-ing proper temperature and humidity in living space suchas residential, commercial, and industrial facilities. Thebasic processes are as follows:

1) simple heating and cooling processes;

2) cooling with dehumidification;

3) heating with humidification;

4) adiabatic mixing of two air streams; and

5) evaporative cooling.

These air conditioning processes are represented inFig. 3-1. Simple diagrams of the psychrometric chart areshown in Figs. 2-5 and 2-6.

Fig 3-1. Fundamental air-conditioning processes

Simple Heating and Cooling (W = constant).—Insome heating applications, air is heated without moisturebeing added. An example of this process is a heat pumpwith heating coil and no humidifier system. In the case ofa simple cooling process, in some chilled water coolingapplications air can be cooled without condensation. Figs.3-2 and 3-4 shows schematics of simple heating process

and a simple cooling process, respectively. The simplepsychrometric diagrams of these processes are shownFigs. 3-3 and 3-5 respectively.

Neglecting the fan work that may be present, the con-servation of mass and energy equations are as follows.

Conservation of mass:

(1)

(2)

(3)

Conservation of energy:

(4)

(5)

(6)

(7)

By substituting Equations (6) and (7) in Equation (5)with assuming ideal gas law and approximating a properacceptable value of W, for HVAC practice Equation (5)can be written in the following convenient form:

(8)

where = heating load, Btu/hr

cfm = air flow rate of dry air, ft3/min

= entering temperature, °F

= leaving temperature, °F

Similarly, in the case of cooling the following conve-nient approximate form is used for HVAC practice:

(9)

where = cooling load, Btu/hr

cfm = air flow rate of dry air, ft3/min

= entering temperature, °F

= leaving temperature, °F

Fig 3-2. Schematic of simple cooling process (sensible cooling)

Process Direction

Simple heating O to C

Simple cooling O to G

Humidification O to A

Dehumidification O to E

Evaporative cooling O to H

Evaporative heating O to D

Heating and humidification O to B

Cooling and dehumidification O to F

A B

D

C

EF

G

H

o

m· a1 m· a2 m· a= =

m· v1 m· v2 m· v= =

W1 W2 constant= =

m· ah1 q·+ m· ah2=

q· m· a h2 h1–( )=

h1 ha1 Whv1+=

h2 ha2 Whv2+=

q· h 1.10 cfm T2 T1–( )××=

q· h

T1

T2

q· c 1.10 cfm T1 T2–( )××=

q· c

T1

T2

1 2

OUT

IN

m

Wh

q

1

1

a

2Whma

2=W1

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AIR CONDITIONING PROCESSES3–2

Fig 3-3. Psychrometric diagram of simple cooling process

Fig 3-4. Schematic of simple heating process

Fig 3-5. Psychrometric diagram of simple heating process

Example 1:Find the required heat to warm 2500 cfm ofair at 60°F at 90% moisture humidity to 120°F withoutaddition of moisture.Solution: The mass flow rate of dry air is

The specific volume of air at 60°F at 90% is 13.2944from the psychrometric chart Fig. 2-5.

From the psychrometric chart Fig. 2-5 h1 = 25.1Btu/lbm and h2 = 39.89 Btu/lbm. By applying Equation (5)

By applying the ASHRAE Equation (8)

Cooling with Dehumidification.—In most of the cool-ing processes, the dew point temperature of the moist airentering the cooling coil is higher than the cooling coilsurface temperature so that the water vapor in the entering

air will be condensed on the cooling coil and then the con-densate will be drained out. Because of this condition, thespecific humidity of the leaving moist air will be lowered.The schematic cooling and dehumidification process isshown in Fig. 3-6. The air conditioning system on psy-chrometric chart representation of this process is shownin Fig. 3-7. The conservation of mass and energy equa-tions for the cooling and dehumidification are as follows:

Conservation of mass:

(10)

(11)

(12)

Conservation of energy:

(13)

(14)

(15)

Fig 3-6. Schematic of cooling with dehumidifying process

Fig 3-7. Psychrometric diagram of cooling with dehumidifying process

Example 2:What is the cooling capacity of a coil if 5000cfm mixed air entering at 80°F and 67°F and leaving at55°F at 90% relative humidity?

Solution: The mass flow rate of dry air is

The specific volume of air at 80°F and 67°F is 13.833from the psychrometric chart (Fig. 2-5).

W1 W2=

12

1 2

OUT

IN

m

Wh

q

1

1

a

2Whma

2=W1

W1 W2=

1 2

m· acfm

ν--------- 2500 60×

13.2944------------------------ 11283 lbm/hr= = =

q· m· a h2 h1–( )=

11283 39.89 25.1–( )=

166876 Btu/hr=

q· 1.10 cfm T2 T1–( )××=

1.10 2500 120 60–( )××=

165000 Btu/hr=

m· a1 m· a2 m· a= =

m· v1 m· v2 m· w+=

m· w m· a W1 W2–( )= where W1 W2>

m· ah1 m· ah2 q· m· whw+ +=

m· ah1 m· ah2 q· m· a W1 W2–( )hw+ +=

q· m· a h1 h2–( ) m· a W1 W2–( )hw–=

IN

OUT1 2

m

Wh1

1

a

q

Condensate drainm w

m

Wh

2

a2

W1

2W

1

x3

m· acfm

ν--------- 5000 60×

13.833------------------------ 21687 lbm/hr = = =

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AIR CONDITIONING PROCESSES 3–3

The enthalpy of air at entering h1= 31.4 Btu/lbm, W1 =0.0112 lbv/lbda, h2 = 22.2 Btu/lbm, W2 = 0.0082 lbv/lbda,and the enthalpy of condensation hw = 23.0 Btu/lbv.Applying the Equation (15)

Heating with Humidification.—In most commercialfacilities such as large office spaces, hospitals, and mod-ern schools where central heating and cooling HVAC sys-tems are used, it is desirable to humidify the suppliedheated air to various room and spaces in order to maintaincomfortable relative humidity, especially in the locationswhere the outdoor relative humidity during winter seasonis very low. In the heating with humidification process,air first is heated by the heating coil or gas furnace andthen is humidified by adding moisture before it is sup-plied to the space.

Fig 3-8. Schematic of heating with humidification process

Fig 3-9. Psychrometric diagram of heating with humidification process

The schematic of this process is shown in Fig. 3-8. Theair conditioning system on psychrometric chart represen-tation of this process is shown in Fig. 3-9.

The conservation of the mass and energy equations areas follows:

Conservation of mass:

(16)

(17)

(18)

Conservation of energy:

(19)

(20)

(21)

Equation (21) can be written in the following usefulform:

(22)

Adiabatic Mixing of Two Air Streams.— Many airconditioning applications require the mixing of two airstreams. This is particularly true for large buildings, andmost process plants, office spaces, and hospitals, in whichthe space return air must be mixed with a certain requiredoutdoor fresh air for proper ventilation before it enters theair conditioning unit. In this process, the heat transfer tothe surrounding space is usually small and can be ignored.The schematic of this process is shown in Fig. 3-10. Thepsychrometric representation of this process is shown inFig. 3-11. The mass and energy conservation equationsfor this process are as follows:

Conservation of mass:

(23)

(24)

(25)

Conservation of energy:

(26)

Combining Equations (23) to (26) gives:

(27)

q· m· a h1 h2–( ) W1 W2–( )hw–( )=

21687 31.4 22.2–( ) 0.0112 0.0082–( ) 23×–( )=

198024 Btu=

16.5 ton=

Heating medium

m ah

hmw

w

21 x

qW11

m ah

W22

1

2

X

W1

2W

m· a1 m· a2 m· a= =

m· v1 m· w+ m· v2=

m· w m· a W2 W1–( )= where W2 W1<( )

m· ah1 q· m· whw+ + m· ah2=

m· ah1 q· m· a W2 W1–( )hw+ + m· ah2=

q· m· a h2 h1–( ) m· a W1 W2–( )hw+=

h2 h1–

W2 W1–--------------------- q·

m· w------- hw+=

m· a1 m· a2+ m· a3=

m· v1 m· v2+ m· v3=

m· a1W1 m· a2W2+ m· a3W3=

m· a1h1 m· a2h2+ m· a3h3=

h2 h3–

h3 h1–-----------------

W2 W3–

W3 W1–---------------------

m· a1

m· a2---------= =

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AIR CONDITIONING PROCESSES3–4

Fig 3-10. Adiabatic mixing of two streams process

Solving Equations (23) to (27) for h3 and W3 gives:

(28)

and

(29)

Fig 3-11. Psychrometric diagram of adiabatic mixing process

Example 3:Find the condition of mixed air in which1500 cfm of outside air 90°F at 30% relative humidity ismixed with 4500 cfm return air of 75°F at 60% relativehumidity.Solution: First we will find out the outside air and return

air properties. We are given these data:

By applying the psychrometry chart (Fig. 2-5)

The condition of the mixed air is

Example 4:Find the heat transfer rate and mass flow rateof a heating and adiabatic humidification process where2000 cfm air enters at 40°F and 40% relative humidity andleaves at 110°F and a relative humidity of 30%.

Solution: First we will find out the outside air and returnair properties. Given

Mass flow rate of dry air

The specific volume of air at 40°F and 40% is 12.62from the psychrometry chart Fig. 2-5.

By applying the psychrometry chart (Fig. 2-5)

1

2

m

wh1

1

a m

wh

a

3

3

3

2whm

2w

h3

m· a1

m· a2---------h1 h2+

1m· a1

m· a2---------+

---------------------------=

W3

m· a1

m· a2---------W1 W2+

1m· a1

m· a2---------+

-------------------------------=

1

23

WW

W1

2

3

cfmoa 1500= cfmra 4500=

Toa 90= Tra 75=

Φoa 30= Φra 60=

νoa 14.04= νra 13.70=

Woa 0.009= Wra 0.0111=

hoa 31.54= hra 30.20=

m· oa1500 60×

14.04------------------------=

6410=

m· ra4500 60×

13.70------------------------=

19708=

m· m m· oa m· ra+ 6410 19708+ 26118= = =

hm

hoa m· oa× hra m· ra×+

m· m------------------------------------------------------=

31.54 6410 30.20 19708×+×26118

-------------------------------------------------------------------------=

30.52 Btu/lbm=

Wm

Woa m· oa× Wra m· ra×+

m· m----------------------------------------------------------=

0.009 6410 0.0111 19708×+×26118

----------------------------------------------------------------------------=

0.0105 lbv lbv⁄=

cfm 2000=

T1 40= T2 110=

Φ1 40%= Φ2 30%=

m1cfm 60×

ν--------------------- 2000 60×

12.62------------------------ 9508 lb m/hr= = =

W1 0.002= W2 0.016=

h1 11.83= h2 44.93=

m· 2 m· a= hw 1135=

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AIR CONDITIONING PROCESSES 3–5

Steam flow rate,

Applying the energy balance equation for heating andhumidifying equation

Psychrometric diagram of Example 4

Evaporative Cooling.—Conventional cooling sys-tems such as rooftop and system air conditioning systemsand heat pump systems operate on a refrigeration cyclethat has high initial and operating and maintenance cost.The high operating cost is associated with the high elec-tricity consumption of the compressor. The conventionalrefrigerant system can be used in any part of the world.However, in hot and dry climates, we can avoid the highcost of cooling by using the evaporative coolers. Theevaporative cooler is based on a simple principle that aswater evaporates, the latent heat of vaporization isabsorbed from the water and the surrounding air. As aresult, both water and the air are cooled during this pro-cess. The schematic process of evaporative cooling isshown in Fig. 3-12. The psychrometric representation ofthis process is shown in Fig. 3-13. During the humidifica-tion process the enthalpy of moist air and the wet-bulbtemperature of the air remain approximately constant.

Conservation of mass:

(30)

(31)

(32)

Conservation of energy:

(33)

Fig 3-12. Evaporative cooling system

Fig 3-13. Psychrometric diagram for evaporative cooling system

Heating and Air Conditioning System Cycles.—Fig.3-14 shows a schematic flow diagram of a simple air con-ditioning cycle. The psychrometric chart representationof a typical cooling and heating systems based on Fig. 3-14 are shown in Figs. 3-15 and 3-16.

Fig 3-14. Air conditioning system

m· 1W1 m· w+ m· 2W2=

m· w m· 1 W2 W1–( )=

9508 0.016 0.002–( )=

133 lbm/hr=

m· 1h1 q·+ m· 2h2 m· whw–=

q· m· 2h2 m· 1h1– m· whw–=

m· 1 h2 h1–( ) mwhw–=

9508 44.93 11.83–( )= 133 1135×–

163760 Btu/hr=

A

B

C

m· a0 m· a1 m· a= =

m· v0 m· w+ m· v1=

m· w m· a W1 W0–( )=

m· ah0 m· ah1=

h0 h1=

or

Twb0 Twb1=

Conditioned 0 1

space

Make-upwater

0

1

2 W

W0

2

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AIR CONDITIONING PROCESSES3–6

Fig 3-15. Psychrometric diagram of heating/humidifying process

Fig 3-16. Air conditioning cooling system

The following examples will provide good practice andan approach to the analysis of HVAC cycles.

Example 5:Determine the sensible and latent heat load,if 5000 cfm conditioned air is supplied to a room at 55°Fand 90% relative humidity. The space is to be maintainedat 75°F at sensible heat factor (SHF) 0.80?

Solution: The total cooling load for the room is

Applying the sensible heat factor equation

where =total heat loss, Btu/hr

=sensible heat loss, Btu/hr

=latent heat loss, Btu/hr

Then latent heat is

Example 6:A room is to be maintained at 75°F and 50%relative humidity. The outside air condition is 95°F and60% relative humidity. The outdoor air requirements forthe occupants is 500 cfm. The total heat gain to the spaceis 60,000 Btu/hr with a 0.80 SHF. Determine the quantityand the state of the air supplied to the space and therequired capacity of cooling and dehumidifying equip-ment.

Solution: Assume that the conditions of air after thecooling coil is 55°F and 90% relative humidity. Nowmake a schematic diagram to locate the points on the psy-chrometric chart.

Applying the energy balance equation around the room

o

m

r s

mix

ing

room

heating

Dry-bulb temperature

Hum

idity

Rat

ioo

m

rs

Dry-Bulb Temperature

Hum

idity

Rat

io

q· t 1.10 cfm T∆××=

1.10 5000 75 55–( )××=

110000 Btu/hr=

SHFq· s

q· s q· l+----------------=

SHFq· s

q· t-----=

q· s q· t SHF×=

110000 0.80×=

88000 Btu/hr=

q· t

q· s

q· l

q· s q· l+ q· t=

q· l q· t q· s–=

110000 88000–=

22000 Btu/hr=

T0 95= Φ0 60=

T2 55= Φ2 90=

T3 75= Φ3 50=

h0 46.4= W0 0.021= v0 14.45=

h2 22.2= W2 0.008= v2 13.13=

h3 28.1= W3 0.009= v3 13.66=

m· 2h2 q·+ m· 2h3=

m· 2q·

h3 h2–( )----------------------=

6000028.1 22.2–( )

-------------------------------=

10170 lb/hr=

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AIR CONDITIONING PROCESSES 3–7

The flow rate of dry air is

The flow rate of outside air is

The return air quantity will be (10170−2076) or 8094lbm/hr. Assume return air condition and room air condi-tion are same.

Now we find the mixed air condition by the mixing ofreturn air and outside air.

Applying the energy balance equation around the cool-ing coil:

Example 7:A room is to be maintained at 75°F and 50%relative humidity. The outside air is 30°F and 50% rela-tive humidity. The outdoor air requirements for the occu-pants is 500 cfm. Sensible and latent heat losses from thespaces are 120,000 Btu/hr and 30,000 Btu/hr. Determinethe quantity of air supplied at 120°F to the space and therequired capacity of heating and humidifying equipment.

Solution: The figure below is the schematic for the prob-lem.

Draw a line at point 3 parallel to SHF= 0.80, whichintersect 120°F at point 2.

Applying the energy balance equation around the room

The flow rate of dry air is

0

132

cfmra m· 2ν310170 13.66×

60---------------------------------- 2315 cfm= = =

m· 4

cfmoa

ν-------------- 500 60×

14.45--------------------- 2076 lbm hr⁄= = =

m· 1 m· 0 m· 4+ 8094 2076+ 10170 lb= = =

h1

h0 m· 0× h4 m· 4×+

m· 1--------------------------------------------=

46.4 2076 28.1 8094×+×10170

----------------------------------------------------------------=

31.84 Btu/lb=

W1

W0 m· 0× W4 m· 4×+

m· 1------------------------------------------------=

0.021 2076 0.009 8094×+×10170

----------------------------------------------------------------------=

0.0115=

m· 1h1 q· c m· 2h2+=

q· c m· 2 h1 h2–( )=

10170 31.84 22.2–( )=

98038 Btu/hr=

8.17 ton=

SHFq· s

q· s q· l+----------------=

120000120000 30000+---------------------------------------=

0.80=

0

1

3

2

x

m· 2h2 m· 2h3 q· t+=

m· 2

q· t

h3 h2–( )----------------------=

15000046.2 28.2–( )

-------------------------------=

8333 lb/hr=

cfmra m· 2ν38333 13.66×

60------------------------------- 1898 cfm= = =

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AIR CONDITIONING PROCESSES3–8

The flow rate of outside air is

The return air quantity will be (8333−2427) or 5906lbm/hr. Assume return air condition and room air condi-tion are the same. Neglecting the return fan effect.

Now we find the mixed air condition by the mixing ofreturn air and outside air.

Applying the energy balance equation around the heat-ing coil:

Applying the mass balance equation around the heatingcoil:

Example 8:An existing building space will be an officespace for 200 people. The space design loads are as fol-lows:

Summer: 300,000 Btu/hr sensible (gain), 75,000Btu/hr latent (gain)

Winter: 600,000 Btu/hr sensible (loss), negligiblelatent

Fan: 4 inch of water pressure drop with 80% efficiency

Find the

A) Summer air flow, cfm

B) Winter air flow, cfm

C) Cooling coil rating, tons

D) Sensible cooling coil rate, Btu/hr

E) Latent cooling coil rate, Btu/hr

F) Heating coil rating, MBH

G) Humidifier rating, gal/hr

Solution:

Summer cooling load:

m· 4

cfmoa

ν-------------- 500 60×

12.36--------------------- 2427 lb/hr= = =

m· 1 m· 0 m· 4+ 5906 2427+ 8333 lb= = =

h1

h0 m· 0× h4 m· 4×+

m· 1--------------------------------------------=

9.07 2427 28.1 5906×+×8333

----------------------------------------------------------------=

22.55 Btu/lb=

W1

W0 m· 0× W4 m· 4×+

m· 1------------------------------------------------=

0.0017 2427 0.009 5906×+×8333

-------------------------------------------------------------------------=

0.0068 lb/lb=

m· 1h1 q· h+ m· 2h2=

q· h m· 2 h2 h1–( )=

8330 46.2 22.55–( )=

197005 Btu/hr=

m· 1W1 m· w+ m· 2W2=

m· w m· 1 W2 W1–( )=

8330 0.012 0.0068–( )=

43.3 lb/hr=

Location

Dry Bulb Tempera-ture, Tdb

Wet Bulb Tempera-ture, Twb

Relative Humidity Enthalpy

Humidity Ratio

Summer

OA 95 74 37.5 37.50 0.0133

RA 75 55.67 29.31 0.0103

SA 55 100 23.30 0.0092

MA

Winter

OA 7 100 2.883 0.0011

RA 72 50 26.42 0.0084

SA 135 7.65 41.77 0.0084

MA

FANCOOLINGCOIL(SUMMER)

HEATINGCOIL WITHHUMIDIFIER

SPACE

winter : 135 deg. Fsummer : 55 deg. F

SA

RA

RAEA

OAMA

q· s 1.10 cfm Tra Tsa–( )××=

cfmq· s

1.10 Tra Tsa–( )×--------------------------------------------=

3000001.10 75 55–( )×---------------------------------------=

13636=

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AIR CONDITIONING PROCESSES 3–9

Mass of air:

Mass of water:

Humidity ratio of room air:

At humidity ratio 0.10338 and 75°F, hra = 29.31Btu/hr.

Outside air requirement as per ASHRAE Code is 20cfm/person. So the total outside air requirement = 200 ×20 = 4000 cfm.

Mass of air

The exhaust air will be 4000 cfm. So the return air willbe 13636− 4000 = 9636 cfm and in mass 59894 −16830 =43064 lb/h.

Mixed air condition:

Fan power:

Cooling coil capacity:

Winter load:

Mass of air:

Outside air requirement as per ASHRAE Code is 20cfm/person. So the total outside air requirement = 200 ×20 = 4000 cfm.

Mass of air:

m· acfm 60×

ν---------------------=

13636 60×13.66

---------------------------=

59894 lb/h=

m· l

q· l

1100------------=

750001100

---------------=

68.18 lb/h=

Wra Wsa

m· l

m· a------+=

0.0092 68.1859894---------------+=

0.010338=

m· oa4000 60×

ν------------------------=

4000 60×14.26

------------------------=

16830 lb/h=

hm

m· oa hoa× m· ra hra×+

m· oa m· ra+------------------------------------------------------=

16830 37.5× 43064 29.31×+59894

-------------------------------------------------------------------------=

31.61 Btu/lb=

Wm

m· oa Woa× m· ra Wra×+

m· oa m· ra+----------------------------------------------------------=

16830 0.0133× 43064 0.0103×+59894

----------------------------------------------------------------------------------=

0.0111=

Pcfm pt∆×6350 ηf×-----------------------=

13636 4×6350 0.80×----------------------------=

10.737 hp=

8 kw=

q· coil m· a hm hs– Wm Ws–( )hc–( )=

59894 31.61 23.30– 0.0111 0.0092–( )32.0–( )=

494078 Btu/hr=

41.2Ton=

q· s 1.10 cfm Tra Tsa–( )××=

cfmq· s

1.10 Tra Tsa–( )×--------------------------------------------=

6000001.10 135 72–( )×------------------------------------------=

8568=

m· acfm 60×

ν---------------------=

8568 60×13.56

------------------------=

37911 lb/h=

m· oa4000 60×

ν------------------------=

4000 60×11.77

------------------------=

20390 lb/h=

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Page 31: HVAC Design&Implementation

AIR CONDITIONING PROCESSES3–20

Cooling coil capacity (condensate water at 64°F hc =32.0 Btu/h)

Secondary cooling coil for room-A:

Secondary heating coil for room-A:

Secondary cooling coil for room-B:

Secondary heating coil for room-B:

qcoil m· a hf hs– Wf Ws–( )hc–( )=

215662

--------------- 32.78 23.30– 0.011 0.0092–( )32.0–( )=

101602 Btu/hr=

8.46 ton=

q· c111982

2--------------- 26.42 23.30–( )=

18692 Btu/hr=

q· h1 48000 1.102728

2------------⎝ ⎠⎛ ⎞ 75 55–( )+=

78008 Btu/hr=

q· c29584

2------------ 26.42 23.30–( )=

14952 Btu/hr=

q· h2 36000 1.102182

2------------⎝ ⎠⎛ ⎞ 75 55–( )+=

60002 Btu/hr=

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HYDRONIC HEATING AND COOLING SYSTEM

10–1

HYDRONIC HEATING AND COOLING SYSTEM

Basic System

Hot water heating systems (hydronic heating) are con-veniently being used in many types of buildings and facil-ities, especially for single family houses and low risemultiple dwelling buildings. Also many HVAC systemsare using hot water systems as the primary source forheating the distribution air. The chilled water cooling sys-tems (hydronic cooling) are popular in certain large resi-dential buildings, hospitals, and office buildings. Themain components of a hydronic system are:1) boiler (heating source) or chiller (cooling source)

2) circulating pump(s)

3) expansion tank(s)

4) Heating load (radiators, convectors, HVAC units,etc.) or Cooling load (terminal units, fan-coil units,HVAC units, etc.)

5) air separator

6) connected piping system

7) make-up and fill water system

8) control system.

The hydronic system can be classified by combinationof:

1) operating temperature; 2) pumping and pipingarrangement; and 3) operating pressure.

Depending on the particular application and the type ofthe facility, the proper selection of the boiler(s) orchiller(s), pumping systems, piping arrangement, andcontrol system are essential for an effective and economi-cal hydronic system. Schematic piping drawings of someheating and cooling systems are given in Figs. 10-1 to 10-5.

Fig 10-1. Heating system for multiple dwelling building with direct return piping system

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HYDRONIC HEATING AND COOLING SYSTEM10–2

Fig 10-2. Heating system for multiple dwelling building with reverse return system

Fig 10-3. Primary system with constant speed heating system pump for multiple buildings

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HYDRONIC HEATING AND COOLING SYSTEM 10–3

Fig 10-4. Closed chilled water system with constant speed chilled water supply pump and mixing valve

Fig 10-5. Closed chilled water system with variable speed chilled water supply pump

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HYDRONIC HEATING AND COOLING SYSTEM10–4

Temperature Classifications.—The temperature clas-sifications of the hydronic systems can be categorized as:1) Low temperature water (LTW) system2) Medium temperature water (MTW) system3) High temperature water (HTW) system4) Chilled water (CW) system5) Dual temperature water (DTW) system.

Low Temperature Water (LWT) System: The maximumtemperature limitation in this case is 250°F, The maxi-mum allowable working pressure is 160 psig. The maxi-mum working pressure depends on the static head of thebuilding (height of the building) and the location of thesystem pump(s). It is recommended for working pressureof higher than 60 psi to use steam to water or water towater heat exchanger(s) so that the heating boiler and itsclosed piping loop can be separated and to operate atlower operating pressure without being affected by thehigh system working pressure. Separating the boiler byusing heat exchanger(s) from the rest of the system mini-mizes boiler leaks and prolong the life of the boiler.

Medium Temperature Water (MTW) System: I n t h i scase, the working temperature is ranged between 250°Fand 350°F with an operating pressure of 300 psig. Themaximum temperature is 400°F.

Chilled Water (CW) System: In this case the chiller(s)operates to provide supply water temperature of 40 to 55°F, and a pressure of up to 120 psig. For supply tempera-ture below 40°F, mostly in process applications, anti-freeze of brine solution may be used.

Dual Temperature Water (DTW) System: In this case,both boiler(s) and chiller(s) are used with common pipingsystem to provide hot water heating and chilled watercooling. The maximum operating temperature of theheating water is limited to 180°F and minimum 40°F forthe chilled water.

Closed Hydronic System Components Design

The closed system is a system with only one expansiontank. The main components of the heating and coolinghydronic systems are (1) the heating or cooling source(such as boiler and chiller), (2) system load (convectors,baseboards, fan coil units, and terminal units, etc.), (3)expansion tank, (4) system pump(s), air separator,mechanical fill system; and (5) piping distribution sys-tem.

Convectors or Terminal Units.—The convector(s)for each room or space must be sized to be equal or greaterthan the calculated designed heating load for that particu-lar room or space. The sum of the total convectors andother terminal units load in the building is called theactual connected load. The flow rate through each con-vector or terminal unit can be calculated from the follow-ing equation:

(1)

where q =heat capacity of the terminal unit, Btu/hgpm = water flow rate, gallon/min

ρ =density of water, lb/ft3

Cp =specific heat of water, Btu/lb ·°F∆T = temperature drop across the convector or ter-

minal unit, °FFor standard conditions in which the density of the

water is 62.4 lb/ft3 and the specific heat is 1 Btu/lb-°F,Equation (1) can be written as

(2)

In many design applications the ∆T of 20°F is recom-mended for small simple hydronic systems, in this casethe above equation can be written as

(3)

Boiler.—For new construction boiler(s) must be sizesbased on the actual connected load and piping and pick uplosses. The actual connected load must be equal or greaterthat the calculated design heating load. The piping andpickup losses for the hydronic (hot water) boiler(s) is 15to 25% of the actual connected load and for steam boilersis 25 to 35%. In design application for which only theboiler needs to be replaced, the boiler(s) must be sized tomatch the actual installed connected load plus the pipingand pickup loss as mentioned above for proper operationof the boiler(s) specially on very cold days.

Air Eliminations Methods.—Air in the hydronic sys-tem can cause water hammer and shock waves in thehydronic system when the dissolved air in the water canbe separated at the low pressure point of the system.

Fig 10-6. Henry’s constant versus temperature for air and water

The solubility of air in the water can be described byHenry’s equation as follow:

(4)

gpm q·

8.02 T CP ρ××∆×----------------------------------------------=

gpm q·

500 T∆×----------------------=

gpm q·

10000---------------=

x pH----=

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HYDRONIC HEATING AND COOLING SYSTEM 10–5

where x =solubility of air in water (% by volume)

p = absolute pressure

H = Henry’s constant

Fig 10-7. Solubility versus temperature and pressure for air/water solution

Henry’s constant is a function temperature as shown inFigure 6. Taking into account the temperature depen-dency of Henry’s constant and combining withEquation(4), the percentage of the solubility of air in water can bedetermined as shown in Fig. 10-7. Fig. 10-7 clearly showswhat percent of air volume would exist in the differentparts of the hydronic system when the pressure and tem-perature are known. For example at 10 psia and 120°F, thepercent air volume if 2.5% from Fig. 10-7. Basically thedissolved air in the water at the higher pressure point ofthe system can be separated at other parts of the systemwhere the pressure is lower. That is the reason air ventsare installed (1) at the top of the supply and return risers(highest point) where the pressure is the lowest and (2) at

the return side of the terminal units (baseboard loop, con-vectors, etc.). Air can get into the hydronic system as fol-low:

1) During the initial fill of the system with citywater, which contains dissolved air. In order tominimize the dissolved air during the initial fill,an inline separator is recommended to be installedin the piping system, as shown in Fig. 10-8.

2) Entrain air at the air water interface of the openexpansion tank and closed steel expansion tankwhere the air is being used as compressible fluid.A diaphragm type expansion tank is preferred tobe installed since no direct contact exists betweenthe compressible gas and water, since they areseparated by a flexible membrane.

3) Through the fittings in the part of the piping sys-tem where the system pressure is below atmo-spheric pressure. Design must ensure that at nopoint in the system the system pressure is lowerthan atmospheric pressure.

4) Other considerations are to ensure that (1) pres-sure at no point in the system will ever becomeslower than saturation temperature of the operatingtemperature and (2) the calculated (theoretical)net positive head (NPSHA) at the pump inlet isalways exceeds the required net positive headgiven by the pump manufacturer.

Fig 10-8. Air separator and expansion tank detail

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HYDRONIC HEATING AND COOLING SYSTEM10–6

Pressure Increase Due to Change in Tempera-ture.— One should know of how much pressure willincrease due to temperature increase; this is especiallyimportant for the sizing of the expansion tank. The rela-tionship between pressure change due to temperaturechange in a piping system is given by the following equa-tions:

(5)

where P = pressure increase, psi;β =volumetric coefficient of thermal expansionof water, 1/°F;

α =linear coefficient of thermal expansion forpiping material, 1/°F;

∆t =water temperature increase, °F;D =pipe diameter, in.;E =modulus of elasticity of piping material, psi;γ =volumetric compressibility of water, in2/lb;and

∆r = thickness of pipe wall, in.

Fig 10-9. Pressure increase resulting from thermal expansion as function of temperature increase

Based on Equation (5), figures can be developed toshow the change in pressure due to temperature changefor specific pipe sizes and pipe material as shown in Fig.10-9 which provides pressure increase vs. pressureincrease for 1″ and 10″ schedule 40 steel pipes. For exam-ple for a 5°F temperature increase for a 10″ schedule 40steel pipe, the pressure increase is 100 psi.

Expansion Tank.—The connected piping in hydronicsystems is subject to expansion and contraction due tochanges in system temperature especially during initialsystem fill. Expansion tanks (or compression tanks) arerequired to protect against thermal expansion of the pip-ing system due to temperature rise. During initial fill thepiping system could experience the largest thermal

expansion which is why the size of expansion tank mustbe based on temperature changes during initial systemfill. For example, in low temperature hydronic heatingsystem when boiler and piping system need to be initiallyfilled during winter time, the city water temperature couldbe as low as 40°F, which must be heated to 200°F. In thiscase, the piping system will experience a large tempera-ture difference and the system expansion tank must besized to handle this large temperature increase. Anotheroption is that to heat the city water initially by means ofelectric heat to reduce the size of the system expansiontank, but same procedure must be followed for the futuresystem fill to avoid drastic damage to the piping systemdue to excessive expansion. It should be noted that theexpansion tanks besides serving a thermal function servesa hydraulic function as well. As a hydraulic device, theexpansion tank provides a reference system pressurepoint analogous to the ground point in an electrical cir-cuit.

Expansion tanks are of three basic configurations: (1) aclosed tank, which contains a captured volume of com-pressed air and water, with an air water interface (some-times called a plain steel tank) as shown in Fig. 10-12; (2)an open tank (i.e., a tank open to the atmosphere) asshown in Fig. 10-10; and (3) a diaphragm tank, in which aflexible membrane is inserted between the air and thewater (another configuration of a diaphragm tank is thebladder tank) as shown in Fig. 10-11.

Equations for sizing the three common configurationsof expansion tanks are as follow:

Open tanks with air/water interface:

Fig 10-10. Open tank

For diaphragm tanks:

Fig 10-11. Diaphragm tank

P∆ β 3α–( ) t∆54---⎝ ⎠⎛ ⎞ D

E r∆----------⎝ ⎠⎛ ⎞ γ+

---------------------------------=

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HYDRONIC HEATING AND COOLING SYSTEM 10–7

For closed tanks with air/water interface:

Fig 10-12. Closed tank air water interact

Expansion Tank Sizing .—Equations for sizing thethree common configurations of expansion tanks follow:

For closed tanks with air/water interface,

(6)

For open tanks with air/water interface,

(7)

For diaphragm tanks,

(8)

where Vt =volume of expansion tank, galVs = volume of water in system, galT1 = lower temperature, °FT2 = higher temperature, °FPa = atmospheric pressure, psiaP1 =pressure at lower temperature, psia P2 =pressure at higher temperature, psia V1 = specific volume of water at lower tempera-

ture, ft3/lbV2 = specific volume of water at higher tempera-

ture, ft3/lbα = linear coefficient of thermal expansion, in/in-°F

= 6.5 ×10 −6 in/in-°F for steel= 9.5 ×10 −6 in/in-°F for copper

∆T = (T2−T1),°F

The higher pressure is normally set by the maximumpressure allowable at the location of the safety reliefvalve(s) without opening them. A tank open to the atmo-

sphere must be located above the highest point in the sys-tem. A tank with an air/water interface is generally usedwith an air control system that continually revents the airinto the tank. For this reason, it should be connected at apoint where air can best be released.

Example 1:Size an expansion tank for dual temperaturesystem that will be operated at a design temperature rangeof 40°F to 200°F. The minimum pressure at the tank is62.3 psig (47.6 psia) and the maximum pressure is 117.3psig (102.6 psia). (Atmospheric pressure is 14.7 psia.)The volume of water is 2500 gal. The piping is steel.

1. Calculate the required size for a closed tank with anair/water interface.

Solution: From Table 2-3:

2. If a diaphragm tank were to be used in lieu of theplain steel tank, what tank size would be required?

Solution: Using Equation (8),

Vt Vs

V2

V1------⎝ ⎠⎛ ⎞ 1– 3α T∆–

⎝ ⎠⎛ ⎞

Pa

P1------

Pa

P2------–

⎝ ⎠⎛ ⎞

----------------------------------------------------=

Vt 2Vs

V2

V1------⎝ ⎠⎛ ⎞ 1– 3α T∆–

⎝ ⎠⎛ ⎞=

Vt Vs

V2

V1------⎝ ⎠⎛ ⎞ 1– 3α T∆–

⎝ ⎠⎛ ⎞

1P1

P2------–

⎝ ⎠⎛ ⎞

----------------------------------------------------=

V1 at 40°F( ) 0.01602=

V2 at 200 °F( ) 0.01663=

Vt Vs

V2

V1------ 1– 3α T∆–

⎝ ⎠⎛ ⎞

Pa

P1------

Pa

P1------–

⎝ ⎠⎛ ⎞

-----------------------------------------------=

2500

0.016630.01602------------------- 1– 3 6.5 10

6–×× 160×–⎝ ⎠⎛ ⎞

14.762.3---------- 14.7

117.3-------------–

⎝ ⎠⎛ ⎞

-----------------------------------------------------------------------------------------------×=

787 gal=

Vt Vs

V2

V1------ 1– 3α T∆–

⎝ ⎠⎛ ⎞

1P1

P2------–⎝ ⎠

⎛ ⎞-----------------------------------------------=

2500

0.016630.01602------------------- 1–⎝ ⎠⎛ ⎞ 3 6.5 10

6–×× 160×–⎝ ⎠⎛ ⎞

1 62.3117.3-------------–

⎝ ⎠⎛ ⎞

-----------------------------------------------------------------------------------------------×=

186 gal=

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HYDRONIC HEATING AND COOLING SYSTEM10–8

Expansion Tank Location: It should be noted that thelocation of the tank has no effect on the system pressurebefore and after the pump as shown in Figs. 10-13 to 10-16. Notice that, when the pump is on, the pressure at thepump inlet decreases equal to the amount of pump headand it increases at the pump discharge equal to the pumphead. In good design practice, in order to reduce the sizeof the expansion tank, it is preferred to install the tankbefore the system pump. The size of the tank can also bereduced when the tank is installed at the highest point ofthe piping system where the pressure is the lowest.

Fig 10-13. Effect of expansion tank location with respect to pump pressure

Fig 10-14. Effect of expansion tank location with respect to pump pressure

Fig 10-15. Effect of expansion tank location with respect to pump pressure

Fig 10-16. Effect of expansion tank location with respect to pump pressure

Characteristics of Centrifugal Pumps

There are two distinct types of centrifugal pumps: (1)the turbine type pump, which uses diffusers or guidevanes in the casing for the conversion of velocity to pres-sure energy, and (2) the volute-type centrifugal pump,most commonly used.

Mechanically, a volute type centrifugal pump consistsof an impeller or runner having curved vanes revolving ona shaft and housed in a shell or casing. Liquid enters the

impeller axially to the shaft and it has energy imparted toit by rotating vanes of the impeller. The fluid leaves theperiphery of the impeller at a relatively high velocity andis collected in the casing or shell. This casing is sodesigned that the velocity of the liquid is graduallyreduced before it is discharged. Here the velocity of theliquid is converted into pressure by reduction of velocityaccording to Bernoulli's theorem.

The quantity of liquid discharged by the pump isalmost always measured in gpm, although sometimes themeasure is cubic feet per second. In this discussion gal-lons per minute is used as the unit.

Pressure developed by a centrifugal pump is specifiedas head in feet of liquid.

where s =specific gravity of the liquid compared towater (water at 60/60°F = 1.00);h =head in feet; andP =pressure in psi.

The head developed by a centrifugal pump is a functionof the impeller diameter and the speed of rotation (rpm).Maximum head that can be developed by a centrifugalpump is when the discharge valve is tightly closed and thepump is discharging zero capacity into the system. This isknown as the shut-off head of the pump. Since there is apredetermined maximum pressure that the pump candevelop and this pressure is taken into account by thedesigner, centrifugal pumps do not require relief valves orother unloading mechanizers that are otherwise necessaryfor the positive displacement type pumps. The maximumor shut-off head h of any centrifugal pump can be veryclosely calculated by the formula:

where D =outside diameter of the impeller in. and;N =rpm.

Fig 10-17. Performance curves for a typical centrifugal pump one with 9.5 in. impeller diameter and 1750 rpm constant speed

Operating Characteristics.—Hydraulic operatingcharacteristics of a typical centrifugal pump, or perfor-mance curve, is shown in Fig. 10-17. The pressure (orhead in feet of liquid) developed by the pump at a speci-

h 2.31Ps

--------------=

hxD N×1840--------------⎝ ⎠⎛ ⎞

2=

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HYDRONIC HEATING AND COOLING SYSTEM 10–9

fied impeller diameter and at a constant rpm is plottedagainst the discharge of the pump in gallons per minute(gpm.)

Note that the maximum head developed by the pump isat zero capacity or shut-off as previously mentioned.

The head-capacity curve extends from shut-off to max-imum or wide-open capacity. In other words, as the pumpdischarges more liquid, its pressure decreases. The slopeof the head-capacity curve is due to (1) the curve or shapeand the number of vanes in the impeller; (2) friction orhead loss within the pump. As the pump discharges moreliquid, there is increased internal friction, and this frictionloss is actually a loss in pressure or head at the dischargeof the pump hence, the slope in head capacity curve. Thepump designer can control to a certain degree the slope ofthe head-capacity curve by the shape or warp of the impel-ler vanes and also by the number of vanes. The internalfriction, however, is a factor over which the pumpdesigner has very little control.

The efficiency curve rises to a maximum within certaincapacity limits and then falls off toward the maximumcapacity of the pump. The brake horsepower curve is usu-ally as shown; that is, brake horsepower graduallyincreases in value as capacity increases. Maximum effi-ciency of a centrifugal pump lies within the design range.A pump designer has a definite capacity and head uponwhich all calculations are based, and the calculations aresuch that the maximum efficiency of the pump will be ator very near design capacity.

Pump Laws.—The efficiency of a centrifugal pump, asfor any machine, is horsepower output divided by thehorsepower input. When efficiency is known the horse-power requirement of the pump is determined by the for-mula:

where DH =dynamic head in feet;

s =specific gravity; and

E =efficiency expressed as a decimal.

This formula holds for any liquid since the specificgravity of liquid as compared with water may be insertedin the formula.

Change of Performance.—The so-called laws ofaffinity relating to centrifugal pumps are theoretical rules

that apply to the change in performance of a centrifugalpump by a change in the speed of rotation or a change inthe impeller diameter of a particular pump. It shouldalways be remembered in using these laws of affinity thatthey are theoretical and do not always give exact results ascompared with tests. However, they are a good guide forpredicting the hydraulic performance characteristic of apump from a known characteristic caused by either alter-ing the speed of rotation or the outside diameter of theimpeller. The laws of affinity may be stated as follows:

At a constant impeller diameter,

1. capacity varies directly as the speed:

2. head varies directly as the square of the speed; and

3. horsepower varies directly as the cube of the speed.

In equation form, the foregoing are expressed as

At constant speed:

1. capacity varies directly as the cube of the impellerdiameter;

2. head varies directly as the square of the impellerdiameter; and

3. horsepower varies directly as the fifth power of theimpeller diameter.

Or, in equation form,HP gpm DH s××3960 E×

-----------------------------------=

gpmy

gpmx-------------

rpmy

rpmx------------=

heady

headx---------------

rpmy2

rpm2

x

---------------=

bhpy

bhpx------------

rpmy3

rpmx3

---------------=

gpmy

gpmx-------------

dy

dx-----=

heady

headx---------------

dy3

dx3

-----=

bhpy

bhpx------------

dy5

dx5

-------=

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HYDRONIC HEATING AND COOLING SYSTEM 10–19

and control valves, that must be available in the form ofpump pressure.

Preliminary Pump Selection: The preliminary selectionshould be based on the pump’s ability to fulfill the deter-mined capacity requirements. It should be selected at apoint left of center on the pump curve and should notoverload the motor. Because pressure drop in a flow sys-tem varies as the square of the flow rate, the flow variationbetween the nearest size of stock pump and an exact pointselection will be relatively minor.

Final Pipe Sizing and Pressure Drop Determina-tion.—Final Piping Layout: Examine the overall pipinglayout to determine whether pipe sizes in some areas needto be readjusted. Several principal circuits should haveapproximately equal pressure drops so that excessivepressures are not needed to serve a small portion of thebuilding.

Consider both the initial cost of the pump and pipingsystem and the pump’s operating cost when determiningfinal system friction loss. Generally, lower heads andlarger piping are more economical when longer amortiza-tion periods are considered, especially in larger systems.However, in small systems such as in residences, it maybe most economical to select the pump first and design thepiping system to meet the available pressure. In all cases,adjust the piping system design and pump selection untilthe optimum design is found.

Final Pressure Drop.— When the final piping layouthas been established determine the friction loss for eachsection of the piping system from the pressure drop charts(Chapter 9) for the mass flow rate in each portion of thepiping system. After calculating the friction loss at designflow for all sections of the piping system and all fittings,terminal units, and control valves, sum them for several ofthe longest piping circuits to determine the pressureagainst which the pump must operate at design flow.

Final Pump Selection.— After completing the finalpressure drop calculations, select the pump by plotting asystem curve and pump curve and selecting the pump orpump assembly that operates closest to the calculateddesign point.

Freeze Prevention.—All circulating water systemsrequire precautions to prevent freezing, particularly inmakeup air applications in temperate climates where (1)coils are exposed to outdoor air at below-freezing temper-atures, (2) undrained chilled water coils are in the winterairstream, or (3) piping passes through unheated spaces.Freezing will not occur as long as flow is maintained andthe water is at least warm. Unfortunately, during

extremely cold weather or in the event of a power failure,water flow and temperature cannot be guaranteed. Addi-tionally, continuous pumping can be energy-intensiveand cause system wear. Designers should take followingprecautions to prevent flow stoppage or damage fromfreezing:

1. Select all load devices (such as preheat coils) that aresubjected to outdoor air temperatures for constant flow,variable control.

2. Position the coil valves of all cooling coils with valvecontrols that are dormant in winter months to the full-open position at those times.

3. If intermittent pump operation is used as an economymeasure, use an automatic override to operate bothchilled water and heating water pumps in below-freezingweather.

4. Select pump starters that automatically restart afterpower failure (i.e., maintain-contact control).

5. Select non overloading pumps.

6. Instruct operating personnel never to shut downpumps in subfreezing weather.

7. Do not use aquastats, which can stop a pump, inboiler circuits.

8. Avoid sluggish circulation, which may cause airbinding or dirt deposit. Properly balance and clean sys-tems. Provide proper air control or means to eliminate air.

9. Install low temperature detection thermostats thathave phase change capillaries wound in a serpentine pat-tern across the leaving face of the upstream coil.

When designing fan equipment that handles outdoorair, take precautions to avoid stratification of air enteringthe coil. The best methods for proper mixing of indoorand outdoor air are the following:

1. Select dampers for pressure drops adequate to pro-vide stable control of mixing, preferably with dampersinstalled several equivalent diameters upstream of the air-handling unit.

2. Design intake and approach duct systems to promotenatural mixing.

3. Select coils with circuiting that allows parallel flowof air and water.

Freeze-up may still occur with any of these precau-tions. If an antifreeze solution is not used, water shouldcirculate at all times. Valve controlled elements shouldhave low-limit thermostats, and sensing elements shouldbe located to ensure accurate air temperature readings.Primary and secondary pumping of coils with three-wayvalve injection is advantageous. Use outdoor reset ofwater temperature wherever possible.

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INDEX 21–1

AAbbreviations scientific and engineering terms 18-8Absorption split systems 13-4AC motors 17-5Acoustical problems

air handling room 16-42apparatus casings 16-42dampers in duct 16-42fan isolation base 16-42flexible connectors 16-43high velocity system 16-40

Adiabatic mixing 3-3, 3-5Air

binding 15-41composition 2-1compressor 9-73discharge pipe capacities 9-78discharge through orifice 9-78flow control 12-27handling 14-1–14-96horsepower 14-1infiltration in fuel oil piping 12-18mixing streams 3-3pipe sizing 9-73piping pressure loss 9-72pressurization 15-64regulators 9-73removal from system 15-49supply outlets 14-56to air heat pumps 13-38to water heat pumps 13-40venting 15-52

Air conditioning process 3-1–3-8heating and cooling 3-1

Air conditioning system 13-1–13-116absorption split system 13-4air handler selection 13-49air handling apparatus 13-77air motion 13-14air systems 13-23, 13-30–13-34all-water systems 13-27apparatus casing 13-79apparatus floor area 13-77attic or crawl space 13-5automatic control 13-81

cold air plenum 13-85cold deck control 13-82counter and parallel flow 13-98damper 13-88damper operation 13-88day cycle 13-88dual duct constant volume 13-94dual duct mixing box 13-93dual duct system 13-95dual duct variable volume 13-94economizer cycle 13-88face and bypass control 13-94–13-95freeze prevention 13-97hot deck control 13-84hot plenum 13-85hot water 13-90hot water converter 13-94hot water pressure 13-92hot water reheat 13-92–13-94hot water system 13-91mixed air 13-85mixed air control 13-88mixed air section 13-82mixing box control 13-94multizone unit 13-84night cycle 13-88night operation 13-89preheat control 13-91pressure control 13-94rooftop multizone units 13-81rotary air to air heat exchanger 13-95single duct variable volume 13-95summer cycle 13-88summer operation 13-95unit ventilator 13-88

Air conditioning system (continued)automatic control

variable speed control 13-95automatic control

winter cycle 13-88winter operation 13-96winterizing chilled water system 13-97zone day-night operation 13-91zone mixing dampers 13-88

backlash 13-79basic arrangement 13-69, 13-75

ceiling plenum 13-70floor layouts 13-69office building 13-73

carryover 13-79check lists 13-114

air distribution 13-116drain facilities 13-115duct system 13-116electric power facilities 13-115heating load 13-115hot water heating supply 13-115refrigeration facilities 13-115sewer facilities 13-115steam supply facilities 13-115water facilities 13-115

cold storage 13-58constant volume mixing unit 13-76construction details 13-80control 13-9, 13-26control panel location 13-9cooling considerations 13-20dehumidification 13-59direct solar heating 13-56double duct 13-9duct joints 13-80energy requirements 13-19equipment maintenance 13-108evaporative air conditioning 13-14–13-16fans 13-79furnace mounting 13-7heat pumps 13-36–13-44heat recovery 13-22–13-29heat recovery air system 13-30heat recovery water system 13-30heating and cooling calculations 13-19high velocity dual duct 13-60

advantages 13-60air quantities 13-64cycles 13-60design factors 13-66design high pressure ducts 13-67design velocities 13-66double fan with dehumidifier 13-61large vs. small ducts 13-65low pressure ducts 13-68maximum velocity 13-66single fan with dehumidifier 13-60–13-61sizing 13-65system design 13-64, 13-68

horizontal package units 13-1humidity control 13-10initial costs 13-18installation of equipment 13-107installations in roof 13-8installed costs 13-79insulation 13-79lighting heating cooling system 13-22location on roof 13-105–13-106

advantages 13-105automatic control 13-105multiple units 13-105size of system 13-105ventilation 13-106

machinery space 13-106maintenance 13-112multizone 13-8–13-9multizone units 13-4noise 13-79outdoor conditions 13-14overlapping 13-21refrigeration chassis 13-2remote condensers 13-2remote condensing units 13-3rooftop 13-6

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Page 43: HVAC Design&Implementation

INDEX21–2

Air conditioning system (continued)selection procedure 13-10services to equipment 13-107servicing of

air handling system 13-107compresser oil 13-107condenser 13-107cooling plant 13-107refrigeration unit 13-108water system 13-107

single package installations 13-5single package units 13-1single package year round units 13-2slab or ground level 13-6solar augmented heat pump 13-57solar energy 13-54solar heating description 13-54solar heating domestic water 13-56solar heating operation 13-54solar heating storage tank 13-56sound lining 13-79split systems 13-7thermostat location 13-10utility off-peak cooling 13-57variable affecting costs 13-80variable volume system 13-17–13-21ventilation air 13-9vertical package units 13-1vibration 13-106wall condensing units 13-8well water 13-54well water precooling 13-55well water refrigerant condensing 13-55winter to summer tank transition 13-58year round remote units 13-3zoning 13-69zoning installation 13-8

Air distribution system 16-43dampers as a noise generating source 16-46dual duct area ratio 16-45duct connectors 16-44duct design method 16-43duct in machine room 16-43duct off fittings 16-45duct velocity 16-43flutter in dual duct mixing units 16-47grilles, registers and diffusers 16-48high velocity ductwork 16-44, 16-46inlets to high velocity terminal points 16-47large terminal units 16-48noise in flexible connections 16-46sound barrier for high velocity ductwork 16-46sound traps 16-46terminal devices 16-47testing of high pressure ductwork 16-47two motor dual duct units 16-47warm connections 16-47

Air filters 9-73, 14-78characteristics 14-80dry filters 14-78electronic air cleaner 14-79selection 14-79viscous impingement 14-78

Air handling unitstrap 15-112–15-116

Air space thermal resistance 5-19Air volume

humidifying or dehumidifying 14-74required 14-75sensible heating or cooling 14-74

Airborne noise through ducts 16-13Aircraft air heater 15-83ANSI Standard abbreviations 18-8Apothecaries

fluid measure 20-2weight 20-2

Apparatus casing 13-79Apparatus casing construction 14-77Application range 14-2Atmospheric pressure 20-2Attenuation 16-1Automatic control 13-81

cold air plenum 13-85cold deck control 13-82

Automatic control (continued)counterflow and parallel flow 13-98damper 13-88damper operation 13-88day cycle 13-88dual duct constant volume 13-94dual duct mixing box 13-93dual duct system 13-95dual duct variable volume 13-94economizer cycle 13-88face and bypass control 13-94–13-95freeze prevention 13-97hot deck control 13-84hot plenum 13-85hot water 13-90hot water converter 13-94hot water pressure 13-92hot water reheat 13-92–13-94hot water system 13-91mixed air 13-85mixed air control 13-88mixing box 13-94multizone unit 13-84night cycle 13-88night operation 13-89preheat control 13-91pressure control 13-94rooftop multizone units 13-81rotary air to air heat exchanger 13-95single duct variable volume 13-95summer cycle 13-88summer operation 13-95unit ventilator 13-88variable speed control 13-95winter cycle 13-88winter operation 13-96winterizing chilled water system 13-97zone day night operation 13-91zone mixing dampers 13-88

Automatic control of dual duct system 13-95Avoirdupois or commercial weight 20-2

BBacklash 13-79Balancing

air flow 14-96and testing 14-99booster fan systems 14-98circuits 15-53duct distribution 14-98

Band pressure level 16-1Bandwidth correction 16-6Bare pipe radiation 15-34Barrel liquid capacity 20-2Below grade wall U-factors 6-3Belts 13-114Binary multiples 20-10Blocked tight static pressure 14-2Boiler

cast iron 15-77cast iron radiators 15-78common return header 15-3connected load 15-73direct return connections 15-3–15-4draft loss 15-76drip end 15-7effect of load variation 15-70emergency protection 15-69furnace volume 15-73, 15-75gas fired 15-75grate area 15-73, 15-75hand fired 15-75Hartford connection 15-3heat emission 15-78heating surface 15-73heating value of coal 15-73hot water system 15-69mechanically fired steel boilers 15-74nameplate 15-75oil fired 15-74, 15-76overhead connections 15-4pipe sizing 15-71pipe, valves, and fittings 15-69

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Page 44: HVAC Design&Implementation

INDEX 21–3

Boiler (continued)piping 15-15piping connections to boilers 15-1ratings 15-30, 15-73, 15-75–15-76return header drip 15-6return piping 15-6return trap 15-29stack dimensions 15-76steam header drip 15-6steam main drop 15-6steam main rise 15-6steam mains 15-6stoker fired 15-75supply and return piping 15-6supply header drip 15-6supply piping 15-6valve installation 15-69venting of piping 15-70welded joints 15-70

Boiler horsepower 12-31Boiling point

calcium chloride 15-81ethylene glycol 15-81glycerine 15-81glycol 15-81oil 15-82tetraanyl silicate 15-82tetracresyl silicate 15-81

Brake horsepower 14-2Branch trunk duct losses 14-60Breeching

access 14-85aerodynamics 14-84construction 14-83, 14-85design 14-83design and construction 14-83expansion 14-83

British standard thermal units, (Btu) 20-7Broadband noise 16-1Building material resistances 5-17, 5-21–5-26Built up roofing coefficient of transmission 5-14Byte 20-10

CCanning 15-30Carat 20-2Carnot cycle 1-4Carryover 13-79Cast iron radiators, capacity 15-79Cavitation on pump 15-68Ceiling

by metal coefficient of transmissions 5-15by wood coefficient of transmissions 5-15

Centimeter-gram-second system of measurement 20-8Cfm and scfm 14-1Check valve 9-139–9-141Cheese vats 15-31Chimney

draft 14-90sizing 14-94velocities 14-90

Circular mil gage for wires 20-1Circulating pumps 15-66–15-67

boilers 15-69cavitation effects 15-68construction 15-68for boiler 15-69net positive suction head 15-68seals 15-68

CLFhooded equipments 7-45–7-46people 7-44–7-45unhooded equipments 7-44

Climaticcooling design data 19-1data 19-1–19-38data applicability 19-1data characteristics 19-1design condition 19-1desumidification design data 19-1heating design data 19-1mean daily range 19-1

Closed system 1-2

Cloud point 12-15CLTD

conduction through glass 7-31multi family 7-49roofs 7-9single family 7-49walls 7-11

Code numberthermal properties 7-27walls and roofs 7-27

Coefficient of performance 1-4, 1-6, 13-36Coefficient of transmissions

built up roofing 5-14ceiling by metal 5-15ceiling by wood 5-15flat masonry roof 5-14–5-15flat metal roof 5-15frame ceiling 5-14frame floor 5-14frame partitions 5-12frame walls 5-11–5-12masonry cavity walls 5-13masonry partitions 5-13masonry walls 5-11–5-12pitched roof 5-16

Cold air plenum 13-85Cold deck control 13-82Combustion 12-1–12-20

air flow control 12-27air heater bypassing 12-17air infiltration in piping 12-18basics 12-1chemistry 12-1control errors 12-20control strategy 12-20draft control 12-24draft measurements 12-17efficiency 12-3efficiency losses 12-4energy losses 12-7excess air cost 12-3feedwater control 12-23firing rate 12-18flue gas 12-6flue gas recirculation 12-28fuel composition 12-1fuel oil 12-16fully metered control 12-22grate 12-16natural gas 12-15oxygen sensor 12-17oxygen trim 12-26parallel positioning 12-21radiation loss 12-5reaction 12-1safe burner set up 12-3short circuiting 12-16single pressure regulator 12-19stack losses 12-5theory 12-1tramp air 12-16troubleshooting 12-15, 12-17varying fuel flow 12-2varying oxygen content 12-2water in the fuel oil 12-18wet atomizing steam 12-18

Combustion controlair considerations 12-12atomizing media 12-12cloud point 12-15considerations 12-11draft 12-13elevation 12-13firing considerations 12-14flashpoint 12-15flue gas considerations 12-13flue gas recirculation 12-14fuel oil firing considerations 12-14natural gas efficiency 12-8nitrogen content 12-15no. 2 oil efficiency 12-9no. 6 oil efficiency 12-10pour point 12-15pressure and flow basics 12-11saving fuel 12-7

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Page 45: HVAC Design&Implementation

INDEX21–4

Combustion control (continued)sulfur content 12-15temperature 12-13viscosity considerations 12-14

Compressed airpipe sizing 9-73receiver 9-74system 9-72system testing 9-74

Compressed liquid 1-1Compresssors 13-114Concrete block 15-31Concrete, ready mix 15-31Condensate drains 14-77Condensate return pump 15-29Condenser 13-113Condensing units in wall 13-8Condensing water circuit 13-111, 13-113Conduction 5-1Connections

heating units to risers 15-8mains to downfeed risers 15-8offset 15-9risers to heating unit 15-9runout 15-9

Conservation of energy 1-3, 3-1–3-3cooling and dehumidifing 3-2

Conservation of energy equations 3-1Conservation of mass 1-3, 3-1–3-3Conservation of mass equations 3-1Continuity equation 1-6Control valve sizing 9-142–9-143Controls 13-9

basic factors for designing 15-96bonnet air temperature 15-96continuous air circulation 15-94continuous blower circulation 15-95errors 12-20fan switch 15-94intermittent blower operation 15-95limit switch 15-94room thermostat 15-94strategies 12-20temperature drop of air in ducts 15-96thermostatics 15-94valve sizing 9-142

Convection 5-2Convection coefficient 5-3Convector piping details 15-4Conversion

fractional inch to millimeter 20-3millimeter to fractional inch 20-3

Cookers, coil 15-31Cookers, jacketed 15-32Cooling and dehumidification 3-2Cooling and dehumidifing 3-2Cooling load 5-33Cooling load calculation 7-1

CLF method 7-6–7-49CLTD method 7-6–7-49cooling coil load 7-1heat extraction rate 7-1heat gain 7-1heat source 7-1latent heat gain 7-1radiation heat gain 7-1residential 7-35SCL method 7-6–7-49sensible heat gain 7-1space cooling load 7-1thermal storage 7-1transfer function method 7-1

Cooling of fuel oil in atomizers 12-18Cooling tower 13-99–13-105

estimating data 13-101, 13-103natural draft 13-102tower height 13-103water requirements 13-104wet bulb temperature 13-103wind velocity 13-102

Cooling tower noise control 16-36configurations 16-38fan noise 16-36half speed operation 16-39

Cooling tower noise control (continued)leaving condition changed 16-39location 16-39oversizing the tower 16-39reducing generated sound 16-39sound absorbers 16-40water noise 16-37

Cooling water 13-113Cooling water system 13-112–13-113Cooling, heat recovery 13-45Counterflow and parallel flow 13-98Cubic measure 20-1

DDamper control 13-88Damper operation 13-88Dampers 13-113Day cycle 13-88Decibel 16-1Degree days 11-1–11-8Degree of saturation 2-2Dehumidification 13-59Demand load 9-28Demand weights of fixtures 9-30Density effects 14-4Design lateral load 14-77Dew point temperature 2-4Direct fired unit heater 15-83Distilleries 15-32Domestic water, solar heating 13-56, 13-58Double duct system 13-9Draft

burning coal 14-95control 12-24, 14-92foot of chimney 14-95measurements 12-17

Drip end 15-7Dripping riser 15-12Dry cleaning 15-32Dry measure 20-2, 20-8Dryers 15-32Dual duct

constant volume control 13-94mixing box control 13-93variable volume control 13-94

Ductbox plenum system 15-88characteristics 15-88design 8-9design by computer 14-72design methods 8-12design procedures 8-13design velocities 8-11equal friction method 8-12equivalent lengths of fittings 15-105equivalent rectangular ducts 8-6extended plenum system 15-88fibrous glass construction 14-73fitting friction loss 8-14fitting loss coefficient

bellmouth, plenum to round 8-24conical diffuser 8-26damper, butterfly 8-19elbow mitered 8-18elbow mitered with vane 8-18elbow with splitter vane 8-17elbow without vanes 8-17elbow Z shaped 8-19exhaust system 8-26fire damper 8-27return system 8-26round tap to rectangular main 8-25tee converging 8-26, 8-31, 8-33–8-34transition in rectangular 8-25transition rectangular to round 8-25transition round to rectangular 8-27transition round to round 8-26varaiable inlet outlet areas 8-24wye converging 8-36wye 30 degree converging 8-28wye, 45 degree 8-30, 8-32

fitting loss coefficient tables 8-17–8-37flat and oval duct 8-5

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Page 46: HVAC Design&Implementation

INDEX 21–5

Duct (continued)individual system 15-88rectangular 8-5resistance in low pressure ducts 8-15static regain method 8-13, 8-15trunk system 15-88turns 14-28vibration and noise 8-12

Duct design 8-1, 8-17Duct design data

diffuser, free discharge 8-21plenum to rectangular 8-21sudden contraction 8-21Tee type, diverging 8-23transition, rectangular to rectangular 8-22transition, round to rectangular 8-22wye type diverging 8-2245 degree entry branch 8-2490 degree elbow 8-21

Duct joints 13-80Duct roughness 8-5Ducts 13-113

air balancing 14-52air distribution 14-56air flow 14-37, 14-53air quantities 13-64air supply outlets 14-56air turning hardware 14-52branches and discharges 14-51cycles 13-60degree of roughness 14-40density of air 14-39design air velocities 14-47design considerarion 8-9design velocities 8-12, 13-66double fan dual duct 13-61dynamic loss 8-7elbows 8-14energy equation 8-1equal friction method 8-14factors for design 13-66fan system interface 8-8fire and smoke management 8-9flexible ductwork 14-62four types 14-53friction chart 8-4–8-5friction losses 8-2, 14-40friction of air 14-41–14-44good turns 14-50high pressure ducts 13-67high velocity 13-60high velocity advantages 13-60high velocity design 14-71high velocity system 14-59insulation 8-9large vs. small in size 13-65local loss coefficients 8-7losses in rectangular elbows 14-46losses in round elbows 14-45losses in round fittings 14-45low pressure ducts 13-68maximum velocity 13-66noise control 8-12non circular 8-5pitot traverse 14-39–14-40pressure change in a system 8-8pressure head 8-1pressure losses 14-48–14-49, 14-61recommended velocities 8-11, 14-57rectangular and round equivalents 14-47rectangular shape 14-40return air ducts 13-68return air plenums 14-54roughness factors 8-2roughness values 8-5sectional losses 8-7single fan dual duct 13-60–13-61sizing 13-65static pressure 14-37, 14-66static pressure loss 14-60static regain 14-59, 14-63, 14-65system design 13-64, 14-56system leakage 8-11tap off fitting 14-62

Ducts (continued)testing and balancing 8-12turns 14-51velocity 14-37velocity pressure 14-37–14-38

Dust collectors 14-78–14-79dry centrifugal types 14-82electrostatic precipitators 14-83fabric collectors 14-82wet collectors 14-82

EEconomizer control cycle 13-88Emissivities 5-4Energy 1-2

internal 1-2kinetic 1-2potential 1-2thermal 1-2

Energy equation 8-1Energy esimation

base temperature 11-1degree days 11-1–11-8

abroad 11-8application 11-2different bases 11-9–11-20U.S. cities 11-9–11-20

empirical constants 11-7fuel consumption 11-4future demands 11-5guide of operation 11-2limitations 11-7load factors 11-7operational hours 11-765 deg, as base 11-1

Enthalpy 1-1, 2-4Entropy 1-1Equation of state 2-1Equipment arrangement 13-44Equipment losses 14-60Equipment maintenance 13-108

air distribution 13-108air handling 13-108central system schedule 13-111cooling 13-108schedule 13-110–13-111water using 13-108

Equivalent direct radiation 15-1Equivalent length of elbow 9-2Erosion 9-3Ethylene glycol 15-81Evaporative air conditioning 13-14–13-16

air motion 13-14outdoor conditions 13-14

Evaporative condensers 13-113Exbi 20-10Excess air 12-3Excess air measurement 12-6Exhaust air heat recovery 13-31Expansion conditions 15-65Expansion joints 15-9Expansion loops 15-9

swing type 15-10Expansion of piping 9-134–9-135Expansion tank 15-65

sizing 15-53, 15-65Expansion valves 13-112Extrinsic property 1-1

FFace and bypass control 13-94–13-95Fan 13-79

acoustic properties 16-21air entry position 14-20axial fan 14-16backward inclined fan 14-14blade pitch variation 14-31class limits 14-16coil unit 13-48comparison 14-36discharge connections 14-27

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Page 47: HVAC Design&Implementation

INDEX21–6

Fan (continued)discharge dampers 14-30double inlet 14-27flywheel effect 14-36formulas 14-31forward curve centrifugal fan 14-14horsepower and actual capacity 14-32inlet connections 14-26inlet dampers 14-29inlet effects 14-23inlet vanes 14-30laws 14-3noise generation 16-23operating limit 14-18–14-19operating point 14-11paralleling 14-11performance curve 14-11performance data 14-36performance modulation 14-29radial blade fans 14-15scroll volume control 14-29selection 14-21, 14-34single inlet 14-27size change 14-3speed modulation 14-31static pressure 14-1surge 14-11system resistance curve 14-11system surge 14-11terminology 14-1total pressure 14-1tubular centfifugal fan 14-15types 14-14velocity pressure 14-1

Feed mills 15-33Feedwater control 12-23Filling pressure 15-53Filters 13-113Filters and ducts 13-112–13-113Fin efficiency 1-16Fin tube piping 15-4Fins and extended surfaces 1-15Fire dampers 14-56Fire protection 14-56Fire protection equipments 9-143Firing rate 12-18First law of thermodynamics 1-3Fixture units with demand 9-28Fixtures demand weights 9-30Flash point 12-15Flash steam

calculations 15-39condensate quantity 15-44–15-45quantities 15-43

Flash tankcapacities 15-42dimension 15-39, 15-45sizing 15-40

Flash trap 15-29Flat masonry roof coefficient of transmission 5-14Flat roof by metal coefficient of transmission 5-15Flat roof by wood coefficient of transmission 5-15Float trap 15-27–15-28Floor furnace 15-83Flow meter piping 12-31–12-32Flowwork 1-2Flue gas composition 12-6Flue gas recirculation 12-28Flush valve capacity 9-30Forced convection 1-12Forced draft 14-92Fractional inch to millimeter conversion 20-3Frame ceiling coefficient of transmissions 5-14Frame floor coefficient of transmissions 5-14Frame partitions coefficient of transmissions 5-12Frame walls coefficient of transmissions 5-11–5-12Free delivery 14-2Freeze prevention 10-19, 13-97Freeze up protection 15-16Freezing point

calcium chloride 15-81glycerine 15-81glycol 15-81oil 15-82

Freezing point (continued)tetra anyl silicate 15-82tetra cresyl silicate 15-81

French thermal unit 20-7Friction

chart 1-9, 15-47–15-48chart, duct 8-4hot water piping 15-46rate 15-23

Friction loss 1-9, 8-2copper piping 9-5equivalent length of elbow 9-2flanged pipe fitting loss 9-2K factors 9-2plastic piping 9-5screwed pipe fitting loss 9-2steel piping 9-5tee fitting 9-6valve and fitting equivalents 9-7–9-27valve and fitting loss 9-6

Fuel composition 12-1Fuel consumption degree days 11-4Fuel oil 12-16Fuel oil handling 12-33

alarm signals 12-39automatic pump alternation 12-38automatic start-stop system 12-38automatic valves 12-38back-up pump operation 12-38burner loop system 12-34continuous operation 12-38day tank 12-33entrained air 12-37flow rate 12-33gravity head 12-36intermittent operation 12-38maximum inlet pressure 12-36multiple day tank 12-33multiple pump 12-34piping system 12-37pump controls 12-37pump discharge pressure requirements 12-37required capacity 12-36safety shutdown 12-39standby generator application 12-33standby generator loop systems 12-34strainer pressure drop 12-36suction line losses 12-36tank overflow 12-37tank venting 12-37

Fully metered control 12-22Furnace mounting 13-7Future needs degree days 11-5

GGallons into cubic inches 20-2Gas laws 2-1Gas piping 9-59–9-72

capacities 9-59pressure loss 9-63–9-70residential 9-59sizes for residential 9-59solution 9-62tables 9-62

Gas pressurization 15-64Gas properties 2-1, 12-1Gate valve 9-139–9-141Gibi 20-10Globe valve 9-139–9-141Ground level installations 13-6Ground source heat pumps 13-41

HHanger spacings 15-16Heat 1-2

coefficients of transmission 5-27exchanger 1-18mechanical equivalent 20-7quantity measurement 20-7scales 20-7storage 15-63

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Page 48: HVAC Design&Implementation

INDEX 21–7

Heat (continued)thermal energy 20-7transfer 1-11

Heat anticipators 13-43Heat emission

bare radiators 15-79bathroom radiators 15-80enclosure effects 15-78front wall radiators 15-80pipe coils 15-80propeller unit capacities 15-80radiator finish 15-78ultra slender tubular 15-80unenclosed ratiators 15-79unit ventilators 15-80wall radiators 15-80

Heat gaincomputer equipment 7-6cooking appliances 7-3–7-5copier 7-6laboratory equipment 7-6laser printer 7-6medical equipment 7-6occupants 7-2office equipment 7-6

Heat loadcoefficients F2 6-4floor slab 6-5infiltration 6-6ventilation 6-6

Heat lossbare pipe 9-146–9-156coefficient 9-158cold surface temperature 9-158heat conductivity 9-158in piping 9-144insulated pipe 9-157, 9-159–9-176

Heat pumpsair to air 13-38air to water 13-40coefficient of performance 13-36electrohydronic heat recovery 13-44equipment arrangement 13-44fan coil units 13-48ground source 13-41heat anticipators 13-43heating performance factor 13-37installation factors 13-42operating factors 13-42optimized data 13-47–13-48outdoor temperature effects 13-42performance factor 13-37reverse cycle principle 13-36sources 13-41thermostats 13-43types 13-37water to air 13-40water to water 13-39

Heat recovery 13-22–13-29, 13-44air systems 13-23, 13-30–13-34all water systems 13-27control 13-26cooling cycle 13-45supplementary heat 13-47system design 13-47temperature limit 13-45

Heat transfer coefficient 1-12combined network 5-9parallel network 5-8series network 5-6

Heating and cooling media 15-81brine 15-81calcium chloride 15-81ethylene glycol 15-81glycerine 15-81glycol 15-81oil 15-82tetraanyl silicate 15-82tetracresyl silicate 15-81

Heating and humidification 3-3Heating load 5-33, 6-1

floors 6-1infiltration 6-1roofs 6-1

Heating load (continued)ventilation 6-1walls 6-1walls below grade 6-2windows 6-1

Heating of fuel oil in atomizers 12-18Heating performance factor 13-37Heating system

cast iron radiators 15-79enclosure effects 15-78forced air system 15-127gravity circulation 15-128hot water heater 15-124–15-125radiator emission 15-78steam or vapor 15-126–15-127

Henry’s constant 10-4Horsepower

electric motor ratings 17-1–17-2, 17-4Hot deck control 13-84Hot plenum control 13-85Hot water control 13-90Hot water heating system 15-49

affecting conditions 15-60affecting design conditions 15-60air pressurization 15-64air removal 15-49air venting 15-52balancing circuits 15-53boiler emergency protection 15-69boiler recirculating pump 15-69boilers 15-69branch pipe sizing 15-59cavitation effects 15-68checking pipe size 15-58circulating pumps 15-66–15-67combination piping system 15-60compare with steam 15-63compressed air 15-54district steam 15-50effect of load variation 15-70expansion conditions 15-65expansion tank sizing 15-53expansion tanks 15-60–15-61filling pressure 15-53gas pressurization 15-64generator 15-6heat storage 15-63high temperature drop 15-63HTW for process steam 15-66main pipe sizing 15-59net positive suction head 15-68nitrogen pressurization 15-64nitrogen pressurizing tank 15-66one pipe diversion 15-50one pipe diversion system 15-59one pipe series 15-50, 15-60operating water 15-49pipe size check 15-59pipe sizing 15-71pipe, valves and fittings 15-69piping design 15-55piping details 15-54pressure drop in fittings 15-56–15-57pressure limitation 15-49pressurization of HTW system 15-63preventing backflow 15-53prevention of freezing 15-49pump construction 15-68pump location 15-52–15-53pump specifications 15-67reduce tank size 15-54seals 15-68service water 15-49steam pressurization 15-63steam pressurizing tank 15-65summer cooling 15-50system adaptability 15-50temperature 15-61two pipe direct return 15-50two pipe direct reverse 15-58two pipe return reverse 15-58two pipe reversed return 15-52types 15-50valve installation 15-69venting of piping 15-70

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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Page 49: HVAC Design&Implementation

INDEX21–8

Hot water heating system (continued)waste steam heat 15-50water circulation below mains 15-49water velocity 15-52welded joints 15-70

Hot water pressure control 13-92Hot water reheat control 13-92–13-94Hot water reheat converter 13-94Hot water system 13-91HTW for process steam 15-66Humidity control 13-10Humidity ratio 2-2Hydronic

close expansion tank 10-7cooling 10-1design layout 10-18diaphragm tank 10-7equipment layout 10-18freeze prevention 10-19heating 10-1medium temperature 10-1open expansion tank 10-7pipe sizing 10-18piping layout 10-19pressure drop 10-19pump selection 10-19temperature classification 10-1

IIdeal gas 2-1Impulse trap 15-29Indoor air quality 4-1

air filter types 4-8carbon media filters 4-10fiber foam filters 4-10HEPA filters 4-10outdoor air requirements 4-7ozone 4-10pollutants and sources 4-5pollutants concentration 4-1, 4-5procedure 4-6standards 4-5ultraviolet light 4-10ventilation procedure 4-1ventilation rates 4-2

Industrial unit heater piping 15-5Infiltration heat loss 6-6Installation in attic 13-5Installation in crawl space 13-5Installation of equipment 13-107Insulation 13-79

prevent sweating 9-177Internal heat

air systems 13-30exhaust air heat recovery 13-31refrigeration heat 13-31refrigeration service 13-31water systems 13-30

Intrinsic property 1-1Inverted bucket trap 15-29Isolation efficiency 16-10

KKibi 20-10Kilns 15-34

LLaundries 15-34Layout plan of piping 9-132Lead lag control 12-28Leaking glands 13-112Length, measures 20-1, 20-8Lifting trap 15-29Lighting heating cooling system 13-22Liquid, measure 20-2, 20-8LMTD method 1-19Load estimating 5-1Lubricants, electric motors 17-39Lubrication of motors 17-39

MMachinery space 13-106Masonery walls coefficient of transmissions 5-12Masonry partitions coefficient of transmissions 5-13Masonry walls coefficient of transmissions 5-11Mebi 20-10Mechanical efficiency 14-2Mechanical equivalent of heat 20-7Metric International System of Units 20-9Microinch 20-1Mil 20-1Minimum deflections 16-9Minimum elevation in drip traps 15-7Mixed air control 13-85, 13-88Mixed air section 13-82Mixing air streams 3-3Mixing box control 13-94Moist air properties 2-6–2-7, 2-18Moisture 13-112Moody’s friction chart 1-9Mortar mixes 14-77Motors

acceleration time 17-9analysis of application 17-18application 17-17application data 17-14bearings 17-20capacitor 17-13capacitor run 17-28–17-29capacitor start 17-28classification by cooling 17-3classifications 17-1

application 17-1electrical type 17-1size 17-1

compressors 17-18, 17-25constant hp 17-21–17-22constant torque 17-21current relay 17-27DC types 17-7design letters 17-1–17-2dynamic loads 17-8dynamics 17-11dynamics of load 17-10enclosure 17-19fans and blowers 17-18full load currents 17-6–17-7heating 17-8, 17-11heating during starting 17-12hermetic compressor 17-25hermetic type 17-25hot wire relay 17-27hp and full load currents 17-6–17-7hp and speed ratings 17-4hp ratings 17-14induction run motor 17-27inertia 17-9internal line break 17-27life 17-11loading 17-17locked rotor current 17-2locked rotor current and torque ratings 17-1locked rotor kva 17-5locked rotor torque 17-5multispeed operation 17-17NEC code 17-6oil burners 17-18open machine 17-3overload with capacitor start 17-27permanent split capacitor 17-27polyphase 17-19polyphase induction motor 17-23protection 17-18quietness 17-20repulsion induction 17-15repulsion start 17-13selections 17-18shaded pole 17-13single phase 17-12, 17-15speed control 17-21speed data 17-14

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Page 50: HVAC Design&Implementation

INDEX 21–9

Motors (continued)squirrel cage induction 17-20–17-21sump pump 17-18synchronous speed 17-24three phase 17-6, 17-28torque and speed 17-2torques 17-9–17-10, 17-14two phase 17-7types 17-12, 17-14, 17-21variable speed 17-24variable torque 17-22–17-23voltage and frequencies 17-3wiring diagram 17-22

Motors and starters 17-1Motors, electric

armature rotors 17-40ball or roller bearings 17-39brushes 17-39commutators 17-39inspection schedule 17-39–17-40lubrication, proper 17-39maintaining and repairing 17-39–17-40maintenance 17-39mechanical condition 17-39monthly inspection 17-40rotors and armatures 17-40squirrel cage rotors 17-40weekly inspection 17-39windings 17-40

Mount types 16-12Multizone system 13-9Multizone unit control 13-84Multizone units 13-4

NNational Electric Code (NEC) 17-6Natural attenuation in ducts 16-24Natural convection 1-12Natural gas 12-15Nautical measure 20-1Net positive suction head 10-11, 15-68Night cycle 13-88Night operation 13-89Nitrogen content 12-15Nitrogen pressurization 15-64Nitrogen pressurizing tank 15-66Noise and vibration 16-1–16-50

addition of decibels 16-14air flow noise 16-27airborne noise through ducts 16-13attenuation 16-1attenuation of a lined duct 16-25band pressure level 16-1bandwidth correction factor 16-6broadband noise 16-1calculation of sound levels 16-14condenser water and chilled water piping 16-13continuous noise 16-1cooling tower location 16-39cooling tower noise control 16-36cooling waters 16-13decibel 16-1, 16-14drive components 16-37duct lining and elbows 16-26duct lining attenuation 16-24ducted system 16-20equipment room and critical spaces 16-7external noise source 16-37fan acoustic properties 16-21fan noise 16-36fan noise estimation 16-23fan noise generation 16-23flow noise by silencers 16-31frequency 16-1frequency limits for octave bands 16-15insertion loss 16-1isolation efficiency 16-10microbar 16-1minimum mounting deflections 16-9mount types 16-12natural attenuation 16-24noise criteria 16-2–16-3

Noise and vibration (continued)octave band 16-1, 16-7, 16-15octave bandwidth correction 16-30open end reflection loss 16-27pitch 16-1ratings and standards 16-7regenerated noise 16-13sabin 16-15sound

absorption coefficients 16-16attenuation 16-10, 16-27attenuation of plenums 16-25level of sources 16-2power allotment at branch 16-24power distribution in branch 16-24power level 16-23–16-24pressure level 16-1, 16-17transmission 16-7

speech interference criteria 16-2steam pressure reducing valves 16-13transformers 16-13vibration isolation 16-7water noise 16-37

Noise criteria 16-2–16-3chart 16-20

Noise from fluid flow 1-11Noise generation 9-3Noise in ducted system 16-20Noise on ducts 13-79

OOff-peak space cooling 13-57Open system 1-2Operating water temperature 15-49Optimized data equations 13-48Optimized data for heat pump 13-47Outdoor air load 5-32Outdoor air requirements 4-4Outdoor temperature effects 13-42Oxygen sensor 12-17Oxygen trim 12-26

PPaper corrugators 15-35Parallel positioning 12-21Partial vapor pressure 2-3Pebi 20-10Performance factor 13-37Pipe

allowable spaces 9-134expansion 9-134layout plan 9-132layout plan length 9-133

Pipe fittings 9-97–9-129dimensions 9-97, 9-129taper pipe thread 9-97–9-129

Pipe sizing 9-1pressure drop 9-1valve and fitting loss 9-1–9-58

Pipingallowances for aging 9-3anchor 15-10application 15-26around door 15-10around obstacle 15-10boiler 15-15capacities, high pressure 15-21capacities, low pressure 15-23capacities, medium pressure 15-21carrying capacity 9-80–9-90closed system 9-4color identification 9-143contraction 15-11corrosion resistance 9-136

metal 9-138design 15-17dimensional capacities 9-80–9-90dimensions 9-80–9-90dripping riser 15-12dripping steam main 15-13erosion 9-3

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Page 51: HVAC Design&Implementation

INDEX21–10

Piping (continued)expansion 15-11flush valve 9-30hydronic system 9-4identification method 9-144lifting condensate 15-14material, protective 9-143–9-144materials 9-4multiple coils 15-14noise 9-4noise generation 9-3obstructions 15-12one pipe system 15-17plastic material 9-29recessed below floor 15-10reducing main 15-10single coils 15-13sizing 15-18, 15-20steam bypass control 15-14steam flow 9-31steam riser 15-10supports 15-16thickness 9-80–9-90two pipe high pressure system 15-18two pipe low pressure system 15-19two pipe medium pressure system 15-19two pipe system 15-17two pipe vacuum system 15-23underwater corrosion 9-136vacuum lift 15-12water 9-3water hammer 9-4

Piping designchecking 15-59checking pipe size 15-58combination system 15-60for branches 15-59for main 15-59one pipe diversion system 15-59one pipe series 15-60two pipe direct return system 15-58two pipe reversed return system 15-58

Piping identification 9-143Plant master control 12-28Plastic piping 9-29, 9-91–9-93

above ground 9-93above ground installation 9-96below ground 9-93below ground installation 9-96chemical resistance 9-94codes and regulations 9-97design parameters 9-93elastomeric seals 9-91flanges 9-93flaring 9-93flow characteristics 9-94heat fusion 9-91insert fitting 9-93installation 9-96joining technique 9-91mechanical couplings 9-91pressure loss 9-92pressure ratings 9-94–9-96solvent cementing 9-91standards and identifications 9-93storage handling 9-96thermal expansion coefficients 9-93threading 9-93types 9-91

Plumbing water piping 9-28Pneumatic pipe sizing 9-73Pneumatic piping 9-72Pour point 12-15Prandtl number 1-12Preheat control 13-91Pressure control 13-94Pressure drop 9-1

air in pipe 9-75–9-77air piping 9-72gas piping 9-63–9-70in fittings 15-56–15-57liquids 9-79return piping 15-23supply piping 15-23vertical piping 9-32

Pressure head 8-1Pressure loss

disk type water meter 9-28plastic piping 9-92

Pressure ratings, plastic piping 9-94–9-96Pressure required in fixtures 9-6Pressure unit conversion 20-2Pressurization of hot water system 15-63Preventing backflow 15-53Prevention of freezing 15-49Process 1-3Propeller unit heat capacities 15-80Properties of gas 12-1Property 1-1, 1-3Psychrometric analysis 2-1Psychrometric chart 2-8Psychrometry 2-1

air composition 2-1degree of saturation 2-2dew point temperature 2-4enthalpy 2-4graphical presentation 2-7humidity ratio 2-2ideal gas 2-1moist air properties 2-6, 2-18relative humidity 2-2saturation 2-4vapor pressure 2-3water properties 2-12wet bulb temperature 2-2, 2-5

Pumpcentrifugal 10-8change of performance 10-9condensate return 15-29construction 15-68location 15-52net positive suction head 10-11operating chsracteristics 10-8specifications 15-67vacuum 15-30

Pumping down 13-112Pure substance 1-1Purging system 13-112

QQuality of steam 1-1

RRadiator capacity 15-79Radiator emission 15-78Rankine degrees 20-7Ratings and standards 16-7Ratings of boilers 15-73Ream, paper 20-3Refrigerant circuit 13-112Refrigerant controls 13-112Refrigerant effect 1-4, 1-6Refrigerant storage in drums 13-112Refrigeration chassis 13-2Regenerated noise 16-13Register 15-89

capacity 15-101, 15-103–15-104loudness 15-106pressure loss 15-101, 15-103–15-104

Reheat system 13-9Relation of air with temperature 14-8, 14-10Relative humidity 2-2Remote condensers 13-2Remote condensing units 13-3Replacing refrigerant 13-112Residential cooling load calculation 7-35Resistance of building materials 5-17, 5-21–5-26Return intake

capacity 15-105pressure loss 15-105

Reverse cycle principle 13-36Reversibility 1-4Reynolds number 1-7

laminar flow 1-8turbulent flow 1-7

Riser drip 15-8

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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Page 52: HVAC Design&Implementation

INDEX 21–11

Roof as a location for AC system 13-105–13-106advantages 13-105automatic control 13-105multiple units 13-105size 13-105ventilation 13-106

Roof numbers 7-8Roof top installation 13-6Roof‘top multizone units 13-81Rotary air to air heat exchanger control 13-95Rotating apparatus 13-114Rotors

heating during starting 17-12wound 17-23

Roughness factors 8-2RPM change 14-3

SSabin 16-15Saturated liquid 1-1Saturated vapor 1-1Saturation 2-4SC for glass 7-50SCL for glasses 7-36Second law of thermodynamics 1-4Selecting air handler units 13-49Service water heating system 15-49Servicing of

air handling system 13-107compresser oil 13-107cooling plant 13-107refrigeration unit 13-108water system 13-107

Shear stress 1-6Shipping measure 20-1Short circuiting 12-16Signs and abbreviations

scientific and engineering 18-8Simple heating and cooling 3-1Single degree freedom vibration isolation 16-7Single duct variable volume control 13-95Single package installations 13-5Single package units 13-1Single package year round units 13-2Single phase induction motors 17-2, 17-4–17-5Single phase motors 17-12Sizing cold water pipe 9-29Slab installations 13-6SLF for glass 7-50Solar augmented heat pump 13-57Solar energy 13-54

cooling system 13-54Solar heating 13-56

operation 13-54storage tank 13-56systems 13-54

Solubility versus temperature 10-5Sound

absorption coefficients 16-16attenuation 16-10duct wall transmission loss 16-32level of sources 16-2levels in a duct 16-32power at branch take off 16-24power level in a duct 16-34pressure 16-35pressure level 16-7, 16-17transmission 16-7, 16-31transmission loss factor 16-32

Sound lining 13-79Space heater 15-83Specific heat 1-2

constant pressure 1-2constant volume 1-2various materials 15-36

Speech interference criteria 16-2Split phase motors 17-12Split system installations 13-7Spray nozzles 13-113Squirrel cage induction motors 17-1–17-2Standard air 14-1Starters

Starters (continued)AC motors 17-31mechanical shocks 17-33motor controllers 17-29open circuit transition 17-36overcurrent protection 17-29overload protection 17-30properties 17-30size with hp 17-32types 17-36winding 17-33

Static efficiency 14-2Steam

ashpalt plants 15-30coils 15-12pressurization 15-63pressurizing tank 15-65riser 15-10

Steam boilerautoclaves 15-37cheese vats 15-31concrete block 15-31dry cleaning 15-34–15-35flat iron work 15-35laundries 15-34ovens 15-35paper corrugators 15-35paper making 15-36pasteurization 15-36platen presses 15-36process heating 15-36restaurants 15-37snow removal 15-37sterilizers 15-37tire recapping 15-38vacuum pans 15-38washers 15-38

Steam heating system 15-1–15-129auditorium type unit ventilator 15-5boiler feed system 15-1boilers

common return header 15-3controlled system header drip 15-6direct return connection 15-3–15-4drip end 15-7Hartford connection 15-3overhead connections 15-4piping connections to boilers 15-1steam main 15-6steam using equipments 15-4supply and return piping 15-6supply header drip 15-6vacuum header drip 15-6

convector piping details 15-4equivalent direct radiation 15-1fin tube piping 15-4hot water generator 15-6industrial unit heater piping 15-5piping connections to boilers 15-1steam supply to heating units 15-1traps 15-1unit heater piping 15-5unit ventilator piping 15-5vacuum heating pump 15-1vacuum pumps 15-1

Steam mainbypass 15-14drip in riser 15-7dripping 15-13rise and drip 15-6splitting 15-7

Steam piping 9-32capacities 9-33chart 9-34–9-58equivalent length of fitting 9-34equivalent length of run 9-33formula 9-31initial pressure 9-33maximum velocity 9-33pressure drop 9-33pressure loss 9-31–9-58size 9-32

Stefan Boltzmann constant 1-14Strainers 13-113Subcooled liquid 1-1

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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Page 53: HVAC Design&Implementation

INDEX21–12

Sulfur content 12-15Summer cycle 13-88Summer operation 13-95Superheated vapor 1-1Supplementary heat 13-47Supply and return header drip 15-6Surface conductance 5-18Surface resistance 5-18Surface temperature calculations 5-9Surroundings 1-2Surveyors measure 20-1, 20-8Symbols

abbreviations 18-8air conditioning piping 18-6fittings 18-7heating piping 18-6piping 18-6plumbing piping 18-7pneumatic tubes 18-7sprinklers 18-7valves, pipe fitting 18-5

System boundary 1-2System design 13-47

TTank transition from winter to summer 13-58Tanks and pans 13-113Tebi 20-10Temperature control 12-28Temperature limit, heat recovery 13-45Thermal

conduction 1-11conduction problems 1-15conductivity 1-11, 5-1–5-2convection 1-12diffusivity 1-12energy 20-7radiation 1-14, 5-4resistance of air space 5-19

Thermodynamiccycles 1-4, 1-6fundamental 1-1system 1-2

Thermostat location 13-10Thermostatic controls 15-94Thermostatic trap 15-28Thermostats 13-43Through wall installations 13-5Tip speed 14-2Ton long and short 20-2Ton, metric 20-8Tramp air 12-16Transmission of coefficients

doors 5-28fenestrations 5-27wood 5-28

Trapair handling unit 15-112–15-116boiler return 15-29cleaning 13-112condensate capacities 15-26connection 15-8flash 15-29float 15-27float sizing 15-41impulse 15-29inverted bucket 15-29lifting 15-29pressure differential 15-26radiation load 15-26safety factor 15-26selection 15-26splitting 15-7thermostatic 15-8types 15-27upright bucket 15-28warm up load 15-26

Troubleshooting 12-15, 12-17Troy weight for gold and silver 20-2Types of heat pumps 13-37

UUnheated temperature calculations 5-9Unit

conversions 20-8systems 20-8

Unit air conditioners 13-114air filters 13-114condensers 13-114cooling coil 13-114fans 13-114motors 13-114piping 13-114

Unit heaterair stream direction 15-120circulation of air 15-120duct furnace 15-118enclosed furnace 15-118exposed wall 15-120floor mounted heavy duty type 15-117floor mounted vertical blower units 15-117full area heating 15-111gas fired 15-109, 15-118–15-119gas fired air heater 15-117industrial type 15-5installations 15-119obstructions 15-120occupants 15-120partial area heating 15-111performance factors 15-109piping 15-5propeller fan type 15-117sizing 15-118spot heating 15-111steam supplied 15-110suspended 15-109suspended blower type 15-117suspended heavy duty units 15-117temperature limits 15-109thermostat locations 15-120too buoyant air 15-109types 15-117

Unit systems 20-8Unit ventilator 13-88, 15-5

auditorium type 15-5piping 15-5

Upright bucket trap 15-28

VVacuum lift 15-12Vacuum pump 15-30Valve and fitting equivalents 9-7–9-27Valve and fitting loss 9-1–9-58Valves 13-113

check 9-139–9-141gate 9-139–9-141globe 9-139–9-141

Variable speed control 13-95Variable volume system 13-17–13-21

cooling considerations 13-20energy requirements 13-19heating and cooling calculations 13-19initial costs 13-18overlapping 13-21

Velocity design criteria 9-3Velocity pressure relation 8-3, 14-38Ventilation 14-1Ventilation heat loss 6-6Vibration 13-106Vibration in pipes 1-11Vibration isolation 16-7Viscosity 1-6Viscosity of liquid 9-78

WWall furnace 15-83Wall type

mass inside insulation 7-28–7-30

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

Page 54: HVAC Design&Implementation

INDEX 21–13

Warm air heating 15-82air volume 15-97–15-99blower characteristics 15-87bonnet capacity 15-85bonnet efficiency 15-85bonnet pressures 15-100combustion air supply 15-93combustion and ventilation air 15-93combustion efficiency 15-85direct fired unit heater 15-83duct arrangement 15-91duct heat loss 15-85duct system 15-88duct transmission efficiency 15-85floor furnace 15-83flue gas loss 15-85forced air furnace 15-83furnace arrangement 15-91gravity furnace 15-82gravity hot air furnace 15-82heat input 15-85industrial warm furnace 15-83pipeless furnace 15-82rating of furnace 15-85register delivery 15-85register free areas 15-100register pressures 15-101register temperature 15-97–15-99registers 15-89return air intake 15-90selection of furnace 15-87selection procedure 15-87space heater 15-83stove 15-82testing of furnace 15-85thermostatic controls 15-94throw from registers 15-100trends 15-88unit heater 15-83wall furnace 15-83

Waste steam heat utilization 15-50Water conditioning 15-16Water flow velocity 15-49Water gauge 14-1

Water hammer 15-11Water in fuel oil 12-18Water piping 9-3, 9-28Water properties 2-12Water to air heat pumps 13-40Water to water heat pumps 13-39Water velocities maximum 9-3Water velocity 15-52Weight

avoirdupois or commercial 20-2measures 20-1, 20-3metric 20-8sheetmetal 14-75–14-76troy, for gold and silver 20-2

Well waterAC systems 13-54precooling 13-55refrigerant condensing 13-55

Wet atomizing steam 12-18Wet bulb temperature 2-2, 2-5Wide open BHP 14-2Window GLF 7-47–7-48Winter cycle 13-88Winter operation 13-96Winterizing chilled water system 13-97Wire, circular mil measurement 20-1Work 1-2

mechanical 1-2shaft 1-2

YYear round remote units 13-3

ZZone day night operation 13-91Zone mixing dampers 13-88Zone types

CLF tables 7-31–7-34SCL tables 7-31–7-34

Zoning installations 13-8

HVAC: Handbook of Heating, Ventilation and Air Conditioning

Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com