Handbook of HVAC for Design and Implementation (1)

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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

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

HVAC: Handbook of Heating, Ventilation and Air Conditioning

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, Muhammed Hussain. 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. TH7011.V46 2006 697--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

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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.

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HVAC: Handbook of Heating, Ventilation and Air Conditioning TABLE OF CONTENTS

1.

FUNDAMENTALS

5.

LOAD ESTIMATING FUNDAMENTALS

(Continued)

1–1 1–3 1–3 1–4 1–4 1–6 1–6 1–11 1–11 1–14 1–15 1–18 1–19

2. 2–1 2–1 2–1 2–2 2–2 2–2 2–2 2–3 2–4 2–4 2–4 2–5 2–6 2–7 2–12 2–18

3. 3–1 3–1 3–2 3–3 3–3 3–5 3–5

4. 4–1 4–1 4–5 4–6 4–8 4–10 4–10 4–10 4–10 4–10

5. 5–1 5–1 5–2 5–4 5–4 5–6 5–8 5–11

5–17 5–18 5–18 5–19 5–21 5–27 5–28 5–29

Fundamentals of Thermodynamics Conservation of Mass First Law of Thermodynamics Second Law, Reversibility, and Possible Processes Thermodynamic Cycles Fundamentals of Fluid Flow Flow in Pipes and Ducts Noise from Fluid Flow Fundamentals of Heat Transfer Overall Heat Transfer Fins and Extended Surfaces Some Details of Heat Exchange Augmentation of Heat Transfer

6. 6–1 6–1 6–2 6–2 6–3 6–3 6–4 6–4 6–6

PSYCHROMETRY Psychrometrics Ideal Gas Approximation Equation of State Humidity Ratio Relative Humidity Degree of Saturation Wet Bulb Temperature Partial Pressure of Water Vapor Dew Point Temperature Saturation Enthalpy Wet Bulb Temperature Properties of Moist Air Psychrometric Chart Presentation Thermodynamic Properties of Water at Saturation Thermodynamic Properties of Moist Air

7. 7–1 7–1 7–2 7–3 7–6 7–6 7–6 7–6 7–7 7–8 7–9 7–11 7–27 7–28 7–31 7–31 7–31 7–35 7–36 7–44 7–46 7–47 7–49 7–50 7–50 7–50

AIR CONDITIONING PROCESSES Introduction Heating and Cooling Process Cooling with Dehumidification Heating with Humidification Adiabatic Mixing of Two Air Streams Evaporative Cooling Heating and Air Conditioning System Cycles

INDOOR AIR QUALITY AND VENTILATION Indoor Air Quality Ventilation Procedure Concentration of Air Pollutants Indoor Air Quality Procedure Filters Hepa Filters Carbon Media Filters Fiber and Foam Filters Ozone Ultraviolet Light

8. 8–1 8–1 8–2 8–7 8–7 8–8 8–8 8–9 8–9 8–12 8–13 8–13 8–14 8–14 8–15 8–15 8–17

LOAD ESTIMATING FUNDAMENTALS Conduction Thermal Conductivities of Materials Convection Thermal Radiation Emissivities of Some Materials Overall Heat Transfer Coefficient Parallel Arrangement Coefficient of Transmission

Relative Thermal Resistances of Building Materials Surface Conductances and Resistances Emittance Values of Various Surafces Thermal Resistances of Plane Airspaces Thermal Properties of Building and Insulating Materials Coefficients of Heat Transmission of Various Fenestrations Transmission Coefficients for Wood and Steel Doors Outdoor Air Load Components

HEATING LOAD CALCULATIONS Introduction Calculating Design Heating Loads Heat loss Through Walls, Roofs, and Glass Area Heat Loss from Walls below Grade Below-Grade Wall U-Factors Heat Loss from Basement Floor Below Grade Heat Loss Coefficients Heat Loss from Floor Slab On Grade Ventilation and Infiltration Heat Loss

COOLING LOAD CALCULATIONS Transfer Function Method (TFM) Heat Source in Conditioned Space Heat Gain from Occupants Heat Gain from Cooking Appliances Heat Gain from Medical Equipments Heat Gain from Computer Heat Gain from Office Equipments CLTD/SCL/CLF Calculation Procedure Cooling Load by CLTD/SCL/CLF Method Roof Numbers CLTD for Roofs CLTD for Walls Code Number for Wall and Roof Wall Types CLTD for Glass Zone Types for CLF Tables Zone Types for SCL and CLF Tables Residential Cooling Load Procedure SCL for Glass CLF for People and Unhooded Equipments CLF for Hooded Equipments Window GLF for Residences CLTD for Residences SC for Windows SLF for Windows Air Exchange Rates

DUCT DESIGN Introduction Pressure Head and Energy Equation Friction Loss Analysis Dynamic Losses Ductwork Sectional Losses Fan System Interface Pressure Changes System Duct System Design Design Considerations Duct Design Methods Duct Design Procedures Automated Duct Design Duct Fitting Friction Loss Example Equal Friction Method Example Resistance in Low Pressure Duct System Example Static Regain Method Example Fitting Loss Coefficients

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HVAC: Handbook of Heating, Ventilation and Air Conditioning iv

9.

TABLE OF CONTENTS

PIPE SIZING

10.

HYDRONIC HEATING AND COOLING SYSTEM

(Continued)

9–1 9–1 9–3 9–3 9–3 9–3 9–3 9–4 9–4 9–6 9–28 9–29 9–29 9–31 9–31 9–32 9–32 9–59 9–59 9–61 9–72 9–72 9–78 9–80 9–80 9–91 9–91 9–93 9–93 9–96 9–97 9–97 9–97 9–132 9–134 9–134 9–136 9–136 9–139 9–139 9–141 9–142 9–142 9–142 9–142 9–143 9–143 9–143 9–144 9–144 9–144 9–144 9–144 9–145 9–157 9–158

10. 10–1 10–4 10–4 10–4 10–4 10–4 10–6 10–6 10–7

Pressure Drop Equations Valve and Fitting Losses Water Piping Flow Rate Limitations Noise Generation Erosion Allowances for Aging Water Hammer Hydronic System Piping Valve and Fitting Pressure Drop Service Water Piping Plastic Pipe Cold Water Pipe Sizing Steam Flow in Pipes Steam Flow Formulas Vertical Pipes Steam Piping Gas Piping For Buildings Residential Piping Commercial-Industrial Piping Compressed Air Systems Compressed Air Viscosity of Liquids Piping Types of Materials Plastics Pipe Joining Techniques Standards for Specification and Identification Design Parameters Installation Codes and Regulations Pipe Fittings Taper Pipe Thread Laying Lengths of Pipe with Screwed Fittings Allowable Spaces for Pipes Expansion of Pipe Corrosion Resistance Pipe Support Spacing Gate, Globe, and Check Valves Operation Maintenance Methods Formulas for Sizing Control Valves To Determine Valve Size To Determine Valve Capacity For Vapors Other Than Steam Identification of Piping Systems Dangerous Materials Fire Protection Materials and Equipment Safe Materials Protective Materials Method of Identification Heat Losses in Piping Heat Losses from Bare Pipe Heat Losses from Steam Piping Heat Loss from Insulated Pipe Cold Surface Temperature

HYDRONIC HEATING AND COOLING SYSTEM Basic System Temperature Classifications Closed Hydronic System Components Design Convectors or Terminal Units Boiler Air Eliminations Methods Pressure Increase Due to Change in Temperature Expansion Tank Expansion Tank Sizing

10–8 Characteristics of Centrifugal Pumps 10–8 Operating Characteristics 10–9 Pump Laws 10–9 Change of Performance 10–10 Centrifugal Pump Selection 10–10 Total Dynamic Head 10–11 Net Positive Suction Head (NPSH) 10–11 Pumping System 10–16 Parallel Pumping 10–17 Series Pumping 10–18 Design Procedures 10–18 Preliminary Equipment Layout 10–19 Final Pipe Sizing and Pressure Drop Determination 10–19 Final Pressure Drop 10–19 Final Pump Selection 10–19 Freeze Prevention

11. 11–1 11–1 11–2 11–4 11–5 11–7 11–7 11–7 11–8 11–9

12.

ENERGY CALCULATION Degree Day 65°F as the Base Application of Degree Days Predicting Fuel Consumption Predicting Future Needs Empirical Constants Load Factor and Operating Hours Limitations Degree-Days Abroad Degree Days for Various US Locations

COMBUSTION

12–1 Combustion Basics 12–3 Efficiency Calculations 12–7 Saving Fuel with Combustion Controls 12–11 Combustion Considerations 12–11 Pressure and Flow Basic Principles 12–12 Atomizing Media Considerations 12–12 Combustion Air Considerations 12–13 Flue Gas Considerations 12–14 Gas Fuel Firing Considerations 12–14 Fuel Oil Firing Considerations 12–15 Operational Rules of Thumb 12–16 Common Application 12–20 Combustion Control Strategies 12–20 Control System Errors 12–20 Combustion Control Strategies 12–21 Parallel Positioning Systems 12–22 Fully Metered Control 12–23 Feedwater Control Systems 12–24 Draft Control 12–26 Oxygen Trim 12–27 Combustion Air Flow Control Techniques 12–28 Flue Gas Recirculation (FGR) 12–33 Fuel Oil Handling System Design 12–33 Determination of Required Flow Rate 12–34 Stand by Generator Loop Systems 12–34 Multiple Pumps 12–34 Burner Loop Systems 12–36 Maximum Inlet Suction 12–37 Pump Discharge Pressure 12–37 Piping System Design 12–37 Pump Set Control System Strategies

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HVAC: Handbook of Heating, Ventilation and Air Conditioning v

TABLE OF CONTENTS

13.

AIR CONDITIONING SYSTEMS

13.

AIR CONDITIONING SYSTEMS

(Continued)

13–1 13–1 13–5 13–7 13–8 13–10 13–14 13–14 13–17 13–18 13–20 13–21 13–22 13–22 13–23 13–26 13–27 13–30 13–31 13–31 13–36 13–36 13–36 13–37 13–37 13–38 13–39 13–40 13–40 13–41 13–41 13–42 13–42 13–43 13–43 13–44 13–44 13–45 13–47 13–47 13–47 13–48 13–48 13–49 13–54 13–54 13–54 13–60 13–60 13–60 13–65 13–65 13–66 13–66 13–67 13–68 13–68 13–69 13–69 13–70 13–73 13–76 13–77 13–80 13–81 13–81 13–84 13–88 13–88 13–88

Air Conditioning Systems Single Package Units Single Package Installations Installation of Split Systems Zoning Unitary Installations Selection Procedure Evaporative Air Conditioning Permissible Air Motion Variable Volume AC System Initial Costs Cooling Considerations Overlapping Heat Recovery Heating Cooling Systems Air Systems Controls Air Water Systems Sources of Internal Heat Heat from Service Refrigeration Exhaust Air Heat Recovery Systems Heat Pumps Reverse-Cycle Principle Coefficient of Performance Heating Season Performance Factor Types of Heat Pumps Air-to-Air Heat Pumps Water-to-Water Heat Pumps Water-to-Air Heat Pumps Air-to-Water Heat Pumps Ground Source Heat Pumps Special Heat Sources Operating and Installation Factors Outdoor Temperature Effects Thermostats Heat Anticipators Equipment Arrangement Electrohydronic Heat Recovery Cooling Cycle System Design Supplementary Heat Optimized Data for Heat Pump Development of Equations Development of Tables Selecting Air Handling Units Well Water Air Conditioning Heat Pump/Solar Energy Application System Description and Operation High Velocity Dual Duct Systems Advantages and Disadvantages Dual Duct Cycles Duct Sizing Technique Large vs. Small Ducts Design Velocity Maximum Velocity Sizing High Pressure Ducts Return Air Ducts Low Pressure Ductwork Basic Arrangement Zoning Ceiling Plenum Modular Type Office Buildings Constant Volume Mixing Units Apparatus Floor Area Construction Details Automatic Control Applications Rooftop Multizone Units Multizone Unit Control Damper Control Economizer Control Cycle Unit Ventilator Control

13–91 13–94 13–95 13–95 13–97 13–97 13–99 13–102 13–104 13–105 13–105 13–106 13–107 13–107 13–107 13–107 13–107 13–107 13–108 13–108 13–108 13–108 13–108 13–108 13–108 13–108 13–110 13–111 13–111 13–111 13–112 13–112 13–112 13–112 13–113 13–113 13–113 13–114 13–114 13–114

14.

Hot Water System Control Mixing Box Control Rotary Air-to-Air Heat Exchanger Control Automatic Control for Dual Duct System Winterizing Chilled Water System Water Circulation to Prevent Freeze-Up Mechanical Draft Cooling Towers Atmospheric Cooling Towers Quantity of Cooling Water Required Roof is a Location for AC Equipment Advantages of Roof Disadvantages of Roof Servicing Cooling Plant Servicing Cooling Plant for Summer Use Water System Air Handling System Compressor Oil Condenser Refrigeration Unit Check Oil Compressor Air Conditioning Equipment Maintenance Air Handling Equipment Air Distribution Equipment Water-Using Equipment Cooling Equipment Air Conditioning Maintenance Schedule Unit Air Conditioners Central Systems Condensing Water Circuit Cooling Water System Filters and Ducts Air Conditioning Maintenance Procedure Refrigerant Circuit and Controls Condensing Water Circuit Cooling Water System Filters and Ducts Rotating Apparatus Unit Air Conditioners Checklist for Air Conditioning Surveys

AIR HANDLING AND VENTILATION

14–1 Terminology, Abbreviations, and Definitions 14–3 Fan Laws 14–11 Fan Performance Curves 14–16 Class Limits for Fans 14–21 Fan Selection 14–26 Fan Inlet Connections 14–27 Fan Discharge Conditions 14–31 Useful Fan Formulas 14–32 Nomographs for Fan Horsepower 14–32 Monographs for Fan Horsepower and Actual Capacity 14–34 Fan Selection Questionnaire 14–37 Air Flow in Ducts 14–40 Pitot Traverse 14–40 Friction Losses 14–40 Correction for Roughness 14–40 Rectangular Duct 14–52 Air Balancing and Air Turning Hardware 14–56 Air Distribution 14–56 Fire Dampers and Fire Protection 14–56 Duct System Design 14–59 High Velocity System Design 14–68 Step by Step Design 14–68 Main Duct 14–70 Branch Trunk Ducts 14–71 Single Branch Lines 14–72 Duct Design by Computer 14–73 Fibrous Glass Duct Construction

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TABLE OF CONTENTS

AIR HANDLING AND VENTILATION

(Continued)

15–1 15–1 15–1 15–3 15–3 15–3 15–4 15–4 15–4 15–26 15–30 15–39 15–40 15–40 15–41 15–41 15–46 15–49 15–49 15–49 15–49 15–49 15–49 15–49 15–49 15–50 15–50 15–50 15–50 15–50 15–52 15–52 15–52 15–52 15–53 15–53 15–53 15–53 15–53

STEAM HEATING SYSTEM DESIGN

(Continued)

14–75 Determining Required Air Volume 14–75 Estimating Weight of Metal 14–77 Apparatus Casing Construction 14–77 Condensate Drains for Air Conditioning Units 14–78 Air Filters and Dust Collectors 14–78 Air Filters 14–79 Dust Collectors 14–82 Dry Centrifugal Collectors 14–82 Wet Collectors 14–82 Fabric Collectors 14–83 Electrostatic Precipitators 14–83 Breeching Design and Construction 14–83 Expansion 14–84 Aerodynamics 14–85 Access 14–85 Round Breeching Construction 14–85 Rectangular Breeching Construction 14–90 Chimney Draft and Velocities 14–92 Forced Draft and Draft Control 14–94 Sizing of Large Chimneys 14–95 Chimney Design and Construction 14–96 Balancing Small Air Conditioning Systems 14–97 Balancing Medium and Large Systems 14–98 Balancing Duct Distribution 14–98 Balancing Systems Using Booster Fans 14–99 Air Balancing by Balancing and Testing Engineers

15.

15.

STEAM HEATING SYSTEM DESIGN Large Systems Equivalent Direct Radiation Piping Connections to Boilers Direct Return Connection Common Return Header Two Boilers with Common Return Header and Hartford Connection Two Boilers with Separate Direct Return Connections from Below Separate Direct Return Connections Connections to Steam Using Equipment Piping Application Industrial and Commercial Steam Requirements Flash Steam Calculations Sizing of Vertical Flash Tanks To Size Flash Tank To Size Float Trap Airbinding Estimating Friction in Hot Water Piping Hot Water Heating Systems Service Water Heating Operating Water Temperature Air Removal from System Water Flow Velocity Prevention of Freezing Water Circulation below Mains Limitation of Pressure System Adaptability Use of Waste Steam Heat Heat from District Steam System Summer Cooling Types of Water Heating Systems Design Recommendations for Hot Water Systems Water Velocity Pump Location Air Venting Balancing Circuits Filling Pressure Preventing Backflow Connecting Returns to Boiler Locating the Circulating Pump

15–53 15–54 15–54 15–55 15–58 15–58 15–58 15–59 15–59 15–59 15–59 15–60 15–60 15–60 15–60 15–61 15–61 15–63 15–63 15–63 15–63 15–63 15–64 15–64 15–64 15–65 15–65 15–65 15–65 15–66 15–66 15–66 15–67 15–67 15–67 15–68 15–68 15–68 15–68 15–69 15–69 15–69 15–69 15–69 15–70 15–70 15–70 15–71 15–73 15–73 15–74 15–76 15–81 15–81 15–81 15–81 15–81 15–82 15–82 15–83 15–85 15–85 15–86 15–87 15–87 15–87 15–88 15–88 15–88 15–89 15–90

Sizing the Expansion Tank Compressed Air to Reduce Tank Size Piping Details Design of Piping Systems Design of Two Pipe Reversed Return System Final Check of Pipe Sizes Design of Two Pipe Direct Return System Piping for One-Pipe Diversion System Sizing Piping for Main Sizing Piping for Branches Pipe Size Check Piping for One-pipe Series System Combination of Piping Systems Sizing Hot Water Expansion Tanks Conditions Affecting Design Sizing Hot Water Expansion Tanks High Temperature Water Systems High Temperature Drop Heat Storage Limitation of Corrosion Pressurization of HTW System Steam Pressurization Gas Pressurization Air Pressurization Nitrogen Pressurization Expansion Tanks Expansion Conditions Determining Expansion Tank Size Location of Steam Pressurizing Tank Nitrogen Pressurizing Tanks Application of HTW for Process Steam Circulating Pumps Pumps for HTW Systems Manufacturer’s Information Pump Specifications Net Positive Suction Head Effect of Cavitation Within Pump Pump Construction for HTW Systems Circulating Pump Seals Boiler Recirculating Pump Boilers for HTW Systems Boiler Emergency Protection Pipe, Valves, and Fittings for HTW Systems Valve Installation Welded Joints Venting of Piping Effect of Load Variation on Operation Pipe Sizing for HTW Systems Ratings of Steel Boilers Ratings Ratings for Steel Boilers Stack Dimensions Heating and Cooling Media Brine Glycerine Glycol Other Media Warm Air Heating Early Types Current Types Furnace Performance Testing and Rating of Furnaces Acceptable Limits Selection of Furnace Rule for Selection Blower Characteristics Blower Sizes Duct System Characteristics Trends Warm Air Registers Return Air Intakes

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HVAC: Handbook of Heating, Ventilation and Air Conditioning vii

TABLE OF CONTENTS

15.

STEAM HEATING SYSTEM DESIGN

(Continued)

15–91 15–94 15–94 15–95 15–95 15–109 15–109 15–112 15–117 15–124

16. 16–1 16–1 16–2 16–2 16–2 16–7 16–7 16–7 16–9 16–13 16–13 16–13 16–14 16–14 16–14 16–15 16–17 16–20 16–23 16–23 16–24 16–24 16–24 16–25 16–26 16–27 16–27 16–31 16–31 16–32 16–36 16–36 16–37 16–37 16–37 16–38 16–39 16–39 16–39 16–39 16–39 16–40 16–40 16–40 16–40 16–42 16–42 16–42 16–42 16–43 16–43 16–43 16–43 16–43 16–44 16–44 16–44

16.

NOISE AND VIBRATION CONTROL

(Continued)

Arrangement of Furnace and Ducts Basic Thermostatic Controls Continuous Air Circulation Continuous Blower Operation Intermittent Blower Operation Steam Supplied Unit Heater Gas Fired Radiant Heaters Sizing of Steam Traps Unit Heaters Checklist for Heating System Servicing

NOISE AND VIBRATION CONTROL Noise and Vibration Definitions and Terminology Noise Criteria Speech Interference Criteria Sound Levels of Sources Ratings and Standards Airborne Sound Transmission Vibration Isolation Isolation Mount Selection Airborne Noise Through Ducts Regenerated Noise Other Mechanical Noise Sources Calculation of Sound Levels from HVAC Systems Description of Decibels Addition of Decibels The Sabin Determination of Sound Pressure Level Noise in Ducted Systems Fan Noise Generation Estimating Fan Noise Distribution of Sound Power at Branch Takeoffs Attenuation of Untreated Duct Duct Lining Attenuation Sound Attenuation of Plenums Duct Lining and Elbows Open End Reflection Loss Air Flow Noise Flow Noise Generation of Silencers Sound Transmission Through Duct Walls Calculation of Sound Levels in Ducted Systems Control of Cooling Tower Noise Fan Noise Water Noise Drive Components External Noise Sources Configuration Factors Location Reducing Sound Generated Half-Speed Operation Oversizing of the Tower Changing Leaving Conditions Sound Absorbers Obtaining Desired Sound Levels Acoustical Problems in High Velocity Air Distribution System Noise Air Handling Apparatus Rooms Selection of Fan Isolation Bases Apparatus Casings Dampers and Air Valves Flexible Connectors Air Distributing Systems Duct Velocities Choice of Duct Design Method Ductwork Adjacent to Apparatus Room Duct Connections to Apparatus Casings Type Duct Construction Fittings for High Velocity Ductwork

16–45 16–45 16–46 16–46 16–46 16–46 16–47 16–47 16–48 16–49

17. 17–1 17–1 17–2 17–2 17–3 17–3 17–6 17–6 17–8 17–8 17–9 17–10 17–11 17–12 17–12 17–12 17–15 17–15 17–16 17–17 17–18 17–18 17–18 17–19 17–19 17–20 17–20 17–20 17–21 17–21 17–21 17–23 17–24 17–24 17–25 17–25 17–29 17–29 17–29 17–30 17–31 17–33 17–33 17–33 17–33 17–36 17–36 17–37 17–39 17–39

Take-off Fittings Dual Duct Area Ratio Dampers as a Noise Generating Source Sound Barrier for High Velocity Ductwork Sound Traps Cross Over of Horizontal Dual Duct Mains Testing of High Pressure Ductwork Terminal Devices Radiation Protection at Wall Openings for Duct or Pipe Medical Installations

MOTORS AND STARTERS NEMA Motor Classifications Locked Rotor Torque Classification of Single-Phase, Induction Motors by Design Letter Torque, Speed, and Horsepower Ratings for Single-Phase Induction Motors Classification by Environmental Protection and Method of Cooling Standard Voltages and Frequencies for Motors The National Electrical Code Grounding Motor and Load Dynamics, and Motor Heating Torque Speed Relationships Torque, Inertia, and Acceleration Time Dynamics of the Motor and the Load Motor Heating and Motor Life Rotor Heating During Starting Single Phase Motors Types of Motors Repulsion-Induction Large Single-Phase Motors Application Loading Motor Protection Motor Selection Analysis of Application Polyphase Motors Enclosure Bearings Quietness Polyphase, Squirrel Cage Induction Motors Speed Control Two-Speed Polyphase, Squirrel Cage Induction Motors Two Speed Motors Come in Two Types Wound-Rotor Polyphase Induction Motors Variable Speed Synchronous Motors Hermetic Type Motor Compressors Hermetic Compressors to 5 hp Starters Motor Controllers Overcurrent Protection Overload Protection Starters for Large AC Motors Winding and Reduced-voltage Starting Electric Utility Limitations Minimizing Mechanical Shocks Application Types of Starters Open Circuit Transition Advantages and Disadvantages Useful Formulas Electric Motor Maintenance

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HVAC: Handbook of Heating, Ventilation and Air Conditioning viii

18.

TABLE OF CONTENTS

DESIGN PROCEDURE, ABBREVIATIONS, SYMBOLS

20.

UNITS AND CONVERSIONS

(Continued)

18–1 18–1 18–1 18–1 18–5 18–6 18–7 18–8 18–9

19.

Design Procedure Contract and Mechanical Drawings HVAC Drawings Floor Plans Valve Symbols Piping Symbols Pipe Fittings Symbols Abbreviations for Scientific and Engineering Terms Lists of Abbreviations and Symbols

CLIMATIC DESIGN INFORMATION

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

20. 20–1 20–1 20–1 20–1 20–1 20–1 20–1 20–2 20–2 20–2 20–2 20–2 20–2 20–2 20–2 20–3

UNITS AND CONVERSIONS

20–4 U.S. System And Metric System Conversion 20–4 Length and Area 20–4 Mass and Density 20–5 Volume and Flow 20–6 Force, Energy, Work, Torque and Power Conversion 20–7 Velocity and Acceleration 20–8 Metric Systems Of Measurement 20–8 Measures of Length 20–8 Square Measure 20–8 Surveyors Square Measure 20–8 Cubic Measure 20–8 Dry and Liquid Measure 20–8 Measures of Weight 20–10 Binary Multiples 20–10 Terminology of Sheet Metal

21.

INDEX

U.S. Customary Unit System Linear Measures Surveyor's Measure Nautical Measure Square Measure Cubic Measure Shipping Measure Dry Measure Liquid Measure Old Liquid Measure Apothecaries' Fluid Measure Avoirdupois or Commercial Weight Troy Weight, Used for Weighing Gold and Silver Apothecaries' Weight Measures of Pressure Miscellaneous

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HVAC: Handbook of Heating, Ventilation and Air Conditioning PREFACE

ix

This Handbook provides comprehensive technical information in a modular form to heating, ventilating, and air conditioning (HVAC) designers and practitioners, namely engineers, architects, contractors, 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 topics and chapters have been introduced and previous information updated or rewritten. Examples using software solution tools have been added alongside traditional solutions using formulae from the handbook. The organization, however, remains, in the literal sense, a handbook. We gratefully acknowledge the contributors and editors of the aforementioned Handbook of Air Conditioning, Heating, and Ventilating, whose knowledge is embedded throughout the present book. We did not have the opportunity to meet any of them, but their written legacy has left an indelible 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 acknowledge their permission to use material from various publications, especially the latest ASHRAE Handbook series. ASHRAE Publications 1791 Tullie Circle, NE Atlanta, GA 30329 Web Site: www.ashrae.org We also acknowledge three corporations for supplying us with material for inclusion in the Handbook. We profusely thank Mr. Michael White of Bell & Gossett (an ITT Division), Mr. Kent Silveria and Mr. Thomas Gorman of Trane Corporation, and Mr. Steven Boediarto of Preferred Utilities, for facilitating the acquisition of these materials. The Bell & Gossett corporation has graciously provided the ESP-PLUS software package to accompany the Handbook. This software, a $100 value, permits users to select components based on design or operating conditions. Bell & Gossett (ITT Fluid Handling) 8200 N. Austin Ave Morton Grove, IL 60053 Web Site: www.bellgossett.com The Trane corporation has generously allowed us to include their Trace Load 700 load calculation limited capability demonstration version software with the Handbook. Trane C.D.S. Department 3600 Pammel Creek Road La Crosse, WI 54601 Web Site: www.trane.com Copyright 2007, Industrial Press Inc., New York, NY - www.industrialpress.com

HVAC: Handbook of Heating, Ventilation and Air Conditioning x

PREFACE

We are also grateful to the Preferred Utilities corporation for making available their publication on the topic of combustion analysis, and consenting to let us base our combustion chapter on it. Preferred Utilities Mfg. Corp 31-35 South Street Danbury, CT 06810 Web Site: www.preferred-mfg.com We acknowledge the input of our good friend, colleague, and HVAC critic, Mr. Naji Raad, whose experience in the profession provided a critical review of the manuscript. We thank our editors at Industrial Press, Mr. Christopher McCauley and Mr. Riccardo Heald, for their editorial input and suggestions, for reading the manuscript as it developed, and keeping the project on track; and Janet Romano for her cover design and production assistance. We acknowledge the effort of the many students at Polytechnic University who helped in researching for material, proofreading the manuscript, 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 Kathleen McKenzie, freelance book editor, for her considerable contribution to this Handbook’s style, format and readability. Every effort has been made to prevent errors, but in a work of this scope it is inevitable that some may creep in. We request your forgiveness and will be grateful if you call any such errors to our attention by emailing them to [email protected]. Ali Vedavarz, Sunil Kumar, Muhammed Iqbal Hussain New York City December 2006

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 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 technical 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 Polytechnic University, Brooklyn, New York, where he teaches courses in HVAC design and energy systems. 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 Polytechnic 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 associate editor of, Machinery’s Handbook.

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HVAC: Handbook of Heating, Ventilation and Air Conditioning

PSYCHROMETRY PSYCHROMETRY

P = P1 + P2 + P3 For atmospheric or moist air

Psychrometrics.—Psychrometrics is the study of the measurement of the moisture content of atmospheric air (moist air). Atmospheric air, or moist air is a mixture of many gases and pollutants plus water vapor. The water vapor (moisture) in atmospheric air exists in a superheated state at a very low pressure, usually less than 1 psia. One can also define atmospheric air as a mixture of dry air and water vapor (moisture). In 1949, a standard composition of dry air was defined by the International Joint Committee on Psychrometric Data as shown in Table 2-1.

P = P N + P O + P CO + P Ar + P v 2

Molecular Mass 32.000 28.016 39.944 44.010

Equation of State.—The ideal gas for dry air and water vapor is as follows: 1. For dry air: P a V = n a RT = m a R a T Pa = ρa Ra T

or

Pa νa = Ra T

or

Pv = ρv Rv T

or

Pv νv = Rv T

K

53.34 38.66

0.240 0.125

1.00 0.523

0.171 0.075

0.716 0.316

1.400 1.667

44.01

35.10

0.203

0.85

0.158

0.661

1.285

( P a + P v )V = ( n a + n v )RT

28.01

55.16

0.249

1.04

0.178

0.715

1.399

0.753 3.153 2.44 10.22 0.403 1.690 0.177 0.741 0.157 0.657 0.335 1.402

1.667 1.404 1.320 1.400 1.395 1.329

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

1.250 5.23 3.430 14.36 0.532 2.23 0.248 1.04 0.219 0.917 0.445 1.863

(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; 1 5 4 5 . 3 2 f t - l b f / l b -m o l -° R , o r 8 3 1 4 . 4 1 J/kg-mol-°K; T =absolute temperature The mixture also obeys the perfect gas equations:

28.97 39.94

4.003 386.0 2.016 766.4 16.04 96.35 28.016 55.15 32.000 48.28 18.016 85.76

(4)

P v V = n v RT = m v R v T

kJ/kg-K

Btu/lbm -R

kJ/kg-°K

Btu/lbm- R

ft -lbf /lbm -R

Relative Molecular Mass

Symbol

or

2. For water vapor:

Table 2-2. Properties of Gases

Gas Air … Argon Ar Carbon CO2 dioxide Carbon CO monoxide Helium He Hydrogen H2 CH4 Methane N2 Nitrogen O2 Oxygen H2O Steam

(3)

Pv =partial pressure of water vapor

Ideal Gas Approximation.—Atmospheric air pressure of 14.7 psi obeys the ideal gas law with sufficient accuracy for most engineering applications. Errors in calculating the fundamental psychrometric parameters, such as enthalpy, specific volume, and humidity ratio of saturated air at 14.7 psi are less than 0.7% for a temperature range of 60°F to 120°F when ideal gas relationships are used. Accordingly, we will assume that atmospheric air behaves as ideal gases with constant specific heat. Table 2-2 gives the properties of some ideal gases. Cv

(2)

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

Volume Fraction 0.2095 0.7809 0.0093 0.0003

Cp

2

P = Pa + Pv

In HVAC study, psychrometry is commonly taken to mean the study of atmospheric moisture and its effect on buildings and building systems.

R

2

Equation (2) can be written as

Table 2-1. Composition of Dry Air Constituent Oxygen Nitrogen Argon Carbon dioxide

(1)

PV = nRT

or

(6)

n =na + nv is the total number of moles in the mixture. To compare values for moist air assuming ideal gas behavior with actual table values, consider a saturated mixture of air and water vapor at 75°F. Table 2-3 gives the saturation pressure Ps of water as 0.43 lbf/ft2. For saturated air this is the partial pressure (Pv) of the vapor. The mass density is 1/v = 1/739.42 or 0.001352 lbm/ft3. By Equation (5) we get

Fundamental Parameters.—Atmospheric pressure or moist air pressure: Dalton’s law for a mixture of ideal gases states that the mixture pressure is equal to the sum of the partial pressures of the constituents: 2–1

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–2

PSYCHROMETRY

Pv 0.43 × 144 --1- = ρ = -------- = --------------------------------------------ν Rv T 85.78 × ( 460 + 75 ) = 0.001349 lb m /ft

Pv V m v = --------Rv T

Pa V m a = --------Ra T

and

(11)

3

This result is accurate within about 0.2 percent. For nonsaturated conditions water vapor is superheated and the agreement is generally better. Humidity Ratio W.— The humidity ratio W is the ratio of the mass of the water vapor mv to the mass of the dry air ma in the mixture. m W = ------v ma

(7)

Pv Ra W = ----------Pa Rv

(12)

For the air-water vapor mixture, Equation (12) reduces to Pv 18.015P W = ----------------------v- = 0.6219 -----Pa 28.965P a 0.6219P = ----------------------v P – Pv

(13)

Combining Equation (10) and Equation (13) gives Relative Humidity φ.— The relative humidity is the ratio of the mole fraction of the water vapor xv in a mixture to the mole fraction xs of the water vapor in a saturated mixture at the same temperature and pressure: x Φ = ----vxs

(8) T, P

For a mixture of ideal gases, the mole fraction is equal to the partial pressure ratio of each constituent: P x v = -----vP

and

P x s = -----s P

(9)

since the temperature of the dry air and the water vapor are assumed to be the same in the mixture. Substituting Equation (9) in Equation (8) we find Pv ⁄ P P Φ = ------------ = -----vPs ⁄ P Ps

(10) T, P

where Pv =partial pressure of water vapor at temperature T ; and Ps =saturation pressure of water vapor at temperature T and pressure P (Values of P s may be obtained from Table 2-3). Using the ideal gas law we can derive a relation between the relative humidity φ and the humidity ratio W: m W = ------v ma

WP a Φ = --------------------0.6219P s

(14)

Degree of Saturation.—The degree of saturation µ is the ratio of the humidity ratio W to the humidity ratio Ws of a saturated mixture at the same temperature and pressure: W µ = -----Ws

(15) T, P

Wet Bulb Temperature (Tw).—Fig. 2-1 is a schematic drawing of a device that measures wet and dry-bulb temperatures. The various instruments used to take these measurements are called psychrometers. When unsaturated air is passed over a wetted thermometer bulb, water evaporates from the wetted surface and latent heat absorbed by the vaporizing water causes the temperature of the wetted surface and the enclosed thermometer bulb to fall. As soon as the wetted surface temperature drops below that of the surrounding atmosphere, heat begins to flow from the warmer air to the cooler surface, and the quantity of heat transferred in this manner increases with an increasing drop in temperature. On the other hand, as the surface temperature drops, the vapor pressure of the water becomes lower, and, hence, the rate of evaporation decreases. Eventually, a temperature is reached where the rate at which heat is transferred from the air to the wetted surface by convection and conduction is equal to the rate at which the wetted surface loses heat in the form of latent heat of vaporization. Thus, no further drop in temperature can occur. This temperature is known as the wet-bulb temperature (Tw).

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–3

PSYCHROMETRY

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

As moisture evaporates from the wetted bulb, the air surrounding the bulb becomes more humid. Therefore, in order to measure the wet-bulb temperature of the air in a given space, a continuous sample of the air must pass around the bulb. The purpose of the fan in Fig. 2-1 is to cause the air to be drawn across the wetted bulb. Conventional air velocities used are between 500 and 1000 fpm for normal size thermometer bulbs. Soft, fine-meshed cotton tubing is recommended for the wick; it should cover the bulb plus about an inch of the thermometer stem. The wick should be watched and replaced before it becomes dirty or crusty. Distilled water is recommended to give greater accuracy for a longer period of time. Fig. 2-2 shows a device called a sling psychrometer. It is commonly used especially for checking conditions on a job. The instrument is rotated by hand to obtain the air movement across the bulbs. The instrument is rotated until no further change is indicated on the wet bulb. The reading taken at that time is the air wet-bulb temperature. Thermodynamic wet-bulb temperature (T*), sometimes called adiabatic saturation temperature, is discussed later.

Pv, P, and Pw must have consistent units, either in Hg or psia. At temperatures below 32°F, Equation (16) applies only to temperatures of air and water vapor over supercooled water. For partial pressures of water vapor over ice, the denominator becomes 3160 − 0.09Tw, and Pw must 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 temperature of 80°F and a wet-bulb temperature of 70°F. The barometric pressure is 29.90 in. Hg. Determine the partial pressure of the water vapor and of the dry air in the sample of moist air. Solution: From Table 2-3 at 70°F wet-bulb temperature, find Pw = 0.3632 psia. The barometric pressure of 29.90 in. Hg is converted by (29.90) (0.491) = 14.681 psia. By Equation (16) ( P – Pw ) ( T – Tw ) P v = P w – -----------------------------------------2831 – 1.43T w ( 14.681 – 0.3632 ) ( 80 – 70 ) = 0.3632 – ------------------------------------------------------------------2831 – ( 1.43 ) ( 70 ) = 0.3107 psia Since P = Pa+ Pv Pa = P – Pv = 14.681 – 0.3107 = 14.37 psia

Partial Pressure of Water Vapor (Pv).—S e v e r a l equations for calculating this partial pressure have been proposed and used. Carrier’s equation, first presented in 1911, has been frequently used with a high degree of accuracy. The equation makes use of the easily obtainable wet and dry-bulb temperatures, and its present form is ( P – Pw ) ( T – Tw ) P v = P w – -----------------------------------------2831 – 1.43T w

(16)

where Pw =partial pressure of water vapor saturated at wet-bulb temperature Tw; P =barometric pressure; and T, Tw = dry and wet-bulb temperatures, respectively, in °F

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

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–4

PSYCHROMETRY

Dew Point Temperature (Td).—During the various seasons of the year, especially during the summer months, in localities where the water supply is cool, it is common to see the outside surface of bare cold water pipes covered with moisture. Another common sight is that of a glass of ice water with its outside surface covered with a film of moisture. The term often used to describe the appearance of moisture on cold surfaces is sweating, as though the moisture came through the walls of the pipe or the glass. What is actually happening is that the outside of the pipe or the glass is at or below the saturation temperature corresponding to the partial pressure of the water vapor in the surrounding air. This saturation temperature is known as the dew-point (Td) temperature, the temperature at which condensation first starts to appear on the cold surface as the moist air is cooled at constant pressure. Example 1, we calculated the partial pressure of the water vapor in the air to be 0.3107 psia. Referring to Table 2-3, we find that the saturation temperature corresponding to a pressure of 0.3107 psia is 65.5°F by interpolation. Therefore, 65.5°F is the dew-point temperature of the air sample. If any surface located in this air sample were at that temperature, moisture would start to condense on the surface. Air itself does not condense nor does it have anything to do with the cooling and condensation of the water vapor. Actually, the same cooling and condensation of the water vapor would take place if no air were present and the entire process were carried out in a closed vessel under vacuum. Since this definition of the dew point temperature is in common use, however, we will use it in our discussion. At the dew-point temperature and below, the air is said to be saturated because the air is mixed with the maximum possible weight of water vapor. If the mixture of air and water vapor is cooled at constant pressure, but remains above the dew-point temperature, there will be no condensation. However, as the mixture of air and water vapor is cooled, the volume of each component will contract in the same proportion because both are cooled through the same temperature range. In other words, if a mixture consisting of 1 pound of dry air and 0.15 pound of water vapor is cooled, the resulting smaller volume will still contain 1 pound of dry air and 0.15 pound of water vapor as both gases will contract in the same proportion. Changes in the temperature of an air-water vapor mixture do not affect the amount of water vapor mixed with each pound of air as long as the mixture is not cooled down to the dew-point temperature. Under these conditions, the mass of water vapor per pound of dry air will remain the same regardless of the temperature changes. An air-water vapor mixture at a dry-bulb temperature higher than its dew-point temperature is said to be unsaturated and the water vapor in the mixture is superheated.

At a given total pressure, the dew-point of a mixture is fixed by the humidity ratio W or by the partial pressure of the water vapor. Thus Td, W, and Pv are not independent properties. Saturation.—The term "saturation" denotes the maximum amount of water vapor that can exist in one cubic foot of space at a given temperature and is essentially independent of the mass and pressure of the air that may simultaneously exist in the same space. Frequently, we speak of "saturated air". However, it must be remembered that the air is not saturated; it is the contained water vapor that may be saturated at the air temperature. Enthalpy.—The enthalpy of a mixture of ideal gases is equal to the sum of the enthalpies of each component: h = h a + Wh s

(17)

Atmospheric air and water vapor mixture is usually referenced to the mass of dry air. This is because the amount of water vapor may vary during some processes but the amount of dry air typically remains constant. Each term in Equation (17) has units of energy per unit mass of dry air. With the assumption of ideal gas behavior, the enthalpy is a function of temperature only. If zero Fahrenheit or Celsius is selected as the reference state where the enthalpy of dry air is zero, and if the specific heats Cpa and Cpv are assumed to be constant, simple relations result: h a = C pa T h s = h g + C pv T

(18)

where hg =enthalpy of saturated vapor at that temperature, at 0°F is 1061.5 Btu/lb m and 2501.2 kJ/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 h = ( 0.24T + W ( 1061.2 + 0.444T ) ) Btu/lb ma

(19)

h = ( 1.0T + W ( 2501.3 + 1.86T ) ) kJ/kg (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) Ps Ps W = 0.6219 ------ = 0.6219 --------------Pa P – Ps 0.3633 = 0.6219 ⎛ ---------------------------------------⎞ ⎝ 14.696 – 0.3633⎠ 0.3633 = 0.6219 × ------------------14.3327 = 0.015764

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–5

PSYCHROMETRY

As per Equation (19) h = 0.24T + W ( 1061.2 + 0.444T ) = ( 0.24 × 70 + 0.015764 ( 1061.2 + 0.444 × 70 ) ) = 34.01 Btu/lb ma Thermodynamic Wet-bulb Temperature (T*).— Fig. 2-3 represents an idealized, fully insulated flow device where unsaturated moist air enters at dry-bulb temperature T1 enthalpy h1, and humidity ratio W1. When

this air is brought into contact with the water at a lower temperature, the air is both cooled and humidified. If the system is fully insulated so that no heat is transferred into or out of the system, the process is adiabatic and if the water is at a constant temperature, the latent heat of evaporation can come only from the sensible heat given up by the air in cooling. The quantity of water present is assumed to be large (large surface area and quantity) compared to the amount evaporated into the air. We assume that 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 the device where it is saturated is identical to the temperature of the water, this temperature is called the adiabatic saturation temperature or, more commonly, the thermodynamic wet-bulb temperature (T*). Thus, in Fig. 2-3, the saturated air leaving the device will have properties T2*, h2*, and W2*. Liquid water must be supplied to the device having an enthalpy hf2 at T2* for the process to be steady-flow. Assuming steady-flow conditions exist, the energy equation for the process is h 1 + ( W 2∗ – W 1 )h f2∗ = h 2∗ (21) The asterisk is used to denote properties at the thermodynamic wet-bulb temperature. The temperature corresponding to h2 for the given values of h1 and W1 is the defined thermodynamic wet-bulb temperature. Equation (21) is exact since it defines the thermodynamic wet-bulb temperature T*. Substituting the approximate ideal gas relationship for h from Equation (19), the corresponding expression for h* and the approximate relationship hf2 at T2* into Equation (21) and then solving for the humidity ratio W1 gives ( 1093 – 0.556T∗ )W 2∗ – 0.240 ( T 1 – T∗ ) - (22) W 1 = -----------------------------------------------------------------------------------------------1093 + 0.444T 1 – T∗ where T1 and T* are in °F. The corresponding equation in SI units is ( 2501 – 2.381T∗ )W 2∗ – ( T 1 – T∗ ) W 1 = ---------------------------------------------------------------------------------2501 + 1.805T 1 – 4.186T∗

(23)

where T1 and T* are in °C. Example 3:In an adiabatic saturator, the entering and leaving air pressure is 14.696 lbf/in2, the entering temperature is 70°F, and the leaving temperature is 60°F. Calculate the humidity ratio W and the relative humidity Φ? Solution: After the adiabatic saturator, the relative humidity is 100% absorbing the water, so Pv2 = Ps2. W2 can be calculated by Equation (13) Pv Pv W 2 = 0.6219 ------ = 0.6219 --------------Pa P – Pv 0.2563 = 0.6219 ⎛ ---------------------------------------⎞ ⎝ 14.696 – 0.2563⎠ = 0.01104 lb v /lb a W1 can be calculated by Equation (22) ( 1093 – 0.556T∗ )W 2∗ – 0.240 ( T 1 – T∗ ) W 1 = -----------------------------------------------------------------------------------------------1093 + 0.444T 1 – T∗ ( 1093 – 0.556 × 60 )0.01104 – 0.24 ( 70 – 60 ) = -----------------------------------------------------------------------------------------------------------1093 + 0.444 × 70 – 60 11.698 – 2.4 = -----------------------------1064.08 = 0.008738 By applying Equation (13)

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–6

PSYCHROMETRY

Pv W 1 = 0.6219 -----Pa Pv 0.008738 = 0.6219 --------------P – Pv 0.6219 × P 0.008738 = ----------------------------v 14.696 – P v P v = 0.2036 By applying Equation (14) Pv Φ = ------ × 100 Ps 0.2036 = ------------------- × 100 0.36328 = 56.04 The process discussed in this section is called the adiabatic saturation process. The usefulness of the foregoing discussion lies in the fact that the temperature of the saturated air-water-vapor mixture leaving the system is a function of the temperature, pressure, and relative humidity of the entering mixture and the exit pressure. Additionally, knowing the entering and exit pressures and temperatures, we may determine the relative humidity and humidity ratio of the entering mixture, as shown in Example 3. In principle, there is a difference between the wet-bulb temperature Tw, and the temperature of adiabatic saturation T*. The wet-bulb temperature is a function of both heat and mass transfer rates, while the adiabatic saturation temperature is a function of a thermodynamic equilibrium process. However, in practice, it has been found that for air-water-vapor mixtures at atmospheric pressures and temperatures, the wet-bulb and adiabatic saturation temperatures are essentially equal numerically. Thermodynamic Properties of Moist Air.—Table 24 shows values of thermodynamic properties, for standard atmospheric pressure 14.696 psia or 29.92 in. Hg. The properties in this table are based on the thermodynamic temperature scale. This ideal scale differs only slightly from the practical temperature scales used for actual physical measurements. Symbols used in Table 2-4 are: T = Fahrenheit temperature; Ws = humidity ratio at saturation, the condition at which the gaseous phase (moist air) exists in equilibrium with a condensed phase (liquid or solid) at the given temperature and pressure (standard atmospheric pressure). At given val-

ues of temperature and pressure, the humidity ratio W can have any value from zero and Ws. vas = vs − va, the difference between the volume of moist air at saturation per lb of dry air, and the specific volume of the dry air itself, ft3/lbda, at the same pressure and temperature. vs = volume of moist air at saturation per lb of dry air, ft3/lbma. ha = specific enthalpy of dry air, Btu/lbda. The specific enthalpy of dry air has been assigned the value of zero at 0°F and standard atmospheric pressure. has = hs − ha, the difference between the enthalpy of moist air at saturation, per lb of dry air, and the specific enthalpy of the dry air itself, Btu/lbda, at the same pressure and temperature. sa = specific entropy of dry air, Btu/lb-°F (abs). The specific entropy of dry air has been assigned the value of zero at 0°F and standard atmospheric pressure. ss = specific entropy of moist air at saturation per lb of dry air, Btu/lbda-°F (abs). hw =hs= specific enthalpy of condensed water (liquid or solid) in equilibrium with saturated air at a specified temperature and pressure, Btu/lbwater. Specific enthalpy of liquid water has been assigned the value of zero at its triple point (32.018°F) and saturation pressure. Note: hw is greater than the steam table enthalpy of saturated pure condensed phase by the amount of the enthalpy increase governed by the pressure increase from saturation pressure to one atmosphere, 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 saturation vapor pressure of pure water Ps, at least for the conditions shown. Example 4:What is the relative humidity of moist air that has a dry-bulb temperature of 70°F and a wet-bulb temperature 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/lb da . At 70°F dry-bulb, find h a =16.818 Btu/lbda. Then, h as = 26.467 – 16.818 = 9.649 Btu/lb da This is the heat of the vapor. Using Table 2-4, the value of has = 9.649 with corresponding value Pv of 0.4205 in. Hg. At 70°F dry-bulb, Ps= 0.73966 in. Hg. So, by Equation (10)

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–7

PSYCHROMETRY

Pv Φ = ------ × 100 Ps

Pv W = 0.6219 --------------P – Pv

0.4205 = ------------------- × 100 0.73966

0.52193 = 0.6219 ⎛ ---------------------------------------⎞ ⎝ 29.92 – 0.52193⎠

= 56.11

= 0.011 lb v /lb da

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

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

Solution: By definition, the 60°F dew-point temperature is the saturation temperature corresponding to the actual partial pressure of the water vapor in the air. From Table 2-4 at 60°F, find Pv = Ps = 0.521930 in. Hg. At 70°F, find Pvs = Ps = 0.739660 in. Hg. The relative humidity is

W 0.0110 µ = ------- = ------------------------- = 0.694795 Ws 0.0158320

Pv Φ = ------ × 100 Ps 0.521930 = ---------------------- × 100 0.739660

From Table 2-4 at 70°F, find Pv = Ps = 0.739660 in. Hg. By Equation (21), Pv 0.52193 Φ = -------- × 100 = ---------------------- × 100 = 70.56 % 0.739660 P vs By Equation (21)

= 70.56 % Example 6:What is the enthalpy of moist air at 80°F drybulb temperature and 40% relative humidity? Barometric pressure 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 = 1.033020 in. Hg. Relative humidity φ = Pv/Ps; then, Pv = φPvs = 0.40(1.033020) = 0.413208 in. Hg. By Equation (13) Pv W = 0.6219 --------------P – Pv 0.413208 = 0.6219 ⎛ ------------------------------------------⎞ ⎝ 29.92 – 0.413208⎠ = 0.00871 lb v /lb da h = 0.24T + W ( 1061 + 0.444T ) = 0.24 × 80 + 0.00871 ( 1061 + 0.444 × 80 ) = 28.75 Btu/lb da Example 7:Moist air exists at 70°F dry-bulb and 60°F dew-point when the barometric pressure is 29.92 in. Hg. Determine (1) humidity ratio, (2) saturation ratio, (3) relative humidity, (4) enthalpy, and (5) specific volume of dry air. Solution: From Table 2-4 at dew-point temperature of 60°F, find Pv = Ps = 0.52193 in. Hg. By Equation (13),

h = 0.240T + W ( 1061 + 0.444T ) = 0.240 × 70 + 0.0110 ( 1061 + 0.444 ( 70 ) ) = 28.8129 Btu/lb da By Equation (5), PaVa=RaT, where Pa is the partial pressure of the dry air in the moist air, may be used to find V a . By Equation (3) P a = P−P v = 29.92−.52193= 29.3981in. Hg.=14.434 psia. By Equation (5) Pa Va = Ra T Ra T V a = --------Pa 53.352 × ( 460 + 70 ) = ------------------------------------------------144 × 14.434 3

= 13.6043 ft ⁄ lb Graphical Representation of Psychrometric Chart.—To facilitate engineering computations, a graphical representation of the properties of moist air has been developed and is known as a psychrometric chart. Richard Mollier was the first to use such a chart with enthalpy as a coordinate. Modern day charts are somewhat different but still retain the enthalpy coordinate. ASHRAE has developed Mollier-type charts Figs. 2-5 and 2-6 the necessary range of variables. These charts contain all the necessary variables for carrying out HVAC computations. Because the chart is complex in design this

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HVAC: Handbook of Heating, Ventilation and Air Conditioning PSYCHROMETRY

section describes how each variable’s curves appear so the user will see to which curves the examples refer. Fig. 2-5 is the psychrometric chart for use at and above sea level. Fig. 2-6 is the psychrometric chart for use at and above 5000 ft. Dry bulb temperature is plotted along the horizontal axis. The dry bulb temperature lines are straight but not exactly parallel and incline slightly to the left. Humidity ratio is plotted along the vertical axis on the right hand side of the chart. The scale is uniform with horizontal lines parallel. The saturation curve slopes upward from left to right.

The location and positioning of the scales of the various properties as well as the constant value lines for these properties are shown in these simple charts which are not drawn to the actual scale. When you read the values or draw lines, always use a sharp drafting-type pencil and straight edge.

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

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

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

v = 13.5 ft 3/lb

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

T = 70 F w

Td = 80

W

W

T w

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

Td

W

The enthalpy scale is drawn obliquely on the left of the chart. Enthalpy lines inclined downward left to right. Although the wet bulb temperature lines appear to coincide with the enthalpy lines, they gradually diverge with respect to one another (i.e. they are not parallel). The spacing of the wet bulb lines is not uniform. Finally we note that specific volume lines also appear inclined from the upper left to the lower right, similar to enthalpy and wet bulb temperature lines they are not parallel.The enthalpy, specific volume, and humidity ratio scales are all based on unit mass of dry air, not unit mass of moist air.

W = 0.010

W Humidity ratio

2–8

Td 80 Dry bulb temperature

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

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

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–9

PSYCHROMETRY

W

Saturation Line (O = 100%)

O = 80%

Td

h =35 Btu/lbda

O = 56.11 h = 26.38 Btu/lb

W

W

h

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

Example 8:The air leaves a cooling coil is at 70°F Td and 60°F T w . What is its humidity ratio φ and specific enthalpy? Solution: The intersection of the 70°F Td and 60°F Tw lines defines the given state. This point on the chart is the reference from which all the other properties are determined. Humidity Ratio W: Move horizontally to the right and read W = 0.008778 lbmv/ lbma on the vertical scale. Relative Humidity φ: Interpolate between the 50 and 60% percent relative humidity lines and read 56.11%. Enthalpy h: Follow a line of constant enthalpy upward to the left and read h = 26.38 Btu/lbma on the oblique scale. Specific Volume v: Interpolate between the 13.5 and 14.0 specific volume lines and read v = 13.65 ft3/lbma. Dew Point Tdp: Move horizontally to the left from the reference point and read Tdp = 53.7 F on the saturation curve.

W = 0.008778

Tdp = 53.7 Td

Tw = 60

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

Td =70

Tdp

Tdp = 70

W

Solution of Example 8

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

Enthalpy h (alternate method): The nomograph in the upper left hand corner of Fig. 2-4g gives the difference D between the enthalpy of unsaturated moist air and the enthalpy of saturated air at the same wet-bulb temperature. 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 several aspects of HVAC design, the availability of computer programs to determine moist air properties has made some of these steps easier to carry out. These programs may be easily constructed from the basic equations of this chapter. Computer programs give the additional convenience of choice of units and arbitrary (atmospheric) pressures.

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 2–22

PSYCHROMETRY

Table 2-4. (Continued) Thermodynamic Properties of Moist Air at Standard Pressure Temp T °F 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200

Humidity Ratio lbw/lbda

Volume ft3/lbda

Enthalpy Btu/lbda

Ws

va

vs

ha

0.3333600 0.3457200 0.3586500 0.3722000 0.3863900 0.4013100 0.4169800 0.4334300 0.4507900 0.4690500 0.4882900 0.5086700 0.5301900 0.5529400 0.5771000 0.6027400 0.6300200 0.6591100 0.6901200 0.7233100 0.7588500 0.7970300 0.8381700 0.8825100 0.9305700 0.9827200 1.0395100 1.1015400 1.1696500 1.2447100 1.3278800 1.4202900 1.5239600 1.6407000 1.7729900 1.9247200 2.0997500 2.3045400

15.699 15.724 15.749 15.774 15.800 15.825 15.850 15.875 15.901 15.926 15.951 15.976 16.002 16.027 16.052 16.078 16.103 16.128 16.153 16.178 16.204 16.229 16.254 16.280 16.305 16.330 16.355 16.381 16.406 16.431 16.456 16.481 16.507 16.532 16.557 16.583 16.608 16.633

24.040 24.388 24.750 25.129 25.526 25.942 26.377 26.834 27.315 27.820 28.352 28.913 29.505 30.130 30.793 31.496 32.242 33.037 33.883 34.787 35.755 36.793 37.910 39.113 40.416 41.828 43.365 45.042 46.882 48.908 51.151 53.642 56.435 59.578 63.137 67.218 71.923 77.426

39.197 39.438 39.679 39.920 40.161 40.402 40.643 40.884 41.125 41.366 41.607 41.848 42.089 42.331 42.572 42.813 43.054 43.295 43.536 43.778 44.019 44.260 44.501 44.742 44.984 45.225 45.466 45.707 45.949 46.190 46.431 46.673 46.914 47.155 47.397 47.638 47.879 48.121

Entropy Btu/lbda-°F hs

416.175 430.533 445.544 461.271 477.739 495.032 513.197 532.256 552.356 573.504 595.767 619.337 644.229 670.528 698.448 728.073 759.579 793.166 828.962 867.265 908.278 952.321 999.763 1050.892 1106.298 1166.399 1231.848 1303.321 1381.783 1468.237 1564.012 1670.431 1789.793 1924.187 2076.466 2251.102 2452.343 2688.205

Enthalpy

Condensate Water Entropy Vapor Press.

sa

ss

Btu/lb hw

Btu/lb-°F sw

0.07298 0.07337 0.07375 0.07414 0.07452 0.07491 0.07529 0.07567 0.07606 0.07644 0.07682 0.07720 0.07758 0.07796 0.07834 0.07872 0.07910 0.07947 0.07985 0.08023 0.08060 0.08098 0.08135 0.08172 0.08210 0.08247 0.08284 0.08321 0.08359 0.08396 0.08433 0.08470 0.08506 0.08543 0.08580 0.08617 0.08653 0.08690

0.71623 0.73959 0.76397 0.78949 0.81617 0.84415 0.87350 0.90425 0.93664 0.97067 1.00644 1.04427 1.08416 1.12624 1.17087 1.21815 1.26837 1.32183 1.37873 1.43954 1.50457 1.57430 1.64932 1.73006 1.81744 1.91210 2.01505 2.12733 2.25043 2.38589 2.53576 2.70208 2.88838 3.09787 3.33494 3.60647 3.91929 4.28477

131.03 132.03 133.03 134.03 135.03 136.03 137.04 138.04 139.04 140.04 141.04 142.04 143.05 144.05 145.05 146.05 147.06 148.06 149.06 150.06 151.07 152.07 153.07 154.08 155.08 156.08 157.09 158.09 159.09 160.10 161.10 162.11 163.11 164.12 165.12 166.13 167.13 168.13

0.2362 0.2378 0.2394 0.2410 0.2426 0.2442 0.2458 0.2474 0.2490 0.2506 0.2521 0.2537 0.2553 0.2569 0.2585 0.2600 0.2616 0.2632 0.2647 0.2663 0.2679 0.2694 0.2710 0.2725 0.2741 0.2756 0.2772 0.2787 0.2803 0.2818 0.2834 0.2849 0.2864 0.2880 0.2895 0.2910 0.2926 0.2941

a Extrapolated to represent metastable equilibrium with under cooled liquid.

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in. Hg ps 10.377600 10.625000 10.877100 11.134300 11.396500 11.664100 11.937000 12.214900 12.498800 12.788000 13.082300 13.383100 13.689400 14.001000 14.319100 14.643000 14.973100 15.309700 15.652200 16.001400 16.356900 16.719000 17.088000 17.463400 17.846200 18.235700 18.632300 19.035800 19.446800 19.865200 20.291300 20.724400 21.166100 21.615200 22.071400 22.536700 23.009200 23.490600

HVAC: Handbook of Heating, Ventilation and Air Conditioning

AIR CONDITIONING PROCESSES AIR CONDITIONING PROCESSES

and a simple cooling process, respectively. The simple psychrometric diagrams of these processes are shown Figs. 3-3 and 3-5 respectively. Neglecting the fan work that may be present, the conservation of mass and energy equations are as follows. Conservation of mass: m· = m· = m· (1)

Introduction.—The conservation of mass and energy is used in the study of air conditioning processes. Analysis of air conditioning processes is required for maintaining proper temperature and humidity in living space such as residential, commercial, and industrial facilities. The basic processes are as follows:

a1

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.

G F

A

E

(2)

W 1 = W 2 = constant

(3) (4)

q· = m· a ( h 2 – h 1 )

(5)

h 1 = h a1 + Wh v1

(6)

h 2 = h a2 + Wh v2

(7)

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

B

q· h = 1.10 × cfm × ( T 2 – T 1 )

C

o

a

Conservation of energy: m· a h 1 + q· = m· a h 2

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

H

a2

m· v1 = m· v2 = m· v

(8)

where q· h = heating load, Btu/hr cfm = air flow rate of dry air, ft3/min

D

T 1 = entering temperature, °F T 2 = leaving temperature, °F Similarly, in the case of cooling the following convenient approximate form is used for HVAC practice:

Fig 3-1. Fundamental air-conditioning processes Process

q· c = 1.10 × cfm × ( T 1 – T 2 )

Direction

(9)

where q· c = cooling load, Btu/hr cfm = air flow rate of dry air, ft3/min

Simple heating

O to C

Simple cooling

O to G

Humidification

O to A

Dehumidification

O to E

T 1 = entering temperature, °F

Evaporative cooling

O to H

T 2 = leaving temperature, °F

Evaporative heating

O to D

Heating and humidification

O to B

Cooling and dehumidification

O to F

IN

1 ma h1 W1

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

2 ma h2 W2 =W1

q

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

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–2

AIR CONDITIONING PROCESSES

W1 = W2

2

1

Fig 3-3. Psychrometric diagram of simple cooling process IN

1 ma h1 W1

m· v1 = m· v2 + m· w

2

m· w = m· a ( W 1 – W 2 )

ma h2 W2 =W1

q

air will be condensed on the cooling coil and then the condensate will be drained out. Because of this condition, the specific humidity of the leaving moist air will be lowered. The schematic cooling and dehumidification process is shown in Fig. 3-6. The air conditioning system on psychrometric chart representation of this process is shown in Fig. 3-7. The conservation of mass and energy equations for the cooling and dehumidification are as follows: Conservation of mass: (10) m· a1 = m· a2 = m· a (11) W 1 > W 2 (12)

where

Conservation of energy: m· a h 1 = m· a h 2 + q· + m· w h w

(13)

m· a h 1 = m· a h 2 + q· + m· a ( W 1 – W 2 )h w

(14)

q· = m· a ( h 1 – h 2 ) – m· a ( W 1 – W 2 )h w

(15)

OUT

Fig 3-4. Schematic of simple heating process

W1 = W2

1

2

Fig 3-5. Psychrometric diagram of simple heating process

Example 1:Find the required heat to warm 2500 cfm of air at 60°F at 90% moisture humidity to 120°F without addition of moisture. Solution: The mass flow rate of dry air is cfm 2500 × 60 m· a = --------- = ------------------------ = 11283 lb m /hr ν 13.2944 The specific volume of air at 60°F at 90% is 13.2944 from the psychrometric chart Fig. 2-5. From the psychrometric chart Fig. 2-5 h 1 = 25.1 Btu/lbm and h2 = 39.89 Btu/lbm. By applying Equation (5) q· = m· ( h – h ) a

2

IN OUT

1 ma h1 W1

2 ma h2 W2

q

mw Condensate drain Fig 3-6. Schematic of cooling with dehumidifying process

3

1

1

W1

x

W2

= 11283 ( 39.89 – 25.1 ) = 166876 Btu/hr By applying the ASHRAE Equation (8) q· = 1.10 × cfm × ( T 2 – T 1 ) = 1.10 × 2500 × ( 120 – 60 ) = 165000 Btu/hr

Cooling with Dehumidification.—In most of the cooling processes, the dew point temperature of the moist air entering the cooling coil is higher than the cooling coil surface temperature so that the water vapor in the entering

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

Example 2:What is the cooling capacity of a coil if 5000 cfm mixed air entering at 80°F and 67°F and leaving at 55°F at 90% relative humidity? Solution: The mass flow rate of dry air is cfm 5000 × 60 m· a = --------- = ------------------------ = 21687 lb m /hr ν 13.833 The specific volume of air at 80°F and 67°F is 13.833 from the psychrometric chart (Fig. 2-5).

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–3

AIR CONDITIONING PROCESSES

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 h w = 23.0 Btu/lbv . Applying the Equation (15) q· = m· a ( ( h 1 – h 2 ) – ( W 1 – W 2 )h w ) = 21687 ( ( 31.4 – 22.2 ) – ( 0.0112 – 0.0082 ) × 23 ) = 198024 Btu

The schematic of this process is shown in Fig. 3-8. The air conditioning system on psychrometric chart representation of this process is shown in Fig. 3-9. The conservation of the mass and energy equations are as follows: Conservation of mass: m· = m· = m· (16) a1

a2

a

m· v1 + m· w = m· v2

= 16.5 ton Heating with Humidification.—In most commercial facilities such as large office spaces, hospitals, and modern schools where central heating and cooling HVAC systems are used, it is desirable to humidify the supplied heated air to various room and spaces in order to maintain comfortable relative humidity, especially in the locations where the outdoor relative humidity during winter season is very low. In the heating with humidification process, air first is heated by the heating coil or gas furnace and then is humidified by adding moisture before it is supplied to the space. Heating medium

ma h1 W1

ma h2 W2

q

x

1

2

mw hw

Fig 3-8. Schematic of heating with humidification process

m· w = m· a ( W 2 – W 1 )

Conservation of energy: m· a h 1 + q· + m· w h w = m· a h 2

W1

(18) (19)

m· a h 1 + q· + m· a ( W 2 – W 1 )h w = m· a h 2

(20)

q· = m· a ( h 2 – h 1 ) + m· a ( W 1 – W 2 )h w

(21)

Equation (21) can be written in the following useful form: h2 – h1 q· - + h -------------------- = -----w · W2 – W1 mw

(22)

Adiabatic Mixing of Two Air Streams.— Many air conditioning applications require the mixing of two air streams. This is particularly true for large buildings, and most process plants, office spaces, and hospitals, in which the space return air must be mixed with a certain required outdoor fresh air for proper ventilation before it enters the air conditioning unit. In this process, the heat transfer to the surrounding space is usually small and can be ignored. The schematic of this process is shown in Fig. 3-10. The psychrometric representation of this process is shown in Fig. 3-11. The mass and energy conservation equations for this process are as follows: Conservation of mass: m· + m· = m· (23) a1

2

where ( W 2 < W 1 )

(17)

a2

a3

m· v1 + m· v2 = m· v3

(24)

m· a1 W 1 + m· a2 W 2 = m· a3 W 3

(25)

Conservation of energy: m· a1 h 1 + m· a2 h 2 = m· a3 h 3 1

X

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

W2

Combining Equations (23) to (26) gives: W2 – W3 m· a1 h2 – h3 ----------------- = -------------------- = -------h3 – h1 W3 – W1 m· a2

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(26)

(27)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–4

AIR CONDITIONING PROCESSES

1

ν oa = 14.04

3

W oa = 0.009

ma h1 w1

ma h3 w3

h oa = 31.54

mw 2 h2 w2 Fig 3-10. Adiabatic mixing of two streams process

h ra = 30.20

1500 × 60 m· oa = -----------------------14.04

4500 × 60 m· ra = -----------------------13.70

= 6410

= 19708

m· m = m· oa + m· ra = 6410 + 19708 = 26118 h oa × m· oa + h ra × m· ra h m = ----------------------------------------------------m· m

(28)

and

31.54 × 6410 + 30.20 × 19708 = ------------------------------------------------------------------------26118 = 30.52 Btu/lb m W oa × m· oa + W ra × m· ra W m = --------------------------------------------------------m· m

m· a1 -------- W + W2 m· a2 1 W 3 = ------------------------------m· a1 1 + -------m·

(29)

0.009 × 6410 + 0.0111 × 19708= --------------------------------------------------------------------------26118 = 0.0105 lb v ⁄ lb v

a2

3

W ra = 0.0111

The condition of the mixed air is

Solving Equations (23) to (27) for h3 and W3 gives: m· a1 -------- h + h2 m· a2 1 h 3 = --------------------------m· a1 1 + -------m· a2

ν ra = 13.70

2

1

W2 W3 W1

Example 4:Find the heat transfer rate and mass flow rate of a heating and adiabatic humidification process where 2000 cfm air enters at 40°F and 40% relative humidity and leaves at 110°F and a relative humidity of 30%. Solution: First we will find out the outside air and return air properties. Given cfm = 2000

Fig 3-11. Psychrometric diagram of adiabatic mixing process

Example 3:Find the condition of mixed air in which 1500 cfm of outside air 90°F at 30% relative humidity is mixed with 4500 cfm return air of 75°F at 60% relative humidity. Solution: First we will find out the outside air and return air properties. We are given these data: cfm oa = 1500

cfm ra = 4500

T 1 = 40

T 2 = 110

Φ 1 = 40%

Φ 2 = 30%

Mass flow rate of dry air cfm × 60 2000 × 60 m 1 = --------------------- = ------------------------ = 9508 lb m /hr ν 12.62 The specific volume of air at 40°F and 40% is 12.62 from the psychrometry chart Fig. 2-5. By applying the psychrometry chart (Fig. 2-5)

T oa = 90

T ra = 75

W 1 = 0.002

W 2 = 0.016

Φ oa = 30

Φ ra = 60

h 1 = 11.83

h 2 = 44.93

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

m· 2 = m· a

h w = 1135

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–5

AIR CONDITIONING PROCESSES

Steam flow rate, m· 1 W 1 + m· w = m· 2 W 2 m· w = m· 1 ( W 2 – W 1 ) = 133 lb m /hr

m· w = m· a ( W 1 – W 0 )

(32)

h0 = h1

Applying the energy balance equation for heating and humidifying equation m· h + q· = m· h – m· h 2 2

(31)

Conservation of energy: m· a h 0 = m· a h 1

= 9508 ( 0.016 – 0.002 )

1 1

m· v0 + m· w = m· v1

(33)

or T wb0 = T wb1

w w

q· = m· 2 h 2 – m· 1 h 1 – m· w h w = m· 1 ( h 2 – h 1 ) – m w h w = 9508 ( 44.93 – 11.83 ) – 133 × 1135

1

0

Conditioned space

= 163760 Btu/hr

Make-up water B Fig 3-12. Evaporative cooling system

C

A

W2

2

Psychrometric diagram of Example 4

1

Evaporative Cooling.—Conventional cooling systems such as rooftop and system air conditioning systems and heat pump systems operate on a refrigeration cycle that has high initial and operating and maintenance cost. The high operating cost is associated with the high electricity consumption of the compressor. The conventional refrigerant system can be used in any part of the world. However, in hot and dry climates, we can avoid the high cost of cooling by using the evaporative coolers. The evaporative cooler is based on a simple principle that as water evaporates, the latent heat of vaporization is absorbed from the water and the surrounding air. As a result, both water and the air are cooled during this process. The schematic process of evaporative cooling is shown in Fig. 3-12. The psychrometric representation of this process is shown in Fig. 3-13. During the humidification process the enthalpy of moist air and the wet-bulb temperature of the air remain approximately constant. Conservation of mass: m· = m· = m· (30) a0

a1

a

0

W0

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 conditioning cycle. The psychrometric chart representation of a typical cooling and heating systems based on Fig. 314 are shown in Figs. 3-15 and 3-16.

Fig 3-14. Air conditioning system

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–6

AIR CONDITIONING PROCESSES

Then latent heat is

g in m

ix

Humidity Ratio

r

q· s + q· l = q· t

room s heating

m

q· l = q· t – q· s = 110000 – 88000 = 22000 Btu/hr

o

Dry-bulb temperature

o m r

Humidity Ratio

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

s Dry-Bulb Temperature Fig 3-16. Air conditioning cooling system

Example 6:A room is to be maintained at 75°F and 50% relative humidity. The outside air condition is 95°F and 60% relative humidity. The outdoor air requirements for the occupants is 500 cfm. The total heat gain to the space is 60,000 Btu/hr with a 0.80 SHF. Determine the quantity and the state of the air supplied to the space and the required capacity of cooling and dehumidifying equipment. Solution: Assume that the conditions of air after the cooling coil is 55°F and 90% relative humidity. Now make a schematic diagram to locate the points on the psychrometric chart.

The following examples will provide good practice and an 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°F and 90% relative humidity. The space is to be maintained at 75°F at sensible heat factor (SHF) 0.80? Solution: The total cooling load for the room is q· t = 1.10 × cfm × ∆T = 1.10 × 5000 × ( 75 – 55 ) = 110000 Btu/hr Applying the sensible heat factor equation

T 0 = 95

Φ 0 = 60

T 2 = 55

Φ 2 = 90

T 3 = 75

Φ 3 = 50

h 0 = 46.4

W 0 = 0.021

v 0 = 14.45

h 2 = 22.2

W 2 = 0.008

v 2 = 13.13

h 3 = 28.1

W 3 = 0.009

v 3 = 13.66

Applying the energy balance equation around the room m· 2 h 2 + q· = m· 2 h 3

q· s SHF = --------------q· + q·

q· m· 2 = ---------------------( h3 – h2 )

q· s SHF = ---q· t

60000 = ------------------------------( 28.1 – 22.2 )

s

l

= 10170 lb/hr

q· s = q· t × SHF = 110000 × 0.80 = 88000 Btu/hr where

q· t =total heat loss, Btu/hr q· s =sensible heat loss, Btu/hr q· l =latent heat loss, Btu/hr

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–7

AIR CONDITIONING PROCESSES

0 1 3

2

Example 7:A room is to be maintained at 75°F and 50% relative humidity. The outside air is 30°F and 50% relative humidity. The outdoor air requirements for the occupants is 500 cfm. Sensible and latent heat losses from the spaces are 120,000 Btu/hr and 30,000 Btu/hr. Determine the quantity of air supplied at 120°F to the space and the required capacity of heating and humidifying equipment. Solution: The figure below is the schematic for the problem. q· s SHF = --------------q· + q· s

l

120000 = --------------------------------------120000 + 30000 = 0.80

The flow rate of dry air is 10170 × 13.66 cfm ra = m· 2 ν 3 = ---------------------------------- = 2315 cfm 60 The flow rate of outside air is cfm oa 500 × 60 m· 4 = ------------- = --------------------- = 2076 lb m ⁄ hr ν 14.45 The return air quantity will be (10170−2076) or 8094 lbm/hr. Assume return air condition and room air condition are same. Now we find the mixed air condition by the mixing of return air and outside air. m· = m· + m· = 8094 + 2076 = 10170 lb 1

0

4

2

h 0 × m· 0 + h 4 × m· 4 h 1 = ------------------------------------------m·

3

1

46.4 × 2076 + 28.1 × 8094 = ---------------------------------------------------------------10170 = 31.84 Btu/lb W 0 × m· 0 + W 4 × m· 4 W 1 = ----------------------------------------------m· 1 0.021 × 2076 + 0.009 × 8094 = ---------------------------------------------------------------------10170 = 0.0115 Applying the energy balance equation around the cooling coil: m· h = q· + m· h 1 1

c

2 2

q· c = m· 2 ( h 1 – h 2 ) = 10170 ( 31.84 – 22.2 ) = 98038 Btu/hr = 8.17 ton

x

1 0

Draw a line at point 3 parallel to SHF= 0.80, which intersect 120°F at point 2. Applying the energy balance equation around the room m· h = m· h + q· 2 2

2 3

t

q· t m· 2 = --------------------( h3 – h2 ) 150000 = ------------------------------( 46.2 – 28.2 ) = 8333 lb/hr The flow rate of dry air is 8333 × 13.66 cfm ra = m· 2 ν 3 = ------------------------------- = 1898 cfm 60

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–8

AIR CONDITIONING PROCESSES

The flow rate of outside air is cfm oa 500 × 60 m· 4 = ------------- = --------------------- = 2427 lb/hr ν 12.36

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

RA

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

RA

SPACE

Now we find the mixed air condition by the mixing of return air and outside air. m· 1 = m· 0 + m· 4 = 5906 + 2427 = 8333 lb h 0 × m· 0 + h 4 × m· 4 h 1 = ------------------------------------------m· 1

SA

OA

COOLING COIL (SUMMER)

FAN

MA

A) Summer air flow, cfm

= 22.55 Btu/lb

B) Winter air flow, cfm C) Cooling coil rating, tons D) Sensible cooling coil rate, Btu/hr

0.0017 × 2427 + 0.009 × 5906 = ------------------------------------------------------------------------8333

E) Latent cooling coil rate, Btu/hr

= 0.0068 lb/lb

F) Heating coil rating, MBH

Applying the energy balance equation around the heating coil: m· 1 h 1 + q· h = m· 2 h 2 q· h = m· 2 ( h 2 – h 1 ) = 8330 ( 46.2 – 22.55 ) = 197005 Btu/hr Applying the mass balance equation around the heating coil: m· 1 W 1 + m· w = m· 2 W 2 m· w = m· 1 ( W 2 – W 1 ) = 8330 ( 0.012 – 0.0068 ) = 43.3 lb/hr Example 8:An existing building space will be an office space for 200 people. The space design loads are as follows: Summer: 300,000 Btu/hr sensible (gain), 75,000 Btu/hr latent (gain) Winter: 600,000 Btu/hr sensible (loss), negligible latent

winter : 135 deg. F summer : 55 deg. F

Find the

× 2427 + 28.1 × 5906= 9.07 --------------------------------------------------------------8333

W 0 × m· 0 + W 4 × m· 4 W 1 = ----------------------------------------------m· 1

HEATING COIL WITH HUMIDIFIER

G) Humidifier rating, gal/hr Solution: Location

Dry Bulb Temperature, Tdb

OA RA SA MA

95 75 55

OA RA SA MA

7 72 135

Wet Bulb Temperature, Twb

Relative Humidity Summer 74 37.5 55.67 100

Enthalpy

Humidity Ratio

37.50 29.31 23.30

0.0133 0.0103 0.0092

2.883 26.42 41.77

0.0011 0.0084 0.0084

Winter 100 50 7.65

Summer cooling load: q· s = 1.10 × cfm × ( T ra – T sa ) q· s cfm = ------------------------------------------1.10 × ( T ra – T sa ) 300000 = --------------------------------------1.10 × ( 75 – 55 ) = 13636

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–9

AIR CONDITIONING PROCESSES

Mass of air: cfm × 60 m· a = --------------------ν 13636 × 60 = --------------------------13.66 = 59894 lb/h

m· oa × W oa + m· ra × W ra W m = --------------------------------------------------------m· oa + m· ra 16830 × 0.0133 + 43064 × 0.0103= --------------------------------------------------------------------------------59894 = 0.0111 Fan power: cfm × ∆p P = -----------------------t 6350 × η f

Mass of water: q· l m· l = ----------1100

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

75000 = --------------1100

= 10.737 hp = 8 kw

= 68.18 lb/h

Cooling coil capacity:

Humidity ratio of room air: W ra

m· l = W sa + -----m·

a

68.18= 0.0092 + -------------59894 = 0.010338 At humidity ratio 0.10338 and 75°F, h ra = 29.31 Btu/hr. Outside air requirement as per ASHRAE Code is 20 cfm/person. So the total outside air requirement = 200 × 20 = 4000 cfm.

q· coil = m· a ( h m – h s – ( W m – W s )h c ) = 59894 ( 31.61 – 23.30 – ( 0.0111 – 0.0092 )32.0 ) = 494078 Btu/hr = 41.2Ton Winter load: q· s = 1.10 × cfm × ( T ra – T sa ) q· s cfm = ------------------------------------------1.10 × ( T ra – T sa ) 600000 = -----------------------------------------1.10 × ( 135 – 72 )

Mass of air

= 8568 4000 × 60 m· oa = -----------------------ν

Mass of air: cfm × 60 m· a = --------------------ν

4000 × 60 = -----------------------14.26

× 60= 8568 ----------------------13.56

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

= 37911 lb/h Outside air requirement as per ASHRAE Code is 20 cfm/person. So the total outside air requirement = 200 × 20 = 4000 cfm. Mass of air:

m· oa × h oa + m· ra × h ra = ----------------------------------------------------m· + m· oa

ra

4000 × 60 m· oa = -----------------------ν

16830 × 37.5 + 43064 × 29.31 = ------------------------------------------------------------------------59894

4000 × 60 = -----------------------11.77

= 31.61 Btu/lb

= 20390 lb/h

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 3–20

AIR CONDITIONING PROCESSES

Cooling coil capacity (condensate water at 64°F hc = 32.0 Btu/h) q = m· ( h – h – ( W – W )h ) coil

a

f

s

f

s

c

21566 = --------------- ( 32.78 – 23.30 – ( 0.011 – 0.0092 )32.0 ) 2

Secondary heating coil for room-A: 2728 q· h1 = 48000 + 1.10 ⎛ ------------⎞ ( 75 – 55 ) ⎝ 2 ⎠ = 78008 Btu/hr Secondary cooling coil for room-B:

= 101602 Btu/hr = 8.46 ton Secondary cooling coil for room-A: 11982 q· c1 = --------------- ( 26.42 – 23.30 ) 2 = 18692 Btu/hr

9584 q· c2 = ------------ ( 26.42 – 23.30 ) 2 = 14952 Btu/hr Secondary heating coil for room-B: 2182 q· h2 = 36000 + 1.10 ⎛ ------------⎞ ( 75 – 55 ) ⎝ 2 ⎠ = 60002 Btu/hr

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HVAC: Handbook of Heating, Ventilation and Air Conditioning

HYDRONIC HEATING AND COOLING SYSTEM HYDRONIC HEATING AND COOLING SYSTEM

5) air separator

Basic System Hot water heating systems (hydronic heating) are conveniently being used in many types of buildings and facilities, especially for single family houses and low rise multiple dwelling buildings. Also many HVAC systems are using hot water systems as the primary source for heating the distribution air. The chilled water cooling systems (hydronic cooling) are popular in certain large residential buildings, hospitals, and office buildings. The main 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.)

6) connected piping system 7) make-up and fill water system 8) control system. The hydronic system can be classified by combination of: 1) operating temperature; 2) pumping and piping arrangement; and 3) operating pressure. Depending on the particular application and the type of the facility, the proper selection of the boiler(s) or chiller(s), pumping systems, piping arrangement, and control system are essential for an effective and economical hydronic system. Schematic piping drawings of some heating and cooling systems are given in Figs. 10-1 to 105.

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

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 10–2

HYDRONIC HEATING AND COOLING SYSTEM

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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HVAC: Handbook of Heating, Ventilation and Air Conditioning HYDRONIC HEATING AND COOLING SYSTEM

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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10–3

HVAC: Handbook of Heating, Ventilation and Air Conditioning 10–4

HYDRONIC HEATING AND COOLING SYSTEM

Temperature Classifications.—The temperature classifications of the hydronic systems can be categorized as: 1) Low temperature water (LTW) system 2) Medium temperature water (MTW) system 3) High temperature water (HTW) system 4) Chilled water (CW) system 5) Dual temperature water (DTW) system. Low Temperature Water (LWT) System: The maximum temperature limitation in this case is 250°F, The maximum allowable working pressure is 160 psig. The maximum working pressure depends on the static head of the building (height of the building) and the location of the system pump(s). It is recommended for working pressure of higher than 60 psi to use steam to water or water to water heat exchanger(s) so that the heating boiler and its closed piping loop can be separated and to operate at lower operating pressure without being affected by the high system working pressure. Separating the boiler by using heat exchanger(s) from the rest of the system minimizes boiler leaks and prolong the life of the boiler. Medium Temperature Water (MTW) System: I n t h i s case, the working temperature is ranged between 250°F and 350°F with an operating pressure of 300 psig. The maximum 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 temperature below 40°F, mostly in process applications, antifreeze of brine solution may be used. Dual Temperature Water (DTW) System: In this case, both boiler(s) and chiller(s) are used with common piping system to provide hot water heating and chilled water cooling. The maximum operating temperature of the heating water is limited to 180°F and minimum 40°F for the chilled water.

q· gpm = ---------------------------------------------8.02 × ∆T × C P × ρ

(1)

where q =heat capacity of the terminal unit, Btu/h gpm = 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 terminal unit, °F For 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 q· gpm = ---------------------(2) 500 × ∆T In many design applications the ∆T of 20°F is recommended for small simple hydronic systems, in this case the above equation can be written as q· gpm = -------------(3) 10000 Boiler.—For new construction boiler(s) must be sizes based on the actual connected load and piping and pick up losses. The actual connected load must be equal or greater that the calculated design heating load. The piping and pickup losses for the hydronic (hot water) boiler(s) is 15 to 25% of the actual connected load and for steam boilers is 25 to 35%. In design application for which only the boiler needs to be replaced, the boiler(s) must be sized to match the actual installed connected load plus the piping and pickup loss as mentioned above for proper operation of the boiler(s) specially on very cold days. Air Eliminations Methods.—Air in the hydronic system can cause water hammer and shock waves in the hydronic system when the dissolved air in the water can be separated at the low pressure point of the system.

Closed Hydronic System Components Design The closed system is a system with only one expansion tank. The main components of the heating and cooling hydronic 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 system. Convectors or Terminal Units.—The convector(s) for each room or space must be sized to be equal or greater than the calculated designed heating load for that particular room or space. The sum of the total convectors and other terminal units load in the building is called the actual connected load. The flow rate through each convector or terminal unit can be calculated from the following equation:

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

The solubility of air in the water can be described by Henry’s equation as follow: p x = ---(4) H

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HVAC: Handbook of Heating, Ventilation and Air Conditioning HYDRONIC HEATING AND COOLING SYSTEM

where x =solubility of air in water (% by volume) p = absolute pressure H = Henry’s constant

10–5

the return side of the terminal units (baseboard loop, convectors, etc.). Air can get into the hydronic system as follow: 1) During the initial fill of the system with city water, which contains dissolved air. In order to minimize the dissolved air during the initial fill, an inline separator is recommended to be installed in the piping system, as shown in Fig. 10-8.

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

Henry’s constant is a function temperature as shown in Figure 6. Taking into account the temperature dependency of Henry’s constant and combining withEquation (4), the percentage of the solubility of air in water can be determined as shown in Fig. 10-7. Fig. 10-7 clearly shows what percent of air volume would exist in the different parts of the hydronic system when the pressure and temperature are known. For example at 10 psia and 120°F, the percent air volume if 2.5% from Fig. 10-7. Basically the dissolved air in the water at the higher pressure point of the system can be separated at other parts of the system where the pressure is lower. That is the reason air vents are installed (1) at the top of the supply and return risers (highest point) where the pressure is the lowest and (2) at

2) Entrain air at the air water interface of the open expansion tank and closed steel expansion tank where the air is being used as compressible fluid. A diaphragm type expansion tank is preferred to be installed since no direct contact exists between the compressible gas and water, since they are separated by a flexible membrane. 3) Through the fittings in the part of the piping system where the system pressure is below atmospheric pressure. Design must ensure that at no point in the system the system pressure is lower than atmospheric pressure. 4) Other considerations are to ensure that (1) pressure at no point in the system will ever becomes lower than saturation temperature of the operating temperature and (2) the calculated (theoretical) net positive head (NPSHA) at the pump inlet is always exceeds the required net positive head given by the pump manufacturer.

Fig 10-8. Air separator and expansion tank detail

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 10–6

HYDRONIC HEATING AND COOLING SYSTEM

Pressure Increase Due to Change in Temperature.— One should know of how much pressure will increase due to temperature increase; this is especially important for the sizing of the expansion tank. The relationship between pressure change due to temperature change in a piping system is given by the following equations: ( β – 3α ) ∆t ∆P = --------------------------------D ⎞ ⎛ 5---⎞ ⎛ --------- +γ ⎝ 4⎠ ⎝ E ∆r⎠

(5)

where P = pressure increase, psi; β =volumetric coefficient of thermal expansion of water, 1/°F; α =linear coefficient of thermal expansion for piping 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.

expansion which is why the size of expansion tank must be based on temperature changes during initial system fill. For example, in low temperature hydronic heating system when boiler and piping system need to be initially filled during winter time, the city water temperature could be as low as 40°F, which must be heated to 200°F. In this case, the piping system will experience a large temperature difference and the system expansion tank must be sized to handle this large temperature increase. Another option is that to heat the city water initially by means of electric heat to reduce the size of the system expansion tank, but same procedure must be followed for the future system fill to avoid drastic damage to the piping system due to excessive expansion. It should be noted that the expansion tanks besides serving a thermal function serves a hydraulic function as well. As a hydraulic device, the expansion tank provides a reference system pressure point analogous to the ground point in an electrical circuit. Expansion tanks are of three basic configurations: (1) a closed tank, which contains a captured volume of compressed air and water, with an air water interface (sometimes called a plain steel tank) as shown in Fig. 10-12; (2) an open tank (i.e., a tank open to the atmosphere) as shown in Fig. 10-10; and (3) a diaphragm tank, in which a flexible membrane is inserted between the air and the water (another configuration of a diaphragm tank is the bladder tank) as shown in Fig. 10-11. Equations for sizing the three common configurations of expansion tanks are as follow: Open tanks with air/water interface:

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

Based on Equation (5), figures can be developed to show the change in pressure due to temperature change for specific pipe sizes and pipe material as shown in Fig. 10-9 which provides pressure increase vs. pressure increase for 1″ and 10″ schedule 40 steel pipes. For example for a 5°F temperature increase for a 10″ schedule 40 steel pipe, the pressure increase is 100 psi. Expansion Tank.—The connected piping in hydronic systems is subject to expansion and contraction due to changes in system temperature especially during initial system fill. Expansion tanks (or compression tanks) are required to protect against thermal expansion of the piping system due to temperature rise. During initial fill the piping system could experience the largest thermal

Fig 10-10. Open tank

For diaphragm tanks:

Fig 10-11. Diaphragm tank

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HVAC: Handbook of Heating, Ventilation and Air Conditioning HYDRONIC HEATING AND COOLING SYSTEM

For closed tanks with air/water interface:

sphere must be located above the highest point in the system. A tank with an air/water interface is generally used with an air control system that continually revents the air into the tank. For this reason, it should be connected at a point where air can best be released. Example 1:Size an expansion tank for dual temperature system that will be operated at a design temperature range of 40°F to 200°F. The minimum pressure at the tank is 62.3 psig (47.6 psia) and the maximum pressure is 117.3 psig (102.6 psia). (Atmospheric pressure is 14.7 psia.) The volume of water is 2500 gal. The piping is steel.

Fig 10-12. Closed tank air water interact

Expansion Tank Sizing .—Equations for sizing the three common configurations of expansion tanks follow: For closed tanks with air/water interface, V ⎛ ⎛ -----2-⎞ – 1 – 3α ∆T⎞ ⎝ ⎝ V 1⎠ ⎠ V t = V s ---------------------------------------------------P a P a⎞ ⎛ ----- – -----⎝P P ⎠ 1 2 For open tanks with air/water interface, V2 V t = 2V s ⎛ ⎛ ------⎞ – 1 – 3α ∆T⎞ ⎝ ⎝ V 1⎠ ⎠ For diaphragm tanks, V ⎛ ⎛ -----2-⎞ – 1 – 3α ∆T⎞ ⎝ ⎝ V 1⎠ ⎠ V t = V s ---------------------------------------------------P 1⎞ ⎛ 1 – ----⎝ P ⎠

10–7

1. Calculate the required size for a closed tank with an air/water interface. Solution: From Table 2-3: V 1 ( at 40°F ) = 0.01602 V 2 ( at 200 °F ) = 0.01663

(6)

⎛ V -----2- – 1 – 3α ∆T⎞ ⎝ V ⎠ 1 V t = V s ----------------------------------------------P a P a⎞ ⎛ ----- – -----⎝P P ⎠ 1 1

(7)

–6 ⎛ 0.01663 ------------------- – 1 – 3 × 6.5 × 10 × 160⎞ ⎝ 0.01602 ⎠ = 2500 × ----------------------------------------------------------------------------------------------14.7 ⎛ 14.7 ---------- – -------------⎞ ⎝ 62.3 117.3⎠

(8)

2

where Vt =volume of expansion tank, gal Vs = volume of water in system, gal T1 = lower temperature, °F T2 = higher temperature, °F Pa = atmospheric pressure, psia P1 =pressure at lower temperature, psia P2 =pressure at higher temperature, psia V1 = specific volume of water at lower temperature, ft3/lb V2 = specific volume of water at higher temperature, ft3/lb α = 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 maximum pressure allowable at the location of the safety relief valve(s) without opening them. A tank open to the atmo-

= 787 gal 2. If a diaphragm tank were to be used in lieu of the plain steel tank, what tank size would be required? Solution: Using Equation (8), ⎛ V -----2- – 1 – 3α ∆T⎞ ⎝ V ⎠ 1 V t = V s ----------------------------------------------P 1⎞ ⎛ 1 – ----⎝ P 2⎠ –6 ⎛ ⎛ 0.01663 ------------------- – 1⎞ – 3 × 6.5 × 10 × 160⎞ ⎝ ⎝ 0.01602 ⎠ ⎠ = 2500 × ----------------------------------------------------------------------------------------------62.3-⎞ ⎛ 1 – -----------⎝ 117.3⎠

= 186 gal

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 10–8

HYDRONIC HEATING AND COOLING SYSTEM

Expansion Tank Location: It should be noted that the location of the tank has no effect on the system pressure before and after the pump as shown in Figs. 10-13 to 1016. Notice that, when the pump is on, the pressure at the pump inlet decreases equal to the amount of pump head and it increases at the pump discharge equal to the pump head. In good design practice, in order to reduce the size of the expansion tank, it is preferred to install the tank before the system pump. The size of the tank can also be reduced when the tank is installed at the highest point of the 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

impeller axially to the shaft and it has energy imparted to it by rotating vanes of the impeller. The fluid leaves the periphery of the impeller at a relatively high velocity and is collected in the casing or shell. This casing is so designed that the velocity of the liquid is gradually reduced before it is discharged. Here the velocity of the liquid is converted into pressure by reduction of velocity according to Bernoulli's theorem. The quantity of liquid discharged by the pump is almost always measured in gpm, although sometimes the measure is cubic feet per second. In this discussion gallons per minute is used as the unit. Pressure developed by a centrifugal pump is specified as head in feet of liquid. 2.31P h = -------------s where s =specific gravity of the liquid compared to water (water at 60/60°F = 1.00); h =head in feet; and P =pressure in psi. The head developed by a centrifugal pump is a function of the impeller diameter and the speed of rotation (rpm). Maximum head that can be developed by a centrifugal pump is when the discharge valve is tightly closed and the pump is discharging zero capacity into the system. This is known as the shut-off head of the pump. Since there is a predetermined maximum pressure that the pump can develop and this pressure is taken into account by the designer, centrifugal pumps do not require relief valves or other unloading mechanizers that are otherwise necessary for the positive displacement type pumps. The maximum or shut-off head h of any centrifugal pump can be very closely calculated by the formula: D×N h x = ⎛ --------------⎞ ⎝ 1840 ⎠

2

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

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 guide vanes in the casing for the conversion of velocity to pressure energy, and (2) the volute-type centrifugal pump, most commonly used. Mechanically, a volute type centrifugal pump consists of an impeller or runner having curved vanes revolving on a shaft and housed in a shell or casing. Liquid enters the

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 operating characteristics of a typical centrifugal pump, or performance curve, is shown in Fig. 10-17. The pressure (or head in feet of liquid) developed by the pump at a speci-

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 10–9

HYDRONIC HEATING AND COOLING SYSTEM

fied impeller diameter and at a constant rpm is plotted against the discharge of the pump in gallons per minute (gpm.) Note that the maximum head developed by the pump is at zero capacity or shut-off as previously mentioned. The head-capacity curve extends from shut-off to maximum or wide-open capacity. In other words, as the pump discharges more liquid, its pressure decreases. The slope of the head-capacity curve is due to (1) the curve or shape and the number of vanes in the impeller; (2) friction or head loss within the pump. As the pump discharges more liquid, there is increased internal friction, and this friction loss is actually a loss in pressure or head at the discharge of the pump hence, the slope in head capacity curve. The pump designer can control to a certain degree the slope of the head-capacity curve by the shape or warp of the impeller vanes and also by the number of vanes. The internal friction, however, is a factor over which the pump designer has very little control. The efficiency curve rises to a maximum within certain capacity limits and then falls off toward the maximum capacity of the pump. The brake horsepower curve is usually as shown; that is, brake horsepower gradually increases in value as capacity increases. Maximum efficiency of a centrifugal pump lies within the design range. A pump designer has a definite capacity and head upon which all calculations are based, and the calculations are such that the maximum efficiency of the pump will be at or very near design capacity. Pump Laws.—The efficiency of a centrifugal pump, as for any machine, is horsepower output divided by the horsepower input. When efficiency is known the horsepower requirement of the pump is determined by the formula: × DH × sHP = gpm ---------------------------------3960 × E where DH = dynamic head in feet; s =specific gravity; and E =efficiency expressed as a decimal. This formula holds for any liquid since the specific gravity of liquid as compared with water may be inserted in the formula. Change of Performance.—The so-called laws of affinity relating to centrifugal pumps are theoretical rules

that apply to the change in performance of a centrifugal pump by a change in the speed of rotation or a change in the impeller diameter of a particular pump. It should always be remembered in using these laws of affinity that they are theoretical and do not always give exact results as compared with tests. However, they are a good guide for predicting the hydraulic performance characteristic of a pump from a known characteristic caused by either altering the speed of rotation or the outside diameter of the impeller. 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 gpm rpm ------------y- = -----------ygpm x rpm x 2

rpm y head y --------------- = -------------2 head x rpm x 3

rpm y bhp y ------------ = -------------3 bhp x rpm x At constant speed: 1. capacity varies directly as the cube of the impeller diameter; 2. head varies directly as the square of the impeller diameter; and 3. horsepower varies directly as the fifth power of the impeller diameter. Or, in equation form, d gpm y ------------- = ----ygpm x dx 3

d head --------------y- = ----y3 head x dx 5

bhp y dy ------------ = ------5 bhp x dx

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HVAC: Handbook of Heating, Ventilation and Air Conditioning HYDRONIC HEATING AND COOLING SYSTEM

and control valves, that must be available in the form of pump pressure. Preliminary Pump Selection: The preliminary selection should be based on the pump’s ability to fulfill the determined capacity requirements. It should be selected at a point left of center on the pump curve and should not overload the motor. Because pressure drop in a flow system varies as the square of the flow rate, the flow variation between the nearest size of stock pump and an exact point selection will be relatively minor. Final Pipe Sizing and Pressure Drop Determination.—Final Piping Layout: Examine the overall piping layout to determine whether pipe sizes in some areas need to be readjusted. Several principal circuits should have approximately equal pressure drops so that excessive pressures are not needed to serve a small portion of the building. Consider both the initial cost of the pump and piping system and the pump’s operating cost when determining final system friction loss. Generally, lower heads and larger piping are more economical when longer amortization periods are considered, especially in larger systems. However, in small systems such as in residences, it may be most economical to select the pump first and design the piping system to meet the available pressure. In all cases, adjust the piping system design and pump selection until the optimum design is found. Final Pressure Drop.— When the final piping layout has been established determine the friction loss for each section of the piping system from the pressure drop charts (Chapter 9) for the mass flow rate in each portion of the piping system. After calculating the friction loss at design flow for all sections of the piping system and all fittings, terminal units, and control valves, sum them for several of the longest piping circuits to determine the pressure against which the pump must operate at design flow. Final Pump Selection.— After completing the final pressure drop calculations, select the pump by plotting a system curve and pump curve and selecting the pump or pump assembly that operates closest to the calculated design point. Freeze Prevention.—All circulating water systems require precautions to prevent freezing, particularly in makeup air applications in temperate climates where (1) coils are exposed to outdoor air at below-freezing temperatures, (2) undrained chilled water coils are in the winter airstream, or (3) piping passes through unheated spaces. Freezing will not occur as long as flow is maintained and the water is at least warm. Unfortunately, during

10–19

extremely cold weather or in the event of a power failure, water flow and temperature cannot be guaranteed. Additionally, continuous pumping can be energy-intensive and cause system wear. Designers should take following precautions to prevent flow stoppage or damage from freezing: 1. Select all load devices (such as preheat coils) that are subjected to outdoor air temperatures for constant flow, variable control. 2. Position the coil valves of all cooling coils with valve controls that are dormant in winter months to the fullopen position at those times. 3. If intermittent pump operation is used as an economy measure, use an automatic override to operate both chilled water and heating water pumps in below-freezing weather. 4. Select pump starters that automatically restart after power failure (i.e., maintain-contact control). 5. Select non overloading pumps. 6. Instruct operating personnel never to shut down pumps in subfreezing weather. 7. Do not use aquastats, which can stop a pump, in boiler circuits. 8. Avoid sluggish circulation, which may cause air binding or dirt deposit. Properly balance and clean systems. Provide proper air control or means to eliminate air. 9. Install low temperature detection thermostats that have phase change capillaries wound in a serpentine pattern across the leaving face of the upstream coil. When designing fan equipment that handles outdoor air, take precautions to avoid stratification of air entering the coil. The best methods for proper mixing of indoor and outdoor air are the following: 1. Select dampers for pressure drops adequate to provide stable control of mixing, preferably with dampers installed several equivalent diameters upstream of the airhandling unit. 2. Design intake and approach duct systems to promote natural mixing. 3. Select coils with circuiting that allows parallel flow of air and water. Freeze-up may still occur with any of these precautions. If an antifreeze solution is not used, water should circulate at all times. Valve controlled elements should have low-limit thermostats, and sensing elements should be located to ensure accurate air temperature readings. Primary and secondary pumping of coils with three-way valve injection is advantageous. Use outdoor reset of water temperature wherever possible.

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–1

INDEX

A Abbreviations scientific and engineering terms 18-8 Absorption split systems 13-4 AC motors 17-5 Acoustical problems air handling room 16-42 apparatus casings 16-42 dampers in duct 16-42 fan isolation base 16-42 flexible connectors 16-43 high velocity system 16-40 Adiabatic mixing 3-3, 3-5 Air binding 15-41 composition 2-1 compressor 9-73 discharge pipe capacities 9-78 discharge through orifice 9-78 flow control 12-27 handling 14-1–14-96 horsepower 14-1 infiltration in fuel oil piping 12-18 mixing streams 3-3 pipe sizing 9-73 piping pressure loss 9-72 pressurization 15-64 regulators 9-73 removal from system 15-49 supply outlets 14-56 to air heat pumps 13-38 to water heat pumps 13-40 venting 15-52 Air conditioning process 3-1–3-8 heating and cooling 3-1 Air conditioning system 13-1–13-116 absorption split system 13-4 air handler selection 13-49 air handling apparatus 13-77 air motion 13-14 air systems 13-23, 13-30–13-34 all-water systems 13-27 apparatus casing 13-79 apparatus floor area 13-77 attic or crawl space 13-5 automatic control 13-81 cold air plenum 13-85 cold deck control 13-82 counter and parallel flow 13-98 damper 13-88 damper operation 13-88 day cycle 13-88 dual duct constant volume 13-94 dual duct mixing box 13-93 dual duct system 13-95 dual duct variable volume 13-94 economizer cycle 13-88 face and bypass control 13-94–13-95 freeze prevention 13-97 hot deck control 13-84 hot plenum 13-85 hot water 13-90 hot water converter 13-94 hot water pressure 13-92 hot water reheat 13-92–13-94 hot water system 13-91 mixed air 13-85 mixed air control 13-88 mixed air section 13-82 mixing box control 13-94 multizone unit 13-84 night cycle 13-88 night operation 13-89 preheat control 13-91 pressure control 13-94 rooftop multizone units 13-81 rotary air to air heat exchanger 13-95 single duct variable volume 13-95 summer cycle 13-88 summer operation 13-95 unit ventilator 13-88

Air conditioning system automatic control variable speed control 13-95 automatic control winter cycle 13-88 winter operation 13-96 winterizing chilled water system 13-97 zone day-night operation 13-91 zone mixing dampers 13-88 backlash 13-79 basic arrangement 13-69, 13-75 ceiling plenum 13-70 floor layouts 13-69 office building 13-73 carryover 13-79 check lists 13-114 air distribution 13-116 drain facilities 13-115 duct system 13-116 electric power facilities 13-115 heating load 13-115 hot water heating supply 13-115 refrigeration facilities 13-115 sewer facilities 13-115 steam supply facilities 13-115 water facilities 13-115 cold storage 13-58 constant volume mixing unit 13-76 construction details 13-80 control 13-9, 13-26 control panel location 13-9 cooling considerations 13-20 dehumidification 13-59 direct solar heating 13-56 double duct 13-9 duct joints 13-80 energy requirements 13-19 equipment maintenance 13-108 evaporative air conditioning 13-14–13-16 fans 13-79 furnace mounting 13-7 heat pumps 13-36–13-44 heat recovery 13-22–13-29 heat recovery air system 13-30 heat recovery water system 13-30 heating and cooling calculations 13-19 high velocity dual duct 13-60 advantages 13-60 air quantities 13-64 cycles 13-60 design factors 13-66 design high pressure ducts 13-67 design velocities 13-66 double fan with dehumidifier 13-61 large vs. small ducts 13-65 low pressure ducts 13-68 maximum velocity 13-66 single fan with dehumidifier 13-60–13-61 sizing 13-65 system design 13-64, 13-68 horizontal package units 13-1 humidity control 13-10 initial costs 13-18 installation of equipment 13-107 installations in roof 13-8 installed costs 13-79 insulation 13-79 lighting heating cooling system 13-22 location on roof 13-105–13-106 advantages 13-105 automatic control 13-105 multiple units 13-105 size of system 13-105 ventilation 13-106 machinery space 13-106 maintenance 13-112 multizone 13-8–13-9 multizone units 13-4 noise 13-79 outdoor conditions 13-14 overlapping 13-21 refrigeration chassis 13-2 remote condensers 13-2 remote condensing units 13-3 rooftop 13-6

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–2

INDEX

Air conditioning system (continued) selection procedure 13-10 services to equipment 13-107 servicing of air handling system 13-107 compresser oil 13-107 condenser 13-107 cooling plant 13-107 refrigeration unit 13-108 water system 13-107 single package installations 13-5 single package units 13-1 single package year round units 13-2 slab or ground level 13-6 solar augmented heat pump 13-57 solar energy 13-54 solar heating description 13-54 solar heating domestic water 13-56 solar heating operation 13-54 solar heating storage tank 13-56 sound lining 13-79 split systems 13-7 thermostat location 13-10 utility off-peak cooling 13-57 variable affecting costs 13-80 variable volume system 13-17–13-21 ventilation air 13-9 vertical package units 13-1 vibration 13-106 wall condensing units 13-8 well water 13-54 well water precooling 13-55 well water refrigerant condensing 13-55 winter to summer tank transition 13-58 year round remote units 13-3 zoning 13-69 zoning installation 13-8 Air distribution system 16-43 dampers as a noise generating source 16-46 dual duct area ratio 16-45 duct connectors 16-44 duct design method 16-43 duct in machine room 16-43 duct off fittings 16-45 duct velocity 16-43 flutter in dual duct mixing units 16-47 grilles, registers and diffusers 16-48 high velocity ductwork 16-44, 16-46 inlets to high velocity terminal points 16-47 large terminal units 16-48 noise in flexible connections 16-46 sound barrier for high velocity ductwork 16-46 sound traps 16-46 terminal devices 16-47 testing of high pressure ductwork 16-47 two motor dual duct units 16-47 warm connections 16-47 Air filters 9-73, 14-78 characteristics 14-80 dry filters 14-78 electronic air cleaner 14-79 selection 14-79 viscous impingement 14-78 Air handling units trap 15-112–15-116 Air space thermal resistance 5-19 Air volume humidifying or dehumidifying 14-74 required 14-75 sensible heating or cooling 14-74 Airborne noise through ducts 16-13 Aircraft air heater 15-83 ANSI Standard abbreviations 18-8 Apothecaries fluid measure 20-2 weight 20-2 Apparatus casing 13-79 Apparatus casing construction 14-77 Application range 14-2 Atmospheric pressure 20-2 Attenuation 16-1 Automatic control 13-81 cold air plenum 13-85 cold deck control 13-82

Automatic control counterflow and parallel flow 13-98 damper 13-88 damper operation 13-88 day cycle 13-88 dual duct constant volume 13-94 dual duct mixing box 13-93 dual duct system 13-95 dual duct variable volume 13-94 economizer cycle 13-88 face and bypass control 13-94–13-95 freeze prevention 13-97 hot deck control 13-84 hot plenum 13-85 hot water 13-90 hot water converter 13-94 hot water pressure 13-92 hot water reheat 13-92–13-94 hot water system 13-91 mixed air 13-85 mixed air control 13-88 mixing box 13-94 multizone unit 13-84 night cycle 13-88 night operation 13-89 preheat control 13-91 pressure control 13-94 rooftop multizone units 13-81 rotary air to air heat exchanger 13-95 single duct variable volume 13-95 summer cycle 13-88 summer operation 13-95 unit ventilator 13-88 variable speed control 13-95 winter cycle 13-88 winter operation 13-96 winterizing chilled water system 13-97 zone day night operation 13-91 zone mixing dampers 13-88 Automatic control of dual duct system 13-95 Avoirdupois or commercial weight 20-2

B Backlash 13-79 Balancing air flow 14-96 and testing 14-99 booster fan systems 14-98 circuits 15-53 duct distribution 14-98 Band pressure level 16-1 Bandwidth correction 16-6 Bare pipe radiation 15-34 Barrel liquid capacity 20-2 Below grade wall U-factors 6-3 Belts 13-114 Binary multiples 20-10 Blocked tight static pressure 14-2 Boiler cast iron 15-77 cast iron radiators 15-78 common return header 15-3 connected load 15-73 direct return connections 15-3–15-4 draft loss 15-76 drip end 15-7 effect of load variation 15-70 emergency protection 15-69 furnace volume 15-73, 15-75 gas fired 15-75 grate area 15-73, 15-75 hand fired 15-75 Hartford connection 15-3 heat emission 15-78 heating surface 15-73 heating value of coal 15-73 hot water system 15-69 mechanically fired steel boilers 15-74 nameplate 15-75 oil fired 15-74, 15-76 overhead connections 15-4 pipe sizing 15-71 pipe, valves, and fittings 15-69

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–3

INDEX

Boiler piping 15-15 piping connections to boilers 15-1 ratings 15-30, 15-73, 15-75–15-76 return header drip 15-6 return piping 15-6 return trap 15-29 stack dimensions 15-76 steam header drip 15-6 steam main drop 15-6 steam main rise 15-6 steam mains 15-6 stoker fired 15-75 supply and return piping 15-6 supply header drip 15-6 supply piping 15-6 valve installation 15-69 venting of piping 15-70 welded joints 15-70 Boiler horsepower 12-31 Boiling point calcium chloride 15-81 ethylene glycol 15-81 glycerine 15-81 glycol 15-81 oil 15-82 tetraanyl silicate 15-82 tetracresyl silicate 15-81 Brake horsepower 14-2 Branch trunk duct losses 14-60 Breeching access 14-85 aerodynamics 14-84 construction 14-83, 14-85 design 14-83 design and construction 14-83 expansion 14-83 British standard thermal units, (Btu) 20-7 Broadband noise 16-1 Building material resistances 5-17, 5-21–5-26 Built up roofing coefficient of transmission 5-14 Byte 20-10

(continued)

C Canning 15-30 Carat 20-2 Carnot cycle 1-4 Carryover 13-79 Cast iron radiators, capacity 15-79 Cavitation on pump 15-68 Ceiling by metal coefficient of transmissions 5-15 by wood coefficient of transmissions 5-15 Centimeter-gram-second system of measurement 20-8 Cfm and scfm 14-1 Check valve 9-139–9-141 Cheese vats 15-31 Chimney draft 14-90 sizing 14-94 velocities 14-90 Circular mil gage for wires 20-1 Circulating pumps 15-66–15-67 boilers 15-69 cavitation effects 15-68 construction 15-68 for boiler 15-69 net positive suction head 15-68 seals 15-68 CLF hooded equipments 7-45–7-46 people 7-44–7-45 unhooded equipments 7-44 Climatic cooling design data 19-1 data 19-1–19-38 data applicability 19-1 data characteristics 19-1 design condition 19-1 desumidification design data 19-1 heating design data 19-1 mean daily range 19-1 Closed system 1-2

Cloud point 12-15 CLTD conduction through glass 7-31 multi family 7-49 roofs 7-9 single family 7-49 walls 7-11 Code number thermal properties 7-27 walls and roofs 7-27 Coefficient of performance 1-4, 1-6, 13-36 Coefficient of transmissions built up roofing 5-14 ceiling by metal 5-15 ceiling by wood 5-15 flat masonry roof 5-14–5-15 flat metal roof 5-15 frame ceiling 5-14 frame floor 5-14 frame partitions 5-12 frame walls 5-11–5-12 masonry cavity walls 5-13 masonry partitions 5-13 masonry walls 5-11–5-12 pitched roof 5-16 Cold air plenum 13-85 Cold deck control 13-82 Combustion 12-1–12-20 air flow control 12-27 air heater bypassing 12-17 air infiltration in piping 12-18 basics 12-1 chemistry 12-1 control errors 12-20 control strategy 12-20 draft control 12-24 draft measurements 12-17 efficiency 12-3 efficiency losses 12-4 energy losses 12-7 excess air cost 12-3 feedwater control 12-23 firing rate 12-18 flue gas 12-6 flue gas recirculation 12-28 fuel composition 12-1 fuel oil 12-16 fully metered control 12-22 grate 12-16 natural gas 12-15 oxygen sensor 12-17 oxygen trim 12-26 parallel positioning 12-21 radiation loss 12-5 reaction 12-1 safe burner set up 12-3 short circuiting 12-16 single pressure regulator 12-19 stack losses 12-5 theory 12-1 tramp air 12-16 troubleshooting 12-15, 12-17 varying fuel flow 12-2 varying oxygen content 12-2 water in the fuel oil 12-18 wet atomizing steam 12-18 Combustion control air considerations 12-12 atomizing media 12-12 cloud point 12-15 considerations 12-11 draft 12-13 elevation 12-13 firing considerations 12-14 flashpoint 12-15 flue gas considerations 12-13 flue gas recirculation 12-14 fuel oil firing considerations 12-14 natural gas efficiency 12-8 nitrogen content 12-15 no. 2 oil efficiency 12-9 no. 6 oil efficiency 12-10 pour point 12-15 pressure and flow basics 12-11 saving fuel 12-7

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–4

INDEX

Combustion control sulfur content 12-15 temperature 12-13 viscosity considerations 12-14 Compressed air pipe sizing 9-73 receiver 9-74 system 9-72 system testing 9-74 Compressed liquid 1-1 Compresssors 13-114 Concrete block 15-31 Concrete, ready mix 15-31 Condensate drains 14-77 Condensate return pump 15-29 Condenser 13-113 Condensing units in wall 13-8 Condensing water circuit 13-111, 13-113 Conduction 5-1 Connections heating units to risers 15-8 mains to downfeed risers 15-8 offset 15-9 risers to heating unit 15-9 runout 15-9 Conservation of energy 1-3, 3-1–3-3 cooling and dehumidifing 3-2 Conservation of energy equations 3-1 Conservation of mass 1-3, 3-1–3-3 Conservation of mass equations 3-1 Continuity equation 1-6 Control valve sizing 9-142–9-143 Controls 13-9 basic factors for designing 15-96 bonnet air temperature 15-96 continuous air circulation 15-94 continuous blower circulation 15-95 errors 12-20 fan switch 15-94 intermittent blower operation 15-95 limit switch 15-94 room thermostat 15-94 strategies 12-20 temperature drop of air in ducts 15-96 thermostatics 15-94 valve sizing 9-142 Convection 5-2 Convection coefficient 5-3 Convector piping details 15-4 Conversion fractional inch to millimeter 20-3 millimeter to fractional inch 20-3 Cookers, coil 15-31 Cookers, jacketed 15-32 Cooling and dehumidification 3-2 Cooling and dehumidifing 3-2 Cooling load 5-33 Cooling load calculation 7-1 CLF method 7-6–7-49 CLTD method 7-6–7-49 cooling coil load 7-1 heat extraction rate 7-1 heat gain 7-1 heat source 7-1 latent heat gain 7-1 radiation heat gain 7-1 residential 7-35 SCL method 7-6–7-49 sensible heat gain 7-1 space cooling load 7-1 thermal storage 7-1 transfer function method 7-1 Cooling of fuel oil in atomizers 12-18 Cooling tower 13-99–13-105 estimating data 13-101, 13-103 natural draft 13-102 tower height 13-103 water requirements 13-104 wet bulb temperature 13-103 wind velocity 13-102 Cooling tower noise control 16-36 configurations 16-38 fan noise 16-36 half speed operation 16-39

(continued)

Cooling tower noise control leaving condition changed 16-39 location 16-39 oversizing the tower 16-39 reducing generated sound 16-39 sound absorbers 16-40 water noise 16-37 Cooling water 13-113 Cooling water system 13-112–13-113 Cooling, heat recovery 13-45 Counterflow and parallel flow 13-98 Cubic measure 20-1

D Damper control 13-88 Damper operation 13-88 Dampers 13-113 Day cycle 13-88 Decibel 16-1 Degree days 11-1–11-8 Degree of saturation 2-2 Dehumidification 13-59 Demand load 9-28 Demand weights of fixtures 9-30 Density effects 14-4 Design lateral load 14-77 Dew point temperature 2-4 Direct fired unit heater 15-83 Distilleries 15-32 Domestic water, solar heating 13-56, 13-58 Double duct system 13-9 Draft burning coal 14-95 control 12-24, 14-92 foot of chimney 14-95 measurements 12-17 Drip end 15-7 Dripping riser 15-12 Dry cleaning 15-32 Dry measure 20-2, 20-8 Dryers 15-32 Dual duct constant volume control 13-94 mixing box control 13-93 variable volume control 13-94 Duct box plenum system 15-88 characteristics 15-88 design 8-9 design by computer 14-72 design methods 8-12 design procedures 8-13 design velocities 8-11 equal friction method 8-12 equivalent lengths of fittings 15-105 equivalent rectangular ducts 8-6 extended plenum system 15-88 fibrous glass construction 14-73 fitting friction loss 8-14 fitting loss coefficient bellmouth, plenum to round 8-24 conical diffuser 8-26 damper, butterfly 8-19 elbow mitered 8-18 elbow mitered with vane 8-18 elbow with splitter vane 8-17 elbow without vanes 8-17 elbow Z shaped 8-19 exhaust system 8-26 fire damper 8-27 return system 8-26 round tap to rectangular main 8-25 tee converging 8-26, 8-31, 8-33–8-34 transition in rectangular 8-25 transition rectangular to round 8-25 transition round to rectangular 8-27 transition round to round 8-26 varaiable inlet outlet areas 8-24 wye converging 8-36 wye 30 degree converging 8-28 wye, 45 degree 8-30, 8-32 fitting loss coefficient tables 8-17–8-37 flat and oval duct 8-5

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–5

INDEX

Duct individual system 15-88 rectangular 8-5 resistance in low pressure ducts 8-15 static regain method 8-13, 8-15 trunk system 15-88 turns 14-28 vibration and noise 8-12 Duct design 8-1, 8-17 Duct design data diffuser, free discharge 8-21 plenum to rectangular 8-21 sudden contraction 8-21 Tee type, diverging 8-23 transition, rectangular to rectangular 8-22 transition, round to rectangular 8-22 wye type diverging 8-22 45 degree entry branch 8-24 90 degree elbow 8-21 Duct joints 13-80 Duct roughness 8-5 Ducts 13-113 air balancing 14-52 air distribution 14-56 air flow 14-37, 14-53 air quantities 13-64 air supply outlets 14-56 air turning hardware 14-52 branches and discharges 14-51 cycles 13-60 degree of roughness 14-40 density of air 14-39 design air velocities 14-47 design considerarion 8-9 design velocities 8-12, 13-66 double fan dual duct 13-61 dynamic loss 8-7 elbows 8-14 energy equation 8-1 equal friction method 8-14 factors for design 13-66 fan system interface 8-8 fire and smoke management 8-9 flexible ductwork 14-62 four types 14-53 friction chart 8-4–8-5 friction losses 8-2, 14-40 friction of air 14-41–14-44 good turns 14-50 high pressure ducts 13-67 high velocity 13-60 high velocity advantages 13-60 high velocity design 14-71 high velocity system 14-59 insulation 8-9 large vs. small in size 13-65 local loss coefficients 8-7 losses in rectangular elbows 14-46 losses in round elbows 14-45 losses in round fittings 14-45 low pressure ducts 13-68 maximum velocity 13-66 noise control 8-12 non circular 8-5 pitot traverse 14-39–14-40 pressure change in a system 8-8 pressure head 8-1 pressure losses 14-48–14-49, 14-61 recommended velocities 8-11, 14-57 rectangular and round equivalents 14-47 rectangular shape 14-40 return air ducts 13-68 return air plenums 14-54 roughness factors 8-2 roughness values 8-5 sectional losses 8-7 single fan dual duct 13-60–13-61 sizing 13-65 static pressure 14-37, 14-66 static pressure loss 14-60 static regain 14-59, 14-63, 14-65 system design 13-64, 14-56 system leakage 8-11 tap off fitting 14-62

(continued)

Ducts testing and balancing 8-12 turns 14-51 velocity 14-37 velocity pressure 14-37–14-38 Dust collectors 14-78–14-79 dry centrifugal types 14-82 electrostatic precipitators 14-83 fabric collectors 14-82 wet collectors 14-82

E Economizer control cycle 13-88 Emissivities 5-4 Energy 1-2 internal 1-2 kinetic 1-2 potential 1-2 thermal 1-2 Energy equation 8-1 Energy esimation base temperature 11-1 degree days 11-1–11-8 abroad 11-8 application 11-2 different bases 11-9–11-20 U.S. cities 11-9–11-20 empirical constants 11-7 fuel consumption 11-4 future demands 11-5 guide of operation 11-2 limitations 11-7 load factors 11-7 operational hours 11-7 65 deg, as base 11-1 Enthalpy 1-1, 2-4 Entropy 1-1 Equation of state 2-1 Equipment arrangement 13-44 Equipment losses 14-60 Equipment maintenance 13-108 air distribution 13-108 air handling 13-108 central system schedule 13-111 cooling 13-108 schedule 13-110–13-111 water using 13-108 Equivalent direct radiation 15-1 Equivalent length of elbow 9-2 Erosion 9-3 Ethylene glycol 15-81 Evaporative air conditioning 13-14–13-16 air motion 13-14 outdoor conditions 13-14 Evaporative condensers 13-113 Exbi 20-10 Excess air 12-3 Excess air measurement 12-6 Exhaust air heat recovery 13-31 Expansion conditions 15-65 Expansion joints 15-9 Expansion loops 15-9 swing type 15-10 Expansion of piping 9-134–9-135 Expansion tank 15-65 sizing 15-53, 15-65 Expansion valves 13-112 Extrinsic property 1-1

F Face and bypass control 13-94–13-95 Fan 13-79 acoustic properties 16-21 air entry position 14-20 axial fan 14-16 backward inclined fan 14-14 blade pitch variation 14-31 class limits 14-16 coil unit 13-48 comparison 14-36 discharge connections 14-27

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–6

INDEX

Fan (continued) discharge dampers 14-30 double inlet 14-27 flywheel effect 14-36 formulas 14-31 forward curve centrifugal fan 14-14 horsepower and actual capacity 14-32 inlet connections 14-26 inlet dampers 14-29 inlet effects 14-23 inlet vanes 14-30 laws 14-3 noise generation 16-23 operating limit 14-18–14-19 operating point 14-11 paralleling 14-11 performance curve 14-11 performance data 14-36 performance modulation 14-29 radial blade fans 14-15 scroll volume control 14-29 selection 14-21, 14-34 single inlet 14-27 size change 14-3 speed modulation 14-31 static pressure 14-1 surge 14-11 system resistance curve 14-11 system surge 14-11 terminology 14-1 total pressure 14-1 tubular centfifugal fan 14-15 types 14-14 velocity pressure 14-1 Feed mills 15-33 Feedwater control 12-23 Filling pressure 15-53 Filters 13-113 Filters and ducts 13-112–13-113 Fin efficiency 1-16 Fin tube piping 15-4 Fins and extended surfaces 1-15 Fire dampers 14-56 Fire protection 14-56 Fire protection equipments 9-143 Firing rate 12-18 First law of thermodynamics 1-3 Fixture units with demand 9-28 Fixtures demand weights 9-30 Flash point 12-15 Flash steam calculations 15-39 condensate quantity 15-44–15-45 quantities 15-43 Flash tank capacities 15-42 dimension 15-39, 15-45 sizing 15-40 Flash trap 15-29 Flat masonry roof coefficient of transmission 5-14 Flat roof by metal coefficient of transmission 5-15 Flat roof by wood coefficient of transmission 5-15 Float trap 15-27–15-28 Floor furnace 15-83 Flow meter piping 12-31–12-32 Flowwork 1-2 Flue gas composition 12-6 Flue gas recirculation 12-28 Flush valve capacity 9-30 Forced convection 1-12 Forced draft 14-92 Fractional inch to millimeter conversion 20-3 Frame ceiling coefficient of transmissions 5-14 Frame floor coefficient of transmissions 5-14 Frame partitions coefficient of transmissions 5-12 Frame walls coefficient of transmissions 5-11–5-12 Free delivery 14-2 Freeze prevention 10-19, 13-97 Freeze up protection 15-16 Freezing point calcium chloride 15-81 glycerine 15-81 glycol 15-81 oil 15-82

Freezing point tetra anyl silicate 15-82 tetra cresyl silicate 15-81 French thermal unit 20-7 Friction chart 1-9, 15-47–15-48 chart, duct 8-4 hot water piping 15-46 rate 15-23 Friction loss 1-9, 8-2 copper piping 9-5 equivalent length of elbow 9-2 flanged pipe fitting loss 9-2 K factors 9-2 plastic piping 9-5 screwed pipe fitting loss 9-2 steel piping 9-5 tee fitting 9-6 valve and fitting equivalents 9-7–9-27 valve and fitting loss 9-6 Fuel composition 12-1 Fuel consumption degree days 11-4 Fuel oil 12-16 Fuel oil handling 12-33 alarm signals 12-39 automatic pump alternation 12-38 automatic start-stop system 12-38 automatic valves 12-38 back-up pump operation 12-38 burner loop system 12-34 continuous operation 12-38 day tank 12-33 entrained air 12-37 flow rate 12-33 gravity head 12-36 intermittent operation 12-38 maximum inlet pressure 12-36 multiple day tank 12-33 multiple pump 12-34 piping system 12-37 pump controls 12-37 pump discharge pressure requirements 12-37 required capacity 12-36 safety shutdown 12-39 standby generator application 12-33 standby generator loop systems 12-34 strainer pressure drop 12-36 suction line losses 12-36 tank overflow 12-37 tank venting 12-37 Fully metered control 12-22 Furnace mounting 13-7 Future needs degree days 11-5

G Gallons into cubic inches 20-2 Gas laws 2-1 Gas piping 9-59–9-72 capacities 9-59 pressure loss 9-63–9-70 residential 9-59 sizes for residential 9-59 solution 9-62 tables 9-62 Gas pressurization 15-64 Gas properties 2-1, 12-1 Gate valve 9-139–9-141 Gibi 20-10 Globe valve 9-139–9-141 Ground level installations 13-6 Ground source heat pumps 13-41

H Hanger spacings 15-16 Heat 1-2 coefficients of transmission 5-27 exchanger 1-18 mechanical equivalent 20-7 quantity measurement 20-7 scales 20-7 storage 15-63

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–7

INDEX

Heat thermal energy 20-7 transfer 1-11 Heat anticipators 13-43 Heat emission bare radiators 15-79 bathroom radiators 15-80 enclosure effects 15-78 front wall radiators 15-80 pipe coils 15-80 propeller unit capacities 15-80 radiator finish 15-78 ultra slender tubular 15-80 unenclosed ratiators 15-79 unit ventilators 15-80 wall radiators 15-80 Heat gain computer equipment 7-6 cooking appliances 7-3–7-5 copier 7-6 laboratory equipment 7-6 laser printer 7-6 medical equipment 7-6 occupants 7-2 office equipment 7-6 Heat load coefficients F2 6-4 floor slab 6-5 infiltration 6-6 ventilation 6-6 Heat loss bare pipe 9-146–9-156 coefficient 9-158 cold surface temperature 9-158 heat conductivity 9-158 in piping 9-144 insulated pipe 9-157, 9-159–9-176 Heat pumps air to air 13-38 air to water 13-40 coefficient of performance 13-36 electrohydronic heat recovery 13-44 equipment arrangement 13-44 fan coil units 13-48 ground source 13-41 heat anticipators 13-43 heating performance factor 13-37 installation factors 13-42 operating factors 13-42 optimized data 13-47–13-48 outdoor temperature effects 13-42 performance factor 13-37 reverse cycle principle 13-36 sources 13-41 thermostats 13-43 types 13-37 water to air 13-40 water to water 13-39 Heat recovery 13-22–13-29, 13-44 air systems 13-23, 13-30–13-34 all water systems 13-27 control 13-26 cooling cycle 13-45 supplementary heat 13-47 system design 13-47 temperature limit 13-45 Heat transfer coefficient 1-12 combined network 5-9 parallel network 5-8 series network 5-6 Heating and cooling media 15-81 brine 15-81 calcium chloride 15-81 ethylene glycol 15-81 glycerine 15-81 glycol 15-81 oil 15-82 tetraanyl silicate 15-82 tetracresyl silicate 15-81 Heating and humidification 3-3 Heating load 5-33, 6-1 floors 6-1 infiltration 6-1 roofs 6-1

(continued)

Heating load ventilation 6-1 walls 6-1 walls below grade 6-2 windows 6-1 Heating of fuel oil in atomizers 12-18 Heating performance factor 13-37 Heating system cast iron radiators 15-79 enclosure effects 15-78 forced air system 15-127 gravity circulation 15-128 hot water heater 15-124–15-125 radiator emission 15-78 steam or vapor 15-126–15-127 Henry’s constant 10-4 Horsepower electric motor ratings 17-1–17-2, 17-4 Hot deck control 13-84 Hot plenum control 13-85 Hot water control 13-90 Hot water heating system 15-49 affecting conditions 15-60 affecting design conditions 15-60 air pressurization 15-64 air removal 15-49 air venting 15-52 balancing circuits 15-53 boiler emergency protection 15-69 boiler recirculating pump 15-69 boilers 15-69 branch pipe sizing 15-59 cavitation effects 15-68 checking pipe size 15-58 circulating pumps 15-66–15-67 combination piping system 15-60 compare with steam 15-63 compressed air 15-54 district steam 15-50 effect of load variation 15-70 expansion conditions 15-65 expansion tank sizing 15-53 expansion tanks 15-60–15-61 filling pressure 15-53 gas pressurization 15-64 generator 15-6 heat storage 15-63 high temperature drop 15-63 HTW for process steam 15-66 main pipe sizing 15-59 net positive suction head 15-68 nitrogen pressurization 15-64 nitrogen pressurizing tank 15-66 one pipe diversion 15-50 one pipe diversion system 15-59 one pipe series 15-50, 15-60 operating water 15-49 pipe size check 15-59 pipe sizing 15-71 pipe, valves and fittings 15-69 piping design 15-55 piping details 15-54 pressure drop in fittings 15-56–15-57 pressure limitation 15-49 pressurization of HTW system 15-63 preventing backflow 15-53 prevention of freezing 15-49 pump construction 15-68 pump location 15-52–15-53 pump specifications 15-67 reduce tank size 15-54 seals 15-68 service water 15-49 steam pressurization 15-63 steam pressurizing tank 15-65 summer cooling 15-50 system adaptability 15-50 temperature 15-61 two pipe direct return 15-50 two pipe direct reverse 15-58 two pipe return reverse 15-58 two pipe reversed return 15-52 types 15-50 valve installation 15-69 venting of piping 15-70

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–8

INDEX

Hot water heating system waste steam heat 15-50 water circulation below mains 15-49 water velocity 15-52 welded joints 15-70 Hot water pressure control 13-92 Hot water reheat control 13-92–13-94 Hot water reheat converter 13-94 Hot water system 13-91 HTW for process steam 15-66 Humidity control 13-10 Humidity ratio 2-2 Hydronic close expansion tank 10-7 cooling 10-1 design layout 10-18 diaphragm tank 10-7 equipment layout 10-18 freeze prevention 10-19 heating 10-1 medium temperature 10-1 open expansion tank 10-7 pipe sizing 10-18 piping layout 10-19 pressure drop 10-19 pump selection 10-19 temperature classification 10-1

I Ideal gas 2-1 Impulse trap 15-29 Indoor air quality 4-1 air filter types 4-8 carbon media filters 4-10 fiber foam filters 4-10 HEPA filters 4-10 outdoor air requirements 4-7 ozone 4-10 pollutants and sources 4-5 pollutants concentration 4-1, 4-5 procedure 4-6 standards 4-5 ultraviolet light 4-10 ventilation procedure 4-1 ventilation rates 4-2 Industrial unit heater piping 15-5 Infiltration heat loss 6-6 Installation in attic 13-5 Installation in crawl space 13-5 Installation of equipment 13-107 Insulation 13-79 prevent sweating 9-177 Internal heat air systems 13-30 exhaust air heat recovery 13-31 refrigeration heat 13-31 refrigeration service 13-31 water systems 13-30 Intrinsic property 1-1 Inverted bucket trap 15-29 Isolation efficiency 16-10

K Kibi 20-10 Kilns 15-34

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

(continued)

M Machinery space 13-106 Masonery walls coefficient of transmissions 5-12 Masonry partitions coefficient of transmissions 5-13 Masonry walls coefficient of transmissions 5-11 Mebi 20-10 Mechanical efficiency 14-2 Mechanical equivalent of heat 20-7 Metric International System of Units 20-9 Microinch 20-1 Mil 20-1 Minimum deflections 16-9 Minimum elevation in drip traps 15-7 Mixed air control 13-85, 13-88 Mixed air section 13-82 Mixing air streams 3-3 Mixing box control 13-94 Moist air properties 2-6–2-7, 2-18 Moisture 13-112 Moody’s friction chart 1-9 Mortar mixes 14-77 Motors acceleration time 17-9 analysis of application 17-18 application 17-17 application data 17-14 bearings 17-20 capacitor 17-13 capacitor run 17-28–17-29 capacitor start 17-28 classification by cooling 17-3 classifications 17-1 application 17-1 electrical type 17-1 size 17-1 compressors 17-18, 17-25 constant hp 17-21–17-22 constant torque 17-21 current relay 17-27 DC types 17-7 design letters 17-1–17-2 dynamic loads 17-8 dynamics 17-11 dynamics of load 17-10 enclosure 17-19 fans and blowers 17-18 full load currents 17-6–17-7 heating 17-8, 17-11 heating during starting 17-12 hermetic compressor 17-25 hermetic type 17-25 hot wire relay 17-27 hp and full load currents 17-6–17-7 hp and speed ratings 17-4 hp ratings 17-14 induction run motor 17-27 inertia 17-9 internal line break 17-27 life 17-11 loading 17-17 locked rotor current 17-2 locked rotor current and torque ratings 17-1 locked rotor kva 17-5 locked rotor torque 17-5 multispeed operation 17-17 NEC code 17-6 oil burners 17-18 open machine 17-3 overload with capacitor start 17-27 permanent split capacitor 17-27 polyphase 17-19 polyphase induction motor 17-23 protection 17-18 quietness 17-20 repulsion induction 17-15 repulsion start 17-13 selections 17-18 shaded pole 17-13 single phase 17-12, 17-15 speed control 17-21 speed data 17-14

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–9

INDEX

Motors squirrel cage induction 17-20–17-21 sump pump 17-18 synchronous speed 17-24 three phase 17-6, 17-28 torque and speed 17-2 torques 17-9–17-10, 17-14 two phase 17-7 types 17-12, 17-14, 17-21 variable speed 17-24 variable torque 17-22–17-23 voltage and frequencies 17-3 wiring diagram 17-22 Motors and starters 17-1 Motors, electric armature rotors 17-40 ball or roller bearings 17-39 brushes 17-39 commutators 17-39 inspection schedule 17-39–17-40 lubrication, proper 17-39 maintaining and repairing 17-39–17-40 maintenance 17-39 mechanical condition 17-39 monthly inspection 17-40 rotors and armatures 17-40 squirrel cage rotors 17-40 weekly inspection 17-39 windings 17-40 Mount types 16-12 Multizone system 13-9 Multizone unit control 13-84 Multizone units 13-4

N National Electric Code (NEC) 17-6 Natural attenuation in ducts 16-24 Natural convection 1-12 Natural gas 12-15 Nautical measure 20-1 Net positive suction head 10-11, 15-68 Night cycle 13-88 Night operation 13-89 Nitrogen content 12-15 Nitrogen pressurization 15-64 Nitrogen pressurizing tank 15-66 Noise and vibration 16-1–16-50 addition of decibels 16-14 air flow noise 16-27 airborne noise through ducts 16-13 attenuation 16-1 attenuation of a lined duct 16-25 band pressure level 16-1 bandwidth correction factor 16-6 broadband noise 16-1 calculation of sound levels 16-14 condenser water and chilled water piping 16-13 continuous noise 16-1 cooling tower location 16-39 cooling tower noise control 16-36 cooling waters 16-13 decibel 16-1, 16-14 drive components 16-37 duct lining and elbows 16-26 duct lining attenuation 16-24 ducted system 16-20 equipment room and critical spaces 16-7 external noise source 16-37 fan acoustic properties 16-21 fan noise 16-36 fan noise estimation 16-23 fan noise generation 16-23 flow noise by silencers 16-31 frequency 16-1 frequency limits for octave bands 16-15 insertion loss 16-1 isolation efficiency 16-10 microbar 16-1 minimum mounting deflections 16-9 mount types 16-12 natural attenuation 16-24 noise criteria 16-2–16-3

(continued)

Noise and vibration octave band 16-1, 16-7, 16-15 octave bandwidth correction 16-30 open end reflection loss 16-27 pitch 16-1 ratings and standards 16-7 regenerated noise 16-13 sabin 16-15 sound absorption coefficients 16-16 attenuation 16-10, 16-27 attenuation of plenums 16-25 level of sources 16-2 power allotment at branch 16-24 power distribution in branch 16-24 power level 16-23–16-24 pressure level 16-1, 16-17 transmission 16-7 speech interference criteria 16-2 steam pressure reducing valves 16-13 transformers 16-13 vibration isolation 16-7 water noise 16-37 Noise criteria 16-2–16-3 chart 16-20 Noise from fluid flow 1-11 Noise generation 9-3 Noise in ducted system 16-20 Noise on ducts 13-79

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

P Paper corrugators 15-35 Parallel positioning 12-21 Partial vapor pressure 2-3 Pebi 20-10 Performance factor 13-37 Pipe allowable spaces 9-134 expansion 9-134 layout plan 9-132 layout plan length 9-133 Pipe fittings 9-97–9-129 dimensions 9-97, 9-129 taper pipe thread 9-97–9-129 Pipe sizing 9-1 pressure drop 9-1 valve and fitting loss 9-1–9-58 Piping allowances for aging 9-3 anchor 15-10 application 15-26 around door 15-10 around obstacle 15-10 boiler 15-15 capacities, high pressure 15-21 capacities, low pressure 15-23 capacities, medium pressure 15-21 carrying capacity 9-80–9-90 closed system 9-4 color identification 9-143 contraction 15-11 corrosion resistance 9-136 metal 9-138 design 15-17 dimensional capacities 9-80–9-90 dimensions 9-80–9-90 dripping riser 15-12 dripping steam main 15-13 erosion 9-3

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–10

INDEX

Piping expansion 15-11 flush valve 9-30 hydronic system 9-4 identification method 9-144 lifting condensate 15-14 material, protective 9-143–9-144 materials 9-4 multiple coils 15-14 noise 9-4 noise generation 9-3 obstructions 15-12 one pipe system 15-17 plastic material 9-29 recessed below floor 15-10 reducing main 15-10 single coils 15-13 sizing 15-18, 15-20 steam bypass control 15-14 steam flow 9-31 steam riser 15-10 supports 15-16 thickness 9-80–9-90 two pipe high pressure system 15-18 two pipe low pressure system 15-19 two pipe medium pressure system 15-19 two pipe system 15-17 two pipe vacuum system 15-23 underwater corrosion 9-136 vacuum lift 15-12 water 9-3 water hammer 9-4 Piping design checking 15-59 checking pipe size 15-58 combination system 15-60 for branches 15-59 for main 15-59 one pipe diversion system 15-59 one pipe series 15-60 two pipe direct return system 15-58 two pipe reversed return system 15-58 Piping identification 9-143 Plant master control 12-28 Plastic piping 9-29, 9-91–9-93 above ground 9-93 above ground installation 9-96 below ground 9-93 below ground installation 9-96 chemical resistance 9-94 codes and regulations 9-97 design parameters 9-93 elastomeric seals 9-91 flanges 9-93 flaring 9-93 flow characteristics 9-94 heat fusion 9-91 insert fitting 9-93 installation 9-96 joining technique 9-91 mechanical couplings 9-91 pressure loss 9-92 pressure ratings 9-94–9-96 solvent cementing 9-91 standards and identifications 9-93 storage handling 9-96 thermal expansion coefficients 9-93 threading 9-93 types 9-91 Plumbing water piping 9-28 Pneumatic pipe sizing 9-73 Pneumatic piping 9-72 Pour point 12-15 Prandtl number 1-12 Preheat control 13-91 Pressure control 13-94 Pressure drop 9-1 air in pipe 9-75–9-77 air piping 9-72 gas piping 9-63–9-70 in fittings 15-56–15-57 liquids 9-79 return piping 15-23 supply piping 15-23 vertical piping 9-32

(continued)

Pressure head 8-1 Pressure loss disk type water meter 9-28 plastic piping 9-92 Pressure ratings, plastic piping 9-94–9-96 Pressure required in fixtures 9-6 Pressure unit conversion 20-2 Pressurization of hot water system 15-63 Preventing backflow 15-53 Prevention of freezing 15-49 Process 1-3 Propeller unit heat capacities 15-80 Properties of gas 12-1 Property 1-1, 1-3 Psychrometric analysis 2-1 Psychrometric chart 2-8 Psychrometry 2-1 air composition 2-1 degree of saturation 2-2 dew point temperature 2-4 enthalpy 2-4 graphical presentation 2-7 humidity ratio 2-2 ideal gas 2-1 moist air properties 2-6, 2-18 relative humidity 2-2 saturation 2-4 vapor pressure 2-3 water properties 2-12 wet bulb temperature 2-2, 2-5 Pump centrifugal 10-8 change of performance 10-9 condensate return 15-29 construction 15-68 location 15-52 net positive suction head 10-11 operating chsracteristics 10-8 specifications 15-67 vacuum 15-30 Pumping down 13-112 Pure substance 1-1 Purging system 13-112

Q Quality of steam 1-1

R Radiator capacity 15-79 Radiator emission 15-78 Rankine degrees 20-7 Ratings and standards 16-7 Ratings of boilers 15-73 Ream, paper 20-3 Refrigerant circuit 13-112 Refrigerant controls 13-112 Refrigerant effect 1-4, 1-6 Refrigerant storage in drums 13-112 Refrigeration chassis 13-2 Regenerated noise 16-13 Register 15-89 capacity 15-101, 15-103–15-104 loudness 15-106 pressure loss 15-101, 15-103–15-104 Reheat system 13-9 Relation of air with temperature 14-8, 14-10 Relative humidity 2-2 Remote condensers 13-2 Remote condensing units 13-3 Replacing refrigerant 13-112 Residential cooling load calculation 7-35 Resistance of building materials 5-17, 5-21–5-26 Return intake capacity 15-105 pressure loss 15-105 Reverse cycle principle 13-36 Reversibility 1-4 Reynolds number 1-7 laminar flow 1-8 turbulent flow 1-7 Riser drip 15-8

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–11

INDEX

Roof as a location for AC system 13-105–13-106 advantages 13-105 automatic control 13-105 multiple units 13-105 size 13-105 ventilation 13-106 Roof numbers 7-8 Roof top installation 13-6 Roof‘top multizone units 13-81 Rotary air to air heat exchanger control 13-95 Rotating apparatus 13-114 Rotors heating during starting 17-12 wound 17-23 Roughness factors 8-2 RPM change 14-3

S Sabin 16-15 Saturated liquid 1-1 Saturated vapor 1-1 Saturation 2-4 SC for glass 7-50 SCL for glasses 7-36 Second law of thermodynamics 1-4 Selecting air handler units 13-49 Service water heating system 15-49 Servicing of air handling system 13-107 compresser oil 13-107 cooling plant 13-107 refrigeration unit 13-108 water system 13-107 Shear stress 1-6 Shipping measure 20-1 Short circuiting 12-16 Signs and abbreviations scientific and engineering 18-8 Simple heating and cooling 3-1 Single degree freedom vibration isolation 16-7 Single duct variable volume control 13-95 Single package installations 13-5 Single package units 13-1 Single package year round units 13-2 Single phase induction motors 17-2, 17-4–17-5 Single phase motors 17-12 Sizing cold water pipe 9-29 Slab installations 13-6 SLF for glass 7-50 Solar augmented heat pump 13-57 Solar energy 13-54 cooling system 13-54 Solar heating 13-56 operation 13-54 storage tank 13-56 systems 13-54 Solubility versus temperature 10-5 Sound absorption coefficients 16-16 attenuation 16-10 duct wall transmission loss 16-32 level of sources 16-2 levels in a duct 16-32 power at branch take off 16-24 power level in a duct 16-34 pressure 16-35 pressure level 16-7, 16-17 transmission 16-7, 16-31 transmission loss factor 16-32 Sound lining 13-79 Space heater 15-83 Specific heat 1-2 constant pressure 1-2 constant volume 1-2 various materials 15-36 Speech interference criteria 16-2 Split phase motors 17-12 Split system installations 13-7 Spray nozzles 13-113 Squirrel cage induction motors 17-1–17-2 Standard air 14-1 Starters

Starters AC motors 17-31 mechanical shocks 17-33 motor controllers 17-29 open circuit transition 17-36 overcurrent protection 17-29 overload protection 17-30 properties 17-30 size with hp 17-32 types 17-36 winding 17-33 Static efficiency 14-2 Steam ashpalt plants 15-30 coils 15-12 pressurization 15-63 pressurizing tank 15-65 riser 15-10 Steam boiler autoclaves 15-37 cheese vats 15-31 concrete block 15-31 dry cleaning 15-34–15-35 flat iron work 15-35 laundries 15-34 ovens 15-35 paper corrugators 15-35 paper making 15-36 pasteurization 15-36 platen presses 15-36 process heating 15-36 restaurants 15-37 snow removal 15-37 sterilizers 15-37 tire recapping 15-38 vacuum pans 15-38 washers 15-38 Steam heating system 15-1–15-129 auditorium type unit ventilator 15-5 boiler feed system 15-1 boilers common return header 15-3 controlled system header drip 15-6 direct return connection 15-3–15-4 drip end 15-7 Hartford connection 15-3 overhead connections 15-4 piping connections to boilers 15-1 steam main 15-6 steam using equipments 15-4 supply and return piping 15-6 supply header drip 15-6 vacuum header drip 15-6 convector piping details 15-4 equivalent direct radiation 15-1 fin tube piping 15-4 hot water generator 15-6 industrial unit heater piping 15-5 piping connections to boilers 15-1 steam supply to heating units 15-1 traps 15-1 unit heater piping 15-5 unit ventilator piping 15-5 vacuum heating pump 15-1 vacuum pumps 15-1 Steam main bypass 15-14 drip in riser 15-7 dripping 15-13 rise and drip 15-6 splitting 15-7 Steam piping 9-32 capacities 9-33 chart 9-34–9-58 equivalent length of fitting 9-34 equivalent length of run 9-33 formula 9-31 initial pressure 9-33 maximum velocity 9-33 pressure drop 9-33 pressure loss 9-31–9-58 size 9-32 Stefan Boltzmann constant 1-14 Strainers 13-113 Subcooled liquid 1-1

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(continued)

HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–12

INDEX

Sulfur content 12-15 Summer cycle 13-88 Summer operation 13-95 Superheated vapor 1-1 Supplementary heat 13-47 Supply and return header drip 15-6 Surface conductance 5-18 Surface resistance 5-18 Surface temperature calculations 5-9 Surroundings 1-2 Surveyors measure 20-1, 20-8 Symbols abbreviations 18-8 air conditioning piping 18-6 fittings 18-7 heating piping 18-6 piping 18-6 plumbing piping 18-7 pneumatic tubes 18-7 sprinklers 18-7 valves, pipe fitting 18-5 System boundary 1-2 System design 13-47

T Tank transition from winter to summer 13-58 Tanks and pans 13-113 Tebi 20-10 Temperature control 12-28 Temperature limit, heat recovery 13-45 Thermal conduction 1-11 conduction problems 1-15 conductivity 1-11, 5-1–5-2 convection 1-12 diffusivity 1-12 energy 20-7 radiation 1-14, 5-4 resistance of air space 5-19 Thermodynamic cycles 1-4, 1-6 fundamental 1-1 system 1-2 Thermostat location 13-10 Thermostatic controls 15-94 Thermostatic trap 15-28 Thermostats 13-43 Through wall installations 13-5 Tip speed 14-2 Ton long and short 20-2 Ton, metric 20-8 Tramp air 12-16 Transmission of coefficients doors 5-28 fenestrations 5-27 wood 5-28 Trap air handling unit 15-112–15-116 boiler return 15-29 cleaning 13-112 condensate capacities 15-26 connection 15-8 flash 15-29 float 15-27 float sizing 15-41 impulse 15-29 inverted bucket 15-29 lifting 15-29 pressure differential 15-26 radiation load 15-26 safety factor 15-26 selection 15-26 splitting 15-7 thermostatic 15-8 types 15-27 upright bucket 15-28 warm up load 15-26 Troubleshooting 12-15, 12-17 Troy weight for gold and silver 20-2 Types of heat pumps 13-37

U Unheated temperature calculations 5-9 Unit conversions 20-8 systems 20-8 Unit air conditioners 13-114 air filters 13-114 condensers 13-114 cooling coil 13-114 fans 13-114 motors 13-114 piping 13-114 Unit heater air stream direction 15-120 circulation of air 15-120 duct furnace 15-118 enclosed furnace 15-118 exposed wall 15-120 floor mounted heavy duty type 15-117 floor mounted vertical blower units 15-117 full area heating 15-111 gas fired 15-109, 15-118–15-119 gas fired air heater 15-117 industrial type 15-5 installations 15-119 obstructions 15-120 occupants 15-120 partial area heating 15-111 performance factors 15-109 piping 15-5 propeller fan type 15-117 sizing 15-118 spot heating 15-111 steam supplied 15-110 suspended 15-109 suspended blower type 15-117 suspended heavy duty units 15-117 temperature limits 15-109 thermostat locations 15-120 too buoyant air 15-109 types 15-117 Unit systems 20-8 Unit ventilator 13-88, 15-5 auditorium type 15-5 piping 15-5 Upright bucket trap 15-28

V Vacuum lift 15-12 Vacuum pump 15-30 Valve and fitting equivalents 9-7–9-27 Valve and fitting loss 9-1–9-58 Valves 13-113 check 9-139–9-141 gate 9-139–9-141 globe 9-139–9-141 Variable speed control 13-95 Variable volume system 13-17–13-21 cooling considerations 13-20 energy requirements 13-19 heating and cooling calculations 13-19 initial costs 13-18 overlapping 13-21 Velocity design criteria 9-3 Velocity pressure relation 8-3, 14-38 Ventilation 14-1 Ventilation heat loss 6-6 Vibration 13-106 Vibration in pipes 1-11 Vibration isolation 16-7 Viscosity 1-6 Viscosity of liquid 9-78

W Wall furnace 15-83 Wall type mass inside insulation 7-28–7-30

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HVAC: Handbook of Heating, Ventilation and Air Conditioning 21–13

INDEX

Warm air heating 15-82 air volume 15-97–15-99 blower characteristics 15-87 bonnet capacity 15-85 bonnet efficiency 15-85 bonnet pressures 15-100 combustion air supply 15-93 combustion and ventilation air 15-93 combustion efficiency 15-85 direct fired unit heater 15-83 duct arrangement 15-91 duct heat loss 15-85 duct system 15-88 duct transmission efficiency 15-85 floor furnace 15-83 flue gas loss 15-85 forced air furnace 15-83 furnace arrangement 15-91 gravity furnace 15-82 gravity hot air furnace 15-82 heat input 15-85 industrial warm furnace 15-83 pipeless furnace 15-82 rating of furnace 15-85 register delivery 15-85 register free areas 15-100 register pressures 15-101 register temperature 15-97–15-99 registers 15-89 return air intake 15-90 selection of furnace 15-87 selection procedure 15-87 space heater 15-83 stove 15-82 testing of furnace 15-85 thermostatic controls 15-94 throw from registers 15-100 trends 15-88 unit heater 15-83 wall furnace 15-83 Waste steam heat utilization 15-50 Water conditioning 15-16 Water flow velocity 15-49 Water gauge 14-1

Water hammer 15-11 Water in fuel oil 12-18 Water piping 9-3, 9-28 Water properties 2-12 Water to air heat pumps 13-40 Water to water heat pumps 13-39 Water velocities maximum 9-3 Water velocity 15-52 Weight avoirdupois or commercial 20-2 measures 20-1, 20-3 metric 20-8 sheetmetal 14-75–14-76 troy, for gold and silver 20-2 Well water AC systems 13-54 precooling 13-55 refrigerant condensing 13-55 Wet atomizing steam 12-18 Wet bulb temperature 2-2, 2-5 Wide open BHP 14-2 Window GLF 7-47–7-48 Winter cycle 13-88 Winter operation 13-96 Winterizing chilled water system 13-97 Wire, circular mil measurement 20-1 Work 1-2 mechanical 1-2 shaft 1-2

Y Year round remote units 13-3

Z Zone day night operation 13-91 Zone mixing dampers 13-88 Zone types CLF tables 7-31–7-34 SCL tables 7-31–7-34 Zoning installations 13-8

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