Analysis and Design of Heating, Ventilating, and Air-Conditioning Systems [2nd ed] 9780429890871, 0429890877

Table of contents :
Content: Cover
Half Title
Title Page
Copyright Page
Contents
Preface
Authors
Section I: Basic Concepts
1. HVAC Basics
1.1 Overview of HVAC
1.1.1 Definition of Air-Conditioning
1.1.2 Energy Impact of HVAC Systems
1.2 Buildings as Thermodynamic Systems
1.2.1 Systems Concepts
1.2.2 Energy Gains and Losses in Building Spaces
1.2.3 Building Envelope Design
1.3 Common HVAC Elements
1.3.1 Structural Support for HVAC Components
1.3.2 Electrical Aspects of HVAC Systems
1.4 Definitions of HVAC Terms
Bibliography
2. The Air-Conditioning Process
2.1 Introduction
2.2 Air and Its Properties 2.2.1 Atmospheric Air2.2.2 Water Vapor
2.2.3 Terminology
2.2.4 Basic Psychrometrics
2.3 Methods of Measurement and Analysis
2.3.1 Thermodynamic Wet-Bulb Temperature
2.3.2 The Psychrometer
2.3.3 The Psychrometric Chart
2.4 Typical Air-Conditioning Processes
2.4.1 Sensible Heating or Cooling
2.4.2 Combined Sensible and Latent Cooling (Dehumidification)
2.4.3 Heating and Humidification
2.4.4 Evaporative Cooling
2.4.5 Air Mixing
2.5 Psychrometric Analysis of Complete Systems
2.5.1 Space Heating and Cooling Loads
2.5.2 Sensible Cooling Load
2.5.3 Latent Cooling Loads 2.5.4 Psychrometric Chart Representation of Space Conditions2.5.5 The Coil Line
2.5.6 Coil Contact and Bypass Factors
2.5.7 Psychrometric Analysis of Complete Systems
Bibliography
3. HVAC Systems Concepts
3.1 Introduction
3.2 All-Air Systems
3.2.1 Single-Zone Systems
3.2.2 VAV Systems
3.2.3 Dual-Duct Systems
3.2.4 Multizone Systems
3.2.5 VAV/Variable Temperature Systems
3.3 Air-Water Secondary Systems
3.3.1 Active and Passive Chilled Beam Systems
3.3.2 FCUs and Unit Ventilators
3.4 Unitary Systems
3.4.1 Incremental Units
3.4.2 Packaged Units
3.4.3 Split Systems 3.4.4 Variable Refrigerant Flow Systems3.5 Heat Pumps
3.5.1 The Heat Pump Concept
3.5.2 Air-Source Heat Pumps
3.5.3 Water-Source Heat Pumps
3.5.3.1 Closed Circuit Heat Pump Systems
3.5.3.2 Closed Circuit Geothermal Heat Pump Systems
3.5.3.3 Open Circuit Geothermal Heat Pump Systems
3.5.3.4 Gas-Fired Engine-Driven Heat Pumps
3.5.3.5 Heat Recovery Chiller/Heat Pump System
3.5.4 Advanced Technology Heat Pumps
Bibliography
Section II: The Design Method
4. HVAC Systems Design
4.1 Introduction
4.2 Criteria for HVAC Design
4.3 Compliance with Building Codes and Standards 4.3.1 International Mechanical Code4.3.2 International Energy Conservation Code
4.3.3 NFPA Standards and Guidelines
4.3.4 ASHRAE Standards and Guidelines
4.4 Designing for Maintainability
4.4.1 HVAC Equipment Location and Access
4.4.2 Mechanical Equipment Rooms for Air-Handling Equipment
4.4.3 Mechanical Equipment Rooms for Boilers and Chillers
4.4.4 Ceiling Cavity Space
4.5 Designing for Energy Conservation
4.5.1 Introduction to ASHRAE Standard 90.1
4.5.2 Simplified Energy Analysis
4.5.3 Building Energy Modeling
4.5.4 Exhaust Air Heat Recovery
4.5.5 Internal Source Heat Recovery

Citation preview

Analysis and Design of ­Heating, Ventilating, and Air-Conditioning Systems ­

Analysis and Design of ­Heating, Ventilating, and Air-Conditioning Systems ­Second Edition

Herbert W. Stanford III and Adam F. Spach

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2019 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-138-60241-0 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the ­copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged, please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, ­including ­photocopying, microfilming, and recording, or in any information storage or retrieval system, without written ­permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Contents Preface............................................................................................................................................ xiii Authors............................................................................................................................................xv

Section I  Basic Concepts 1. HVAC Basics.............................................................................................................................3 1.1 Overview of HVAC........................................................................................................3 1.1.1 Definition of Air-Conditioning.......................................................................3 1.1.2 Energy Impact of HVAC Systems...................................................................4 1.2 Buildings as Thermodynamic Systems......................................................................5 1.2.1 Systems Concepts..............................................................................................5 1.2.2 Energy Gains and Losses in Building Spaces...............................................6 1.2.3 Building Envelope Design...............................................................................7 1.3 Common HVAC Elements............................................................................................9 1.3.1 Structural Support for HVAC Components..................................................9 1.3.2 Electrical Aspects of HVAC Systems........................................................... 12 1.4 Definitions of HVAC Terms........................................................................................ 25 Bibliography............................................................................................................................ 31 2. The Air-Conditioning Process............................................................................................ 33 2.1 Introduction.................................................................................................................. 33 2.2 Air and Its Properties..................................................................................................34 2.2.1 Atmospheric Air.............................................................................................34 2.2.2 Water Vapor..................................................................................................... 35 2.2.3 Terminology.................................................................................................... 35 2.2.4 Basic Psychrometrics...................................................................................... 36 2.3 Methods of Measurement and Analysis................................................................... 36 2.3.1 Thermodynamic Wet-Bulb Temperature.................................................... 36 2.3.2 The Psychrometer........................................................................................... 37 2.3.3 The Psychrometric Chart............................................................................... 38 2.4 Typical Air-Conditioning Processes......................................................................... 41 2.4.1 Sensible Heating or Cooling.......................................................................... 41 2.4.2 Combined Sensible and Latent Cooling (Dehumidification)...................42 2.4.3 Heating and Humidification.........................................................................43 2.4.4 Evaporative Cooling.......................................................................................44 2.4.5 Air Mixing....................................................................................................... 45 2.5 Psychrometric Analysis of Complete Systems......................................................... 46 2.5.1 Space Heating and Cooling Loads............................................................... 46 2.5.2 Sensible Cooling Load.................................................................................... 47 2.5.3 Latent Cooling Loads..................................................................................... 48 2.5.4 Psychrometric Chart Representation of Space Conditions....................... 49 2.5.5 The Coil Line................................................................................................... 50 2.5.6 Coil Contact and Bypass Factors.................................................................. 51 v

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2.5.7 Psychrometric Analysis of Complete Systems........................................... 52 Bibliography............................................................................................................................ 52 3. HVAC Systems Concepts..................................................................................................... 53 3.1 Introduction.................................................................................................................. 53 3.2 All-Air Systems............................................................................................................ 53 3.2.1 Single-Zone Systems....................................................................................... 56 3.2.2 VAV Systems.................................................................................................... 58 3.2.3 Dual–Duct Systems........................................................................................ 59 3.2.4 Multizone Systems.......................................................................................... 62 3.2.5 VAV/Variable Temperature Systems............................................................ 62 3.3 Air–Water Secondary Systems...................................................................................65 3.3.1 Active and Passive Chilled Beam Systems..................................................65 3.3.2 FCUs and Unit Ventilators............................................................................. 67 3.4 Unitary Systems........................................................................................................... 68 3.4.1 Incremental Units........................................................................................... 68 3.4.2 Packaged Units................................................................................................ 69 3.4.3 Split Systems.................................................................................................... 69 3.4.4 Variable Refrigerant Flow Systems.............................................................. 70 3.5 Heat Pumps................................................................................................................... 72 3.5.1 The Heat Pump Concept................................................................................ 72 3.5.2 Air-Source Heat Pumps................................................................................. 74 3.5.3 Water-Source Heat Pumps............................................................................. 76 3.5.3.1 Closed Circuit Heat Pump Systems.............................................. 76 3.5.3.2 Closed Circuit Geothermal Heat Pump Systems.......................77 3.5.3.3 Open Circuit Geothermal Heat Pump Systems..........................80 3.5.3.4 Gas-Fired Engine-Driven Heat Pumps........................................80 3.5.3.5 Heat Recovery Chiller/Heat Pump System.................................80 3.5.4 Advanced Technology Heat Pumps............................................................. 81 Bibliography............................................................................................................................ 82

Section II  The Design Method 4. HVAC Systems Design.........................................................................................................85 4.1 Introduction.................................................................................................................. 85 4.2 Criteria for HVAC Design........................................................................................... 87 4.3 Compliance with Building Codes and Standards................................................... 88 4.3.1 International Mechanical Code.................................................................... 88 4.3.2 International Energy Conservation Code................................................... 88 4.3.3 NFPA Standards and Guidelines.................................................................90 4.3.4 ASHRAE Standards and Guidelines...........................................................90 4.4 Designing for Maintainability................................................................................... 91 4.4.1 HVAC Equipment Location and Access...................................................... 92 4.4.2 Mechanical Equipment Rooms for Air-Handling Equipment................. 93 4.4.3 Mechanical Equipment Rooms for Boilers and Chillers........................... 93 4.4.4 Ceiling Cavity Space...................................................................................... 94 4.5 Designing for Energy Conservation......................................................................... 95

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4.5.1 Introduction to ASHRAE Standard 90.1...................................................... 95 4.5.2 Simplified Energy Analysis........................................................................... 96 4.5.3 Building Energy Modeling............................................................................ 97 4.5.4 Exhaust Air Heat Recovery........................................................................... 99 4.5.5 Internal Source Heat Recovery................................................................... 102 4.5.6 Thermal Energy Storage.............................................................................. 103 4.6 Designing for Sustainability.................................................................................... 105 4.6.1 High-Performance Building Elements....................................................... 105 4.6.2 Introduction to ASHRAE Standard 189.1.................................................. 108 4.6.3 Net Zero/Sum Zero-Energy Buildings...................................................... 108 4.7 Construction Documents Quality Control............................................................. 110 Bibliography.......................................................................................................................... 112 5. Heating/Cooling Load Calculation.................................................................................. 113 5.1 Introduction................................................................................................................ 113 5.1.1 Building Thermal Balance........................................................................... 113 5.1.2 Purpose of Load Calculations..................................................................... 113 5.2 Mechanics of Building Heat Loss and Gain.......................................................... 113 5.2.1 Design Conditions........................................................................................ 114 5.2.2 Heat Transfer through Walls and Roofs.................................................... 115 5.2.3 Heat Transfer through Fenestration........................................................... 118 5.2.4 Heat Loss through Floors and Basements................................................. 122 5.2.5 Internal Heat Gains...................................................................................... 124 5.2.6 Infiltration Loads.......................................................................................... 125 5.3 Load Computation Methodologies.......................................................................... 128 5.3.1 Heat Balance and Radiant Time Series...................................................... 128 5.3.2 Total Equivalent Temperature Difference with Time Averaging.......... 130 5.3.3 Transfer Function.......................................................................................... 131 5.3.4 Computer-Based Calculation Tools............................................................ 131 5.5 Benchmark Heating/Cooling Loads....................................................................... 132 Bibliography.......................................................................................................................... 134 6. Air Tempering and Distribution...................................................................................... 135 6.1 Heating and Cooling Coils....................................................................................... 135 6.1.1 Direct Expansion Refrigerant Cooling Coils............................................ 138 6.1.2 Chilled Water Cooling Coils....................................................................... 140 6.1.3 Hot Water Heating Coils.............................................................................. 141 6.1.4 Steam Heating Coils..................................................................................... 141 6.1.5 Electric Resistance Heating Coils............................................................... 141 6.1.6 Preheating and Precooling Coils................................................................ 143 6.1.7 Desiccant Cooling and Dehumidification................................................. 146 6.2 Air Distribution Design............................................................................................ 147 6.2.1 Room Air Diffusion...................................................................................... 147 6.2.2 Typical Air Distribution Patterns............................................................... 148 6.2.3 Large Space Air Distribution...................................................................... 154 6.2.4 Displacement Ventilation Air Distribution............................................... 155 6.3 Terminal Units............................................................................................................ 157 6.3.1 VAV Single-Duct TUs................................................................................... 157

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6.3.2 VAV Single-Duct Fan-Powered TUs........................................................... 160 6.3.3 VAV Dual Duct TUs...................................................................................... 160 Bibliography.......................................................................................................................... 161 7. Duct Design.......................................................................................................................... 163 7.1 Introduction................................................................................................................ 163 7.1.1 Steps in Duct System Design....................................................................... 163 7.1.2 Duct Air Balancing Rationale..................................................................... 164 7.2 Energy and Pressure Relationships........................................................................ 164 7.3 Friction Losses............................................................................................................ 166 7.3.1 Calculation of Friction Losses in Ducts..................................................... 166 7.3.2 Calculation of Friction Losses in Fittings.................................................. 170 7.4 Methods of Duct Design........................................................................................... 171 7.4.1 Constant Velocity Method........................................................................... 171 7.4.2 Velocity Reduction Method......................................................................... 171 7.4.3 Static Regain Method................................................................................... 171 7.4.4 Equal Friction Method................................................................................. 172 7.4.5 Duct Construction Criteria.......................................................................... 173 7.4.6 Duct Design Guidelines............................................................................... 174 7.5 Special Exhaust Systems Design.............................................................................. 176 7.5.1 Laboratory Exhaust Systems....................................................................... 176 7.5.2 Industrial Exhaust Systems......................................................................... 179 7.6 Duct Insulation........................................................................................................... 181 7.7 Fire and Smoke Control in Duct Systems............................................................... 182 Bibliography.......................................................................................................................... 183 8. Piping Design....................................................................................................................... 185 8.1 Introduction................................................................................................................ 185 8.1.1 Viscosity......................................................................................................... 185 8.1.2 Weight Density, Specific Volume, and Specific Gravity.......................... 185 8.1.3 Mean Velocity of Flow.................................................................................. 186 8.1.4 Piping Basics.................................................................................................. 187 8.2 Hydronic Piping......................................................................................................... 191 8.2.1 Pipe Routing and Sizing.............................................................................. 192 8.2.2 Pressure Loss Calculation........................................................................... 196 8.2.3 Expansion and Air Removal....................................................................... 198 8.2.4 Freeze Protection.......................................................................................... 201 8.3 Steam and Condensate Piping................................................................................. 202 8.3.1 Pipe Routing and Sizing.............................................................................. 203 8.3.2 Steam Trap Application and Sizing............................................................ 206 8.3.3 Control of Steam Piping Expansion........................................................... 209 8.4 Refrigerant Piping...................................................................................................... 210 8.4.1 Design Considerations................................................................................. 210 8.4.2 Suction Lines................................................................................................. 213 8.4.3 Liquid Lines................................................................................................... 215 8.5 Piping Insulation........................................................................................................ 215 8.5.1 Hot Piping Insulation................................................................................... 215 8.5.2 Cold Piping Insulation................................................................................. 215 Bibliography.......................................................................................................................... 218

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Section III  Systems and Components 9. Pumps and Fans................................................................................................................... 221 9.1 Introduction................................................................................................................ 221 9.2 Pumps and Applications........................................................................................... 221 9.2.1 Pump Types and Characteristics................................................................ 221 9.2.2 Pump Arrangements....................................................................................225 9.2.3 Water Flow Volume Control........................................................................ 230 9.3 Fans.............................................................................................................................. 231 9.3.1 Fan Energy Relations.................................................................................... 231 9.3.2 Fan Types and Characteristics.................................................................... 233 9.3.3 Fan and System Characteristics.................................................................. 237 9.3.4 System Effects................................................................................................ 238 9.3.5 Variable Air Volume Fan Control............................................................... 242 9.4 Pump and Fan Affinity Laws................................................................................... 243 Bibliography.......................................................................................................................... 243 10. Terminal Systems and Components................................................................................ 245 10.1 Systems Types and Applications............................................................................. 245 10.1.1 Selecting the Right System for the Application........................................ 245 10.1.2 Space Needs and Other Requirements for Terminal Systems............... 245 10.2 AHUs and Components............................................................................................ 249 10.2.1 AHUs.............................................................................................................. 249 10.2.2 Particulate Air Filtration.............................................................................. 253 10.2.3 Gas-Phase Filtration..................................................................................... 255 10.2.4 Ultraviolet Air and Surface Treatment...................................................... 256 10.2.5 Airside Economizer Cycle........................................................................... 257 10.2.6 Cooling Coils Condensate Drainage.......................................................... 261 10.3 Humidification........................................................................................................... 262 10.4 Ventilation and Building Pressurization................................................................ 264 10.4.1 Outdoor Air Intakes..................................................................................... 265 10.4.2 Understanding and Applying ASHRAE Standard 62.1.......................... 267 10.4.3 Demand Control Ventilation....................................................................... 271 10.4.4 Dedicated Outdoor Air Systems................................................................. 274 Bibliography.......................................................................................................................... 275 11. Refrigeration Systems and Components........................................................................ 277 11.1 Refrigeration Basics................................................................................................... 277 11.1.1 Refrigerant Issues......................................................................................... 277 11.1.2 Vapor Compression Refrigeration Cycle................................................... 278 11.1.3 Vapor Absorption Refrigeration Cycle...................................................... 282 11.2 Direct Expansion Refrigeration Systems................................................................ 285 11.3 Chilled Water Refrigeration Systems...................................................................... 288 11.3.1 Determining Chilled Water Supply Temperature................................... 289 11.3.2 Establishing Chilled Water Temperature Range...................................... 289 11.3.3 Vapor Compression Cycle Water Chillers................................................. 290 11.3.4 Scroll Compressor Water Chillers.............................................................. 292 11.3.5 Rotary Screw Compressor Water Chillers................................................ 297 11.3.6 Centrifugal Compressor Water Chillers.................................................... 297

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11.3.7 Absorption Water Chillers.......................................................................... 299 11.3.8 Chilled Water System Configurations.......................................................300 11.3.9 Chilled Water Buffer Tanks......................................................................... 307 11.4 Condensers and Cooling Towers.............................................................................308 11.4.1 Air-Cooled Condensers...............................................................................308 11.4.2 Cooling Tower Fundamentals.....................................................................309 11.4.3 Tower Configuration and Application....................................................... 314 11.4.4 Closed Circuit Evaporative Cooler............................................................. 319 11.5 Evaporative Air Cooling........................................................................................... 320 11.6 Waterside Economizer Cycle.................................................................................... 320 Bibliography.......................................................................................................................... 323 12. Heating Systems and Components.................................................................................. 325 12.1 Firing Fossil Fuels...................................................................................................... 325 12.1.1 Oil-Fired Systems.......................................................................................... 325 12.1.2 Gas-Fired Systems........................................................................................ 328 12.2 Furnaces...................................................................................................................... 329 12.3 Boilers.......................................................................................................................... 330 12.3.1 Boiler Types, Ratings, and Efficiency......................................................... 330 12.3.2 Application Considerations......................................................................... 331 12.3.3 Boiler/Furnace Venting................................................................................ 332 12.4 Hydronic Heating Systems....................................................................................... 333 12.5 Steam Heating Systems............................................................................................. 335 12.5.1 Steam Quality................................................................................................ 335 12.5.2 Steam Heat Transfer..................................................................................... 338 12.5.3 Steam-to-Water Heat Exchangers............................................................... 338 12.5.4 Feedwater System......................................................................................... 339 12.5.5 Steam Pressure Reducing Valves................................................................ 339 12.5.6 Steam Condensate Receivers and Pumps.................................................343 Bibliography..........................................................................................................................344 13. HVAC Controls....................................................................................................................345 13.1 DDC Fundamentals...................................................................................................346 13.2 DDC Input/Output Points........................................................................................ 351 13.2.1 Input/Output Basics..................................................................................... 351 13.2.2 DI Devices...................................................................................................... 352 13.2.3 AI Devices...................................................................................................... 353 13.2.4 DO Devices.................................................................................................... 363 13.2.5 AO Devices....................................................................................................364 13.3 Final Control Elements.............................................................................................. 366 13.3.1 Control Valves............................................................................................... 366 13.3.2 Control Dampers........................................................................................... 368 13.4 Direct Digital Controllers and Systems.................................................................. 370 13.4.1 DDC System Architecture........................................................................... 370 13.4.2 Controllers and Control Loops................................................................... 371 13.4.3 Networks and Communication.................................................................. 372 13.5 HVAC Sequences of Operation................................................................................ 375 13.6 DDC System Security................................................................................................ 377

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13.7 DDC System Design Checklist................................................................................. 379 Bibliography.......................................................................................................................... 380

Section IV  Special Considerations 14. Special HVAC Design Considerations............................................................................ 383 14.1 Indoor Air Quality..................................................................................................... 383 14.2 Antiterrorism Design for HVAC Systems............................................................... 385 14.2.1 Introduction................................................................................................... 385 14.2.2 Terror Threats against Buildings................................................................ 386 14.2.3 HVAC Design to Minimize Explosive Threats......................................... 387 14.2.4 HVAC Design to Minimize CBR Threats.................................................. 388 14.3 HVAC Water Treatment............................................................................................. 390 14.3.1 Hot and Chilled Water Systems Chemical Treatment............................. 390 14.3.2 Evaporative Cooling Water Systems Chemical Treatment..................... 390 14.3.3 Evaporative Cooling Water Systems Nonchemical Treatment............... 394 14.3.4 Steam and Condensate Systems Chemical Treatment............................ 396 14.3.5 Legionella Risk Management in HVAC Water Systems............................ 399 14.4 Vibration and Noise Mitigation...............................................................................400 14.4.1 Noise Definition and Design Criteria........................................................400 14.4.2 Indoor Noise Control in HVAC Systems................................................... 401 14.4.3 Outdoor Noise Issues in HVAC Systems...................................................404 14.5 HVAC Systems Start-Up and Commissioning....................................................... 407 14.5.1 HVAC Systems Operation Prior to Commissioning................................ 407 14.5.2 The Commissioning Process.......................................................................408 14.6 Correcting HVAC Performance for Altitude and Temperature.......................... 410 Bibliography.......................................................................................................................... 411 15. Engineering Economics and Design Decision-Making.............................................. 413 15.1 Introduction................................................................................................................ 413 15.2 Defining HVAC Design Alternatives...................................................................... 415 15.3 Estimating Capital Requirements............................................................................ 417 15.3.1 Capital Cost Estimating............................................................................... 417 15.3.2 Time/Money Relationships......................................................................... 418 15.4 Recurring Costs Determination............................................................................... 420 15.4.1 Utilities Costs................................................................................................ 420 15.4.2 Maintenance Costs........................................................................................ 421 15.5 Component Service Life and Replacement............................................................422 15.6 Comparing Alternatives and Dealing with Uncertainty..................................... 424 15.6.1 Alternatives with Different Economic Lives............................................. 427 15.6.2 Sensitivity Analysis...................................................................................... 427 15.6.3 Selecting Alternatives within the Project Budget.................................... 428 15.7 Overview of LCCA.................................................................................................... 429 15.7.1 Basic Practices for LCCA.............................................................................. 429 15.7.2 Calculations and Analysis Tools................................................................ 429 Bibliography..........................................................................................................................430

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16. Building Information Modeling...................................................................................... 431 16.1 Introduction................................................................................................................ 431 16.2 BIM Advantages......................................................................................................... 432 16.3 Applying BIM.............................................................................................................434 16.3.1 BIM Use by HVAC Designers...................................................................... 435 16.3.2 BIM Use by Contractors/Subcontractors................................................... 436 16.3.3 BIM Use by Owners...................................................................................... 436 16.4 AIA Contracts............................................................................................................. 436 Bibliography.......................................................................................................................... 437 17. Construction Contract Administration........................................................................... 439 17.1 Introduction................................................................................................................ 439 17.2 Design Period Considerations..................................................................................440 17.3 Preconstruction Procedures and Practices.............................................................442 17.4 Construction Period Procedures and Practices.....................................................444 17.5 Completion and Closeout Procedures and Practices............................................448 17.6 Avoiding Litigation Pitfalls...................................................................................... 449 17.7 Construction Administration Checklist................................................................. 452 17.7.1 Construction Administration Practices and Procedures Checklist...... 453 Index��������������������������������������������������������������������������������������������������������������������������������������������� 457

Preface The first edition of this book came about as the outgrowth of a conversation between a group of practicing heating, ventilating, and air-conditioning (HVAC) design engineers in 1983 concerning their dissatisfaction with both the textbooks used in HVAC college courses (what few there were) and the design handbooks then available. Thus, I set out to write a text that I would have liked to have had as a student and one that I would have retained as a practicing engineer. I feel that the first edition had some success in meeting the following objectives: 1. To build a text around a strong “systems” point of view with emphasis on the energy consumption ramifications of design decisions 2. To primarily address HVAC applications for institutional, commercial, and industrial buildings 3. To make this text valuable as a resource tool for the practicing engineer 4. To use the methodologies of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Handbook as the primary reference source. These objectives continue to apply in this second edition. Another major impetus to the writing of this book was the fact that for many years I made a very good living investigating and solving HVAC system operating problems in buildings, many of which were the result of inadequate or incorrect design. Even now, a recent survey conducted by one major industry magazine indicates that the majority of all building owners queried responded that there were problems and ongoing dissatisfaction with the HVAC systems in their buildings. These experiences indicate that HVAC design engineers are still too often doing a less-than-adequate job in the delivery of the final ­product: an HVAC system that “satisfies.” The “science” of HVAC design is well developed. One has only to read the ASHRAE Handbook and other texts currently in use in the academic environment to realize that the basics of psychometrics, heat gain/loss calculations, fluid flow, fan and pump operations, and so on are well defined and readily available to the practicing engineer. Thus, while this text also addresses these fundamental topics, it is, rather, the “art” of successful HVAC design, including proper system and component application, which was incorporated into the first edition and significantly expanded in this second edition. Design goes beyond load calculations and duct and pipe sizing. In fact, these are the smallest parts of the design effort. It is more important for the design engineer to have a proper grasp of systems applications, controls, and the basics of “fitting the right solution to solve the problem.” In this text, significant emphasis is placed on “systems” considerations of each basic topic. A word about units: In 1981, ASHRAE published their Handbook-Fundamentals in which the primary unit designations were in accordance with the Système International (SI). The result was a handbook that was useless to the practicing professional in the United States, and there subsequently was a “revolt” within the membership of ASHRAE between the academic and practicing sides of the organization. The compromise was the publishing of xiii

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Preface

the 1985 Handbook-Fundamentals (and all subsequent volumes) in two separate editions, one using the inch-pound (IP) system and the other using SI. The first edition of this book, published in 1988, utilized only IP units. Since then, though, the HVAC market has become more global in nature and now ASHRAE requires dual unit publications. Thus, this edition uses IP units and equations as primary, with SI units and equations as secondary, in accordance with the SI Guide for HVAC&R, American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., Atlanta, Georgia, 2013. Now, 30 years since the first edition of this book was published, a number of HVAC topics have changed: heating/cooling load calculation methodologies, indoor air-­quality considerations, control systems and sequences of operation, increased emphasis on energy ­efficiency and sustainability, etc. Since my semiretirement in 1998, I have written and taught on a number of these developing issues in HVAC design and this new text ­incorporates much of that material. However, the HVAC design business has also changed over the last 30 years…­ production methods (the transition from hand drafting to computer-aided drafting to building ­information modeling), the general reduction in contractor skills and capabilities (­resulting in a need for the detail and coordination within design documents), the impact of greatly expanded building codes and industry standards, etc., are all markedly different that they were in 1988. This created the need for a coauthor who had the expertise and experience to address these areas in this edition. Therefore, I asked Adam F. Spach, P.E., a friend and colleague with whom I’ve worked over the last 15 years and consider to be one of the brightest younger engineers I’ve ever met, to join me in the writing of this new edition. Finally, I rededicate this book to Guy Hammer Cheek, P.E. (1927–1987), my friend, my mentor, and the man who introduced me to the idea of “HVAC systems concepts” and who diligently encouraged me to pick the right one(s) for each application. Herbert W. Stanford III, P.E. North Carolina 2019

Authors

Herbert W. Stanford III, P.E, is a North Carolina native and 1966 graduate of North Carolina State University with a B.S. in mechanical engineering. He is a registered ­professional engineer in North Carolina. In 1977, he founded Stanford White, Inc., an engineering ­consulting firm located in Raleigh, North Carolina and semiretired in 1998. Currently, Mr. Stanford is actively engaged in investigative and forensic engineering, teaching, and writing within a broad range of topics relative to buildings, especially HVAC systems, indoor ­environmental quality, and building operations and maintenance. Mr. Stanford developed the Facilities Condition Assessment Program for the State of North Carolina and the Life Cycle Cost Methodology used by North Carolina to evaluate building design ­decisions. He has taught a series of short courses on current building topics at the University of Toledo (Ohio), North Carolina State University, and the University of North Carolina at Charlotte and is a life member of the ASHRAE. Mr. Stanford is the author of HVAC Water Chillers and Cooling Towers: Fundamentals, Application, and Operation (Second Edition, CRC Press, 2011); The Health Care HVAC Technician (MGI Systems, Inc., 2008), a program and training manual for hospital HVAC maintenance personnel; and Effective Building Maintenance (Fairmont Press, 2010). Adam F. Spach was born in upstate New York and graduated from Alfred University with a B.S. in mechanical engineering in 2000. After graduation, he relocated to North Carolina and has called it his home since. Mr. Spach has worked as an HVAC consulting engineer since 2001 and is licensed as a professional engineer in North Carolina and several other states. He joined Stanford White, Inc., Raleigh, NC in 2005 and is now an associate with that firm. He currently focuses on providing engineering services for educational (K-12 and university), commercial, recreational, research, and health care facilities. Mr. Spach has a passion for sustainable design in the built environment. He was appointed to the Wake County Citizen’s Energy Advisory Committee, serving as the vice chair in 2010–2014, and currently co-chairs the High Performance Building Task Force sponsored by North Carolina Chapter of the American Institute of Architects. He has made presentations at the annual N.C. State Construction Conference on three occasions and at the annual North Carolina Sustainable Energy Conference on five occasions. Mr. Spach routinely lectures at the North Carolina State Design School.

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Section I

Basic Concepts

1 HVAC Basics

1.1 Overview of HVAC 1.1.1 Definition of Air-Conditioning Modern-day air-conditioning was created in the early 20th century based on the vision and works of Hermann Rietschel, Alfred Wolff, Stuart Cramer, and Willis Carrier. Cramer, a textile engineer in Charlotte, North Carolina, is credited with coining the phrase “airconditioning” in 1906. Willis Carrier, though he did not actually invent air-conditioning or take the first documented scientific approach to applying it, is credited with integrating the scientific method, engineering, and business of this developing technology and creating the industry we know today as heating, ventilating, and air-conditioning (HVAC). By 1929, the American Society of Heating and Ventilating Engineers defined comfort airconditioning as “… the process of treating the air so as to control simultaneously its temperature, humidity, cleanliness, and distribution.” Today the organization incorporates that term in its current name: The American Society of Heating, Refrigerating and AirConditioning Engineers, Inc. (ASHRAE). The same definition of air-conditioning applies today, but, of course, there have been major refinements in the art since 1929. Comfort air-conditioning means the maintenance of those indoor atmospheric factors affecting comfort:

1. The desired range of air temperatures 2. An acceptable humidity 3. Minimal atmospheric particulates, including pollens and bacteria 4. An acceptable odor level 5. An acceptable degree and pattern of air motion

Air-conditioning, in its broadest sense, is the engineering science of designing means of controlling the air in the human environment for comfort and health. This broad area includes control of humidity and heating, as well as cooling. It is distinguished from ­refrigeration, in that refrigeration is one of the processes typically involved in an airconditioning system (i.e., refrigeration systems cool the air, either directly or indirectly). However, it is still true that the term air-conditioning is taken by the lay public to refer only to cooling and dehumidification of air. For this reason, the acronym HVAC is still the most common term used when referring to the multipurpose systems found in modern buildings.

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Analysis and Design of HVAC Systems

This book is concerned with the engineering design involved in application, sizing, component selection, layout, and control of HVAC systems in buildings. These tasks are generally performed by consulting engineers and designers, working with the building owner (and, as applicable, the architect for the building). These designers are not concerned with the detailed design of HVAC components themselves (fans, pumps, chillers, and so on), although HVAC engineers are expected to know the general operating characteristics and respective advantages of, for example, centrifugal-electric refrigeration machines versus steam absorption water chillers, they need not necessarily be familiar with the detailed heat transfer characteristics or the internal control mechanisms of the machines. HVAC designers are best referred to as “assemblers” who bring together multiple components under common control to satisfy the performance requirements listed previously. But, long gone are the days when an HVAC designer had to know only about HVAC systems and components. Today, there are a myriad of issues that impact HVAC design and have to be included as part of the design process, including general construction elements, energy efficiency and consumption, indoor air quality, anti-terrorism, and others addressed by this book. 1.1.2 Energy Impact of HVAC Systems Before any building is constructed, the space that the building will occupy consumes no energy. However, the moment the building is created, there arises a need to provide an internal environment that is different from the surrounding environment (i.e., the building must be either warmer or cooler and more or less humid than outdoors as outdoor conditions change over time). And, since walls and roofs block natural light, artificial lighting must usually be provided even during daylight hours. Thus, an energy-use burden is created by almost every building in satisfying these environmental requirements. Although there were Roman hot air heating systems and ice-based cooling was applied by the Egyptians, HVAC is basically a modern technology dating, realistically, only from the early 20th century. Significant scientific and practical development did not occur until after World War I and the widespread use of building cooling did not take hold until after World War II. The design and application of HVAC systems can be divided into five historical periods: 1. Pre-1960. Prior to the late 1960s, HVAC systems tended to have noncritical design criteria and were basically simple in scope. Heating systems were designed for 65°F [18°C] to 70°F [21°C] indoor temperature, while the indoor temperature for cooling was generally selected to be 15°F [8°C] below the outside peak temperature (typically, about 80°F [27°C]). Systems tended to be single zone, multi-zone, or, in very large buildings, dual-duct or induction types. Emphasis in this period was on low first cost, and since energy was cheap, little or no attention was paid to operating efficiency. 2. 1960–1975. This period was the “heyday” of complex and very inefficient HVAC systems. No longer was 80°F [27°C] interior design and multi-zone air distribution acceptable. Summer indoor design temperatures fell as low as 72°F [22°C] and every space had to have a thermostat to maintain temperature control within ±1.5°F [0.8°C]. Ventilation air quantities equivalent to 25% of the system supply airflow were very common. To satisfy these more critical design criteria while keeping first costs reasonable, reheat systems became very popular.

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3. 1975–1984. The energy cost upheavals of 1973–1974 and 1977–1978 forced designers to reevaluate design criteria and system concepts to reduce energy consumption and cost. During this period, design temperatures were 76°F–78°F [24°C–26°C] for cooling and 68°F–72°F [20°C–22°C] for heating. Design ventilation airflow rates were reduced to about 20% of the 1960–1975 values. Non-reheat systems, particularly those incorporating variable air volume concepts, gained wide acceptance. The first energy codes came into being during this period. 4. 1984–1998. In the early 1980s, the “energy crisis” had disappeared. But, many of the lessons learned worked to help offset the rapid inflation of energy costs during that period. Variable air volume systems became more common. However, design indoor temperatures returned to values that resulted in real comfort conditions and, by 1989, ventilation rates had returned to about 75% of their pre-1975 values due to widespread complaints about indoor air quality and the common occurrence of “sick building syndrome.” 5. 1999-Today. In addition to ever more stringent limits on building energy consumption imposed by building codes, in the mid-1990s, the term “sustainability” began to enter the HVAC designer’s lexicon. Some building owners wanted their buildings and systems to be not only energy efficient but also to reduce their negative imprint on the environment in general. While the definition of what constitutes “sustainable building design” is still evolving, modern HVAC designers are often required by their clients to focus their designs on sustainability, without the function and performance of HVAC systems being impaired. Today, while the primary goal for any HVAC system remains its satisfactory function and performance, there are two other important secondary goals for the HVAC systems designer, as discussed in Chapter 14.



1. Minimize the energy burden imposed by the system. ASHRAE standards, energy conservation building codes, and simply good design stewardship are all imposed to meet this goal. 2. Minimize the system’s overall negative impact on the environment, not limited to just energy consumption, making it more “sustainable.”

1.2 Buildings as Thermodynamic Systems 1.2.1 Systems Concepts Buildings may be viewed as thermodynamic systems. The advantage of such an approach is that it allows an overall view of the processes of heat gain and loss that are operating continually to change the environmental conditions felt by the occupants. Figure 1-1 shows the general concept of a system as applied to a building. The system boundary is a real or imaginary separation between the area “inside” and the external environment. We are concerned with maintaining some desired conditions of temperature and humidity within the boundary. However, the energy inputs and outputs act to change these conditions unless we compensate for them. According to the first law of thermodynamics, all

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Analysis and Design of HVAC Systems

Chemical energy input (fuel combustion) C

mha Energy in infiltration and/or ventilation air

mha Energy in exfiltration and/or exhaust air Ti = inside temperature Wi = inside air moisture content

Qin Input thermal energy (heat gain)

Qout Output thermal energy (heat loss)

E To = outside temperature Wo = outside air moisture content

Building envelope

Electrical energy input

FIGURE 1-1 Building viewed as a thermodynamic system.

of the energy entering the system boundaries can be accounted for … it is either stored in the system or it is returned back through the system boundaries. Virtually all of the energy that enters the boundaries of a building is transformed eventually into thermal energy, and it is typically felt as an increase in indoor temperature (internal energy) of the building. Some energy enters or leaves the building directly in the form of thermal energy. The energy that enters or leaves as a result of a differing inside and outside temperature is referred to as “heat” (although heat is also loosely used to refer to any form of thermal energy). 1.2.2 Energy Gains and Losses in Building Spaces Figure 1-2 shows the typical methods by which energy enters and leaves building spaces. From this figure, it is quite clear that energy typically enters in one form and leaves in another. For example, on a hot summer day, the building is heated by the solar radiation on the walls (which results in conduction through the walls) and by direct solar radiation through glass (which results in heating of the interior surface). Conduction through the walls and glass due to indoor/outdoor temperature differences also occurs. The electrical energy that enters the building is eventually converted to heat, either mechanically by fans or other motor-operated devices, or indirectly, such as by lighting. The important concept is that all of this energy must eventually begin to leave the building at roughly the same daily rate that it enters or else the building will just become increasingly warmer. The primary mechanism for relieving the buildup of thermal energy is conduction (and convection) through the envelope, which will occur when the outside temperature falls below the inside temperature (such as during the evening). This is, in the

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HVAC Basics

Solar heat gain

Transmission through roof and/or ceiling

Internal heat gains from lights, people, and appliances

Transmission through walls and windows Solar heat gain through walls and windows

Infiltration/ exfiltration through cracks at doors and windows

Transmission through floors FIGURE 1-2 Basic elements of heat transfer to and from a building space.

absence of mechanical cooling, a self-limiting process; the building would lose heat until only the indoor temperature becomes nearly equal to the outside temperature, at which point the conduction heat transfer would cease. If there were significant internal heat generation. The temperature inside would continue to climb and conduction from inside to outside would resume. At some point, however, the temperature may be just high enough to maintain a conduction rate that would balance the internal heat generation rate and a steady-state condition would have been achieved. This sort of dynamic temperature fluctuation happens continuously in all buildings, although it may be diminished by mechanical heating or cooling. This is a simplified look at the process, and there are several complicating factors. For example, the walls of the building have mass, which has a thermal storage capacity. The effect of thermal mass is to retard the flow of thermal energy (since a portion of it must be stored in the walls along the way). That is, the wall materials are heated or cooled as the “wave” of energy makes its way from the hotter to the cooler side of the wall. 1.2.3 Building Envelope Design Every building must have both a thermal and a moisture envelope, and it is an important part of the HVAC designer’s role to ensure that the envelope is correctly designed and constructed, even though that is not normally part of his or her direct design responsibility. The role of the thermal envelope is to reduce or eliminate heat transfer across envelope boundaries driven by temperature differences and solar radiation. The role of the moisture

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Analysis and Design of HVAC Systems

envelope is to prevent the migration of water, in liquid or vapor form, into the building. The moisture envelope always consists of the rain barrier to stop liquid water from entering the building, the air barrier to stop water vapor introduced by infiltration, and the vapor barrier (roofs) or retarder (walls) to stop moisture vapor migration due to humidity differences. Figure 1-3 defines the various climate zones in the United States and can be used for establishing envelope design criteria. Note, however, that ASHRAE and the U.S. Department of Energy may revise the boundaries of climate zones every 3–5 years in response to climate change that is underway. Designers should always review climate zones as defined in the most current edition of ASHRAE Standard 90.1. In all climate zones, the thermal envelope should be located at or near the inside of walls, roofs, and floors. The thermal envelope performance depends on selection of appropriate U-factors for walls, roofs, and floors and solar transmission and shading requirements for building fenestration. The HVAC engineer’s role is to advise the architect to ensure high thermal performance and reduced heat loss and heat gain due to each of these factors. The moisture envelope design is equally important. This envelope element consists of a rain barrier, an air barrier, and a vapor barrier or retarder. The configuration of the moisture envelope depends on the outdoor climate and it is a primary requirement for the HVAC designer to ensure that the wall design(s) correctly define the correct configuration. In all climate zones, the rain barrier and the air barrier must be installed at or immediately inboard of the wall cladding. The role of these two barriers is to prevent liquid

FIGURE 1-3 Climate zones in the United States. (Public Domain (U.S. Department of Energy) https://basc.pnnl.gov/system/ files_force/images/IECCmap_Revised.jpg?download=1)

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moisture from entering the exterior wall and, ultimately, into the air-conditioned building. But, the location of the vapor barrier or retarder, which is designed to prevent water vapor from entering the exterior wall, is more complex and varies by the type of climate as defined in the following: 1. In hot, humid climate zones 1, 2A, 2B, and 3A, the vapor retarder must never be placed on the indoor wall since the outdoor moisture will be trapped in the wall. Vinyl wallcovering is an effective vapor barrier that should never be used in hot, humid climates. Rather, the vapor retarder must be located immediately inboard (or as part of) the air barrier, near the outer boundary of the wall construction. 2. In a mixed, humid climate such as zone 4A and in a mixed, dry climate such as zone 4B, the placement of the vapor retarder requires more analysis by the designer. In this type of climate, the vapor retarder should be installed roughly in the “thermal middle” of the wall assembly. An interior vapor barrier would be detrimental, as it would prevent the wall assembly from drying toward the interior during cooling periods. The wall assembly is more forgiving without the interior vapor barrier than if one were installed. For hospitals, laboratories, and so on, located in mixed, humid climates, for which humidification is provided during the winter and the indoor dew point temperature remains above 40°F [4°C], detailed analysis of the vapor retarder placement is required to establish the correct vapor retarder location. 3. In cold climate zones 5, 6, and 7, indoor moisture levels tend to be higher than outdoor levels during winter, and thus, the vapor retarder must be located at or near the inside surface of the wall. 4. In hot, dry climates, such as zone 3B, no vapor retarder is required since there is little moisture vapor outdoors or indoors to negatively impact wall construction.

1.3 Common HVAC Elements There certain elements that apply to almost all HVAC systems that are generally referred to as “common work” or “common elements.” Again, while these elements may not be part of the HVAC designer’s direct design responsibility, he or she is charged with insuring that they are addressed correctly. 1.3.1 Structural Support for HVAC Components HVAC systems typically consist of many different components that must be installed, supported, and anchored individually. HVAC equipment must be supported in accordance with the equipment manufacturer’s requirements, coordinated with the equipment location within the building and building structural system. 1. Floor and Housekeeping Pad Installation. Floor-mounted equipment must always be installed on concrete housekeeping pad (or equivalent). The pads for air-handling units should be 6+″ [150+ mm] high to allow for the installation of drain pan traps,

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Analysis and Design of HVAC Systems

while pads for all other equipment should be 4″ [100 mm] high. The equipment should be anchored and grouted to housekeeping pads. 2. Structural Slab, Pier, or Foundation Installation. Cooling towers, tanks, chillers, and (sometimes) boilers are typically heavy enough to require a structural slab, pier(s), or foundations for support. Review each component with the project structural designer to determine requirements. 3. Suspended Installation. For suspended equipment, structural steel framing to distribute the imposed operating loads without stressing building structural elements or causing damage to the building substrate is normally required. This frame, which is then suspended from the building structure with vibration isolators, an appropriately sized all-thread rod, serves an equipment platform. 4. Rooftop Installation. The equipment may be mounted on structural steel supports (the preferred method) or on continuous roof curb: a. Structural steel supports must be as detailed on the drawings, and their design requires the input of a structural engineer. The supports must allow clear space under the equipment for roof maintenance and replacement (at least 36″ [1,000 mm] under equipment up to 60″ [1,500 mm] wide and at least 48″ [1,200 mm] under equipment over 60″ [1,500 mm] wide) and include appropriate service walkways and handrails, steps, ladders, and so on. b. Continuous roof curb tops are required to be at least 17″ [430 mm] above the roof surface to prevent leakage into the building in the event of roof flooding due to blocked roof drains. The top of all roof curbs must be level, with pitch built into curb when deck slopes are 2% or greater. Often, structural steel reinforcement below the roof is required to avoid stressing building structural elements and must be reviewed with the project structural designer. Ductwork support requirements are well defined in HVAC Duct Construction Standards— Metal and Flexible, Sheet Metal and Contractor’s National Association’s (SMACNA), with which every HVAC designer should become familiar. 1. Horizontal Suspended Installation. Ductwork hangers may be fabricated with sheet metal straps or all-thread rod. SMACNA HVAC Duct Construction Standards provides numerous details for individual duct hanger methods. Where multiple ducts are routed together, they may be supported by a common “trapeze” hanger, essentially a single cross member with two or more vertical hangers. 2. Vertical Installation. Vertical ducts must be anchored and supported at each floor. 3. Rooftop Installation. Horizontal ductwork installed above a roof must be supported by roof support rails integrated with the building roof and structural members to both support the weight of the duct and to provide vertical and horizontal anchoring against wind forces. Consult with the project structural designer to determine requirements and provide details as necessary. Piping systems are generally classified on the basis of their service temperature, which impacts strength, potential thermal expansion/contraction, and insulation requirements (see Chapter 6), as summarized in Table 1-1. Based on these classifications, hangers and supports for piping systems are typically selected in accordance with the requirements of Standard Practice-58, Pipe Hangers and Supports, Manufacturers Standardization Society (MSS).

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HVAC Basics

TABLE 1-1 Piping Systems Classification Classification Type 1: Hot systems

Type 2: Ambient systems Type 3: Cold systems

Temperature Range Type 1A: 120°F–250°F [50–120°C] Type 1B: >250°F [120°C] 71°F–120°F [22–50°C] Type 3A: 32°F–70°F [0°C–49°C] Type 3B: 15 psig [100 kPa]), high pressure boiler feedwater, high temperature hot water Condenser water (indoor), oil, fuel gas Chilled water, cooling coil condensate, condenser water (outdoor), condenser water (all) with waterside economizer cycle Liquid and cold gas refrigerant, chilled water with ice thermal storage system

1. Suspended Horizontal Installation. Horizontal piping is typically supported by factory-fabricated horizontal-piping hangers complying with MSS 58. Where multiple horizontal pipes are routed together, “trapeze” hangers may be field fabricated from structural steel members or from preformed channel members and suspended by two or more all-thread hanger rods. Each pipe on a trapeze hanger must be individually supported, and if the piping is insulated, the insulation must be protected by using MSS Type 39 pipe saddles for Classification Type 1B piping and MSS Type 40 insulation shields for Classification Types 1A, 2, and 3 piping at each pipe support. Install supports with maximum spacing and all-thread hanger rods sized in accordance with Table 1-2, where NPS defines nominal pipe size. 2. Vertical Installation. Vertical piping requires the use of factory-fabricated riser clamps complying with MSS Type 8 for support. Vertical piping must be anchored and supported at each floor. In tall, concrete structure buildings, it is typically necessary to provide expansion devices on every other floor or so to account for long-term “creep” or shrinkage of the structure. 3. Rooftop Installation. Horizontal rooftop piping requires the use of factory-fabricated roof pipe rails with individual pipe supports (as for trapeze hangers). TABLE 1-2 Pipe Hanger Spacing and Hanger Rod Sizes NPS (in.) [DN] 600 V), with a frequency of 50 or 60 Hz. An electrical circuit has the following three basic components: 1. Voltage (V) is defined as the electrical potential difference that causes electrons to flow. 2. Current (I) is defined as the flow of electrons and is measured in amperes (amps). 3. Resistance (R) is defined as the opposition to the flow of electrons and is measured in ohms. These components are defined by Ohm’s law in accordance with Eq. (1-1). V = I × R (1-1)



In order to flow, electricity must have a continuous, closed path. The word circuit refers to the entire course an electric current travels, from the source of power, through an electrical device, and back to the source. Every circuit is comprised of three major components:

1. A conductive “medium,” such as a wire. 2. A “source” of electrical power. 3. A “load” that needs electrical power to operate.

The current flows to the loads through a “hot” wire and returns via a “neutral” wire, under normal conditions, maintained at zero volts. There are also two optional components that can be included in any electrical circuit: control devices and protective devices. Control and protective devices, however, are not required for a circuit to function. A power circuit is defined as any circuit that carries power to electrical loads. A control circuit is a special type of circuit that uses control devices to determine when loads are energized or de-energized by controlling the current flow. In direct current (DC) circuits, power (P) is simply a product of voltage and current (amps), as shown by Eq. (1-2).

P = V × I (1-2)

where P = Power (W or kW) For AC circuits, power factor (PF) must be considered. PF is defined as the ratio of the “real” power flowing to the load to the “apparent” power in the circuit. A PF of less than one means that the voltage and current waveforms are not in phase, and real power is the capacity of the circuit for performing work under specific loading, while apparent power is the product of the current and voltage of the circuit. For resistive loads, such as electric heating coils, and so on, PF = 1.0. For inductive or capacitive loads, such as motors, the PF can be estimated from Table 1-3. For single-phase power circuits, power is defined by Eq. (1-3).

P = V × I × PF (1-3)

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Analysis and Design of HVAC Systems

TABLE 1-3 Typical Motor PF PF Motor Nameplate (HP) 0–5 5–20 20–100 100–250

Speed (rpm)

50% Load

75% Load

100% Load

1,800 1,800 1,800 1,800

0.72 0.74 0.79 0.81

0.82 0.84 0.86 0.88

0.84 0.86 0.89 0.91

For three-phase power circuits, there are three conductors supplying the load rather than only two as for single-phase loads. The current in one conductor supplying the threephase load is 120° shifted in phase from the current flowing in each of the other wires. A factor that takes all of this into account is the number 1.73, the square root of three. Thus, polyphase power is defined by Eq. (1-4).

P = 1.73 × V × I × PF (1-4)

For motors in the United States, power is typically defined by the actual load imposed on the motor in terms of brake horsepower (bHP), while the motor nameplate rating is given as horsepower (HP). In either case, the conversion from W to bHP or HP is defined by Eq. (1-5).

bHP or HP = P × EFF/746 (1-5)

Where EFF is the motor efficiency at the given load percentage. The total amount of energy consumed by the load in a power circuit is computed by multiplying the P by the length of time the load is “on” (hours). This is most commonly expressed in “Kilowatt Hours” (or kWh), where a kW is equal to 1,000 W. While the design of the electrical service to HVAC equipment is typically performed by the project electrical engineer, the HVAC designer must carefully coordinate HVAC electrical loads, voltage requirements, and safety and control devices required by the NEC to ensure that (1) electrical power is provided as needed, (2) in each case it is the right type of power (voltage and phase), and (3) procedures of connection of electrical power to each HVAC component is clearly defined in the project specifications. The general term conductor applies to anything that conducts the flow of electricity. In the United States, electrical wires are conductors that are sized using two different systems: the American Wire Gauge System (AWG) and the Thousand Circular Mill System. Both systems designate wire size based on diameter or cross-sectional areas. In the AWG system, every six-gauge decrease corresponds to a doubling of the wire diameter and every three-gauge decrease doubles the wire’s cross-sectional area. In the SI system, wire gauge is defined as 10 times the wire diameter in millimeters, so a 50-gauge metric wire would be 5 mm in diameter. Note that in AWG, the diameter goes up as the gauge goes down, but for SI gauges, it is the opposite. To avoid confusion, in SI units, wire size is more commonly specified in millimeters rather than in gauges. The current carrying capacity of a particular wire is dictated by its “capacity,” it can be allowed to conduct, as limited to the maximum permitted by the NEC, based on the type of wire (copper or aluminum) and the maximum temperature rating of the wire’s insulation (60°C, 75°C, or 90°C).

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As electrical energy is generated, it is transformed and transported through a network of wires, substations, and transformers to the consumer. Typically, electric energy leaves the utility distribution substation and is distributed via three-phase distribution lines to switchboards within the building. Switchboards take a large block of power and break it down into separate circuits, each of which is controlled and protected by the fuses or switchgear of the switchboard. A panel board is an enclosed assembly with circuit breakers. Branch circuits feed power to receptacles, switches, and equipment in the building. Likewise, motor control centers, with integral switches and/or motor starters, may be supplied as part of the electrical distribution system ready to connect field wiring to the electrical motors served. Overcurrent protection is installed to provide automatic means for interrupting (“opening”) a circuit in which the current rises above their rating due to a fault or short circuit. Two types of over-current devices are in common use: circuit breakers and fuses, both rated in amperes. A circuit breaker is a switching device capable of protecting the distribution line or feeder connected to it from overloads and faults. If a circuit is overloaded, the mechanism inside the breaker trips the switch and breaks the circuit. The circuit breaker may be reset by simply flipping the switch. A circuit breaker is capable of ignoring short-period overloads (such as the initial current required in the starting of a motor) without “tripping” but protects against prolonged overloads. A fuse is a thermal device used for protecting, typically, switchgear equipment and cables against over-currents. When a fuse element overheats due to an over-current condition and “blows,” the circuit breaks. A ground fault interrupter is a device that detects small current leaks and disconnects the hot wire to the circuit. It can also be part of a circuit breaker or part of an electrical outlet. Relays are small, very fast-acting automatic switches designed to protect an electrical system from faults and overloads. It is usually an electromagnetic device which has a coil. When this coil is supplied with power, a magnetic field is created which will operate a mechanical switch. When a relay senses a problem, it quickly sends a signal to one or many circuit breakers to open, or trip, thus protecting it from damage as well as human life from injury. A contactor is an electrically operated switch, a large relay in effect, which can be made to switch a motor, heater bank, capacitor bank, and so on, on and off directly or by a remote controller, such as a thermostat, humidistat, timer, pilot devices, or any other protective devices. Although it is a switch, a contactor is designed to interrupt an electric current repeatedly and frequently. When a contactor breaks the current, an electrical arc is established across the contacts and a good amount of heat energy is generated. This increases when the frequency of breaking the current increases and may result in the “welding” or fusing of the contacts and contactor failure. The simplest and most common starting device for HVAC electrical motors is the acrossthe-line (ACL) starter, consisting of a main contactor and a thermal or electronic overload relay. The disadvantage of the direct-on-line method is very high starting current (6–10 times the rated motor currents) and high starting torque, causing slipping belts, heavy wear on bearings, and gear boxes, and so on. ACL starting is typically applied to motors only 40 HP [30 kW] or less. For larger motors, reduced voltage starters are typically applied: 1. Wye-delta starting device consists normally of three contactors, an overload relay, and a timer for setting the time in the star position (starting position). The starting current is about 30% of the direct-on-line starting device. The starting torque

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Analysis and Design of HVAC Systems

is about 25% of the direct-on-line starting torque. The stress on an application is reduced compared to the direct-on-line starting method. 2. Part-winding starting uses only a portion (usually one-half but sometimes twothirds) of the motor winding, increasing the impedance seen by the power system. It is to be used only for voltage recovery and must not be left on the start connection for more than 2–3 s. The motor is not expected to accelerate on the start connection. The advantages of part-winding starting include the following: a. Starting current is 60%–75% of normal, depending on the specific winding connection. b. Starting torque is very low (may not even turn the shaft). c. Winding heating is very high on start connection. 3. An autotransformer starter is connected so the motor is on the secondary of an autotransformer during starting. The autotransformer has taps, to limit the voltage, applied to the motor at 50%, 65%, or 80% of full voltage. Because the line current varies as the square of the impressed voltage, these same taps equate to 25%, 42%, and 64% of the full-voltage value of line current. The autotransformer starter was historically the most flexible of reduced voltage starters until the advent of the solid-state starter. 4. Solid-state starters use back-to-back thermistors for each line to the motor. These six thermistors control power to the motor. The power adjusts by not completely turning on the thermistors during starting. In other words, only a portion of the three-phase sinusoidal wave is supplied to the motor during start. Because of these control features, the big advantage of the solid-state starter is the large number of starting characteristics. The standard soft-start mode simply ramps the voltage from a preset initial torque value to 100% during a user-selected time of 0–30 s. Another available control mode is a start based on current limitation. In this mode, the current is limited (between 50% and 600%), as is the duration (between 0 and 30 s). Other available operating modes include kick start, soft stop, and pump control options. The last option starts a pump motor on a curve rather than a straight line ramp. This causes the hydraulic system to react as if there were a closed discharge valve behind the pump, opening during starting. 5. A variable frequency drive (VFD) is a type of motor controller that includes an advanced solid-state power controller. Instead of simply opening and closing the power circuit such as an ACL starter or ramping the motor voltage up or down such as a soft start to turn the motor on and off, a VFD controls motor speed and, thus, power. The distance between the VFD and the motor it controls can create an opportunity for motor winding failure due to reflected wave HVs caused by locating the motor too distant from the VFD. Several drive manufacturers have Internet-based calculators that will tell designers if the distance between the motor and the drive is too far, but the common recommendation is to keep the VFD within 50 ft. [15 m] and within the line of sight. VFDs utilized for most HVAC applications are the integrated gate bipolar transistor pulse width modulation type in accordance with National Electrical Manufacturers Association (NEMA) Publication ICS 2, listed and labeled as a complete unit and arranged to provide variable speed of an inverter duty induction motor by adjusting output voltage and frequency.

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As building electrical systems have incorporated more and more electronic devices that are “nonlinear load,” including electronic lighting ballasts, computers, and VFDs, problems with harmonic interferences have arisen. Consequently, some designers require the VFD manufacturer to demonstrate compliance with IEEE Standard 519, which is written to manage harmonic contributions from facilities into the primary electrical distribution system operated by an electric utility. The context of the standard is to provide a basis for determining if a customer reflects an excessive amount of harmonic content, with respect to the electrical demand load and the size of electrical service infrastructure, into the utility distribution system. However, applying IEEE Standard 519 to a VFD makes no sense! This is the equivalent of an HVAC designer requiring an air handler manufacturer to demonstrate that his products do not compromise the ability to achieve a 30% energy reduction in the building. Thus, project specifications for VFDs should not include a reference to IEEE Standard 519. Typical HVAC VFDs are six pulse drives that are adequate for most applications if the electrical designer is competent in configuring the electrical distribution system for the imposed HVAC equipment loads and potential harmonics. For electrical motors exceeding 75 HP [56 kW] (such as for large fans, pumps, or chillers), 12 or even 18 pulse drives may be specified as needed. Basic VFD requirements for HVAC applications include the following: 1. Input AC Voltage Tolerance. Plus or minus 10% 2. Input Frequency Tolerance. Plus or minus 2 Hz 3. Minimum Efficiency. Ninety-six percent at design frequency and full load 4. Minimum Harmonics. VFDs should be equipped with internal 5% impedance DC link reactors to minimize power line harmonics and to provide near unity PF. VFDs without DC link reactors should include 5% impedance line side reactors. Total harmonic distortion should not exceed 10% for motors 95%

Humidifier dust

Hospital laboratories

9

40%–45%

>90%

Lead dust

Schools

Box filters Rigid style cartridge filters. 150–300 mm (6–12 in.) deep may use lofted (air laid) or paper (wet laid) media.

Milled flour Coal dust Auto emissions Nebulizer drops Welding fumes Pleated filters Disposable, extended surface, 25–125 mm (1–5 in.) thick with cotton– polyester blend media, cardboard frame. Better residential Cartridge filters Graded density viscous-coated cube or pocket filters, synthetic media Throwaway Disposable Industrial synthetic media panel filters workplaces

8

30%–35%

>90%

3.0–10.0 μm particle Commercial buildings

7

25%–30%

>90%

Mold

6