Control Systems lor Heating, Ventilating and Air Conditioning Control Systams lor Haating, Vantilating and Air Conditioning Fourth Edition ROger W. Haines Consulting Engineer rt7m5l VAN NOSTRAND REINHOLD ~ _ _ _ New York ISBN -13 :978-1-4684-6595-2 e-ISBN -13 :978-1-4684-6593-8 DOT: 10.1007/978-1-4684-6593-8 Softcover reprint of the hardcover I st edition 1987 Copyright © 1987 by Van Nostrand Reinhold Library of Congress Catalog Card Number 87-2144 All rights reserved. Certain portions of this work © 1983, 1977, 1971 by Van Nostrand Reinhold Company Inc. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems-without written permission of the publisher. Van Nostrand Reinhold 115 Fifth Avenue New Yorlc, New York 10003 Chapman & Hall 2-6 Boundary Row London SEI 8HN, England Thomas Nelson Australia 102 Dodds Street South Melbourne, Victoria 3205, Australia Nelson Canada 1120 Birchmount Road Scarborough, Ontario MIK 5G4, Canada 16 15 14 13 12 11 10 9 8 7 6 5 Library of Congress Cataloging-in-Publication Data Haines, Roger W. Control systems for heating, ventilating, and air conditioning. Bibliography: p. Includes index. 1. Heating-Control. 2. Air conditioning-Control. I. Title. TH7466.5H34 1987 697 87-2144 Preface to the Fourth Edition There are two reasons why we have a new edition every four or five years. The first is that technology changes. Chapter 10, on computer-based con trols, has had to be almost completely rewritten. Fundamentals don't change, but the tools available to us do change. Evaluation and proper use of those tools makes it even more imperative that we understand fundamentals. Many of our control problems stem from the use of new devices as a solution to problems that are, in fact, control design errors. New gadgets, for example, Direct Digital Controls (DDC), will not solve basic problems and may even compound them. None-the-Iess, you will find an extensive discussion of DDC because I think it is the probable "future" in HVAC control. But it must be applied with a good understanding of fundamentals. The second reason is that I keep learning and need to pass on my new and improved understanding to my readers. Thus you will find a number of small but important revisions, a dissertation on control "modes," and a much more detailed discussion of how electronic control devices work. There are a few places where I have corrected what I now perceive to be errors. I apologize for these. I have been much encouraged by the acceptance of this book in the past, and I hope that this new edition will be helpful. Thank you for your support. Roger W. Haines v Preface to the First Edition This book is intended for the guidance of the engineer who is designing a heating, ventilating or air conditioning system and wants a simple, practical explanation of how best to control that system. It could also be used as a supplemental text in a college or technical school course on refrigeration and air conditioning. It does not include mathematical analyses of control systems, response factors, Fourier transforms and the like. These are adequately and thoroughly covered in a number of up-to-date college-level texts. What is presented here is an elementary but comprehensive explanation of control system theory, control hardware, and both simple and complex control systems. There are also discussions on supervisory controls and the use of computers in control systems. Throughout, the reader should be aware of the interrelationship between the HVA C controls, the HVA C system, the electrical power system and the building. There have been examples of control systems which failed to con trol because inherent deficiencies in the building or HVAC system made it uncontrollable; or of control failures because the designer failed to make his intent clear to others. It is hoped that the reader will be helped to avoid some of these pitfalls. Roger W. Haines january, 1971 vii Acknowledgments Nothing gets done without help and I've had some of the best. First and foremost, Frank Bridgers and Don Paxton provided my basic training in con sulting engineering and control design. My debt to them is large. Many friends in ASH RAE, particularly those on TC 10.1 (Controls) gave encourage ment and help. Tom Guiterrez, a colleague at Collins Radio, served as sounding board, critic, research assistant and advisor. Don Bahnfleth, edito rial director of Heating, Piping and Air Conditioning magazine read the man uscript and gave much good advice. My wife encouraged and helped me as she has so often, besides typing the manuscript. Professor Clark Pennington and Dr. Joseph Gartner read and criticized the manuscript and their comments were most helpful. Several manufacturers graciously gave permission to reproduce parts of their literature. Roger W. Haines ix Contents Preface, vii Acknowledgments, ix 1 Control Theory and Terminology, 1 1.1 Introduction, 1 1.2 What is "Control"?, 2 1.3 Elementary Control System, 2 1.4 Purposes of Control, 3 1.5 Control Action, 4 1.6 Energy Sources for Control Systems, 9 1.7 Measurement, 10 1 .8 Symbols and Abbreviations, 11 1.9 Psychrometries, 11 1.10 Relationships, 11 1. 11 Summary, 12 2 Pneumatic Control Devices, 13 2.1 Introduction, 13 2.2 Pneumatic Control Devices, 14 2.3 Control Cabinets, 36 2.4 Air Supply, 37 3 Electric and Electronic Control Devices, 41 3.1 Electric Control Devices, 41 3.2 Electronic Control Devices, 54 4 Fluidic Control Devices, 66 4.1 Introduction, 66 4.2 Wall Attachment Devices, 66 xi xii Contents 4.3 Turbulence Amplifiers, 68 4.4 Vortex Amplifiers, 69 4.5 Radial Jet Amplifier, 69 4.6 Fluidic Transducers, 70 4.7 Manual Switches, 71 5 Flow Control Devices, 73 5.1 Dampers, 73 5.2 Steam and Water Flow Control Valves, 77 5.3 System Gains, 86 5.4 Summary, 87 6 Elementary Control Systems, 88 6.1 Introduction, 88 6.2 Outside Air Controls, 88 6.3 Air Stratification, 94 6.4 Heating, 95 6.5 Cooling Coils, 100 6.6 Hwmidity Control, 105 6.7 Dehumidifiers, 112 6.8 Static Pressure Control, 114 6.9 Electric Heat, 115 6.10 Gas-Fired Heaters, 118 6.11 Oil-Fired Heaters, 120 6.12 Refrigeration Equipment, 120 6.13 Fire and Smoke Control, 127 6.14 Electrical Interlocks, 128 6.15, Location of Sensors, 128 6.16 Summary, 129 7 Complete Control Systems, 130 7.1 Introduction, 130 7.2 Single-Zone Systems, 130 7.3 Multizone Air Handling Systems, 139 7.4 Dual-Duct Systems, 145 7.5 Variable-Volume Systems, 150 7.6 Reheat Systems, 157 7.7 Heat Reclaim, 162 7.8 Fan-Coil Units, 165 7.9 Induction Systems, 173 7.10 Unit Ventilators, 175 Contents xiii 7.11 Packaged Equipment, 176 7.12 Other Packaged Equipment, 180 7.13 Radiant Heating and Cooling, 181 7.14 Radiators and Convectors, 182 7.15 Heat Exchangers, 184 7.16 Solar Heating and Cooling Systems, 188 7.17 Summary, 192 8 Electric Control Systems, 193 8.1 Introduction, 193 8.2 Electric Control Diagrams, 194 8.3 Electrical Control of a Chiller, 196 8.4 Electrical Control of an Air Handling Unit, 199 8.5 Example: A Typical Small Air Conditioning System, 200 8.6 Electric Heaters, 204 8.7 Reduced-Voltage Starters, 204 8.8 Multispeed Starters, 210 8.9 Variable Speed Controllers, 212 8.10 Summary, 214 9 Special Control Systems, 215 9.1 Introduction, 215 9.2 Close Temperature and/or Humidity Control, 215 9.3 Controlled Environment Rooms for Testing, 223 9.4 Some Examples from Practice, 225 9.5 Summary, 239 10 Supervisory Control Systems, 240 10.1 Introduction, 240 10.2 Hard-Wired Systems, 240 10.3 Multiplexing Systems, 241 10.4 Computer-Based Systems for Monitoring and Control, 243 10.5 The Economics of Supervisory Systems, 257 10.6 Benefits of the Computer System, 258 10.7 Training for Maintenance and Operation, 259 10.8 Summary, 259 11 Psychrometrics, 260 11.1 Introduction, 260 11.2 Psychrometric Properties, 260 11.3 Psychrometric Tables, 262