HVAC
`
`ECOBEE 1008
`
`CONTROLS anpb
`SYSTEMS
`
`JOHN |. LEVENHAGEN
`DONALD H. SPETHMANN
`
`ECOBEE 1008
`
`001
`
`

`

`002
`
`

`

`HHEEttt
`
`——————————
`HVAC Controls
`and Systems
`
`003
`
`

`

`HVAC Controls
`and Systems
`
`John |. Levenhagen, P.E.
`Donald H. Spethmann,P.E.
`
`McGraw-Hill, Inc.
`New York St Loula San Francleco Auckland Bogota
`Corecos Lisbon London
`id
`Milan
`Montreal New Delhl Paris San Juan Sio Paulo
`
`004
`
`

`

`Library of Congress Cataloging-in-Publication Date
`
`Levenhagen, John 1
`HVAC controle and systems / John |, Levenhagen, Donold H.
`Spethmann,
`Bom
`ISBN 0-07-097509-7
`1. Henting—Control,
`I. Bpethmann, Donald H,
`THT466.4.L48
`1992
`6o7—de20
`
`2 Air conditioning—Control.
`M1. Title,
`
`02-25594
`OIF
`
`Copyright © 1993 by MeGraw-Hill, Inc. All rights reserved. Printed
`in the United States of America, Except us permitted under the
`United States Copyright Act of 1976, na part of this publication may
`be reproduced or distributed in any form or by any menna, or stored
`in o dota bese or
`retrieval aystem, without
`the prior written
`permission of the publisher.
`1294567890 DOCDOC SETESAR2
`
`ISBN N-0?-037509-7
`
`The sponsoring editor for this book way Robert W. Houserman, dhe
`editing supervisor was Kimberly A. Goff, and the production
`supervisor was Pomela A. Pelton, This book wos set in Century
`Schoolbook, Jt was composed by MeGrow-Hill’s Professional Book
`Group composition writ,
`
`Printed and bownd by RR, Donnelley & Sons Company.
`
`&) Thisbookisprintedonrecycled,acid-freepaper
`
`containing a minimum of 50% recycled de-inked
`fiber.
`
`
`Information contained in this work has been obtained by MoGraw-
`
`Hill, Inc., from wources believed to be reliable. However, neither
`
`Moetirew-Hill norite suthors guarantera the accurmcy or complete-
`ness of any information published herein and neither McGraw-Hill
`
`nor its authora shall be responsible for any errors, omissions, or
`damages arising out of use of this information. This worl is pub-
`
`lighed with the understanding(hat McGraw-Hill and ite authors are
`supplying information but are not attempting bo render engineering
`or other professional services, If euch services are required, the as
`
`I dedicate this book first.and foremost to my wife
`Theresa whose patience and strength over the
`months and years in the writing of this book was
`conspicuous,
`I alsa dedicate this book to the many friends and
`associates at ASHRAE (The American Society of
`Heating, Refrigerating and Air Conditioning
`Engineers), as well as the ones at some of the major
`conirol companies who helped with the research, in
`particular people like: Ron Caffery, Rob Stchi,
`Geno Strelow, Kirk Drees, Jim. Grevers, Bob Weeks,
`Mark Maduza, George Hunkie, Jerry Kubiak, Don
`Krajna, John Meyer, Trish Woolfer, John Trabor,
`and Dave Podeszwa. My thanks go out to them os
`well as others who helped in the final composition
`of this book,
`
`dohn J. Levenhagen, PE.
`
`I would like to dedicate my portion of this book ta
`control application engineers, those people who
`strive for an understanding of total system
`operation to provide proper control of eack unique
`total HVAC systent.
`I would also like to thank those who helped me
`write my portion of this book: My wife, Rose, for
`her encouragement and understanding; Bull Pienta
`for his helpful review of building automation and
`DDC explanations; Anil Saigal for sharing hia
`considerable knowledge of the proposed ASHRAE
`standard, “BACnet: A Data Communications
`Protocol for Building Automation and Control
`Networks"; and Dick Poey af Haneywell and Bob
`Parsons of ASHRAE for arranging for the use of
`drawings.
`
`
`
`Donald H, Spethmann, P.E.
`
`005
`
`

`

`
`
`Contents
`
`Prefaca
`
`xiii
`
`Chapter 1. Overview
`HVAC Design Considerations
`HVAC Systeme
`Basle Control
`
`Supervisory Control (Bullding Automation)
`Optimizing Control
`Sources of Supply
`History of Supply
`
`Chapter 2. Thermostats
`Room Thermostats
`Unit Thermostats
`Special Thermostatea
`
`Chapter 3. Dampers and Damper Motors
`Dampers
`Peralle! Blade Versus Opposed Blade Dampers
`Fire and Smoke Dampers
`Manual Dampers
`Static Control Dampers
`Sizing of Automatic Dampers
`Damper Motors
`Preumatic Damper Motors
`Electric Damper Motors
`
`Chapter 4, Automatic Valves
`
`Types of Automatic Valves
`Two-Way Automatic Valves
`Three-Way Automatic Valveo
`
`aHtsHOeee
`
`ok a_i
`
`So3
`
`BEREEEGS
`
`22
`
`a=
`
`BERS
`
`006
`
`

`

`—
`
`Callbrating Controls
`Operating and Maintaining Bullding Automation Systema
`Summary
`
`Chapter 17, Total Facility Approach to Planning Controta
`Buliding Usage and Zoning
`Bullding Manegement Method
`Total Mechanical System Design
`Selection of Types of Control Systems
`Mathods of Specifying and Procuring a Control System
`
`Index
`
`327
`
`Contents
`
`xl
`
`ava
`Ha
`315
`
`x17
`aT
`o18
`
`323
`
`Contents
`
`Hoat Recovery/Heat Pump Systems
`Heat Recovery
`
`Chapter 14. Distribution Systemsof All Types
`Water Distribution Systems
`Two-Pipa Systeme
`Three-Pipe Systema
`Four-Plpe Sysioms
`Pumping Control and Olfferential Pressure Regulation
`Primary-Secondary Pumping Variations
`Steam Distribution Systema
`
`Chapter 15. Supervisory Control and Total System Optimization
`Definition and Historical Background
`System Configurations and Communications
`Proprietary Versus Open Systems
`Possible Supervisory Functions
`Customized Global Control Functions
`Standard Energy Management Functions
`Optimum Start and Stop
`Demand Control
`Duty Cyele
`Load Resot and Zero Enorgy Band
`Hight Cycle and Night Purge
`Enthalpy Control
`Interface to Local Loop Control
`Operator Interface Functions
`Custom Programming and Time Event Programming
`Application Eng!neering Functions and Tools
`Specifying Bullding Automation Needs
`Check Out Commissioning and Acceptance
`Documentation
`
`Chapter 16. Operating and Maintaining Control and HVAC Systems
`Operating and Malntaining Primary Systems and Controls
`Pumps
`Bollers
`Chillers
`
`Steam Distribution Systems
`Primary Alr Systems
`Operating ind Maintaining Terminal Equipment
`Radiators and Convectors
`Operating and Malntaining Controls
`Preumatic Controls
`Electric Controle
`
`PEPSEERRESRESES8
`282SSeeeee8&
`
`222
`
`6 —a
`
`007
`
`

`

`
`
`Preface
`
`During the past. 40 years HVAC systems in nonresidential buildings
`in North America have been tried with varying degrees of success. As
`these new systems were tried, new and innovative control systems
`were designed to allow them to work satisfactorily, As with anything
`new, problems developed and the solutions were not always quickly
`forthcoming. But, in time, solutions did surface and the owners and
`operators of the building were in most cases satisfied with the results.
`Some of the solutions to those problems were never published: oth-
`ers were published as in-house papers for employees only, The need
`therefore existed to uncover the practical and unknown solutiona.
`‘'o respond to that need, HVAC Controls and Systems covers the
`major components of HVAC commercial control systems in as much
`detail as necessary to provide the solutions to the problems that ex-
`isted. These problems involve everything from automatic dampers,
`automatic valves, unit thermostats, and electronic controls to the
`problems caused by faulty or poorly designed controls in the systems.
`The book, therefore, covers room thermostats, room humidistats, and
`all of the devices they as well as other inetruments control, It aleo in-
`cludes pneumatic controls, analog electronic controls, digital elec-
`tronic controls, and standard electric controls. Residential controls are
`covered, although the emphasis is on nonresidential building controls.
`Some mention is made of industrial controls, where that field comes
`close to the commercial field. The information presented will enable
`you to work on problems not mentioned in other books and solve those
`problems based upon the practical knowledge of the authors,
`A discussion of digital controls, as well as analog electronic controls
`brings out the disadvantages and advantages of all of the systems,
`from unit ventilators to today’s VAV systems. These systems are the
`ones used in all types of commercial buildings from schools and hos-
`pitals to high-rise office buildings.
`To understand the complexities of today's modern systema and the
`controls used to maintain the conditions in them, HVAC Controls and
`Systems presents the history of systema as they were developed.
`
`John I, Levenhogen, PE.
`
`008
`
`

`

`HVAC Controls
`and Systems
`
`009
`
`

`

`
`Chapter
`
`1
`
`Overview
`
`Controls for heating ventilating and air conditioning (HVAC) cover a
`broad range of products, functions, and sources of supply. Control can
`be defined as the starting and stopping or modulation of a process to
`regulate the condition being changed by the process. In this book the
`process involved is heating, ventilating and air conditioning. HVAC
`commonly refers to buildings of public, commercial, or institutional
`usage that require a provision for ventilation as well as heating and
`cooling. This book deals with the common practices in using control
`devices and systems to control HVAC systems. It does not deal with
`the control of residential heating and cooling, except in some special
`causes where residential controls crossover into light commercial con-
`trols. The application of controls starts with an understanding of the
`building and HVAC systems and the use of the spacea to be condi-
`tioned and controlled. The type of HVAC system determines the con-
`trol sequence. The basic control sequence can then be done by several
`types of control products such as pneumatic, electric, analog elec-
`tronic, or electronic direct digital control (DDC).
`The use of building spaces and the general strategy of managing
`and running the building(s) determines the benefits to be ohtained
`from additional controls for centralization, automation, and/or optimi-
`tation, The sources of supply vary with the simplicity or complexity of
`the products planned for the project. This chapter will discuss the gen-
`eral range of choices and the considerations in making these choices.
`Later chapters will give more detail.
`A brief historical review of HVAC control can help us understand the
`subject. Back when heating was controlled by draft. dampers, the ther-
`mostat was invented to control the dampers. The use of mechanical stok-
`ers for coal firing required another step in the use of control, When oil
`burners were introduced, the conceot of combustion safety control be-
`
`010
`
`

`

`Chapter One
`
`Overview
`
`3
`
`came necessary, This involved the sensing and proof of flame in the
`proper time sequence of introducing draft, fuel, and ignition.
`The use of steam and hot water radiators led to the concept of zone
`control and eventually individual room control (IRC). Forms of zone
`control included closed loop control using zone thermostats and open
`loop control with outside conditions setting the rate of heat delivery to
`the sone. Both of these forms of control were used to regulate the de-
`livery of heat, The meana of regulation included the following: valves
`to control the flow of steam or hot water, controlling pumps to circu-
`late hot water, and controlling boiler operation. When IRC was used,
`the central supply was maintained and radiator valves were con-
`trolled by room thermostats.
`The use of fans to deliver ventilation es well as heated air was con-
`trolled by dampers, which varied the source and volumeof air. This
`inclided unit ventilators in classrooms. The typical control of unit
`ventilators was by pneumatic controla and included the following
`features: minimum outside air, discharge air, low-temperature limits,
`and thermostats with lower night settings activated by compressed air
`supply pressure level. The increased usage of air conditioning led to
`more complex control sequences and in larger systems to centralized
`monitoring and control, The increased complexity of sequences to ac-
`commodate air conditioning included the following: control of cooling
`in sequence with heating and ventilation, control of dehumidification
`by subcooling and reheat, and control by economizer sequence that
`used outdoor air for cooling when it was a suitable source ofcooling, In
`larger systems, centralized monitoring and control was typically done
`with electronic sensing and some form of multiplexed wiring to the
`centralized monitoring point, The operator interface at the central lo-
`cation initially used gauges, meters, and switches mounted on panels
`that included a graphic representation of the piping schematic for the
`system being controlled. The use of photographic slide projectors in-
`ereased the graphic capacity and flexibility. The shared wiring
`schemes initially had control cables that switched the connection of 6
`data cable from one system's wires to another. The use ofdigital codes
`and time-shared transmission allowed communication of many chan-
`nels of information over a single pair of wires.
`The industrywide development and use of computers and micropro-
`cessors has caused great changes in the HVAC controla industry.
`First, minicomputers were installed on very large jobs to collect data
`and provide centralized control. Then, microprocessors were used in
`remote data-pathering panels to gather data and provide direct digital
`control. Computers are used both as on-site central controllers with
`operator interface and as computer assisted engineering (CAE) tools
`
`pls with DDC, as well as in smaller wnit controllers and smart ther-
`muosteats.
`The scope of HVAC control has grown to include building automa-
`tion. Building automation systems can include fire alarm or life safety
`systems and security systems. This book will not deal with these sys-
`tems, however, but will confine coverage to HVAC control.
`From this brief historical review we see that the evolution of HVAC
`equipment and systems caused the evolution of the basic controls for
`HVAC and that the evolution of control technology finds new ways to
`improve the operation and maintenance of mechanical and electrical
`systema by what is broadly called building automation. Also, technol-
`ogy has led to the use of direct digital control and is pushing the ap-
`plication of expert systems in control of HVAC.
`In reviewing the scope of HVAC control,this chapter will briefly ex-
`amine each of the following subjects:
`
`HVAC Systems
`Basic control
`
`Supervisory control
`Optimizing control
`Sources of supply
`
`HVAC Design Considerations
`
`Before considering the description of controla or HVAC systema, it
`would be wise to take a long look at what is involved in the design of
`HVAC for commercial buildings, Although this book is about controls,
`it is also about systems, and understanding systems is far more im-
`portant than understanding controls.
`A amart engineer once said, All the controls in the world will not
`correet the problema with a poorly designed HVAC system." Truer
`words have never been spoken, Engineers must be responsible and de-
`aign systems that can be controlled and can work at all levels of load,
`This involves knowing load profiles for all hours of operation forall
`zones of usage and also understanding part load operating character-
`istics of the HVAC equipment to be used.
`There is another phrase used by knowledgeable control engineers,
`the kiss principle, which means keep it simple stupid. Controla piled
`on top of controls will only accentuate a problem if the problem is with
`the system itself, A high percentage ofthe troubleshooting done in the
`past where the indicated problem was said to be a control problem
`
`011
`
`

`

`(Chapter One
`
`Overview
`
`6
`
`balancing, The state of the art has progressed greatly in the past 15
`years, and balancing is now almost an exact science, so much eo thal a
`system that is properly designed with no scrimping on the duct work
`or piping and that has adequate balancing dampers or valves can be
`balanced to the satisfaction of all concerned,
`If a project is straightforward,like an office building with no special
`conditions, a normal variable air volume (VAV) or similar system is
`in order. If, however, the project is not straightforward and has special
`requirements such as a hospital, a smart engineer does not try to do
`the job with one all-purpose HVAC unit. Whatever type of system ia
`designed, it should be able to be operated properly at all loads before
`the controls are added,
`
`HVAC Systems
`
`HVAC system types can be classified aa either self-contained unitary
`packages or as central systems. With unitary packages the one pack-
`age converts a primary energy source (auch as electricity or gas) and
`provides final heating and cooling to the space to be conditioned. Ex-
`amples of self-contained unitary packages are rooftop HVAC aystems,
`packaged terminal air conditioning (ac) units for rooms, and air-to-air
`heat pumps.
`The typical uses of packaged unitary systems are in single-story
`structures where there is easy access to outside air or rooftop mount-
`ing. They are also used in situations where first cost is more impor-
`tant than operating costa.
`Central systems are a combination of central supply subsystem and
`multiple end use subsystems. End use subsystems can be fan syatems
`or terminal units. If the end use subsystems are fan systems, they can
`be single or multiple zone type.
`Whatever controlled HVAC unit maintains space temperature, it
`can be referred to as the end use zone system. The central supply can
`be packaged boilers and chillers in smaller sizes or custom applied
`boilers and chillers in larger sizes, In addition to size, the difference
`between a package and a custom-applied unit is the extent of control
`and auxiliary equipment furnished with the unit. The safety controls
`associated with chillers and boilers are applied by the unit manufac-
`turer because their locations and control actions are directly depen-
`dent.on the mechanical equipment design. These are original equip-
`ment manufacturer (OEM) furnished controls that come with the unit
`whether it is a packaged or a custom-applied unit. Additional controls
`for capacity to maintain supply temperature levels and auxiliary
`aquipment such as pumps are included in a package but not necessar-
`
`With central systema, the primary conversion from fuel such as gas
`or electricity takes place in a central location, with some form ofther-
`mal energy distributed throughout the building or facility,
`There are many variations of combined central supply and end use
`zone systems. The most frequently used combination is central hot
`and chilled water distributed to multiple fan systems, The fan systems
`use water to air heat exchangers called coils to provide hot and/or cold
`air to condition the controlled spaces. Another combination central
`supply and end use zone system is 8 central chiller and boiler for the
`conversion of primary energy, as well as a central fan syatem to deliv-
`ery hot and/or cold air. The multiple end use zone systems are mixing
`or VAV boxes. The typical uses of central systema are in larger,
`multistoried buildings where access to outside air is more restricted.
`Typically central systems have lower operating. costa,
`Besides. packaged unitary and central systems, there are a variety
`of special-purpose systems. These include
`
`1. Heat pump cycles on chillers that use rejected heat or towerfree
`cooling
`2. Thermal storage
`3. Cogeneration of electricity and heat
`
`Bach special-purpose system has unique control strategy require-
`mente. These are discussed in the chapters on primary supply (Chap.
`12) and heat pump cycles (Chap. 19),
`
`Basic Contro)
`
`Beste control regulates the amount of heating or cooling necessary to
`meet the load in conditioned spaces. Minimum outside air needed for
`ventilation is provided whenever a space is occupied. When outside air
`temperature is a auitable source for free cooling, it is controlled as
`needed at values greater than minimum,
`The approach in packaged unitary equipmentis to control the gen-
`eration of heating or cooling by space thermostats. The approach in
`central syatema is to control the delivery of heating and cooling by the
`end use zones to match the load in the space. The supply (or rate of
`primary conversion) is controlled to match the load imposed by the
`sum of the end use zones. A typical method of doing this is for end use
`zones to be controlled by room thermostats and central supplies to be
`controlled by discharge controllers, Generally, discharge temperature
`controllers control the rate of primary conversion (chillers or boilers),
`and pressure controls determine the delivery rate of the pumpsor fans
`
`012
`
`

`

`(Chapter One
`
`Overview
`
`Tf
`
`ers and/or chillers and pumps put on or off line as necessary to provide
`proper capacity. Those on line are modulated as necessary to meet
`load needs, The controls to put units on and off line would normally be
`job applied to meet the system needs.
`
`Supervisory Control (Bullding Automation)
`The role of supervisory control, as a generic class of control, is to control
`scheduling and interaction of all the subsystems to meet building needa
`with appropriate operator input. Supervisory control systems have had
`many names, each used for a particular emphasis. Among the names and
`their acronyms are the following: building automation system (BAS), en-
`ergy monitoring and control syetem (EMCS), facility management sys-
`tem (FMS), and energy management system (EMS). In the context ofthis
`book on HVAC control, the most appropriate name is building automa-
`tion system. The important thing is that there is a clear understanding of
`what a system is expected to do and that this is clearly communicated te
`the people who will make it happen,
`The term direct digital control is sometimes used to describe every-
`thing done by a computer- or microprocessor-based contro] system. The
`original use of direct digital control referred to providing closed loop con-
`tral of local loops by a digital computer or microprocessor. These local
`loops were originally controlled by a hardware set composed of a sensor,
`a controller, and a controlled device such as a damper or valve actuator.
`With DDC the controller was replaced by a calculation in a digital com-
`puter or microprocessor. One benefit was that a single computer or mi-
`eroprocessor could do many such calculations and replace many hard-
`ware controllers. Building automation was also being done by centrally
`located computers or microprocessors. The functions of these systems
`were general monitoring, scheduled starting and stopping, and changing
`local loop set points, These programs were generally described as energy
`management applications,
`Direct digital control is implemented both in stand-alone panels and
`in intelligent data-gathering panels that are the remote panels of a
`building automation system. Energy management programs that
`were originally in the central computer of a building automation sys-
`tem are sometimes placed in the remote data-gathering panels or even
`in stand-alone DDC controllers. This has led some people to use DDC
`to describe all functions of control done by microprocessor-based con-
`trol systems, This book, however, uses the narrower definition, where
`DDC refers to local loop control.
`Energy management application programs are different than local
`loop control and ere named for their specific function, such as opti-
`
`of building and of HVAC system. For instance, the optimum start—
`atop programa are not appropriate for a hospital that has 24-h opera-
`tion end use of spaces. Aleo load reset of supply temperatures is ap-
`propriate for
`systema that
`supply both heating and cooling
`simultaneously, such as reheat syaterms or hot and cold deck mixing
`box systems. These guidelines are given in the chapters discussing the
`type of system being controlled, such as Chap. 10 “Air-Handling
`Units” and Chap. 12 "Primary Supply Systems."
`
`Optimizing Control
`
`The concept of optimizing control is not only to control space condi-
`tions but also to do it in a manner that minimizes the energy and costs
`when different forms of energy are available. An optimizing strategy
`is generally to improve the efficiency of primary supply equipment or
`to reduce the losses of energy in end use systems. The sizing of equip-
`ment is to meet maximum loads, but the majority of time equipmentis
`run at much less than maximum load. This means that the part load
`characteristics of the equipment determines the efficiency in meeting
`a given load. When there are multiple chillers or boilers, an optimiz-
`ing strategy would be to choose the most efficient equipment that has
`the capacity to meet the load at any given time, Also, with some types
`of end use systems, energy wasted by bucking heating against cooling
`can be minimized by resetting supply temperature levels to be no
`more than is necessary to meet a given load condition. Another way to
`optimize is to use the thermal storage of a building massor of a stor-
`age facility to make use of energy stored at low cost and used when
`needed and when it would be high cost to generate it. Aleo, moving
`heat from one area of a building to another can he an optimizing op-
`portunity.
`These optimizing principles are used for specific types of HVAC sys-
`tema or building load circumstances. The measured variable in all of
`these circumstances is the amount of heating or cooling load and the
`control action to make some change in the way a loadis supplied. This
`process has led to the use of the terms load reset and dynamie load
`control to describe this general approach to optimising control. The se-
`lection of the most efficient combination of chillers to supply a cooling
`load has been called optimized chiller selection. These strategies are
`covered in more detail in the chapters pertinent to the systems and
`equipment involved,
`
`Sources o7 Supply
`
`013
`
`

`

`Chapter One
`
`installed as a part of the construction process when making a new
`building. Adding controls to existing buildings is another way to im-
`prove building performance. Frequently, energy retrofit is an econom-
`ically viable project that involves updating a control system with en-
`ergy management strategies and DDC. The marketing of controls can
`be through different channels, which include the following:
`
`Full-line control companies that provide turnkey installed systema
`and comprehensive service for all typea of control, including the
`most complex building automation. Their marketing is typically
`through multiple channele, which include OEM sales and distribu-
`tor sales of control products in addition to direct sale of installed
`systems,
`Control distributors selling and, in some cases, installing and ser-
`vicing controls. At times, simple energy management systems for
`light commercial type buildings are also installed by distributors
`with specialized training.
`Full-line HVAC equipment companies that include a limited line of
`controls and simple building automation in their product line. They
`typically offer packages that integrate the HVAC equipment and
`controls in pupular configurations.
`Specialized control companies that have a limited product line deal-
`ing with some niche in the overall HVAC control field. Their mar-
`keting may be through direct sales, installing contractors, or man-
`ufacturer's representatives.
`
`As stated at the beginning of this chapter, the application of con-
`trols for HVAC starts with an understanding of the HVAC system and
`the use of the spaces to be conditioned. The use of the spaces deter-
`mines the desired environment, the time schedules involved, and to a
`great extent the ventilation and air-conditioning load levels and tim-
`ing. The HVAC system characteristics determine the sequence of con-
`trol required and levels of costs and results that will be achieved. The
`selection of the type of HVAC system is beyond the scope of this book.
`The characteristics of basic control and optimizing controlfor different
`types of HVAC aystems will, however, be covered, The organization of
`this book is into two sections, one dealing with control devices and one
`with HVAC and supervisory control or building automation systems.
`
`History of Supply
`A brief history of the evolution ofcontrols suppliers will helpyou under-
`
`Overview
`
`R
`
`promoted pneumatic controls. Of the three major companies in this field,
`two started as electric control companies; one of them even manufactured
`electric cars before seriously getting in the control business: The second
`one purchased a pneumatic controls company so as to participate in that
`business as well. The third company started in business by selling con-
`trols and other plumbing items to the industry,
`The one thing that was common amongthe original big three was
`the concept that controls for commercial buildings were too compli-
`cated to sell over the counter and had to be installed and supervised
`by the controle manufacturer. This concept included having branch of-
`fices with installers and servicepeople.
`Electric control systema for commercial buildings were modulating
`type controls and were sold on a supervised basis. When several other
`companies entered the commercial controls market with electric and
`electronic controls, some of their distribution was through diatributors
`2s well ag branches. Some of the newcomers who started with electric
`and electronic controls expanded into pneumatic controls either by
`their own development or by association with foreign companies.
`When computer-based supervisory control syatems came to market,
`some larger companies with computer-based products entered the
`HVAC controls market but eventually gave up. As international busi-
`ness developed and companies became multinational, some foreign-
`based controls companies expanded into the U.S. markets directly or
`through associations with amaller U.S, control companies, During the
`period when energy conservation was a hot button and application of
`microprocessors became commonplace, some small companies evalved
`with limited product lines for energy management functions. When
`DDC became accepted, some small companies developed micro-
`processor-based DDC controllers and supervisory systems.
`With all this activity, there has been considerable change in the
`sources of supply at any given time. A number of companies have
`come and gone from the HVAC ‘control scene, Presently the full line
`control companies that started out as major players remain as major
`playera but with a few more competitors with limited systeme if not
`full lines of controls. Some major HVAC systems manufacturers have
`acquired or developed control capabilities. They market packaged
`HVAC eystems with controls and supervisory control systems,
`Some small companies provide products for specific applications,
`The understanding of the HVAC system and its control needs will al-
`ways be a key element in the successful purchasing and ownership of
`euch a facility. The goal of this book ia to help in that understanding,
`The selection of a source of supply should consider the life cycle needs
`and costs as well as the track record of potential suppliers.
`
`014
`
`

`

`
`
`Chapter
`
`2
`
`Thermostats
`
`This chapter will discuss room thermostats, room humidistats, unit
`capillary thermostats, insertion thermostats, insertion humidistats,
`safety thermostats, and special thermostata and their uses in the var-
`ious systems, It will also deal with problems involving thermostats
`and present solutions based upon experience and tests performed over
`the years. The discussions will refer mostly to pneumatic controls,
`only because pneumatic control systems have been the standard ofthe
`commercial industry for many years. Some of the principles also apply
`to electronic and/or electric controls. Self-contained controls are also a
`factor to be reckoned with, but usage of those types of controls is min-
`imal in the field of commercial controls and systems.
`
`Room Thermostats
`
`The mounting of room thermostats and room humidistats has been the
`subject of much discussion in the past, and for many years the indus-
`try standard has been for the thermostat to be mounted near the door
`ofa room 5 ft from the floor. The only problem is that if the room is
`Full of short people, such as school children, the thermostat is not con-
`trolling the temperature where the occupants are. Although many
`rooms are not filled just with children, the point is that too often the
`conditions that are or will be in the space are forgotten. Thus, the
`placement of a room thermostat or humidistat is important enough
`that we need to study its location with the view of trying to keep the
`occupants comfortable where they are.
`Further, it is important to study the location of the room thermostat
`or humidistat as to the affect of conditions at the thermostat, Remem-
`ber, the thermostat. knows only what is going on at its location, If
`
`015
`
`

`

`Ohopter Two
`
`Thermostats
`
`13
`
`therefore, important to think of a thermostat on the wall as a device
`that knows only what is going on in its immediate vicinity. The ther-
`mostat cannot think; it ca