ASHRAE 90551-2010 Fundamentals of HVAC Control Systems I-P.pdf

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1、Fundamentals of HVAC Control Systems Inch/Pound EditionISBN,978-1-93-374292-2, 152x229mm, PPCSpine 20.5mm.803”Ross Montgomery, P.E., CPMP, BEMPRobert McDowall, P.Eng.American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.FundamentalsofHVACControl SystemsI-P EDITIONMontgomeryM

2、cDowallFundamentals of HVAC Control SystemsThis book is an excellent “stand-alone” text for owners and operators, mechanical engineers, mechanical contractors, and facility engineers. It serves as an introduction to the specification, design, manufacture, installation, operation and maintenance of H

3、VAC control systems. Specific topics include: Control theory and how to evaluate, select, position andsequence the appropriate type of control The electrical knowledge needed to understand controls and the use of electrical circuit drawings The various types of valves and dampers, and their selectio

4、n, installation and operation Terminology and attributes of sensors, the selection of moisture sensors, pressure, flow, and auxiliary devices Self-powered and system-powered controls Electric controls, control diagrams and control logic The components of pneumatic systems and control applications di

5、agrams Wiring conventions, application-specific electronic controllers and how to use them in HVAC applications The use of written specifications, schedules, and drawings toclearly identify what is to be installed, how it is to be installed,and how it is expected to operate Direct Digital Controls (

6、DDC) components, their inputs andoutputs, and the programming of DDC routines DDC Networks and Protocols DDC Specification, Installation and CommissioningThis book is also an extremely useful reference for subscribers to the eLearning course, Fundamentals of HVAC Control Systems.9 781933 742922About

7、 the AuthorsRoss D. Montgomery, P.E., CPMP, BEMPAn ASHRAE Vice-President, past DRC and DAL, Ross Montgomery has worked in ASHRAE activities for over 28 years, and has served on over 34 committees, councils and boards for ASHRAE. He has authored several Journal articles on controls and commissioning.

8、 Montgomery owns and operates QST-Inc, which specializes in commissioning/controls, maintenance/operations, and energy audit/modeling. He also works as a certifying engineer for testing, adjusting, and balancing HVAC nor may any part of this book be reproduced, stored in a retrieval system, or trans

9、mitted in any way or by any meanselectronic, photocopying, recording, or otherwithout permission in writing from ASHRAE.Library of Congress Cataloging-in-Publication DataApplication submittedTransferred to Digital Printing 2011Contentsx1 Introduction to HVAC Control Systems 11.1 Why Do We Need Contr

10、ols? 21.2 A Brief History of Controls 31.3 Control Loops 41.4 Control Modes 9Two-position Control 10Floating Control 14Modulating Control 15Pulse-width Modulating, and Time-proportioning Control 201.5 Gains and Loop Tuning 211.6 Control Actions and Normal Position 241.7 Control Range, and Sequencing

11、 271.8 Controls Documentation, Maintenance, and Operations 28The Next Step 292 Basics of Electricity 302.1 Simple Circuits and Ohms Law 312.2 AC Circuits 352.3 Transformers and Power Services 392.4 Relays 422.5 Motors and Motor Starters 452.6 Variable Speed Drives 512.7 Relay Logic and Ladder Diagra

12、ms 54The Next Step 603 Control Valves and Dampers 61Introduction 613.1 Two-way Control Valves 62Styles and Principles of Operation 623.2 Three-way Control Valves 723.3 Selecting and Sizing Valves 76Flow Characteristic Selection 81Close-off Pressure 853.4 Control Dampers 87Styles and Principles of Op

13、eration 873.5 Selecting and Sizing Dampers 91Two-position Duty 91Capacity Control Duty 92Mixing Duty 98The Next Step 1044 Sensors and Auxiliary Devices 1064.1 Introduction to Terms 107Accuracy 107Range 107Reliability 108Repeatability, Precision 108Transmitter 1084.2 Temperature Sensors 109Bimetal 10

14、9Fluid Expansion 111Electrical, Self-powered 113Electrical Resistance 1134.3 Humidity and the Psychrometric Chart 118Indoor Air is a Mixture of Dry Air and Water Vapor 118Relative Humidity 1194.4 Moisture Sensors 128Relative Humidity Sensors 1284.5 Pressure Sensors 1334.6 Flow Sensors and Meters 136

15、4.7 Auxiliary Devices 148The Next Step 1595 Self- and System-powered Controls 1605.1 Principles of Operation Self-powered Controls 1605.2 Examples of Self-powered Controls 161Thermopile Controls 161Hot Water Control Valve 162Self-powered VAV Diffuser 1625.3 System-powered Controls 164System-powered

16、Air Valves 164System-powered Water System Valves 165The Next Step 1666 Electric Controls 1676.1 Sensors 1676.2 Controllers, Two-position 1696.3 Controllers, Modulating 1716.4 Example Application 1746.5 Actuators 1776.6 Auxiliary Devices 178The Next Step 179vi Contents7 Pneumatic Controls 1807.1 Prin

17、ciples of Operation 1817.2 Sensors 1837.3 Controllers 1847.4 Actuators 1887.5 Auxiliary Devices 1907.6 Compressed Air Supply 1967.7 Example Applications 198The Next Step 2048 Analog Electronic Controls 2058.1 Principles of Operation 2058.2 Sensors 2068.3 Controllers 2068.4 Actuators 2118.5 Auxiliary

18、 Devices 2128.6 Example Applications 212The Next Step 2159 Control Diagrams and Sequences 2169.1 Control Systems Design Criteria 2179.2 Control Systems Design Process 2189.3 Control Diagrams and Symbols 2189.4 Control Sequences 2209.5 Example Applications 222Typical Single-Zone System 222Typical Con

19、stant Air Volume System with Face and BypassDampers 226Typical Constant Air Volume System with Multiple Zones orReheat 227Typical Variable Air Volume System 227Typical Constant Air Volume System, with Variable SpeedFan for Filter Loading 237Chiller Plant, Pumps, and Boilers Monitoring and Control 23

20、9Temperature and Humidity Monitoring and Control 240Carbon Dioxide Control 241Exhaust Fan Control 242Fume Hood Control 243Condensate Management and Control 245Ventilation Monitoring and Control 245Filtration Monitoring and Control 246Outside Air Monitoring and Control 246DX Direct Expansion Systems

21、246Water Source Heat Pumps 247viiContents10 DDC Introduction to Hardware and Software 25010.1 Introduction, and Input and Output Points 25010.2 I/O Point Characteristics 25410.3 Control Sequences 25810.4 Software Introduction 26010.5 Specific Programming System Features and Parameters 26910.6 Operat

22、or Terminal 27811 DDC Networks and Controls Protocols 28511.1 Interoperability 28611.2 System Hardware Architecture 288Sample Controllers 29511.3 Network Standards 296Ethernet (IEEE 802.3) 298ARCNET 299RS-485 299Wireless 29911.4 BACnet 301What is a PICS? 3031 Devices Groups of Objects to Manage Acti

23、vity 3032 Objects To Represent Information 3043 Services Making and Responding to Requests 3054 Network Transporting Request and Responses 30611.5 LonWorks 308The Next Step 31012 Digital Controls Specification 31112.1 Benefits and Challenges of DDC 31212.2 Design 31612.3 Bidding and Interoperability

24、 32312.4 Monitoring 32512.5 Wiring 330Network Wiring 330Fiber Optic Cable 333Power Wiring 33312.6 Commissioning and Warranty 33412.7 Resources 336Index 339viii ContentsChapter 1Introduction to HVAC ControlSystemsContents of Chapter 1Study Objectives of Chapter 11.1 Why Do We Need Controls?1.2 A Brie

25、f History of Controls1.3 Control Loops1.4 Control Modes1.5 Gains and Loop Tuning1.6 Control Actions and Normal Position1.7 Control Range and Sequencing1.8 Controls Documentation, Maintenance, and OperationsThe Next StepBibliographyStudy Objectives of Chapter 1Chapter 1 introduces basic control conce

26、pts. It begins with a discussion ofwhy controls are required in HVAC systems and a brief history of the devel-opment of control products. Next, we introduce the concept of a control loop,the basic building block of all control systems, and the various control strate-gies and algorithms used in contr

27、ol loops. After studying this chapter, youshould understand:Why controls are necessary in HVAC systems.The difference between open and closed control loops.How two-position, floating, and modulating control loops work.Proportional control.Integral and derivative control action in modulating control

28、loops.How to tune control loops.The difference between direct acting and reverse acting.Difference between normally open and normally closed.How controlled devices may be sequenced using a single controller.1.1 Why Do We Need Controls?We need controls and control systems because, in our modern age o

29、f technol-ogy, they make our lives more convenient, comfortable, efficient, and effec-tive. A control enables equipments to operate effectively and sometimesgives the ability to change their actions as time goes on and conditions oroccupancies change. Controls can be devices used to monitor the inpu

30、ts andregulate the output of systems and equipments. You use controls every day.For example, when you shower in the morning you sense the water tempera-ture and manually modulate the hot and cold water valves to produce thedesired temperature. When you drive to work, you monitor your speed usingthe

31、speedometer and manually control the accelerator of your car to maintainthe desired speed. When you get to your office, you sense a shortage of lightso you manually switch on the overhead lighting.These are all examples of closed-loop manual controls. The term manualmeans that you (a person, rather

32、than a device) are acting as the controller;you are making the decisions about what control actions to take. The termclosed-loop means that you have feedback from the actions you have taken.In these examples, the feedback comes from your senses of touch and sight:as you open the hot water valve in y

33、our shower, you can sense the tempera-ture of the water increase; when you depress the accelerator, you can see thatyour speed is increasing by viewing the speedometer; and when you turn onthe light, you can see that the brightness in the space has increased.Your car may also be equipped with cruise

34、 control, to automatically main-tain speed on a clear road, which is an example of an automatic control. Anautomatic control is simply a device that imitates the actions you would takeduring manual control. In this case, when you press the set-button on thecruise control panel, you are telling the c

35、ontroller the speed you desire, orthe set point. The controller measures your speed and adjusts the position ofthe accelerator to attempt to maintain the cars speed at set point the desiredspeed just as you do when you manually control the speed.You may notice that your cruise control system is able

36、 to maintain yourcars speed at a given set point more precisely than you can manually. Thisis generally because you are not paying strict attention to controlling yourspeed; you must also steer, watch for traffic and perform all of the other func-tions required for safe driving. This is one reason w

37、hy we use automatic con-trols: we do not have the time or desire, or perhaps the ability, to constantlymonitor a process to maintain the desired result.Controls of heating, ventilating and air-conditioning, and refrigerating(HVAC it controlled boiler output byopening and closing the boiler door, or

38、a combustion air damper to controlthe rate of combustion. These devices were known as regulators. Other appli-cations were to control steam radiators and steam heating coils. (Most steamradiators at that time were turned on and off by hand.)Dr. Andrew Ure was probably the first person to call his re

39、gulator a thermo-stat and we still use this name 150 years later. These devices were soon used tocontrol temperatures in incubators, railway cars, theaters, and restaurants.Two other devices were developed to compete with the bimetallic strip. Thefirst was a mercury thermometer column, having a cont

40、act low in the mercuryand one or more contacts above the top of the column. Increasing temperature3Introduction to HVAC Control Systemscaused the mercury to rise and make contact with an upper electrode, therebycompleting the circuit. This extremely accurate thermostat was nonadjustable.The second d

41、evice, a mercury switch uses a drop of mercury in a small,sealed glass tube with contacts at one or both ends. The horizontal glass tubeis concave upwards, must be mounted level, and will make or break a circuitwith a slight impulse from a bellows or bimetal sensor. This slight impulse ismultiplied

42、by the mass of the moving mercury. This device (discussed inChapter 4) still is used to control countless HVAC systems.Refrigeration systems used thermostats to cycle the motor driving the com-pressor, or to open and close valves to modulate capacity. The first refrigera-tion systems controlled the

43、flow of refrigerant by hand. When smallerautomatic equipment was developed, high side floats, low side floats, andconstant pressure valves (automatic expansion valves) came into use.These early control devices were generally electric; their function was tomake or break an electric circuit that turne

44、d on a fan or pump, opened a valveor damper, etc. Some early controls (particularly burner controls on furnacesand boilers) were self-powered; meaning they drew their energy from the pro-cess itself rather than from an external source such as electricity. The need forinexpensive modulating controls

45、(controls that could regulate output over acontinuous range rather than cycling from full-on to full-off) lead to the devel-opment of pneumatic controls that use compressed air as the control powerrather than electricity.Pneumatic controls are inherently analog (modulating). With the invention ofthe

46、 electron tube, analog electronic controls were developed. These controlsnowuseanalogsolid-state(semiconductor)devicestoprovidethedesiredcontrolfunctions.Finally,withtheemergenceofpowerfulandinexpensivemicroproces-sors, digital controls were developed. Digital controls (often called direct digitalco

47、ntrols or DDC) use software programmed into circuits to effect control logic.Thesefivecontrolsystemtypesself-poweredcontrols(describedinChapter6),electric controls (Chapter 7), pneumatic controls (Chapter 8), analog electroniccontrols (Chapter 9), and digital controls (Chapter 10)are the basis of mo

48、d-ern control systems. Most control systems today use a combination of the fivesystem types and are more accurately called hybrid control systems.All of the various types of hardware used in temperature control systems(in the past, currently, and in the future) are based on the same fundamentalprinc

49、iples of control. While the technology used to implement these principlesmay change, the fundamental concepts generally remain the same. Theseprinciples are the subject of the rest of this chapter.(The historical information in this section is from the ASHRAE publication,Heat and Cold: Mastering the Great Indoors.)1.3 Control LoopsThe process of driving your car at a given speed is an example of a controlloop. You use your speedometer to measure your cars speed. If you are belowthe desired speed, you press the accelerator and observe the response. If youc