008055234X HVAC

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control systems

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FundamentalsofHVACControlSystemsThispageintentionallyleftblankFundamentalsofHVACControlSystemsThe reading text for this course was originally written by Steven T. Taylor, P.E.ItwasthenpartiallyrevisedbyRossMontgomeryP.E.beforebeingeditedandpartlyrewrittenbyRobertMcDowallP.Eng.#2009AmericanSocietyofHeating,RefrigeratingandAir-ConditioningEngineers,Inc.1791TullieCircle,NEAtlanta,GA30329www.ashrae.orgElsevierScienceisanimprintofElsevier30CorporateDrive,Suite400Burlington,MA01803,USAAllrightsreserved.ISBN978-0-08-055234-7PrintedintheUnitedStatesofAmerica.ASHRAEhascompiledthispublicationwithcare,butASHRAEhasnotinvestigated,andASHRAEexpresslydisclaimsanydutytoinvestigate,anyproduct,service,process,procedure,design, or the like that may be described herein. The appearance of any technical data or editorialmaterialinthispublicationdoesnotconstituteendorsement,warranty,orguarantybyASHRAEof any product, service, process, procedure, design, or the like. ASHRAE does not warrant that theinformation in the publication is free of errors, and ASHRAE does not necessarily agree with anystatementoropinioninthispublication.Theentireriskoftheuseofanyinformationinthispublicationisassumedbytheuser.NopartofthisbookmaybereproducedwithoutpermissioninwritingfromASHRAE,exceptbyareviewerwhomayquotebriefpassagesorreproduceillustrationsinareviewwithappropriatecredit;normayanypartofthisbookbereproduced,storedinaretrievalsystem,ortransmittedinanywayorbyanymeanselectronic,photocopying,recording,orotherwithoutpermissioninwritingfromASHRAE.LibraryofCongressCataloging-in-PublicationDataApplicationsubmittedWorking together to grow libraries in developing countrieswww.elsevier.com|www.bookaid.org|www.sabre.orgContentsForeword ix1 IntroductiontoHVACControlSystems 11.1 WhyDoWeNeedControls? 21.2 ABriefHistoryofControls 31.3 ControlLoops 41.4 ControlModes 9Two-positionControl 10FloatingControl 14ModulatingControl 16Pulse-widthModulating,andTime-proportioningControl 201.5 GainsandLoopTuning 211.6 ControlActionsandNormalPosition 241.7 ControlRange,andSequencing 271.8 ControlsDocumentation,Maintenance,andOperations 29TheNextStep 302 BasicsofElectricity 312.1 SimpleCircuitsandOhmsLaw 322.2 ACCircuits 362.3 TransformersandPowerServices 402.4 Relays 432.5 MotorsandMotorStarters 462.6 VariableSpeedDrives 522.7 RelayLogicandLadderDiagrams 55TheNextStep 613 ControlValvesandDampers 62Introduction 623.1 Two-wayControlValves 63StylesandPrinciplesofOperation 633.2 Three-wayControlValves 733.3 SelectingandSizingValves 77FlowCharacteristicSelection 82Close-offPressure 853.4 ControlDampers 88StylesandPrinciplesofOperation 883.5 SelectingandSizingDampers 91Two-positionDuty 92CapacityControlDuty 94MixingDuty 99TheNextStep 1064 SensorsandAuxiliaryDevices 1074.1 IntroductiontoTerms 108Accuracy 108Range 108Reliability 109Repeatability,Precision 109Transmitter 1094.2 TemperatureSensors 110Bimetal 110FluidExpansion 112Electrical,Self-powered 113ElectricalResistance 1144.3 HumidityandthePsychrometricChart 119IndoorAirisaMixtureofDryAirandWaterVapor 119RelativeHumidity 1204.4 MoistureSensors 130RelativeHumiditySensors 1304.5 PressureSensors 1354.6 FlowSensorsandMeters 1384.7 AuxiliaryDevices 149TheNextStep 1615 Self-andSystem-poweredControls 1625.1 PrinciplesofOperationSelf-poweredControls 1625.2 ExamplesofSelf-PoweredControls 163ThermopileControls 163HotWaterControlValve 164Self-poweredVAVDiffuser 1645.3 System-poweredControls 166System-poweredAirValves 166System-poweredWaterSystemValves 167TheNextStep 1686 ElectricControls 1696.1 Sensors 1696.2 Controllers,Two-position 1716.3 Controllers,Modulating 1736.4 ExampleApplication 1766.5 Actuators 1796.6 AuxiliaryDevices 180TheNextStep 181vi Contents7 PneumaticControls 1827.1 PrinciplesofOperation 1837.2 Sensors 1857.3 Controllers 1867.4 Actuators 1907.5 AuxiliaryDevices 1927.6 CompressedAirSupply 1987.7 ExampleApplications 200TheNextStep 2068 AnalogElectronicControls 2078.1 PrinciplesofOperation 2078.2 Sensors 2088.3 Controllers 2088.4 Actuators 2138.5 AuxiliaryDevices 2148.6 ExampleApplications 214TheNextStep 2179 ControlDiagramsandSequences 2189.1 ControlSystemsDesignCriteria 2199.2 ControlSystemsDesignProcess 2209.3 ControlDiagramsandSymbols 2209.4 ControlSequences 2229.5 ExampleApplications 224TypicalSingle-ZoneSystem 224TypicalConstantAirVolumeSystemwithFaceandBypassDampers 228TypicalConstantAirVolumeSystemwithMultipleZonesorReheat 229TypicalVariableAirVolumeSystem 229TypicalConstantAirVolumeSystem,withVariableSpeedFanforFilterLoading 239ChillerPlant,Pumps,andBoilersMonitoringandControl 241TemperatureandHumidityMonitoringandControl 242CarbonDioxideControl 243ExhaustFanControl 244FumeHoodControl 245CondensateManagementandControl 247VentilationMonitoringandControl 247FiltrationMonitoringandControl 248OutsideAirMonitoringandControl 248DXDirectExpansionSystems 248WaterSourceHeatPumps 249vii Contents10 DDCIntroductiontoHardwareandSoftware 25210.1 Introduction,andInputandOutputPoints 25210.2 I/OPointCharacteristics 25610.3 ControlSequences 26010.4 SoftwareIntroduction 26210.5 SpecificProgrammingSystemFeaturesandParameters 27010.6 OperatorTerminal 28011 DDCNetworksandControlsProtocols 28711.1 Interoperability 28811.2 SystemHardwareArchitecture 290SampleControllers 29711.3 NetworkStandards 300Ethernet(IEEE802.3) 300ARCNET 301RS-485 301Wireless 30111.4 BACnet 304WhatisaPICS? 3051. DevicesGroupsofObjectstoManageActivity 3062. ObjectsToRepresentInformation 3063. ServicesMakingandRespondingtoRequests 3084. NetworkTransportingRequestandResponses 30911.5 LonWorks 311TheNextStep 31312 DigitalControlsSpecification 31412.1 BenefitsandChallengesofDDC 31512.2 Design 31912.3 BiddingandInteroperability 32612.4 Monitoring 32812.5 Wiring 334NetworkWiring 334FiberOpticCable 336PowerWiring 33612.6 CommissioningandWarranty 33712.7 Resources 339Index 342viii ContentsForewordWelcome tothe ASHRAELearningInstitutes Fundamentals of HVAC&ReLearningSystemSeries.This is a Course Reader to accompany the Fundamentals of HVAC ControlSystemsonlinemodules.Tohelpyoulearnatyourconvenience,thisCourseReaderisalsoavailabletoyouasaneBookwiththeonlineCourseModules.TheCourseReaderwillprovideyouwithbackgroundinformationtohelpyou develop in-depth knowledge of the Fundamentals of HVAC Control Sys-tems, toimproveyourskillsinHVAC&Randtoearnthe47PDHs/4.7CEUsawardedfor successful completionof theFundamentals of HVACControlSystemsLearningcourse.Welookforwardtoworkingwithyouandhelpingyouachievemaximumresultsfromthiscourse. Chapter1IntroductiontoHVACControlSystemsContentsofChapter1StudyObjectivesofChapter11.1 WhyDoWeNeedControls?1.2 ABriefHistoryofControls1.3 ControlLoops1.4 ControlModes1.5 GainsandLoopTuning1.6 ControlActionsandNormalPosition1.7 ControlRange,andSequencing1.8 ControlsDocumentation,Maintenance,andOperationsTheNextStepBibliographyStudyObjectivesofChapter1Chapter 1introducesbasiccontrol concepts. It beginswithadiscussionofwhycontrolsarerequiredinHVACsystemsandabriefhistoryofthedevel-opment of control products. Next, we introduce the concept of a control loop,the basic building block of all control systems, and the various controlstrategiesandalgorithmsusedincontrol loops. Afterstudyingthischapter,youshouldunderstand:WhycontrolsarenecessaryinHVACsystems.Thedifferencebetweenopenandclosedcontrolloops.Howtwo-position,floating,andmodulatingcontrolloopswork.Proportionalcontrol.Integralandderivativecontrolactioninmodulatingcontrolloops.Howtotunecontrolloops.Thedifferencebetweendirectactingandreverseacting.Differencebetweennormallyopenandnormallyclosed.Howcontrolleddevicesmaybesequencedusingasinglecontroller.1.1WhyDoWeNeedControls?Weneedcontrolsandcontrol systemsbecause, inourmodernageof tech-nology, they make our lives more convenient, comfortable, efficient, andeffective. Acontrol enablesequipment tooperateeffectivelyandsometimesgivestheabilitytochangetheir actionsastimegoesonandconditionsoroccupancieschange. Controlscanbedevicesusedtomonitortheinputsandregulatetheoutput ofsystemsandequipment. Youusecontrolseveryday.Forexample, when youshowerin the morning you sense the watertempera-tureandmanuallymodulatethehot andcoldwatervalvestoproducethedesired temperature. When you drive to work, you monitor your speed usingthe speedometer and manually control the accelerator of your car to maintainthedesiredspeed.Whenyougettoyouroffice,yousenseashortageoflightsoyoumanuallyswitchontheoverheadlighting.Theseareall examples of closed-loopmanual controls. Thetermmanualmeansthat you(aperson, ratherthanadevice)areactingasthecontroller;youaremakingthedecisionsabout what control actionstotake. Thetermclosed-loopmeansthatyouhavefeedbackfromtheactionsyouhavetaken.Intheseexamples, thefeedbackcomesfromyoursensesoftouchandsight: asyouopenthehotwatervalveinyourshower,youcansensethetemperatureof the water increase; when you depress the accelerator, you can see that yourspeedisincreasingbyviewingthespeedometer; andwhenyouturnonthelight, you can see that the brightness in the space has increased.Yourcarmayalsobeequippedwithcruisecontrol,toautomaticallymain-tainspeedona clear road, whichis anexample of anautomatic control.Anautomaticcontrol issimplyadevicethatimitatestheactionsyouwouldtakeduringmanual control. Inthiscase, whenyoupresstheset-buttononthecruisecontrol panel, youaretellingthecontrollerthespeedyoudesire,orthesetpoint. Thecontrollermeasuresyourspeedandadjuststhepositionof the accelerator toattempt tomaintainthecars speedat setpoint thedesiredspeedjustasyoudowhenyoumanuallycontrolthespeed.Youmaynoticethat your cruisecontrol systemisabletomaintainyourcarsspeedat agivensetpoint morepreciselythanyoucanmanually. Thisisgenerallybecauseyouarenot payingstrict attentiontocontrollingyourspeed; youmust alsosteer, watchfor traffic andperformall of theotherfunctionsrequiredforsafedriving.Thisisonereasonwhyweuseautomaticcontrols: we do not have the time or desire, or perhaps the ability, toconstantlymonitoraprocesstomaintainthedesiredresult.Controls of heating, ventilating and air-conditioning