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1、CHAPTER45DESIGNANDAPPLICATIONOFCONTROLSControlofHVACElements..........................................................................................................45.1ControlofSystems.........................................................................................
2、.............................45.10SpecialApplications...................................................................................................................45.16DesignConsiderationsandPrinciples.....................................................................
3、..................45.17AUTOMATICcontrolofHVACsystemsandequipmentusuallyincludescontroloftemperature,humidity,pressure,andflowrate.Automaticcontrolsequencesequipmentoperationtomeetloadrequirementsandprovidessafeoperationoftheequipment,usingpneumatic,mechanical,electrical,ande
4、lectroniccontroldevices.Table1TYPICALRESETThischaptercovers(1)thecontrolofHVACelements,(2)con-SCHEDULEtroloftypicalsystems,(3)limitcontrolforsafeoperation,and(4)OUTDOORHOTWATERthedesignofcontrolsforspecificHVACapplications.Chapter37ofTEMP.,°CSERVICE,°Cthe1997ASHRAEHandbook—F
5、undamentalscoversthefunda--2080mentalsofcontrol,typesofcontrolcomponents,andcommission-1560ingofthecontrolsystem.CONTROLOFHVACELEMENTSBoilerFig.1BoilerControlLoadaffectstherateofheatinputtoahydronicsystem.Ratecon-trolisaccomplishedbycyclingandmodulatingtheflameandbyturningbo
6、ilersonandoff.Flamecyclingandmodulationarehan-dledbytheboilercontrolpackage.Thecontroldesignerdecidesunderwhatcircumstancestoaddordropaboilerandatwhattem-peraturetocontroltheboilersupplywater.Hotwaterdistributioncontrolincludestemperaturecontrolatthehotwaterboilersorconverte
7、r,resetofheatingwatertemperature,andcontrolformultiplezones.Otherfactorsthatneedtobeconsid-eredinclude(1)minimumwaterflowthroughtheboilers,(2)pro-tectionofboilersfromtemperatureshock,and(3)coilfreezeprotection.Ifmultipleoralternateheatingsources(suchascon-denserheatrecoveryo
8、rsolarstorage)areused,thecontrolstrategyFig.2Steam-to-WaterHeatExchangerCon
