ALLWATER SYSTEMS.docx
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ALLWATER SYSTEMS.docx
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ALLWATERSYSTEMS
ALL-WATERSYSTEMS
All-watersystemsarethosewithfan-coilunitventilatororvalance-typeroomterminalswithunconditionedventilationairsuppliedbyanopeningthroughthewallorbyinfiltration.Coolingandhumidificationareprovidedbycirculatingchilledwaterorbrinethroughafinnedcoilintheunit.Heatingisprovidedbysupplyinghotwaterthroughthesameoraseparatecoilusingtwo-three-orfour-pipewaterdistributionfromcentralequipment.Electricheatingoraseparatesteamcoilmayalsobeused.Humidificationisnotpracticalinall-watersystemsunlessaseparatepackagehumidifierisprovidedineachroom.
Thegreatestadvantageoftheall-watersystemisitsflexibilityforadaptationtomanybuildingmodulerequirements.
Afan-coilsystemappliedwithoutprovisionforpositiveventilationoronetakingventilationairthroughanapertureisoneofthelowestfirst-costcentralstationtypeperimetersystemsinusetoday.Itrequiresnoventilationairductsiscomparativelyeasytoinstallinexistingstructures,andaswithanycentralstationperimetersystemutilizingwaterinpipesinsteadofairducts,itsuseresultsinconsiderablespacesavingsthroughoutthebuilding.
All-watersystemshaveindividualroomcontrolwithquickresponsetothermostatsettingsandfreedomfromrecirculationofairfromotherconditionedspace.Thesesystemshaveremotechillingandheatingequipment.Whenfan-coilunitareusedwiththethree-orfour-pipewaterarrangementseachisitsownzonewithachoiceofheatingorcoolingatalltimesandnoseasonalchangeoverisrequired.All-watersystemscanbeinstalledinexitingbuildingswithaminimumofinterferenceintheuseoftheoccupiedspace.
All-watersystemsasusuallyinstalleddonotmeettheconditionsofthedefinitionofairconditioninginASHRAEStandard55-74,ThermalEnvironmentalConditionsforHumanOccupancy,becausetheylackhumiditycontrolandbecausethequantityofoutdoorairislimitedtotheeffectoftheexhaustfromtheroomandthesizeofthewallopening.
Thereisnopositiveventilationunlesswallopeningsareusedandtheseareaffectedbywindpressuresandstackactiononthebuilding.Specialprecautionsarerequiredateachunitwithanopeningtopreventfreezingofcoilandpotentialwaterdamagefromrain.
Seasonalchangeoverisrequiredinmostclimates.Withatow-pipesystemzoningandpipingarerequiredtoreduceoperatingdifficultiesduringintermediateseasonswhenasun-exposedzonemayneedcoolingwhileotherzonesneedheat.Whenheating,unitscannotbeusedasconvectorsinunoccupiedroomsandfansmustbekeptrunning.
Ifatwo-pipesystemhasonlyonepump.Thesamequantityofhotandcoldwateriscirculatedeventhoughtherequirementsforeachmaybedifferent.Withthree-andfour-pipesystemshotandcoldwatermaybefurnishedthroughouttheyear.
Maintenanceandserviceworkhastobedoneintheoccupiedareas;astheunitsbecomeolderthefannoisecanbecomeobjectionable.Eachunitrequiresacondensatedrainlinethatperiodicallyhastobeflushedoutandcleaned.Itisdifficulttolimitbacterialgrowthintheunit.Inextremelycoldweatheritisoftennecessarytoclosetheoutsideairdamperstopreventfreezingofcoilsreducingventilationairtothatobtainedbyinfiltration.Filtersaresmallandinefficientandrequirefrequentchangingtomaintainairvolume.
Fan-CoilUnits(UnitVentilators)
Figure9-14showsatypicalair-conditioningunitventilatorequippedwithacombinationhot-chilledwatercoilforuseinatow-pipesystem.Thistypeofunitisusuallyprovidedwithface-and-bypassdampersforcapacitycontrol.
Figure9-15illustratesatypicalair-conditioningunitventilatorwithtowseparatecoils,oneusedforheatingandtheotherforcoolingwithafour-pipesystem.Theheatingcoilmayusehotwater,steam,orelectricity.Thecoolingcoilcanbeeitherachilledwatercoiloradirectexpansionrefrigerantcoil.Heatingandcoolingcoilsaresometimescombinedinasinglecoilbyprovidingseparatetubecircuitsforeachfunction.Insuchcasestheeffectisthesameashavingtowseparatecoils.
CentralEquipment
Thetotalcoolingloaddeterminestheinstalledrefrigerationcapacityrequired.Itisgenerallylessthanthesunoftheindividualmoduleloadssincepeakdesignloadsdonotoccurinallmodulessimultaneously.Themaximumsolarheatgainvaluesusedtoselectthefan-coilunitsoccuroneachexposureatdifferenttimesofdayoryear.Innorthernlatitudesthemaximumdesignsolarloadonthesouthexposureoccursduringthefallandwintermonthswhenthesunisloweronthehorizon.Intermittentshadingofsunlitexposuresalsoinfluenceszoneloads.
Thetotalheatingloaddeterminestheinstalledheatingcapacity.Sincemaximumheatingcapacitycalculationsarebasedontheabsenceofsolarload.Totalheatingloadwillgenerallyequalthesumofindividualmoduleheatinglodes.
Whiletotalloadcalculationsmustbemadeproperlyforselectionofthecentralequipment.Itisalsonecessarytodeterminehowtheseloadswillvaryoverthefullrangofoutdoortemperaturetochecktheequipmentperformanceatpart-loadconditions.Thisloadinformationisalsovaluableindeterminingsupplywatertemperatureschedulestotheroomfan-coilunitsandwhereaircoolingortheuseofheatbalanceprinciplescanbeapplied.
9-7UNITARYANDROOMAIRCONDITIONERS
UnitaryAirConditioners
Unitaryairconditioningequipmentconsistsoffactorymatchedrefrigerantcyclecomponentsforinclusioninair-conditioningsystemsthatarefielddesignedtomeettheneedsoftheuser.
Thefollowinglistofvariationsisindicativeofvastnumberoftypesofunitaryairconditionerspresentlyavailable.
1.Arrangement:
singleorsplit
2.Heatrejection:
aircooled,evaporativecondenser,watercooled
3.Unitexterior:
decorativeforin-spaceapplication.Functionalforequipmentroomandducts,weatherproofedforoutdoors
4.Placement:
floorstanding,wallmounted,ceilingsuspended
5.Indoorair:
verticalupflow,counterflow,horizontal,90and180degreeturns,withfanorforusewithforcedairfurnace
6.Locations:
indoor—exposedwithplenumsorfurredinductwork,concealedinclosets,attics,crawlspaces,basements,garages,utilityrooms,orequipmentrooms:
wall—builtin,window,transom;outdoor—rooftop,wallmounted,oronground
7.Heat:
intendedusewithupflow,horizontal,orcounterflowforcedairfurnace,combinedwithfurnace,combinedwithelectricalheat,combinedwithhotwaterorsteamcoil
Unitaryairconditionersascontrastedtoroomairconditionersaredesignedwithfancapabilityforductwork,althoughsomeunitsmaybeappliedwithplenums.
Heatpumpsarealsoofferedinmanyofthesametypesandcapacitiesasunitaryairconditioners.
Packagedreciprocatingandcentrifugalwaterchillerscanbeconsideredasunitaryairconditionersparticularlywhenappliedwithunitary-typechilledwaterblowercoilunits.
Figure9-16depictsasinglepackageairconditionerwhilefig.9-17showsatypicalresidentialsplitsystem.Thenearlyinfinitecombinationofcoilconfigurations,evaporatortemperatures,airhandlingarrangements,refrigeratingcapacities,andothervariationsthatareavailableincentralsystemsarerarelypossiblewithunitarysystems.Consequentlyinmanyrespectshigherlevelofdesignofingenuityandperformanceisrequiredtodevelopsuperiorsystemperformanceusingunitaryequipmentthanforcentralsystems.
Theneedforzoningiswidelyrecognizedbecauseitisdesirabletogivetheoccupantsomecontroloverhisenvironmentbothduringnormaloccupancyandintoazonedsystemwitheachzoneservedbyitsownunit.Theroomconditionercarriesthisconcepttorelativelysmallrooms.
Forlargesinglespaceswherecentralsystemsworkbesttheuseofmultipleunitsisoftenanadvantagebecauseofthemovementofloadsourceswithinthelargespace,givingflexibilitytomanysmallerinterlockedandindependentsystemsinsteadoflargecentralsystem.
Recognizingthataroommaybeassmallasatelephoneboothorlargerthanasupermarket,roomwithlessthan0.5ton(1.8kw)orover25tons(88kw)coolingloadareseldomconditionedbytheirownsingleunitinmultipleunitsystems.
RoomAirConditioners
Aroomairconditionerisanencasedassemblydesignedasaunitprimarilyformountinginawindow,thoughawall,orasaconsole.Theseunitsaredesignedtoprovidecomfortthoughcoolingandtoprovidedeliveryofconditionedairtotheroomeitherlackingductsorhavingveryshortducts.Theyincludeaprimesourceofrefrigeration,dehumidification,meansforcirculatingandcleaningair,andmayalsoincludemeansforventilating,andorexhaustingandheating.
Thebasicfunctionofairconditioneristoprovidecomfortbycooling,dehumidifying,filteringorcleaning,andcirculatingtheroomair.Itmayalsoprovideventilationbyintroducingoutdoorairintotheroom,andbyexhaustingtheroomairtotheoutside.Theconditionermayalsobedesignedtoprovideheatingbyreversecycle(heatpump)operation,bysteamorhotwatercoils,orbyelectricresistanceelements.
Figure9-18showsaschematicviewofatypicalroomairconditioner.
Through-The-WallConditionerSystems
Athrough-the-wallsystemusesanair-cooledroomairconditionerdesignedformountingthroughthewallandnormallycapableofprovidingboththeheatingandcoolingfunction.Designandmanufactureparametersvarywidely.Specificationgradesrangefromappliancegradethoughheavydutycommercialgrade.Thelatteriscalledapackagedterminalairconditioner.
Thethrough-the-wallconceptincorporatesacompleteaircooledrefrige
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