Conair MPW User's Guide download pdf (Page 24)

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OperatingPrinciples

CoolantCircuit

Thecoolantpump,externaltothechiller,circulatescoolantthroughtheprocesspipingand

thenbacktothechiller.Uponenteringthechiller,thecoolantwillpassthroughaY‐Strainer

thatfilterstheprocessfluidbeforeenteringtheevaporator.Heattransferredfromthecoolant

totherefrigerantoccursintheevaporator.Varyingtheamountofheattransferredinthe

evaporatordeterminestheloadingofthecompressor,whichmaintainsthetemperature

setpointofthecoolantdeliveredtotheprocess.A“ProcessReturn”temperaturesensorsenses

thetemperatureofthecoolantasitenterstheevaporator.

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Afterleavingtheevaporator,thecoolantpassesbyaflowswitchandthe“ProcessSupply”

temperaturesensor.Thesensorsensesthetemperatureofthecoolantdeliveredtoprocess

andcommunicatesthistemperaturetothePLCcontroller.Thissensoristhecontrolsensorfor

thePLCcontrolsystem.

RefrigerantCircuit

Theheattransferredintheevaporatorfromthecoolanttotherefrigerantchangesthestateof

therefrigerantfromaliquidtoagas.Thisrefrigerantgasthenmovesfromtheevaporatorto

thecompressor.

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Thecompressoristheheartoftherefrigerationcircuit.Cool,low‐pressuregasentersthe

compressorandhot,high‐pressuregasexitsthecompressor.Sincethecompressorisnot100%

efficient,someextraheatgainoccursastherefrigerantiscompressed.



Thehot,high‐pressuregasexitingthecompressorgoestothecondenser.Inwater‐cooled

condenserunits(EP2Wmodels),theheatistransferredfromtherefrigerantflowaroundthe

tubestothewaterthatisflowingthroughthetubes.Inair‐cooledcondenserunits(EP2A&

EP2Rmodels),theheatistransferredfromtherefrigerantinthefinnedtubestotheairthatis

flowingacrossthefinnedtubes.Astheheattransferoccurs,therefrigerantchangesfromagas

toaliquid.Thecondenserremovestheheatfromtheprocessloadandtheheatthatisadded

bythecompressor.

Afterleavingthecondenser,theliquidrefrigerantpassesthroughthefilterdryerandsight

glass.Thefilterdryerfiltersoutanyparticlesand/ormoisturefromtherefrigerant.Usethe

sightglasstomonitorthestreamofliquidrefrigerant.Theliquidrefrigerantthenpasses

throughthethermostaticexpansionvalve,whichmeterstheflowintotheevaporatorwhere

theprocessbeginsagain.

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Capacitycontrolisachievedbyredirectingsomeofthehotgasfromthecompressoroutlet

away

fromthecondenser.Thisgasismeteredthroughanelectronicallycontrolled,stepper

motordrivenHotGasBypassValve.Thehotgasisinjectedintotheevaporatorinlet,reducing

thechiller’scoolingcapacityduringlightloading.TheHotGasBypassValveisopenedbythe

PLCwhenthesupplywatertemperature

isbelowtheTemperatureSetpoint.

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Conair MPW User's Guide Page 24

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