CO2 Transcritical Systems Training Manual 042718€¦ · Transcritical CO 2 Training Manual I Pg. 4 Introduction Transcritical CO 2 refrigeration systems are gaining acceptance in

CO2 Transcritical Systems Training ManualRevision 1, April 2018

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Table of Contents

Introduction................................................................................................................................................4

CO2asaRefrigerant....................................................................................................................................5

-GeneralCO2Information.......................................................................................................................8

-EnvironmentalBenefits.....................................................................................................................8

-SafetyConsiderations..........................................................................................................................10

-Asphyxiation....................................................................................................................................10

-Pressure...........................................................................................................................................11

-DryIce..............................................................................................................................................13

-Properties............................................................................................................................................15

-PHDiagram......................................................................................................................................15

-Pressure/Temperature....................................................................................................................16

-OtherProperties..............................................................................................................................16

SystemLayout...........................................................................................................................................18

-TranscriticalBoosterSystems..............................................................................................................18

-SystemSchematicCorrelationwithPHDiagram.................................................................................20

HussmannPuritySystem-PrimarySystemComponents........................................................................23

-FlashTank............................................................................................................................................24

-LowTemperatureLiquid/SuctionHeatExchanger(Optional).............................................................24

-Liquid/SuctionHeatExchangerBypassSystem(WhereApplicable)...................................................24

-ElectronicExpansionValves................................................................................................................24

-LowTemperatureCompressors..........................................................................................................25

-Evaporators.........................................................................................................................................25

-HotGasDefrostSystem.......................................................................................................................25

-FlashGasBypassValve........................................................................................................................25

-IntermediateHeatExchangers............................................................................................................25

-MediumTemperatureCompressors...................................................................................................26

-HeatReclaim........................................................................................................................................26

-HeatRejection.....................................................................................................................................26

-ThrottlingValve...................................................................................................................................26

-OilManagementSystems....................................................................................................................26

-Controls...............................................................................................................................................26

-EmergencyBack-UpSystems...............................................................................................................27

-ParallelCompression...........................................................................................................................27

InstallationGuidelines..............................................................................................................................28

-PressureRatings...................................................................................................................................28

-PipingMaterials....................................................................................................................................30

-Brazing..................................................................................................................................................31

-PipingPractices....................................................................................................................................31

-Supports...............................................................................................................................................32

-Insulation..............................................................................................................................................32

-ReliefValves.........................................................................................................................................33

EvacuationandCharging..........................................................................................................................34

-LeakTesting..........................................................................................................................................34

-PressureTesting...................................................................................................................................34

-Evacuation/Charging............................................................................................................................34

-OilCharging..........................................................................................................................................35

StartupandMaintenance.........................................................................................................................36

-StartupSequence................................................................................................................................36

-AfterStartup........................................................................................................................................37

-OilChanges..........................................................................................................................................37

AppendixA-HotGasDefrost...................................................................................................................39

-Introduction.........................................................................................................................................40

-Schematic............................................................................................................................................41

-HotGasDefrost-AdditionalConsiderations.......................................................................................41

Note:Thisdocumentispresentedfortrainingpurposesonlyandissubjecttochangewithoutnotice.Foradditionaltechnicalsupport,pleasecontacttheHussmannTechnicalSupportCenter:HussmannTechnicalSupportLine:1-800-592-2060.

TranscriticalCO2TrainingManualIPg.4

Introduction

TranscriticalCO2refrigerationsystemsaregainingacceptanceinthesupermarketrefrigerationindustry.NationalandinternationalpoliciesthatoriginallytargetedthereductionofCFCsarebeingexpandedtoincludeHCFCsandHFCs.TechnologyadvancementsinCO2systemsaremakingthesesystemsmoreeconomicallyviable,intermsofbothequipmentandinstallationcostbutalsoenergyandoperatingcosts.TheintentofthisdocumentistoserveasatrainingmanualtosupportHussmann’sCO2transcriticalboostersystemtraining.Thistrainingwilldescribeaspectsofthedesign,installation,andoperationofthesesystems.Thecurrentcontextforthistypeofsystemisprimarilysupermarketrefrigeration.

CO2asarefrigerantwillbecomparedtoHCFCssuchasR-22,andHFCssuchasR-404aandR407a,forthepurposesofthismanual.OtherHFOblendssuchasR448aandR449awillalsobecompared.Thecontenthereinispresentedwiththeassumptionthatusershaveknowledgeofhowtheserefrigerantsoperateindirectexpansionrefrigerationsystems.


CO2 as a Refrigerant

CarbonDioxide,orCO2,isanaturallyoccurringcompoundinEarth’satmosphere.Itisthefourthmostcommonatmosphericcompound,behindnitrogen,oxygen,andargon.Carbondioxideisanintegralpartofthelifecycleofplantandanimals,astheprimaryproductofrespirationinanimalsandhumans,andtheprimarycarbonsourceforplantsviaphotosynthesis.

Inrecentdecades,carbondioxidehasbeenidentifiedasthemostsignificantgreenhousegasinEarth’satmosphere.Itiscurrentlyusedasthecomparativeunitofmeasurewhendiscussingtheglobalwarmingimpactsofvariousactivities,leadingtotheterm“carbonfootprint.”

CO2asarefrigeranthasemergedasoneofthefrontrunnerstobetherefrigerantofthefuture.Ithastheadvantagesofbeingenvironmentallyfriendly,hasgoodheattransferpropertieswithahighlatentheatofvaporization.CO2isalsonon-flammableandnon-toxic.TheprimarydisadvantageofCO2asarefrigerantisrelativelyhighoperatingpressures.Eachoftheseaspectswillbeexplainedaspartofthistraining.

Atranscriticalsystemisdefinedasasystemthatoperatesabovethecriticalpoint.ThefollowingchartshowsthePHdiagramofR-22,indicatingliquid,saturatedmixture,andgaseousstates.Thetopofthesaturated“dome”isthecriticalpoint.Abovethispoint,therefrigerantisnotconsideredliquidorgas,butanundefinedfluid.


CO2 as a Refrigerant continued

R22 P/H Diagram

*DiagramcreatedusingREFPROP–NISTReferenceFluidProperties

Ascanbeseen,thecriticalpointofR-22ismorethan200°F,placingitwellabovetheoperatingconditionsoftypicalrefrigerationsystems.ThiscanbecontrastedwiththeCO2PHdiagram,withacriticalpointof88°F.Thistemperatureisoftenexceededwhenambientairisusedasthecondensingheatsink.


CO2 as a Refrigerant continued

CO2 P/H Diagram



General CO2 Information

Environmental Benefits RegulationintheUnitedStatesregardingrefrigerantshasbeencenteredontwofactors,ozonedepletionpotential(ODP)andglobalwarmingpotential(GWP).ODP–OzoneDepletionPotentialODPisameasureofthepotentialofasubstancetoharmtheozonelayerifreleasedintotheatmosphere.ODPisaunitlessnumberrelativetoareferencevalue,usingR-11asthereferenceof1.0.SubstancesthathaveanODPofzeroareconsiderednottobeharmfultotheozonelayer.

GWP–GlobalWarmingPotentialGWPmeasuresthepotentialofasubstancetocontributetoglobalwarming.GWPquantifiesasubstanceinunitsofequivalentpoundsofCO2.Forinstance,R-404ahasaGWPof3940,meaningthatthereleaseofonepoundofR-404ahasthesameglobalwarmingeffectasthereleaseof3,940poundsofCO2.


General CO2 Information continued

ThetablebelowshowstheODPandGWPofsomecommonrefrigerants.Alsoshownarethesafetyclassifications,perASHRAE34.

Refrigerant CommonName ODP GWPSafety

ClassificationR-11 1 4660 A1R-12 0.73 10800 A1R-22 0.034 1760 A1R-32 methylenefluoride 0 677 A2

R-134a 0 1300 A1R-290 propane 0 5 A3R-404A 0 3940 A1R-407A 0 1920 A1R-407C 0 1620 A1R-407F 0 1824* A1R-408A 0.02 3260 A1

R-410A 0 1920 A1R448a 0 1273* A1R449a 0 1397† A1R-507A 0 3990 A1R-717 ammonia 0 <1 B2

R-744 carbondioxide 0 1 A1Source:ASHRAEFundamentals2017,page29.5

*Source:HoneywellProductLiterature†Source:LindeProductLiterature

TheUnitedStatessignedtheMontrealProtocolin1987,committingtoeliminatetheuseofozonedepletingsubstances.AllmembersoftheUnitedNationseventuallysignedthetreaty.ThefirstphaseofthistreatytargetedCFCs,suchasR-12.In1992,thetreatyexpandedtophaseoutHCFCs,suchasR-22.Themostrecentamendment,knownastheKigaliAmendmentin2016,addedphasedownofHFCs.

Ironically,carbondioxideasarefrigeranthasanextremelylowcarbonfootprint,comparedtoallcommonsyntheticrefrigerants.TheabsenceofODPandextremelylowGWPmakeCO2attractiveasarefrigerantfromanenvironmentalandregulatoryperspective,becauseitisalreadysignificantlybelowcurrentlegallimits.


Safety Considerations

ThephysicalpropertiesofCO2presentauniquesetofconsiderationstoensuresafety.CO2isclassifiedasanA1refrigerantbyASHRAEStandard34andtheInternationalMechanicalCode,meaningitisnon-toxicandnon-flammable.However,alargeenoughleakinaconfinedspacecandisplaceavailableoxygenforbreathing.Attypicalcommercialrefrigerationtemperatures,CO2operatesatahigherpressurethansyntheticrefrigerants.Whenreleasedatthesepressurestotheatmosphere,CO2canchangephasetosolidform,causingrestrictionsintheflowthatcanleadtoabuildupinpressure.

Asphyxiation AsanA1refrigerant,CO2isconsideredtohavelowtoxicityandlowflammability.TheconcernremainsthatalargeleakofCO2candisplaceexistingairinaspace,reducingtheoxygenlevels.Iftheoxygenlevelsarereducedconsiderably,thiscanleadtohealthhazardsuptoandincludingasphyxiation/death.Averageoutdoorairconsistsofaround400partspermillionofCO2,or0.04%.TheOccupationalSafetyandHealthAdministration(OSHA)hassetthepermissibleexposurelimitof5000PPM(0.5%)for8hoursperday(comparetomostHFCsat1000PPMallowable,CO2islesshazardous).Thetablebelowlistssomeadditionalconcentrationlevelsandtheeffectsonthehumanbody.

CO2Concentration Effects1%(1,000PPM) Breathingrateincreasesslightly.2%(2,000PPM) Breathingrateincreasesto50%abovenormallevel.Prolongedexposurecan

causeheadaches,tiredness.3%(3,000PPM) Breathingincreasestotwicethenormalrateandbecomeslabored.Weak

narcoticeffect.Impairedhearing,headache,increasedbloodpressureandpulserate.

4-5%(4,000-5,000PPM)

Breathingincreasestoapproximatelyfourtimesnormalrate,symptomsofintoxicationbecomeevident,andslightchokingmayoccur.

5-10%(5,000–10,000PPM)

Characteristicsharpodornoticeable.Verylaboredbreathing,visualimpairment,headache,andringingintheears.Judgmentmaybeimpaired,followedwithinminutesbylossofconsciousness.

10-100%(>10,000PPM)

Unconsciousnessoccursmorerapidlyabove10%level.Prolongedexposuretohighconcentrationsmayeventuallyresultindeathfromasphyxiation.

CO2atambientpressureisheavierthanair,soleakdetectionsystemsshouldbeplacedlow,typically18”abovethefloororasdictatedbylocalrequirements.


Safety Considerations continued

Pressure CO2asarefrigerantoperatesathigherpressuresthantypicalHCFCsorHFCs,duetotheinherentthermodynamicpropertiesofthesubstance.Thetablebelowshowscomparablepressuresforsomecommonrefrigerantsatthreedifferentsaturatedoperatingconditions.

SystemOperatingPoint R-22 R-404a R-407a R-744(CO2)LowTemperatureEvaporation(-25°F) 7.4 12.9 -2.7 181MediumTemperatureEvaporation(+20°F) 43.1 55.8 34 407.2CondensingPressure(86°F) 158.2 191.4 165.6 1031.5*Allpressureslistedinpsig

HFCdirectexpansion(DX)refrigerationsystemsareoutfittedwithasinglepressurereliefdevicelocatedatthereceiver.Thispressurereliefdeviceisratedforpressuresaround400psig,dependingontherefrigerantused.Additionalmechanicalsafetiesandcontrolsetpointsshutthesystemdownaround350psigdischargepressuretopreventanyrefrigerantfromdischargingthroughthepressurereliefsafetyvalve.Theentirepipingsystemisratedforworkingconditionsabovethesafetyreliefpressure,sonosecondaryreliefdevicesarenecessary.Iftherefrigerationsystemshutsdownduetopoweroutageorservicing,theinternalpressuresdonotexceedtheratedpressure.

ThehighsaturatedpressureofCO2atsummertimeambientconditionsexceedsthepressureratingoftypeKcopperpiping,alongwithmoststandardDXrefrigerationvalves.Thisrequiresthe“highside”oftheCO2systemtobeconstructedusinghigherpressureratedmaterialsandinstallationpractices,atahighercost.Toreduceoverallsysteminstalledcost,the“lowside”portionsofaCO2systemaredesignedfortheloweroperatingpressures,allowingcoppertobeusedforthelowsidepiping.Whenthesystemisoperatingnormally,pressuresaremaintainedbelowtheratedpressureofthesystem.



NOTE:NEVERALLOWLIQUIDCO2TOBECOMETRAPPEDINTHESYSTEMWITHOUTMEANSFORPRESSURERELIEF,THISCANBEEXTREMELYDANGEROUS!CO2systempressurebecomesasafetyconcernwhenliquidbecomestrappedinaportionofthesystemthatisnotratedforthefullpressureathighertemperature.Whereveramixtureofliquidandgasexist,thepressureandtemperaturearedirectlyrelated.ThetablebelowshowstheP-TchartforCO2,inincrementsof5°F.

CO2SaturationTableTemperature Pressure

°F psig-20 200-15 221-10 243-5 2660 2915 31810 34615 37620 40725 44130 47635 51340 55345 59450 63855 68460 73365 78470 83875 89580 95585 101887.8 1055

Note:87.8°FisthecriticaltemperatureofCO2,nosaturatedstateexistsabovethispoint



Asthetemperatureofasaturatedmixturerises,pressurewillriseuntilitreachesthesaturationpressureinthetableabove.Iftherefrigerantpressureexceedstheratingofthepiping,valves,orothercomponentsofthesystem,thiscanleadtoleaksandpossiblyburstingofsystemcomponents.

Tominimizetheriskofpressurebuildupinthesystem,measuresmustbetakeninsystemdesigntoensurethatpressurecannotbuildupinanyportionofthesystem.Allcomponents,valves,piping,fittings,andjoiningmethodsmustbeverifiedtoensurepressureratingsabovethemaximumanticipatedsystempressures.Pressurereliefdevicesmustbelocatedappropriatelytoallowthesystemtoventsafelyintheeventofasystemshutdownorothereventthatcausespressuresabovesystemratings.Allpointswithinthesystemmustbeallowedtoventbacktothepressurereliefvalveswithoutrestriction.Checkvalvesaretypicallyutilizedtoallowportionsofthesystemtoventbacktoreceivers,wherepressurereliefvalvesarelocated.Anyportionofthesystemthatcannotventbacktothereceivermusthaveitsownpressurereliefvalve.

Dry Ice PressurereliefdevicesontraditionalDXrefrigerationsystemsarelocateddirectlyontheoutletofthereceiver,andthenpipedoutdoorsforsafedischarge.ThispracticewouldbehazardousifappliedtoaCO2system,duetotheformationofdryice.

DryiceissimplyCO2insolidform.ThePHdiagramofCO2isshownbelow,includingtheregionwherethesolidstatecanexist.




Inarefrigerationsystem,therearetwocommonconditionswherethismayoccur.Thefirstandpotentiallydangerouslocationisatapressurereliefvalve.Whenapressurereliefvalveisopen,therefrigerantisundergoingarapiddropinpressurefromsystempressuretoatmosphericpressure.IfliquidCO2isbeingreleased,thePHdiagramshowsthatadropbelowthetriplepointpressureof75.1psia(60.4psig)willresultinasolidandvapormixture.Forthisreason,pressurereliefvalvesshouldnothaveanypipinginstalleddownstreamofthevalve.Ifthepressuredrophappensinsidethepipe,dryicewillform,blockingflowandpreventingpressurefrombeingreleased.

Thesecondconditionwheredryicemayformiswhenchargingthesystem.Ifsystemvacuumisbrokenwithliquid,dryicecanforminsidethesystem,againrestrictingflow.Thisconditionislessdangerousbecauseitdoesnotcausepressurebuildupbeyondsystemratings,butshouldstillbeavoided.


Properties

ThepropertiesofCO2havebenefitsaswellaschallengeswhencomparedtocommonsyntheticrefrigerants.Someofthesepropertieshavebeendescribedinprevioussectionsastheypertaintosafetyandenvironmentalconsiderations.ThefollowingsectionswilldescribekeypropertiesofCO2astheypertaintotheoperationofarefrigerationsystem.

PH Diagram ThepressureenthalpydiagramforCO2isshownbelow.


SeveralcharacteristicscanbereadilyseenonthePHdiagram.

1. Saturatedregion–ThegeneralshapeoftheCO2PHdiagramissimilartootherrefrigerants;onlythespecificvaluesaredifferent.

2. Criticalpoint–thecriticalpointofCO2is1070psia(1055.3psig)and87.8°F.Thisishighestpressureandtemperaturewhereliquidandgascanexistsimultaneously.Theregionabovethispointisconsideredsupercritical,belowthispointissubcritical.


Properties continued

3. Flatconstanttemperaturelinesinthesaturatedregion–CO2isapuresubstance,soitdoesnothaveatemperatureglidebetweenthesaturatedliquidandsaturatedvaporlines.Thismeansevaporatortemperatureswillremainconstantthroughouttheevaporatorcoil,allowingeasymeasurementofsuperheat.

4. Solid/Vaporregion–belowthetriplepointtemperatureof-69.8°F,CO2existsasamixtureofsolidandgas.Notethatthetriplepointpressureis75psi,meaningthatifaliquidorsaturatedmixtureisreducedtothispressure,itwillchangephasetoasolid/vapormixture.Thetriplepointofcommonsyntheticrefrigerantsisoutsideofthefeasiblerangefortemperatureandpressure,andisnotshownonmostP/Hdiagrams.

Pressure/Temperature Aswithotherpuresubstances,CO2hasadirectpressure/temperaturerelationshipinsaturatedcondition(mixtureofliquidandgas).

SystemOperatingPoint R-22 R-404a† R-744(CO2)LowTemperatureEvaporation(-25°F) 7.4 12.9 181MediumTemperatureEvaporation(+20°F) 43.1 55.8 407.2CondensingPressure(86°F) 158.2 191.4 1031.5

*Allpressureslistedinpsig †R-404aisablend,butwithnegligibleglide

Attypicallowtemperaturesuctiontemperatures,CO2operatesaround180psig.Atmediumtemperaturesuctiontemperatures,thepressureisaround400psig.UnlikesomerefrigerantblendssuchasR-407a,CO2doesnothaveatemperatureglide,meaningthedewpointtemperatureandbubblepointtemperatureareequalatagivenpressure.

Abovethecriticalpoint,pressureandtemperaturedonothaveadirectrelationship.

Other Properties CO2iscommerciallyavailableatseveraldifferentpuritylevels.Thecommonnamesandpercentpurityarelistedbelow.HussmannrecommendsusingCO2withapurityequaltoorgreaterthanBoneDryPurity.

Grade PurityIndustrialGrade 99.5%BoneDry(HussmannRecommended) 99.8%AnaerobicGrade 99.9%Coleman(Instrument)Grade 99.99%ResearchGrade 99.999%Ultra-PureGrade 99.9999%

*MedicalgradeCO2shouldnotbeused,duetotheoutletpressureregulatorstypicallypresentontanks


Properties continued

TheuseofBone-Drygradeensuresproperoperationoftheequipmentandispureenoughtopreventaccumulationofnon-condensablegasesinthesystem.MixingofhigherpuritygradesofCO2isacceptable.LowergradesofCO2willbelessexpensive,butarenotrecommendedforuseinHussmannPuritysystems.Thesecontainhigherlevelsofcontaminantsandwater,andmaydecreasesystemperformance.HigherlevelsofmoisturemayreactwiththeCO2andformcarboxylicacidthatcandegradecomponentintegrity.Hussmannrecommends,dependingonlocationandavailabilityofCO2,thatenoughrefrigerantchargebekeptonsitetofilltheentiresystem.

OneofthebenefitsofCO2comparedtosyntheticsisahighvapordensity.R-22hasadensity0.43lb/ft3leavinga-25°Fevaporator.CO2inthissameconditionhasadensityof2.2lb/ft3,roughly5timesmoredense.Inpractice,thistranslatestosmallerpipesizes,becausethesamemassflowcanoccuratamuchlowervolumetricflowrateandassociatedvelocitythanmostsyntheticrefrigerants.

15MBH@-20°F R-404a CO2

1-1/8”Suction ½”Liquid 5/8”Suction 3/8”Liquid

15MBH@+20°F R-404a CO2

7/8”Suction ½”Liquid 1/2”Suction 3/8”Liquid


System Layout

Transcritical Booster Systems CO2hasfounduseinthesupermarketindustryinawidevarietyofsystemlayouts.EarlyadoptionintheUnitedStateswasprimarilyasalowstagefluid,withaprimaryrefrigerantprovidinghighsidecooling.Thisallowedoperatingpressurestoremainlowwithgoodefficiency.Thiswasappliedbothasapumpedsystemandasacascadedirectexpansionsystem.Bothsystemtypeshaveprosandcons,andcanbereferencedinmoredetailinotherdocumentation.

TranscriticalCO2systemoperatewithoutanyotherrefrigerant,rejectingheatremovedfromrefrigeratedcasesandwalk-inboxesdirectlytowaterorambientair.AbasicschematicofaCO2transcriticalsystemwithflashgasbypassisshownbelow.


System Layout continued

Thesystemisdividedintotwostages,lowandhigh.Thelowstagebeginsattheoutletofthehighpressureexpansion(throttling)valve.Here,amixtureofliquidandgasispipedintotheliquid/vaporseparator.Fromthebottomoftheseparator,liquidCO2at20-30°Fisfedtothelowtemperatureevaporatorsthroughanexpansionvalve.TheCO2isfullyevaporatedandreturnedtothelowstagecompressorsasavapor.Lowstagecompressorsdischargeintotheinletofthehighstagecompressors.Mediumtemperatureevaporatorsarefedwiththesameliquidasthelowtemperatureevaporators.Vaporfrommediumtemperatureevaporatorsispipeddirectlytothesuctioninletofthehighstageevaporators.Athirdrefrigerantstreamknownasflashgasisalsopipeddirectlyfromthetopoftheliquid/vaporseparatorthroughaflashgasbypassvalvetothesuctionsideofthehighstagecompressors.

Highstagecompressorstakelowstagedischarge,mediumtemperaturevapor,andflashgasandcompressthemuptoapressuresufficienttorejecttheheatfromthesysteminthegascooler/condenser.Thegascoolerisnamedassuchbecausetherefrigerantisnottechnicallycondensingifitisoperatingintranscriticalmode.Atpressuresabovethecriticalpointknownasthesupercriticalregion,therefrigerantisconsideredanundefinedfluid,andcannotbecalledliquidorvapor.Dependingonambientconditionsorthetemperatureoftheheatsink,transcriticalsystemscanoperateeithertranscriticallyorsubcritically.Thisoperationiscontrolledprimarilybythethrottlingvalve.Theseoperatingmodeswillbedescribedinmoredetailinthehighstagesectionbelow.



System Schematic Correlation with PH Diagram Thediagrambelowshowsthesamegenericsystemschematic,withstatepointsidentifiedwithnumbers.



ThisschematiccanbecorrelatedwiththePHdiagramasshownbelow.


1. Enteringtheliquid/vaporseparatora. Therefrigeranthasleftthethrottlingvalveandisnowaliquid/vapormixtureatan

intermediatepressure,normallyaround480psi.Dependingonthegascoolerpressureandtemperature,thismixturewillhaveaqualityaround0.3,meaningitis70%liquid,30%vapor(bymass).Themixtureseparatesintoliquidandvaporintheseparatorduetothedifferenceindensityofthetwostates.

2. Leavingtheliquid/vaporseparatorfromthebottoma. Locatedatthebottomofthevessel,therefrigerantleavesthevesselasasaturated

liquid,typicallyaround30°Fand480psig.3. Enteringmediumtemperatureevaporators

a. Liquidrefrigeranttravelsthroughanexpansionvalveandleavesatevaporatorpressure.Asmallamountofexpansionhappensinthevalveandtherefrigerantentersasanearlysaturatedliquid,at20°Fand410psig.



4. Leavingmediumtemperatureevaporatorsa. Refrigeranthasboiledcompletelyandhasasmallamountofsuperheatat410psig.

5. Enteringlowtemperatureevaporatorsa. Saturatedliquidfromtheseparatorhaspassedthroughthelowtemperatureexpansion

valveandisnowatlowtemperatureevaporatorpressure,typicallyaround-20°Fand200psig.

6. Leavinglowtemperatureevaporatorsa. Therefrigeranthasboiledcompletelyandhasasmallamountofsuperheatat200psig.

Thisisalsothelowtemperaturecompressorsuction.7. Flashgasbypassvalve

a. Flashgashaspassedthroughtheliquid/vaporseparatorasasaturatedvapor,ataround480psia.Theflashgasbypassvalvemetersthisflowtocontrolliquid/vaporseparatorpressureandhighstagesuctionsuperheat.

8. Lowtemperaturecompressordischargea. Lowtemperaturecompressordischarge-Refrigeranthasbeencompressedtoslightly

abovethehighstagesuctionpressure,around410psi.Italsohassignificantsuperheat,leavingataround200°F.

b. Lowtemperature9. Highstagecompressorsuction

a. Thehighstagecompressorsuctionheaderistheconvergencepointofthreeflows.i. Lowtemperaturecompressoroutletii. Mediumtemperatureevaporatoroutletiii. Flashgasbypassvalveoutlet

10. Highstagecompressordischargea. Therefrigeranthasbeencompressedandisnowatthehighesttemperatureand

pressureinthesystem.Dependingonambientconditions,thistemperaturemayreach250–300degreesFand1350-1500psi.Inthisexample,thisisalsotheinletconditionofthegascooler.Theconditionatthisstatepointcanvarywithfluctuationsinloadortemperatureoftheheatsink.Forair-cooledsystems,lowambientconditionsoftenallowthesystemtooperatesubcritically,minimizingthepressurerequiredandassociatedenergyconsumption.Primarilythethrottlingvalve,alongwithgascoolercapacitymodulation,controlsthepressureatthispoint.

11. Gascooler/condenseroutleta. Heathasbeenremovedfromtherefrigerantinthegascooler.Intranscriticalmode,the

refrigerantatthispointisanundefinedfluid,notliquidorgas.Insubcriticalmode,therefrigerantatthispointisaliquid.

12. Throttlingvalveoutleta. Refrigerantfromthegascoolerhasbeenreducedinpressuretotheliquid/vapor

separatorpressure.Intranscriticalmode,therefrigeranthereisamixtureofliquidandgas.Insubcriticalmode,therefrigerantis100%liquid.


Hussmann Purity System - Primary System Components

ThefollowingsectionswilldescribeoperationalanddesignaspectsofthekeycomponentsoftheHussmannPuritySystem.Theschematicofthissystemisshownbelow.


Hussmann Purity System continued

Ascanbeseen,therearesomevariationsfromtheexampleschematicshownintheprevioussection.First,thereisaliquid/suctionheatexchangerbetweentheliquidfeedtothelowandmediumtemperatureevaporatorcoilsandthelowtemperaturesuctiongas.Thepurposeofthiscomponentistoensurecompletelysaturatedandpossiblysubcooledliquidisfedtotheelectronicexpansionvalves.Italsoservedtoensureadequatesuperheatbacktothelowtemperaturecompressors,preventingliquidfloodback.Thisheatexchangerisequippedwithseriesofvalvestoallowvaporflowtobypasstheheatexchangerforsuperheatcontrol.Second,aheatexchangersisusedtowarmthevaporenteringthehighstagecompressors,ensuringadequatesuperheat.Thisheatexchangerhasabypassvalvetocontrolthissuperheat.Finally,nodesuperheaterisusedonthelowtemperaturecompressors.Notshownontheschematicistheliquidinjectionsystem,whichallowsomissionofthisdesuperheater.

Flash Tank Theflashtankisalsoknownastheliquid/vaporseparator.Thisvesselservesseveralpurposes.Itprovidesalocationwithlowvelocitytoallowtimeforthefluidleavingthehighpressureexpansionvalvetoseparateintoconstituentliquidandvapor.Itallowsthevaportobypassthemajorityofthelowsideofthesystemandreenterthehighstagecompressors.

Thepressureoftheflashtankiscontrolledbytheflashgasbypassvalve.Thisvalveensuresproperflowthroughthemediumtemperatureevaporators.

Flashtanksaresizedtoallowanappropriateinterfaceareaforproperseparationofliquidandvapor,aswellasvolumetoallowformassfluctuationsintheremainderofthesystem.

Low Temperature Liquid/Suction Heat Exchanger (Optional) Thelowtemperatureliquid/suctionheatexchangertransfersheatfromtheliquidtothevapor.Thisservestwofunctions.Theprimaryfunctionistoprovideadditionalsuperheattothevaporleavingthelowtemperatureevaporators,ensuringnoliquidfloodbackoccurstothecompressors.Italsocoolstheliquidbelowthesaturatedcondition,ensuring100%liquidisprovidedtotheexpansionvalves.Thisalsoaidsinoilflowtothecompressors.Thisunitissizedtoprovideadequateheatexchangewithminimalpressuredropespeciallyonthevaporside.

Liquid/Suction Heat Exchanger Bypass System (Where Applicable) HussmannPurityracksutilizeaseriesofmodulatingvalvestoallowsuctiongastobypassthelowtemperatureliquid/suctionheatexchanger.Thesevalvescontrolbasedonreturngastemperature,ensuringtheappropriateamountofsuperheatenteringthelowtemperaturecompressors.Thissystemtargetsaminimumof36°Fcompressorsuperheat.Thisalsoaidsinoilflowtothecompressors.

Electronic Expansion Valves CO2systemsutilizeelectronicexpansionvalves(EEVs)insteadoftraditionalthermostaticexpansionvalves(TXVs).Individualcasecontrollersprovidecontrolofthesevalves.EEVsarenecessarywithCO2duetoimprovedresponsetimesandabilitytobeadjustedbythecontroller.Thesevalvesaretypicallysuppliedfactorypipedinrefrigeratedcases.Walk-inevaporatorsmaybefactoryorfieldpiped.



Low Temperature Compressors LowtemperaturecompressorsoperateverysimilarlytotraditionalDXHFCcompressors.Suctiongasiscompressedfromlowtemperatureevaporatorpressure,typicallyaround200psi,uptotheinletpressureofthemediumtemperaturecompressors,typicallyaround400psi.Aswithtraditionalsystems,compressorsarecycledtomaintainsuctionpressure.Thesecompressorshaveliquidinjection,tomitigatehighdischargetemperatures.

Evaporators EvaporatorsforCO2systemsmustbedesignedspecificallyforCO2,duetothehigheroperatingpressuresthantypicalHFCsystems.Inadditiontopressureratings,theseevaporatorsaredesignedtominimizeinternalvolume,topreventrapidpressurebuildupintheeventofasystemshutdown.NormaloperatingpressuresforlowtemperatureCO2evaporatorsrunat200psi,whilemediumtemperatureevaporatorsrunat400psiorhigher.Regardlessofoperatingpressure,theevaporatorsmustbedesignedtoresistpressuresabovethepressurereliefsettings.

Hot Gas Defrost System HussmannPuritysystemsareavailablewithoptionalhotgasdefrostsystemsforlowtemperatureandmediumtemperatureevaporators.Thissystemisdescribedinmoredetailinaccompanyingdocuments.

Flash Gas Bypass Valve Theroleoftheflashgasbypassvalveistoregulatethepressureintheflashtank.The“flashgas”isthevaporportionoftherefrigerantfluidmixturecomingfromthegascooler.Thisportionwillvarybasedonloads,ambientconditions,andpressuresettingsinthegascooler,normallybetween25%and50%bymass.Thepressureinthetankismonitoredbythecontrollerandtheflashgasbypassvalveisopenedwiderifpressureneedstobereduced.Conversely,thevalvemodulatesclosediftankpressureneedstobeincreased.

Intermediate Heat Exchangers Themediumtemperaturesystememploysasimilarliquid/suctionheatexchangerstrategyasthelowtemperatureportionofthesystem.Fluidleavingthegascoolerisusedtoprovideheattosuctiongas.Aswiththelowtemperaturesystem,bypassvalvesaremodulatedtomaintainappropriatesuperheattothemediumtemperaturecompressors.Thisalsoprovidescoolingtothegascooleroutletfluid,ultimatelyreducingtheamountofflashgas.Thisheatexchangermustberatedtofullgascoolerpressure,typically1600psi.



Medium Temperature Compressors MediumtemperaturecompressorsalsooperateverysimilarlytotraditionalDXHFCcompressors.Suctiongas(comprisedofflashgas,lowtemperaturecompressordischarge,andmediumtemperatureevaporatorsuction)iscompressedfrommediumtemperatureevaporatorpressure,typicallyaround400psi,uptothepressurerequiredforheatrejection,upto1350psi.Compressorscycletomaintainsuctionpressure.Theoutletofthesecompressorsisthepointofhighestpressureandhighesttemperaturewithintheentiresystem.

Heat Reclaim HussmannoffersanoptionalheatreclaimsystemwithPuritysystems.Thisheatreclaimisavailableinseveralconfigurations.ThefirstconfigurationplacesaCO2coilinanairhandlerfordirectrefrigeranttoairheatreclaim.Thesecondconfigurationutilizesasinglewallheatexchangetoheatanintermediateglycolfluid,whichispipedtoanairhandlerorothersystemtoutilizetheheat.Thethirdconfigurationutilizesadoublewallheatexchangerfordomesticwaterheating.

Thestandardconfigurationofthissystemistopipetheheatreclaimheatexchangerinparallelwithamotorizedballvalveandamodulatingvalve.Thesevalvesmodulatetobypassaportionofthecompressordischargearoundtheheatreclaimsystem.Valvesshouldbedesignedandsetsuchthatifthemotorfails,thevalvemovestoapartiallyopenpositiontopreventheadpressurebuildup.

Heat Rejection Gascoolersaretypicallyaircooleroradiabatic(hybrid).Forair-cooledgascoolers,fansaremodulatedbasedonsetpointsdefinedbythecontroller.Adiabaticgascoolersutilizewetprecoolingpadstocoolincomingairpriortoenteringthegascoolingportionoftheunit.

Throttling Valve Thethrottlingvalveistheprimarycontrolforgascoolerpressure.Becausetemperatureandpressureareindependentfromoneanotherinthesuper-criticalregion,gascoolerpressureisnotascloselycorrelatedtoambientconditionsastypicalair-cooledcondensers.Optimumgascoolerpressureforsystemefficiencyandcapacityiscalculatedusingcomplexalgorithms.

Oil Management Systems Hussmannappliesapatentedmethodforstablelubricationofthecompressors.Thislowpressure(60-80psiaboveMTsuction)systemusesstandardoilcontrolsonallcompressors.

Controls HussmannPuritysystemsarecompatiblewithproductsavailablefromseveralcontrolsystemsmanufacturers,dependingonownerpreference.TheseincludeDanfoss,CPC,andMicroThermo,amongothers.Hussmannsystemscomestandardwithfactoryinstalledbatterybackupsystemsforcontrollersandcriticalvalves,toensuresystemsafetyandpreventliquidfloodbackduringpoweroutages.



Emergency Back-Up Systems Emergencyback-upsystemsareanoptionalcomponentofaCO2system.Thesesystemsconsistofasmallcondensingunit,fedwithemergencypower.Thiscondensingunitprovidescoolingtoanevaporatorintendedtomaintainflashtanktemperatureandassociatedpressurewhentheremainingportionofthesystemisoff,suchasduringapoweroutage.Thispreventspressureintheflashtankfromrisingabovethepressureratingofthesystem,thuspreventingdischargeofCO2throughthepressurereliefsystem.

Parallel Compression Hussmannoffersparallelcompressionasanoption.Themodificationtotheschematicisshownfollowing:

Withthissystem,theflashgasiscompressedinaseparatesuctiongroupfromthemediumtemperatureloadsandlowtemperaturedischarge.Thisimprovesenergyefficiencyofthesystembyallowingthehigherpressure“load”tobecompressedatanimprovedCOP(coefficientofperformance).(Parallelcompressionstrategiesareunderdevelopment,futurecontenttobeadded)


Installation Guidelines

HussmannPuritysystemsareinstalledmuchlikeatraditionalDXsystem,withafewimportantdifferences.ThesedifferencesareprimarilyduetothehigheroperatingorpotentialpressuresfoundinCO2systems.

Pressure Ratings PipingmaterialsforCO2systemsmusttakeintoaccountthepressureratingneededforthespecificapplication.Whilevariouspointsinthesystemexperiencearangeofpressures,Hussmannrecommendsonlytworatinglevels.Thishelpsensuresystemsafetyandavoidconfusioninpiping.Thesetwopointsarebestdescribedaslow-pressureandhigh-pressure.Thedividingpointsoftheseregionsisshownintheschematicbelowwithorangeindicatinghighpressureandblueindicatinglowpressure.


Installation Guidelines continued

Thehigh-pressureportionofthesystembeginsattheoutletofthemediumtemperaturecompressors,continuesthroughtheheatreclaimsystemandgascooler,andendsatthehigh-pressureexpansionvalve.Pressurereliefdevicessetat1600psiprotectthisportionofthesystem.Allcomponentsandpipinginthisportionofthesystemmustbecapableofwithstandinginternalpressuresofmorethan1600psi.



Thelow-pressureportionofthesystembeginsattheoutletofthehighpressureexpansionvalve,andincludestheremainderofthesystem.Thisincludestheentirelowtemperatureportionofthesystem,theflashtank,andthesuctionsideofthemediumtemperaturecompressors.Pressurereliefdevicessetat650psiprotectthisportionofthesystem.Nocomponentinthesystemshouldberatedatlessthan650psi.

Tomaintainsafetyofthesystemwithminimalpressurerelieflocationsandcost,bypasscheckvalvesareplacedaroundpotentialrestrictionsinthesystem.Thesecheckvalvesallowflowbacktotherackifthesystemisshutdown,butremainclosedundernormalsystemoperation.Anexampleofthisisshownbelow.

Piping Materials Toachieveapressureratingabove650psiforthelowsidepiping,severalpipingmaterialsareavailable.Theseincludecertaincopperproducts,copper-ironalloyproducts,andstainlesssteel.

TypeKCopper–TypeKcoppermaybeusedforpipinginthelowsideofthesystem,upto1-1/8”pipesize(only7/8”forhotgassystems).Asthepipesizesgetlarger,thepressureratingsgodown.Pipesizesof1-3/8”andabovearenotadequatelypressureratedforCO2intypeK.AtableofratedworkingpressuresforTypeKcopperisprovidedbelow.

TypeKCopperRatedWorkingPressures MuellerXHPPipe-Nominal

ODS-6000psi,

100°FS-5100psi,

150°F90Bar/1300PSI,

250°F130Bar/1885PSI,

250°F3/8" 1074 913 1093 1093

1/2" 1130 960 809 10935/8" 891 758 809 10787/8" 852 724 799 109311/8" 655 557 824 112513/8" 532 452 834 111215/8" 494 420 824 110921/8" 435 370 846 1127

25/8" 398 338 842 1141



K-65–K-65isacopperalloythatcontainsiron,producedbyWieland.K-65isavailableatapressureratingof120bar(1740psi),makingitviablefortranscriticalCO2systems.Thispipingmaybeusedinthehighorlowsidepipingofthesystem,usingthecorrectfittingsandinstallationpractices.Note:K-65isnotapprovedforuseinsomejurisdictions,verifylocalcodedbeforeproceeding.

XHP–XHPisacompetitortoK-65,availablefromMueller.Thisproductisavailableinseveralpressureratings,socaremustbetakentousetheappropriatepipingfortheapplication.AswithK-65,joiningmethodsaresimilartotraditionalcopperrefrigerantpiping.Note:XHPisnotapprovedforuseinsomejurisdictions,verifylocalcodedbeforeproceeding.

Stainlesssteel–priortotheintroductionofK-65andXHPtothemarket,stainlesssteelwasrequiredforuseonallhighsidepiping.Thisisstillaviableoption.ForCO2pressurerating,buttweldsarenotallowedforjoints;appropriatefittingsmustbeused.

AswithtraditionalDXsystems,shortradiusfittingsarenotrecommended.Longradiusellsareavailablefromseveralmanufacturers.Alwaysbesuretouseappropriatepressureratedfittings.

Brazing Allweldedjointsshouldbemadeupusing15%silver"Silphos."Use45%to56%silver"EasyFlo"onsweatvalvesandothercontroldevices.Buttweldsshouldnotbeused;alwaysuseappropriatefittings.Extremecareshouldbetakentokeeptheentiresystemcleananddryduringinstallation.Nitrogengasshouldflowthroughthepipingbeingweldedtopreventoxidation(scaling)duringtheweldingoperation.Aflowmetershouldbeinstalledtoensureappropriateflowrates.Jointsshouldbeallowedtoaircool;therapidcoolingfromawetragwillcausestrengthissuesinthejointleadingtoleaks.

Piping Practices ManyofthebestpracticesusedfortraditionalrefrigerationpipingareapplicabletoCO2systempiping.Undernoconditionsshouldcopperpipestoucheachother,solidstructure,sharpedges,othermetals,foreignobjects,etc.,duetotheriskofabrasionandresultingleaks.Whennecessarytocrosspipes,theyshouldbeoffsetorinsulated(andproperlysupported)toensurethereisnocoppertocoppercontact,orcontactwithothermetals.Nylonorplasticspacers(asmanufacturedbyHydra-Zorb)shouldbeusedbetweenun-insulatedtubingandclampstopreventlinechafinginthecases.Besuretousehightemperatureinsertswhensupportingdischargeanddrainlines.Allunderslabsuctionlinesandothersuctionlineswithverticalriserslongerthan6ft.shouldhavea"P"typeoiltrapinstalledatthebottom.Risersgreaterthan16feettallshouldhaveaninvertedtrapatthetopoftheriser.Suctionlinesshouldbeslopeddownwardinthedirectionofflow.



Individualcircuitpipingshouldberoutedwithagoalofequalpressuredroptoallevaporators,especiallyforhotgassystems.Thefigureontheleftbelowlooksgoodonaschematic,butisnotgoodpipingpracticemultipleevaporatorswithinonehotgascircuit.SeeappendixAformoreinformationonhotgassystems.

Acceptableforelectric Requiredforhotgasdefrostorofftimedefrostonly

Supports Commercialgradenylonstopnutsshouldbeusedonallclamps.Supportchannelsshouldbe"Unistrut"P-4000orheavier.Clampsshouldbeinthe"Unistrut"seriesP-2024to2043.Alternatechannel"SuperStrut"A-1200,B-1200,A-1202,B-1202withseriesA-716O.D.clamps,"WesancoInc."W-200,W-500ChannelwithseriesW-6229toW-6243O.D.clamps,or5-1/2”x1-5/8”16gaugegalvanizedsteel“C”stud.

AlloverheadsuctionandliquidlinesshouldbesecuredwithHydra-ZorbtypeclampsunlessonoverheadhorizontalrunsusingtrapezehangerswithInsulguardsaddles,whichshouldbesecuredtotheunistrutwithzipscrews.Iftheprojectisinseismiczone,pipingandequipmentshouldbebraced,supportedandinstalledtocomplywithlocationrequirements.Clampallverticallinesandlinesfromandtothegascoolerwithunistrutatleastevery6'.Allhorizontallinesneedtobesupportedwithunistrutatleastevery8'.

Insulation PipinginsulationshouldbeArmacell"Armaflex"orRubatex"Insul-Tube180".AlljointsshouldbesealedwithArmacell#520,RubatexR-374whitelatexpaintorRubatex"R-320"adhesive.HeatReclaimlinesshouldbeinsulatedwithArmacell“HT/Armaflex”orequivalentRubatexinsulation.Suctionlinesformediumtemperaturesystemsshouldhave3/4"wallthicknessinsulationfromfixtureorcoiloutlettothecompressorunlessotherwisenotedonplans.Suctionlinesforlowtemperaturesystemsshouldhave1"wallthicknessinsulationfromfixtureorcoiloutlettothecompressor.Alldischargelinestoheatreclaimcoilandwaterheatershouldbeinsulatedwith1/2"wallthicknessinsulation.Liquidlinesshouldbeinsulatedwith1/2"wallthicknessinsulation.Insulationmaybeslippedoverpiping,onlysplitwheninsulationcannotbeslippedon.



Relief Valves Itisveryimportantthattheproperpipingbeinstalledforthereliefvalves.Hussmannwillsupplythe4reliefvalvesandthechange-overforthelowside.Thesevalveswillautomaticallyopenat650psi.Forthehighside2reliefvalvesandachange-overwillbesuppliedinwhichthevalvesareregulatedfor1600psi.Twocopperlinesandonestainlesssteellinemustbepipedoutside.Itisveryimportantthatlocalcoderequirementsbefollowed.

1. Highpressurereliefline1600psimustbein“Stainlesspipeschedule40withadiameterof3/4”.2. LowpressurerelieflinefromtheFlashtankmustbeinstalled“7/8typeK“.3. LowpressurerelieflinefromtheDefrostreturnmustbeinstalled“7/8typeK“.4. Reliefvalvesmustbeinstalledwiththedischargingsidetowardsthebottomortheside.Itis

veryimportantthatreliefvalvesdonotfacetowardsthetopastherecouldbewaterandiceaccumulationandforcetherelieftoburp.

5. Alwaysusebrassfittingsonthebottomofthechangeover.6. Safetylinemustslopetothecompressorroomandtrapsmustbeavoided.

(Hydraulicpressurerelief)


Evacuation and Charging

Therearetwoprimaryreasonstotestthesystemwithpressure.Thefirsttest,typicallyatalowerpressure,isusedforleaktesting.Thesecondtest,typicallyatahigherpressure,isusedforpressureratingofasystem.

Leak Testing Allrefrigerationlinesunderthefloorshouldbetestedandinspectedpriortobackfilling.Stub-uprisersfromthefloorshouldbetestedwithdrynitrogento600psi.Theappliedpressureshouldremainovernightandapprovalofthesetestsshouldtypicallybemadebythecustomer.Overheadlinesshouldbetestedinanidenticalmanner.Whentherefrigerantconnectionshavebeencompletedatcases,testthebalanceofthesystemto600psi.Allthepipingshouldbetestedinthefloorandoverheadpriortotyingintothecasesandrack.

Allrefrigerationlinesshouldbetestedwithandhold600psigfor24hoursbeforeconnectingtocases/walk-ins.Allrefrigerationlinesshallbetestedwithandhold600psig(lowerifmanufacturerofcoilsorcaseslimitsleaktest).Finalleaktestingshouldbecompletedwiththecompressorsuctionanddischargevalvesclosed,andallothervalvesinthesystemopen,withtheexceptionofthetransducerswhichmustbekeptclosedduringpressuretestingandevacuationprocedures(somelocalcodesmayrequirehighertestpressures).LeaktestingshouldbeperformedwithanInficonD-TEKElectronicLeakDetector.Refrigerationpipingwillnotbeacceptableunlessitisleaktight.Ifanyleaksarefound,isolatetheleaks,dischargethegasandrepairtheleaks,andthenrepeatthetest.Whentestinghasbeencompleted,releaseallpressure.Iftestofoverheadandcasepipingisnotpossiblebeforeconnectingtotherack,therackshouldbeleaktestedbeforethesystemisconnected.

Pressure Testing Pressuretestingisperformedonsystemstoensuresafetyofthesystem,andverifytherestofthesystemwillnotburstbeforethepressurereliefdeviceopens.Applicablecodesorauthoritieshavingjurisdictiontypicallydeterminetheprocedureforpressuretesting.

Evacuation/Charging Thevacuumofthesystemisthemostimportantpartofthestartup.Itisveryimportanttoensurethatalltheindividuallinetestshavebeencompleted,andallthenitrogenhasbeenremovedbeforecompletingthevacuumprocess.Usingthecorrectpump(minimumof10CFM)andtechniqueforthevacuumisveryimportant.Pleasefollowthestepsbelowtoobtainthetargetof250microns.Itisveryimportantthatyouhaveacoppermanifoldtojoinyourconnectionsonthehighandlowsidesimultaneously.Ensurethattheconnectionsyouuseforyourpumpcanbemanuallyclosed.Amaximumof2vacuumpumpswillbeallowed,addinguptoatleast10CFM.Itisimportantthattheoilinthepumpsbechangedregularlyuntilthemicronlevelhasbeenreached:

• Firstoilchangeafter4hoursofuse• 2ndoilchangeafter12hours• 3rdoilchangeafter24hours


Evacuation and Charging continued

Afewthingsshouldbeconsideredwhenstartingthevacuumprocess:1. Ensurethatyoursystemis100%freeofleaks.2. Alltheconnectionsfromthevacuumpumptotherackmustbesoftdrawncopperlines

5/8”.3. Ensurethattheconnectionshavebeentestedbeforeyoustartyourpump.4. Allthecapsontherackandinthecasesneedtobeinstalledandtightened.5. Allthevalvepackingsneedtobetightened.6. Ensurethatyourliquidfiltersareinstalledbeforestartingyourvacuum.7. AllthetransducersonthecasesandtheTCRackshouldbeinstalledbeforeyourvacuum.8. Crankcaseheatersshouldbeturnedon.9. NOTE:ITISEXTREMELYIMPORTANTTHATHIGHPRESSURESANDLOWVACUUMNOTBE

PULLEDONTRANSDUCERSDUETOPOTENTIALDAMAGE.Transducersshouldbeisolatedduringtheseconditions.

Werequireoursystemstomaintain250micronswhenthepumpshavebeenstoppedfor2hours.Itisimportantthatourstartupsheetbefilledoutandapictureofthegaugeindicating250micronsbesenttoHussmann.

Thereshouldbeaminimumof1000lbs.ofbonedryCO2with99.8%purity.AvoidusingmedicalgradeCO2;the500psipressureregulatorsonthesetankspreventspropersystemcharging.Oncethevacuumisbroken,chargethesystemthruthemainfilterdrier.Tanksshouldbeusedwithoutthediptubeforcharginguntilthesystemisabove100psi,topreventformationofdryice.After100psi,thediptubemaybeused,drawingliquidCO2fromthetanksforfastercharging.Closetheoutletoftheflashtanksothiswillgiveyouchancetofilltheflashtank.Onceyouhave3siteglassesfloating,stopfillingtheflashtank.(Note:Ifaheatreclaimsystemisoperating,only2siteglassesshouldbefloating.)

Oncetheflashtankisfloating3glasses,makesureyouhaveaminimumof40percentcoolingloadonthemediumtemperatureportionofthesystem.Thesystemwillnotoperatewithlessthan40percentofthemediumtemperatureload.Runningwithlowtemperatureloadonlywillresultinunacceptablyhighdischargetemperatures,causingoilbreakdown.

Oil Charging Oilselectionisdependentoncompressormanufacturer.CopelandcompressorsmayuseeitherBSE-85orEmkarate68oil.BitzercompressorsorablendofbothmanufacturersrequiresBSE-85Oil.Compressorareshippedwithoil.Initialoilchargingshouldbeperformedwhilethesystemisundervacuum.Checkallcompressorsforproperoillevelsandadjustifnecessary.Addsufficientoiltofilltheoilreservoir.Unlessotherwisenoted,oilisprovidedbythecontractor(otherthantheoilshippedinthecompressors).Anoilchangetypicallyrequiresonegallonofoilpercompressor,plustheamountnecessarytofillthereservoir.Neverchargeoildirectlyintotheoilseparator;oilshouldbeaddedatthereservoirorcompressorsonly.


Startup and Maintenance

Startup Sequence 1. Priortostartingtherackuporputtingpowertotherack,makesurealltheelectrical

connectionsintherackpanelsandcompressorsaretight.Allcasecontrollerpanelsforallcoolersandfreezers,andcasespanelssuppliedbyrackmanufacturer,shouldbechecked.

2. Atleast40%oftherackevaporatorloadshouldbeavailablepriortorackstartup.3. Severaltestsshouldbeperformedontherack,priortorunning.(Note:Controlmustbe

poweredup.)a. Doaphaselosstesttomakesureallthesuctionvalvesontherackshutdown.b. Oncethephaselossisreset,allthesuctionvalvesshouldstarttoopenslowly.c. SimulatearackshutdowntoensurecasecontrollersautomaticallycloseallEEVs.d. Simulatealowsuperheatontheallthecasestoverifytheliquidandsuctionwillshutdown.

Ifnotthiscouldcauseexcessiveliquidfloodbacktotherack.e. Ifheatreclaimispresentontherack,verifythe3-wayvalvefailsinGascoolermode.

Note:thisisveryimportantiftheheatreclaimsystemisnotcomplete.f. Leakdetectioninallboxesandmotorroommustbetested,andfullyfunctional.

Theexhaustfanshouldbeinoperationpriortochargingofthesystem.g. Ifthereisaleakinthemotorroom,itisnotrecommendedtoshutdowntherack,asthis

willresultinmoredischarge.h. Verifyrotationonfansongascooler.Ifusinganadiabaticgascoolermakesurewateris

pipedandthePLCissetup.i. Verifythattheshipped-loosetemperaturesensorusedtocontrolthehighpressure

expansionvalveisproperlyinstalledattheoutletofthegascoolerandisreadingproperly.4. WhenstartingtherackrunallthecompressorsotherthantheleadwiththeVFDdrive.

Aftereverythingelserunningthelead(VFD)compressorshouldbeturnedon.5. Whenstartingthelowtemperaturesystemusingscrolls,itisrecommendedtobumpthe

compressortocheckrotationdirection.6. Checkalltheoilcontrolsthenpullthecontrolplugontheoilcontrolsystemtomakesurethe

compressorshutsdownandalarms.7. Theoilregulatorvalue(Swagelok)shouldbesetfor575psig.Thisshouldbecheckedagainonce

therackisrunningat100percent.a. Afterthesystemhasbeeninoperationforaminimumof7days,allexpansionvalve

strainersmustbecleaned.b. Checkthesystemoperatingtemperaturesanddefrosttime.Thelengthandnumberof

defrostcyclesshallbesetinaccordancewithcasemanufacturers'recommendationsandownerprovidedschedulefordefrost.

c. Afinaldefrostscheduleshallbeprovidedtothestoremanagerduringtheweekofgrandopeningaswelladdedtothedooroftherack.Allworkwithinstart-upprocedureneedstoberecordedinalogbookkeptinthemotorroom.

d. Afterthecompressorisstarted,continuecharginguntilthesystemhassufficientrefrigerantforproperoperation.Duringstart-up,nocompressoristobeleftoperatingunattendedandunwatcheduntilthesystemisproperlychargedwithrefrigerantandoil.


Startup and Maintenance continued

After Startup 1. Aftertherackhasrun48hoursandloadedto100percent,allthefilters,onthesuction,liquid

andoilshouldallbechangedaswellastheoil.Hussmannsuppliesfiltersandoilforstartupandenoughforonechangeafterstartup.Oilchangeprocedureisdefinedinthefollowingsection.

2. Oilandfiltershouldbechangedagainafter3weekstoensurethattheoilandfiltersarecleanaftertheinitialinstallation(materialsandlabortypicallysuppliedbyinstaller).

3. LeaktestwithaCO2sniffertypetool.4. Defrostlengthsandpressuresshouldbeverifiedtoensurethatenergyconsumption

isataminimum.5. Alwayscheckthateachcaseafterdefrostthetemperatureexceeds32°Fintheevaporator

andthecoilisclear.6. IfthecoilisnotclearingusingtherecommendeddefrostsettingscallHussmannforreview.7. Ensurethatalltheprogrammingisfinishedandwellunderstoodbyservicingcontractor.8. Ensurethatalltemperaturesensorsandpressuresensorsarewellcalibrated.9. Ensureallcontrolpanelsareclosed.10. RecordCO2levelinreceiverforfuturereference.11. FilloutstartupformandsendtoHussmannamaximumof3weeksafterstartup.

Oil Changes OilChangesshouldbeaccomplishedfollowingtheprocedurebelow:

DAY1

2technicians,8hrs(estimate,individualresultsmayvary)

1. Hussmannsuggestreplacingtheoilseparatorandsuctionfiltersonthefirstday.2. Proceedwithapumpdownandensurethatflashtankdoesnotexceed80%ofcapacity,

closeliquidandsuctionballvalves3. Depressurizedischargeandreplaceddischarge(Temprite)filterandsuctionfilter,

whichcanbedoneinasecondstep.

DAY2

5technicians,6hrs(estimate,individualresultsmayvary)

1. Itisrecommendedthat1personsupervisetheshutdownfortheballvalve,compressorandwatchthepressure.

2. Evaluatetheamountofcompressorsrunningonthemediumtemperature.3. Ifpossible,draintheoilonthefirsthalfofthecompressorsonmediumtemperature

andfillthosewithnewoilreadytorun.4. Lowertheoillevelintheoilreservoirbyabout80-90%.


Startup and Maintenance continued

5. Whenthesestepsarecompleted,pumpthemediumtemperaturesystempartiallyto80%ofthetank,alwayshaveagaugeontankpressure.

6. Ifyouhaveabackupcondensinguniewithplateheatexchangersatthetank,startmanuallytokeepthepressureaslowaspossible.

7. Closeallsuctionballvalvesonalllowandmediumcircuitsaswellasliquidballvalves(orsolenoids)

8. Turnallcompressorsoff.9. Finishdrainingtheoilreservoirandfillitasquicklyaspossible,ifyouhaveanelectricoilpump

thatwillhelptoshortenthetime.10. 2othertechnicianscandraintheoilontheothercompressors.11. Whentheoilreservoirisfullandreadytostartagain,themediumtemperatureloadmustbe

graduallymovedtothecompressors,theoilofwhichhasbeendrainedandreadytostartagain.12. Completetheoilchangeontheothermediumtemperaturecompressorsaswellasthoseofthe

lowtempcompressors.13. Restartthelowtemperaturesgradually.14. TheoilusedforoilchangeisthePOERL68HBforCopelandandBSE85KforBitzer.

*Thetimewasbasedonanaveragedualtemprack,8compressorsonmediumtempand3compressorsonlowtemp.


APPENDIX A – HOT GAS DEFROST

CO2 Transcritical Systems Training ManualRevision 0, February 2018


Appendix A

Introduction HussmannoffershotgasdefrostasanoptionwithPurityTranscriticalCO2systems.Thisdocumentprovidesspecificinformationaboutthisoption,intendedtoserveasasupplementtotheHussmannCO2TranscriticalTrainingManual.

Schematic ThestandardhotgasdefrostschematicforHussmannPuritysystemsisprovidedbelow.

Hotgasdefrostsareperformedbylowtemperaturecompressors.Aminimumoftwocompressorsareusedfordefrosts.Fora-22°Fgroup,thesuctionpressureismaintainedtoaminimumof200psigwithachargetransferfrommediumtemperaturetolow,whichopensondemandandonlyduringthedefrostcycle.Duringnormaloperation,thetransferisclosed.Thegasdefrosttypeusedisareversecyclehotgassystem,andwheninitiated,theelectronicexpansionvalve(EEV)ofthecircuitstartsclosingandwhenitiscompletelyclosed,thehotgassolenoidisenergized.


Appendix A continued

Themaindischargevalveisanelectronicvalve,whichduringthedefrostcycleoperatesfrom100%toabout25%openingtokeepapressureofapproximately565psig.Thevalvewillreturnto100%whendefrostingiscomplete.

Defrostreturnissentbacktotheflashtank,andthepressureiscontrolledbytwopressureregulatingvalvesinparallel.Returnpressureisadjustedfrom500to526psigdependingonlocation.Thesevalvesareinpressurecontrolmodeatalltimes.

Whenthecircuitiscompletelydefrostedandthedripcycleisfinished,thecircuitsuctionpressureregulatingvalvegoesintopressuredrainagemode.Thisdrainageisperformedin5steps.Thecircuitsuctionmodulatingvalvewillre-openatdifferentpercentagesevery2minutesinordertodraintheexcesspressureinthesystem,beforeopeningto100%.

Hot Gas Defrost – Additional Considerations Forsystemswithhotgasdefrost,thefollowingadditionalconsiderationsneedtobemadetoensureproperoperationofthesystem:

• PipingpracticesaresimilartoHFChotgassystems.Expansionloopsandchangesofdirectionshouldbeusedtoaccountforexpansionandcontractionofpipinglengthsduetochangesintemperature.

• Hotgassystemssubjectsuctionlinestohighertemperatures,reducingthepressurerating.ThismeansthemaximumpipesizeforTypeKcopperis7/8”,insteadofthe11/8”allowedfornon-hotgassuctionlines.

Hussmann Corporation 12999 St. Charles Rock Rd. Bridgeton, MO 63044-2483 Ph: 314.291.2000

www.hussmann.com

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CO2 Transcritical Systems Training Manual 042718€¦ · Transcritical CO 2 Training Manual I Pg. 4 Introduction Transcritical CO 2 refrigeration systems are gaining acceptance in