Refrigerant Mixtures as HCFC-22 Alternatives

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International Refrigeration and Air ConditioningConference

School of Mechanical Engineering

1992

Refrigerant Mixtures as HCFC-22 AlternativesM. B. ShieDu Pont Fluorochemicals

A. YokozekiDu Pont Fluorochemicals

D. B. BivensDu Pont Fluorochemicals

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Shie, M. B.; Yokozeki, A.; and Bivens, D. B., "Refrigerant Mixtures as HCFC-22 Alternatives" (1992). International Reigeration andAir Conditioning Conference. Paper 139.hp://docs.lib.purdue.edu/iracc/139
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REFRIGERANT MIXTURES AS HCFC-22 ALTERNATIVES

M. B._ Sh if le t t A. lokozeki, D. B, Bivensou Pont FluorochemicalsWilmington, E

SUMMRYA recent in ternationa l assessment of the atmospheric sciencehas provided a basis to accelera te the chlorofluorocarbon CFC)phase-out. In addition, the assessment p rovided a basis foradvancing the phase-out schedule fo r long-lived hydrochlorofluorocarbons such as c hlorodifluoromethaneHCFC-22). The objective of th is study was to identify p o ten tia l alternatives to HCFC-22 and evaluate the ir performance in aroom a i r conditioner. Compute rmodel simulations of atheore tica l refr igera tion cycle suggested that a mixture ofhydrofluorocarbons HFCs) might perform the same as HCFC-22. Thea ir conditioner te s tresu lts indicate tha t mixtures may be usedas a lte rna tives to HCFC-22.

INTRODUCTIONHCFC-22 has been widely used in the a ir conditioning industry especially in residentia l unitary and centra l a i r conditioning systems for many years. In the United States approximately 5 million room i r conditioners are sold each year,ndmost of them are used _for res iden tia l s e r v i c ~ /1 / Because HCFC-22 has been read ily available, low cost, and less harmful to the environment than CFCs, i t has become thealternative of choice for many new applications. For example ,HCFC-22 is currently being used for some commercial and transportrefr igera tion applications which trad it iona lly used R-502, new -design industr ia l ch il le rs which t rad it iona lly used CFC-11, and some sta tionary medium temperature applications which -t rad it iona lly used CFC-12.Recently, sc ien t if ic information has indicated th a t ozone is being depleted over la t i tude bands tha t encompass the UnitedStates a t fas ter ra tes than antic ipated. /2 / This finding hasincreased concern over the poten tia l long-term effec ts of certa in long-lived HCFcs (such as HCFC-22) on atmospheric ozoneconcentrations.Based on th is new information, ou Pont CompanyFluorochemicals announced inten tions to discontinue sa le ofHCFC-22 for l l but service applications by January 1, 2005 andfor l l applications by January 1, 2020.Because HCFC-22 is used in a large variety of applications,more than one a lte rna tive may be needed to provide optimum performance for l lapplica tions. This study will focus onidentify ing possible HFC alterna tives to HCFC-22 for use in res iden tia l cooling applications.

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REFRIGERNT LTERNTIVESCYCLEPERFORMNCEA search was conducted to identify nonflammable compounds ormixtures which provided the same refrigeration capacity andenerqy efficiency as HCFC22 a t the RIa ir conditioning and heatpumpra ting points /3 / Nosingle nonflammable compound was

iden tified which provided the same theoretical capacity and

energy efficiency as HCFC22 (see figure I : HFC134a was theonly nonflammable refrigerant which offere a sim ilar energyefficiencywith about a 35 lower refr igeration capacity based onthe same compressor displacement. Several HFCmixtures have beenproposed as HCFC22 alte rna tives based on mode l calculations (seefigure I I . /4 /

1.41.2

0.8 0.60.40.2

0

1.4

1.2

0.80.60.40.20

HCFC22 HFCt3 -4a HFC-125 HFC-32 HFC1-4 3a HFC152a

0 Capacity Bc.o.P.Figure I

HCFC-22 HFC32/HFC13-4 HFC32/HFC126HFC32/HFC162e.(32wtfo /118wt'llo l (80wtllo/40wtl lol (-40w tfo /80w t'l lo lD Capacity llilmC.O .P.

Figure II

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T

Amixture ofHFC-32anaHFC-134a offered the closestmatchin theore tica l capacityana energyefficiency comparedwithHCFC-22whilehaving thepoten tia lto be nonflammable. ThemixtureOf32weigh t (wt )HFC-32and 68 wt HFC-l34a is azeotropicmixture, having abubblepoint/dewpoint temperaturedifference of 6 c(11F)a t apressure of 620kPa (90ps ia.Many questions have been raisedconcerning the use of~ e o t r o p i refrigeran tmixtures such as HFC-32/HFC-134afor use inrefrige ra t ion equipment. Inorder to verify themodelcalculations and answer someof these concerns, we decided tocompare theperformance of th is mixture in arooma ir conditionerdesigned to useHCFC-22.

AIRCONDITIONERANDINSTRUMENTATIONThe a ir conditionerwas rated bythe manufacturer to have acooling capacity of 4787kcal/hr (19000btufhr . Theunitwasequippedwith aro tary compressor, accumulator, and the~ v p o r t o r and condenser eachhad three c ircu itsThea ir conditionerwas se t u in an environmentallycontrolled chamber so th a t the dry and wet bulb temperaturescould be held constant and/or adjustedduring theexperiments. /S/ Thetemperatures were varied over awideoperating range in order to study the effec ts onperformance.Thea ir conditionerwas not modified except to accommodatefor the instrumentation necessary to take measurements. Aschematic of the instrumentation is provided in Figure I I I

T..... oE T

MSS FLOWMTER.

Figure I I I

37

IIIII

___ AIRFlOW* SMPLEPORTT THERMOCOUPLE.p PRESSURETRNSDUCER

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several thermocouples and pressure transducerswereins ta lled for makingmeasurements around the cycle. Using thesemeasurementswith our thermodynamicmodel allowed us to calculatethe enthalpy a t eachpoint. Acorio listypemass flowmeterwasin sta lled in the liquid l inebefore the capilla ry tubes andseveral sample portswere added for liquid and vapor phasesamples. These sampleswere la te rrun on a gas chromatographGC) tocheckmixture composition.

Apower meterwas used to measure the volts and amperesdrawn by the a ir conditioner. The power meter softwarecalculated thewatts drawn and applied a power factor to adjustfor anydis tortedwaveforms. The refr igera tion capacitywascalculated by taking the enthalpydifference across theevaporator times themass flow ra te . The energy effic iency ra tioE.E.R.) was calculatedby dividing the refr igera tion capacity bythe to ta lenergy consumption. Adata acquisition systemwas usedto process themeasurements.The rotary compressor was charged with naphthenicmineralo il . The HFC refr igerants have l i t t l to no miscibility withmineral o i l ,but theo ilwas not changed in order to eliminateeffec ts ofdifferen t lubricants. Also, we wanted to determine i fthe a irconditioner could operate during the te s t periodwith animmiscible refr igerant/lubrican t combination.

TEST_PROCEOURESThe f i r s tse tof experiments were conducted to verify ourmeasuring techniques. The systemwas evacuatedwith a two-stagevacuum pump and chargedwith 1100 grams of HCFC-22 recommendednameplate charge size). The mass flow ra te and capacitymeasurements were compared with theperformance curves providedby the compressor manufacturer see figures IV andV). Themeasurements agreedwithin / - 4t for mass flow and / - St forcapacity. This small differencewas probably due to the o ilcirculation through themass flowmeter. Based on th iscloseagreement we had confidence in ourmeasurement techniques andbegan evaluating themixtures.

30125120 *115110105

1 0 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ 100 105 110 115 120 125 130 135 140

Measured Mass Flow Rate kg /hr)Figure IV

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Compressor Ratin g kca l/h r)5 6 0 0

5400

5200

5000

4800

4600

C

*

4 4 0 0 ~ ~ ~ ~ ~ ~ ~ ~ 4400 4600 4800 5000 5200 5400 5600Measured apacitykca l/h r)Figure v

The a ir conditioner was operated over a range of indoor and outdoor conditions and the steady-sta te performance measured a teach condition.To ensure there were no slow leaks which might a l te rperformance measurements or change the mixture composition, the HCFC-22 charge was recovered in a cylinder cooled n a dryicejacetone bath. The charge was weighed and over 98 wasrecovered.Amixture of 32 wt HFC-32 and 68wt HFC-134a was preparedn the lab by weight and composition checked with a gaschromatograph. The mixture was charged into the a ir conditionerl iqu id phase by inverting the cylinder which had a vapor onlyvalve. The material was charged through the sample port a t the in le t to the accumulator (see figure I I I . In order to determinethe optimum charge s ize the mixture was added in small incrementsand the re frigera tion capacity and E.E.R. plotted as a functionof charge size . The optimum charge size for the HFC-32/HFC-134amixture was 943 grams.The a ir conditioner was operated a t the same conditions asHCFC-22 and steady-sta te performance measured at each condition.To determine i f the mixture composition changes around the cycleduring operation, several samples were taken while the a ir conditioner was running. The refrigeran t charge was recoveredusing the same method and the composition analyzed.

PERFORMANCERESULTSFigure VI provides a comparison of the experimental

measurements between HCFC-22and the HFC-32/H FC-134a mixture.HCFC-22 and HFC-32/HFC-134a had an average capacity of 4938and 4888 kcalfhr 19600 and 19400 btu jhr) , respectively . HCFC-22and HFC-32/HFC-134a both had an average E.E.R. of 3.0(10.5 btujhr/W). The average deviation in the capacitymeasurement was +/- 100 kcaljhr 400 btujhr) and the E.E.R.deviation was +/- o.os (0.2 btujhrfW).

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The compressor discharge l ine temperaturewas measured10.2 em 4 inches) from the compressor she ll . TheHFC-32/HFC-134a mixture had an average compressor discharge linetemperature of about 9 c 16 F) lower than HCFC-22. Thecompression ra tio s for HCFC-22 and HFC-32fHFC-134a were 2.79 and2,89, respectively.The evaporator and condenser in le t and ou tle tpressuresweremeasured and the overall pressure drop for both refr igeran tscalculated. The HFC-32/HFC-134amixture had about the samepercentpressuredrop asHCFC-22 3,8 \ versus 3,9\ in theevaporator and 6.8 \versus 6.4 \ in the condenser). The averageevaporating and condensing temperatureswere calculated by usingthe average pressures. BothHCFC-22 and HFC-32/HFC-134a had thesame average evaporating and condensing temperatures of9 C 48 F) and 48 C 118 F), respectively.Themass flow ra te for the HFC-32/HFC-134a mixturewas about10\.lower thanHCFC-22 because the suction gas density is aboutlOt lower 22.6 kgfm J 1.41 lb /f t3 a t 18.3 C 65 F) and 627 kPa

90.9 psia) versus 25.5 kg/m3 1.59 lb / f tJ a t 18.3 c 65 F) and642 kPa 93.1 ps ia , respectively) . The overall powerconsumption for theHFC-32/HFC-134a mixturewas also s ligh t ly lower thanHCFC-22.HCFC22 HFC32/HFC134a

CPIllly kcal/hr, Biu/hd 4938 19600) 4888 19400)

e.e.R. W/W, BIU/hr/W) 3.0 10.5) 3.0 10.5)

Comp. Dlacharge Temp. C,F) 96 205) 87 189)

Evap. Inlet Pre kPa, psla) 667 96.8) 661 94.4)Outlet Prea kPa, psia) 6


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5

20

s L ~ ~ Distance along Evapora to rHCFC-22 --+- HFC32/HFC134a

FigureVIICondenser Temperature (C)1 0 0 r ~

8070 \6050

Distance along Condenser- HCFC-22 HFC-321HFC-134a

FigureVIIseveral refrigerant samples were taken while the a ir onditionerwas inoperation. The f i r s t se t of sampleswererom the liquid l ine jus tbefore themass flow meterwith noefrigerant flashing in the accumulator inactive) . The seconde t of sampleswere taken a t a low ambient conditionwithefrigeran t flashing in the accumulator (active) ecomparedhs sampleswith the in i t ia l re fr igeran t charged andwithin theccuracy of theGcmethod +/- 0.3 wt)did not see anyomposition changes in the.l iquid l ine samples (see figure IX).herefore, l iqu id in the accumulator in ternal volume of 722 cc)ad no effect on the circulating l iqu id composition.

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Sample

In it ia l Charge

Accum ulator InactiveLiQuidLine

Accum ula tor ActiveLiQuidLine

Mixture C om posit ion(w t )HFC-32 HFC-134a

32.2 67.8

32.1 67.9

32.2 67.8Figure IX

FLAMMABILITYTESTINGAND VAPOR/LIQUID MEASUREMENTSTheflammable l im its forHFC-32inHFC-l34a were measuredaccording totheASTM681Ete s tmethod. /6 / Thel iquid andvapor compositions formixtures of HFC-32 /HFC -l34a werecalcula ted tvarious temperatures toensure th t the flammablecomponent HFC-32did not exceed the flammability lim it .ThemaximumnonflammableHFC-32concentration in HFC-l34a t

atmospheric pressurewas about 56wt troomtemperature andabout 52wt t80c(176F). Thevapor composition of acylinder containing 30 wt HFC-32 and 70wt HFC-134awascalcula ted over arange of temperatures between -25 -13 F) and40 C(104F). Thevapor compositionwasalso calcula ted for amixture containing 25wt HFC-32and 75 wt HFC-134a.C om posit ion(W eight )6 0 r ~ ~

Room Temperatu re Flammabili ty limit55

80C Flammabil ity Limit 50 -- 45 --- ---

4 0 ~ ~ ~ -25 Tem perature (C)H FC -32 Vapor Cone. - - H F C -3 2 Vapor Cone.

30 wt \ 32 I 70 wt\ HFC-134a 25 wl \ 32 75 wtor HFC134aFigureX

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FiqQre X shows th t t room temperature and above a mixtureof 30 wtt HFCJ2 and 70 wtt HFC-134a crosses t h e ~ S Cflammability boundary. At a temperature of about 20 c -4 F)the same mixture crosses the room temperature boundary. Amixture containing 25 wtt HFC32 and 75 wtt HFC-134a remainedbelow both flammability boundaries. Therefore, mixtures ofHFC32 and HFC-134a which contain in excess of 25 wtt HFC-32 inthe l iquid phase may have a flammable vapor space under certainconditions.

Using the refr igera t ion cycle model, a mixture of 25 wtHFC-32 and 75 wtt HFC-134a would have a capacity about 9 lowerthan HCFC22 with the same energy eff iciency. The lower capacitycould be increased to HCFC22 capacity mechanically by increasingthe compressor displacement or chemically by adding HFCl25. Aternary mixture of 30 wtt HFCJ2, 10 wtt HFC-125, and 60 wttHFC-134a should provide the same capacity and energy eff ic iencyas HCFC-22 based on model calculat ions. Adding small amounts ofHFC-125 allows more HFC-32 to be added to HFC-134a because i tlowers the HFC-32 concentration in the vapor space and acts as abet ter flammability suppressant. The ternary mixture remainsbelow the flammability l imits over the range of temperaturesstudied.

CONCLUSIONSThe objective of th is study was to ident i fy a l ternat ives toHCFC-22 and evaluate the i r performance in a room i r conditioner.A mixture of 32 wtt HFC-32 and 68.wt HFC-l34a provided thesame performance as HCFC-22 in a unmodified room i r conditioner.The t es t s verif ied the cycle calculat ions which showed themixture should have the same capacity, energy eff iciency, and

about a 9 c lower compressor discharge temperature compared withHCFC-22.The t es t s proved th t no major equipment changes may benecessary in order to switch from HCFC-22 to a zeotropic mixturesuch as HFC-32/HFC134a in cer ta in applications such as room i rconditioners. The i r conditioner operated with an immisciblerefr igerant/ lubricant combination with no apparent effects onperformance for almost 1000 hours; however, polyol esterlubricants may be required for long-term acceptable compressordurabi l i ty .Refrigerant samples taken before and f ter operation suggest

th t zeotropic mixtures such as HFC-32/HFC-134a can be chargedand recovered with no measurable composition changes. Also, nocomposition changes were detected during operation from samplestaken t the l iquid l ine.Flammability tes ts and vaporjl iquid composition measurementsshow th t mixtures of HFC-32/HFC-134a which contain in excess of25 wtt HFC-32 may be flammable under certain conditions.A mixture of 25 wt\ HFC-32 and 75 wt HFC-l34a would haveabout a 9 lower capacity with the same energy eff iciency asHCFC-22. The lower capacity could be increased to HCFC-22'capacity by increasing the compressor displacement or by addingHFC-125. A ternary mixture of 30 wt HFC-32, 10 wtt HFC-125, and60 wt\ HFC-134a may provide the same capacity and energyeff iciency as HCFC-22, while remaining below the flammabilityl imits over the range of temperatures studied.

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Based oncyclecalcu lationsand te s ts resu lts thesemixturesaswell asHFC-134a werenominated totheARI taskforcewhich is investigatingpoten tia lHCFC-22 alternat ives /7 / Thenextstepi s toverifytheperformanceof theternary ~ i x t u r andte s t themixtures inotherapplicationssuchasunitaryheatpumps.ACI{NOWLEDGMENTS

We would l i ~ togivea special thanks toseveralothermembers who contributedto th is project: M.H. Bland, L. Bracale,K.M. Henschen, J,A. Gehrig, R.R. Parkell, o .M . Patron, R.W.Martin, andJ.T. Nicholas. We wouldalso l ike to thankW.O. Roberts and J F Shillingforallowingus tousetheenvironmentalchamberand fina lly D.L. Klug andS.C. Gidum al forth e ir s1.1pport. REFeRENCES

1. Stoecker,W.F. and Jones,J.W., RefrigerationandAir

Conditioning, 2nd Edition, 1982 1 pg 4.2. Scien tific Assessment ofozoneDepletion: 1991 ExecutiveSummary, W orldMeteorological Organization, UnitedNationsEnvironmentProgramme, NationalAerona1.1tics andSpaceAdministration, NationalOceanicandAtmosphericAdministration, andUnitedKingdom DepartmentofEnvironment,October 1991.J Air-conditioningandRefrigerationIn s t i tu te (ARI)standard, 210/240-89,4. Bivens, O.B., ChoosingAlternativeFluids for

AirConditioning, 1991 CFC Conference, Baltimore, MD, 12/4/91.

5. AssociationofHome ApplianceManufacturersStandardsAHAM RAC-1, July1990).6. TheAmericanSociety forTesting andMaterials, ASTM) 1StandardTestMethod forConcentrationLimitsofFlammabilityofChemicals , DesignationE681-85.7, Bivens, O.B . andKlug, O .L , HCFC-22 Alternatives -OuPontCompany Nominations, ARI TestProgram, 2/4/92.

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Refrigerant Mixtures as HCFC-22 Alternatives