Hydrocarbon Refrigerants

and

Motor Car Air-Conditioning∗

I. L. Maclaine-cross

School of Mechanical and Manufacturing Engineering

The University of New South Wales

Sydney Australia 2052

Tel: (02) 385 4112 Fax: (02) 663 1222

Contents

1 On Refrigerant EnvironmentalImpacts 1

2 Refrigerant Characteristics 2

3 ‘Drop-In’ Replacement Refriger-ants for R12 3

4 Hydrocarbons Mixtures as Refrig-erants 3

5 Hydrocarbon Hazards 4

6 Car Air-ConditioningExperiments 4

7 From R12 to Greenfreeze 47.1 Tools, equipment and supplies . 47.2 Mixing procedure . . . . . . . . 57.3 Charging procedure . . . . . . 67.4 Further tests . . . . . . . . . . 6

8 Conclusion 6

9 References 6

1 On Refrigerant Environ-mental Impacts

Jacob Perkins patented refrigeration byvapour compression in 1834. Early refriger-ants were toxic or flammable. Early refrigera-∗Paper presented at Green Fridge Quest, Master

Class Workshop, 22nd November 1993, National Sci-ence & Technology Centre, Canberra.

tors leaked refrigerant rapidly, mainly throughthe drive shaft seals, creating a fire and healthrisk. A hermetic motor is sealed inside therefrigerant circuit so there is no shaft seal toleak. Except for car air-conditioning all smalland most large compressors now have hermeticmotors.

Thomas Midgley Jr proposed the use ofchlorofluorocarbons (CFCs) as refrigerants in1930. He had already achieved fame asa research engineer for General Motors byproposing the addition of lead to petrol in1921. CFCs have two important advantagesas refrigerants, high molecular mass and non-flammability.

Centrifugal compressors are cheap, highlyefficient and easy to drive with hermetic mo-tors but they require refrigerants with highmolecular mass. Centrifugal chillers for air-conditioning large buildings gave CFCs aninitial market which could afford their highdevelopment cost. Replacement refrigerants(Nowak 1990) require screw chillers which are50% more expensive. After 1995 the cost ofpremature replacement of centrifugal chillerswith imported high-technology chillers will fallmainly on finance and tourism. Low cost non-CFC refrigerants which do not require equip-ment replacement are available for almost allother applications and will be discussed in thefollowing.

A car air-conditioner may lose 400 g/year ofdichlorodifluoromethane (R12) through hoses,pipe joints and shaft seals. Domestic refrig-erators lose about 1 g/year in operation andassuming no recovery 10 g/year on a life cy-

2 REFRIGERANT CHARACTERISTICS 2

cle basis. Consider the future population ofa wealthier world as 10 billion people. Thisimplies 2 billion car air-conditioners and 2billion refrigerators. If R12 were still used,cars would emit 800 thousand tonnes/year andfridges only 20 thousand tonnes/year. Otherenvironmental impacts are similar. Power con-sumption averaged over a lifetime for typicalfridges and car air-conditioners are both of theorder of 50 W.

Hoffman (1987) and his team for the UnitedStates Environment Protection Agency pre-dicted 3% global ozone depletion for constantCFC emissions of 700 thousand tonnes/year.The ozone impact of car air-conditioners can-not be ignored. For fridges, a replacement re-frigerant must reduce both energy consump-tion and ozone depletion to reduce environ-mental impact after manufacture.

Many environmentalists and scientists be-lieve Hoffman’s estimates of ozone damage tobe a factor of ten too low. If you are one ofthese, I suggest you should never buy a newfridge. Always buy a secondhand R12 fridgeto prevent it being crushed for scrap and theR12 released to the atmosphere. Only afterthe last functioning R12 fridge in the countryhas expired should you consider a new ozonefriendly fridge. Your slogan should be ‘keepthat fridge.’

‘Polluter pays’ policies have been very effec-tive in reducing other pollutants. They wouldmake selecting the refrigerant with the lowestlife-cycle cost give the lowest environmentalimpact. Unfortunately they were not adoptfor CFCs and so our progress in eliminatingCFCs has been expensive and ineffectual.

Domestic water heaters with lifetime aver-age power consumption of 500 W are a moreimportant problem. Domestic heating andcooling is typically a 1000 W. Application ofeffort to these areas would reduce pollutionmore quickly and cheaply than redesigningfridges (Gudgeon 1990).

Refrigerant changes are not even the bestoption for reducing fridge energy consumption.The U. S. Department of Energy has beenfunding the development of vacuum (or super)insulation for fridges at the National Renew-able Energy Laboratory, Golden CO for overten years. This insulation design is two thinstainless steel foils with low emissivity coatingsheld apart by glass beads. The overall thick-ness is less than 2 mm but it has the same

thermal resistance as 200 mm of foam. Proto-type fridges have been built and test marketedwith half the energy consumption.

The reasons for this workshop are partly thecontentious and competing claims of Green-peace and some executives of a chemical cartelabout replacement refrigerants for CFCs (Vi-dal 1992). My colleagues and students in theRefrigeration and Air-Conditioning laboratoryhave accumulated much relevant informationover the years. In addition, Vidal’s article mo-tivated us to perform some inexpensive exper-iments to test the claims. Our results and in-formation to help you duplicate them are alsohere.

2 Refrigerant Characteris-tics

Vapour compression refrigerants are chemicalcompounds or mixtures with small moleculesand high vapour pressure. At refrigeratortemperatures they should be stable and non-reactive. Thermal design and performance de-pend on the mass of the molecules and theforces between them.

The van der Waals forces exist betweenall molecules. They are believed due to os-cilations in the relative positions of the pos-itively charged nuclei and surrounding elec-tron clouds. If only van der Waals forces actbetween the molecules, pure compounds withsimilar boiling points have similar energy con-sumption and require similar compressor dis-placement and motor sizes. There may bedifferences but neither basic thermodynamicdata nor performance measuring techniquehave been sufficiently accurate to tell whatthese are.

Some molecules e.g., water, ammonia, havethe centres of positive and negative charge per-manently displaced from one another. Thedipole electric moment is the product of theelectric charge times its displacement. Polarmolecules have a large dipole electric moment.These dipole forces are much larger than thevan der Waals forces and follow a differentlaw. Ammonia (R717) a polar molecule andR12 only slightly polar have similar boilingpoints. Their thermal performance has fre-quently been compared for simple ideal refrig-eration cycles and ammonia is usually found to

3 ‘DROP-IN’ REPLACEMENT REFRIGERANTS FOR R12 3

be 1 or 2% better (ASHRAE 1993, Threlkeld1970).

This slight advantage of polar molecules isfrequently outweighed by the practical difficul-ties created by their insolubility in hydrocar-bon oils and their miscibility with water. Theinsolubility may require either special circuitryor special oils. The miscibility usually requiresmore expensive driers which must be replacedmore frequently. These disadvantages are botha consequence of their polarity. Ammonia hasthe additional difficulty of being corrosive tocopper.

The capacity of both fridges and car air-conditioners is so small that only positive dis-placement compressors can be considered. Forboth applications the size of these must bekept small. The compressor size depend prin-cipally on the boiling point. A boiling pointover -20◦C will result in an unacceptably largecompressor in either application.

Noncondensible gases such as air even issmall quantities greatly increase energy con-sumption and reduce capacity. The simplestway of ensuring that air does not enter a refrig-erant circuit is to select a refrigerant that willbe above atmospheric pressure for every con-ceivable operating condition. The design tem-perature of freezers is -18◦C (ASHRAE 1988).A refrigerant boiling point below -20◦C is es-sential to maintain a pressure in the circuitabove atmospheric.

Low boiling points imply increased frictionlosses in the compressor but may allow gainsin piping losses. It is unlikely that boilingpoints below -45◦C would ever be consideredfor fridges. The increased refrigerant leakagefor car air-conditioners are unlikely to be bal-anced by the reduced compressor size.

New computer codes called REFPROP 4.0have been released by the National Instituteof Standards and Technology, GaithersburgMD (Gallagher et al. 1993). They calculatethermodynamic and transport properties ofa broad range of refrigerants and refrigerantmixtures. These codes summarize the lat-est knowledge of refrigerant properties and al-low accurate prediction of performance with-out building numerous prototypes.

3 ‘Drop-In’ ReplacementRefrigerants for R12

Fridges are charged at the factory and thecharge is intended to last over twenty years.Their replacement refrigerant for R12 neednot be a ‘drop-in’. If design modificationsare necessary, the manufacturer can includethem at the factory. Consumers should notworry about what the replacement refrigerantis. Any of the chemicals in Table 1 would besatisfactory and many others besides. Theyshould be concerned about the overall energyconsumption, reliability and utility.

Many existing car air-conditioners use R12and refrigerant must be added annually. A‘drop-in’ replacement would save the cost of aconversion and may be a substantially cheaperrefrigerant. The boiling point of R12 is -29.8◦C and its dipole moment is low. Theclosest match to R12 in Table 1 is RC270. Aliterature search showed that the data avail-able on RC270 was considerable but also Gal-lagher et al. (1989) have made computer codesavailable.

Kuijpers et al. (1988) have reported resultson an R12 fridge using RC270. The increasedenergy consumption over R12 they reportedwas consistent with the higher motor load-ings resulting from its high refrigerating effectcompared with R12. With car air-conditionersthis higher refrigerating effect is an advantagenot a disadvantage. You get a bigger air-conditioner for the price of a change in refrig-erant.

Evaporator superheat is not a refrigerantproperty but an operating parameter of theair conditioning system. It is the differencebetween the refrigerant temperature leavingthe evaporator and the vapour pressure or dewpoint near the evaporator outlet. This must beseveral kelvin or liquid may enter the compres-sor and damage the valves. Cyclopropane’shigher vapour pressure will result in a highersuperheat with most control valves. ASHRAE(1991) discusses such design details of car air-conditioners.

Cyclopropane was first prepared by AugustFreund in 1881. Commercial preparation is bycatalytic reaction of acetylene with methaneensuring a bulk price under 10$/kg. Its majorapplications are as an anesthetic and a feedstock for synthesis of fine chemicals and insec-

6 CAR AIR-CONDITIONING EXPERIMENTS 4

Table 1: Some chemical compounds with boiling points at 101325 Pa between -45 and -20◦Cwhich do not contain chlorine.

ANSI 34-1992 Chemical Boiling at Chemical Name DipoleDesignation Formula 101325 Pa Moment

R290 C3H8 -42.1◦C propane lowR717 NH3 -33.3◦C ammonia highRC270 C3H6 -32.8◦C cyclopropane noneR134a CF3CH2F -26.2◦C 1,1,1,2{tetra uoroethane moderateR152a CH3CHF2 -25.0◦C di uoroethane moderate

ticides. Unfortunately stocks are not held inAustralia and it must be imported from NorthAmerica or Europe.

4 Hydrocarbons Mixturesas Refrigerants

Kuijpers et al. (1988) recommended a mixtureof propane and isobutane as a refrigerant. Vi-dal (1992) reported claims that Greenfreezea mixture of commercial propane and butanecould achieve between 10 and 20% greater en-ergy efficiency than conventional fridges.

Non-azeotropic mixtures of refrigerants canreduce energy consumption when cooling isrequired over a broad range of temperaturesand heat is discharged over a range of tem-peratures. This effect is however small forpropane/butane even with two compartmentrefrigerators. If the reported figures are cor-rect the improvement must have been con-tributed to by better engineering and im-proved lubrication conditions in the compres-sor using hydrocarbons.

Australia is both a major producer and amajor consumer of commercial propane (bar-becue gas) and butane. So shipping would notdelay our experiments.

5 Hydrocarbon Hazards

The liquid density of R12 is 1460 kg/m3 and ofR134a 1350 kg/m3. The liquid densities in Ta-ble 2 show that even for cyclopropane a 1 kgcharge of R12 is equivalent to only a 460 gcharge. This low density and the matchinghigh latent heat reduce both the cost and fireand explosion hazard of hydrocarbon refriger-ants.

Even a large fridge releasing its 100 g chargesuddenly in a small 12 m3 kitchen creates amixture only 0.6% by volume so the data inTable 2 show explosion is impossible. Manyaerosol cans have a larger charge but very fewfires or explosions have caused injury.

Fire is a hazard for cars. The 300 g chargein a car air-conditioner is only 1% of the 30 kgpetrol mass in a fuel tank. For a fire to occurnot only must the refrigerant be released butthe autoignition temperatures in Table 2 showa spark or flame must be present.

6 CarAir-Conditioning Exper-iments

The composition of a commercialpropane/butane mixture suitable as ‘drop-in’replacement for R12 was calculated crudely as64% propane and 36% butane by mass.

In March 1993, students and staff of theRefrigeration and Air-Conditioning Labora-tory at the University of New South Walescharged an R12 air-conditioner on a FordLaser with a mixture of 64% propane and36% butane by mass. They encountered nodifficulties in charging and measured super-heats between 5 and 10 K depending on theoperating condition. A month later compar-ative capacity measurements were made onpropane/butane, R12 and cyclopropane. Theydetected no difficulties or differences in op-eration except the cooling capacity was 10%higher for propane/butane and 20% higherfor cyclopropane than for R12. The cyclo-propane was a small quantity imported fromGermany so this month I added readily avail-able propane/butane mixture.

7 FROM R12 TO GREENFREEZE 5

Table 2: Data on the fire and explosion hazard of hydrocarbon refrigerants.

Code Name Density Flammability Autoignitionliquid limits by vol. temperature

R290 propane 560 kg/m3 2.4% to 9.6% 494–549◦CRC270 cyclopropane 677 kg/m 3 2.4% to 10.4%R600 n-butane 624 kg/m3 1.8% to 8.6% 482–538◦C

7 From R12 to Greenfreeze

The Refrigeration and Air Conditioning Lab-oratory has a full range of refrigerant recoveryand charging tools. You may wish to repeatour experiments with or without the high tech-nology. This is reasonable provided you are fa-miliar with the operation and maintenance ofmotor vehicle air-conditioners and the hazardsand precautions in handling propane and bu-tane. If you do not have copies of the suppliersmaterial safety data sheets you should ask forthem. You should read these data sheets.

The following information applies only tomotor vehicle air-conditioners designed for usewith R12. New cars are now fitted for R134aor other ozone friendly refrigerants. Do notuse this procedure with any refrigerant otherthan R12. No warranty or representation ofany kind is made about the results to be ex-pected. Personal injury and damage to themotor vehicle is possible. There may be er-rors and there are omissions in the followingdescription and you must use your engineer-ing knowledge to rectify them. The R12 air-conditioner should be operating normally ex-cept for gas bubbles in the sight glass indicat-ing low charge.

7.1 Tools, equipment and sup-plies

The hand tools required are a screwdriver, asharp knife and a multigrip wrench.

The equipment and supplies which we pur-chased from K-Mart were:

No Item Price $1 Taymar LG870 Butane Gas

Blowlamp with gas can 42.002 Taymar RF80 gas cans 8.802 Jackeroo gas hoses 27.701 1.25 kg Jackeroo L.P. gas cylinder 22.951 Packet of two small hose clamps 3.95

Total 105.40

The equipment purchased from CIG Gas &Gear Centre was:

No Item Price $

1 36in long 0.25in SAErefrigerant charging hose 14.88

1 0.25 in Schrader access valvesolder union type 2.66

Total 17.54

The supplies purchased from Mitre 10 were:

No Item Price $

1 partial gas cylinder �ll with propane 1.95

7.2 Mixing procedure

1. Attach hose to gas cylinder (This is a left-hand thread so turn it in the opposite di-rection to normal.) then cut the end fur-thest from cylinder off with the knife.

2. Unpack Taymar blowlamp, use screw-driver to remove flame holder and themmultigrips to remove nozzle.

3. Place one hose clamp over hose, insertblowlamp tube 25 mm into hose and fas-ten hose to blowlamp with clamp.

4. Tighten hose to cylinder finger tight, closecylinder and blowlamp valve.

5. The remainder of this procedure shouldbe performed outside or in a garage withthe main door and several windows open.All flames and cigarettes should be extin-guished.

7 FROM R12 TO GREENFREEZE 6

6. Take first can and shake to check contentsthen fasten to blowlamp.

7. With butane can upside down abovecylinder, open blowlamp valve and cylin-der valve to allow butane liquid to flowinto cylinder.

8. Hold butane can upside down in bothhands for 30 seconds to warm and encour-age liquid flow.

9. Take screwdriver and turn air releasescrew at side of cylinder valve to releasesome air then tighten after two seconds.

10. Shake can to check liquid flow.

11. Warm can again for 30 seconds to encour-age liquid flow.

12. Repeat the can warming and air releaseuntil the liquid in the can is transferredthen close the blowlamp valve and removethe can.

13. In similar fashion empty the other twocans of butane into the cylinder.

14. Close the cylinder valve, remove the hosewith blowlamp valve and store.

15. Take cylinder to propane filling station(our’s was Mitre 10) and ask assistant toadd the propane on top of the butane.

16. Thoroughly mix the propane and butaneby rotating the cylinder for at least 60seconds.

17. In open air, hold the cylinder upside downfor 30 seconds.

18. With the valve pointing to the ground andaway from any person, open it slightlyfor 1 second to expel any water from thecylinder. Keep your hands clear of thevalve outlet.

7.3 Charging procedure

1. Attach the other gas hose to the gas cylin-der and cut off the end furthest from thecylinder.

2. Take the Schrader valve, slip it 25 mminto the hose and fasten with hose clip.

3. Unscrew the knurled cap from theSchrader valve and with needle nosed pli-ers unscrew and remove the valve stemfrom inside the body.

4. Screw the charging hose to the Schradervalve body.

5. Open and raise the engine hood and sup-port it on its stand.

6. Locate the compressor of your air-conditioner and its inlet and outletSchrader valves. The outlet Schradervalve will be closest to the hose connectedto the condenser which is in front of theradiator.

7. Locate the sight glass on your system.

8. Start your engine and air conditioner. Ifthe air conditioner is working and thesight glass is showing bubbles it is timeto add refrigerant.

9. Stop the engine, support the cylinder up-side down from hood and attach charginghose loosely to the Schrader valve on thecompressor inlet.

10. Open the gas cylinder valve for two sec-onds to expel air from the charging line.

11. Tighten the charging hose on the com-pressor inlet until it opens the Schradervalve.

12. Start the engine and air-conditioneragain.

13. Observe the sight glass, if bubbles are stillpresent open the cylinder valve slowly un-til you can hear the hiss of refrigerantflowing slowly.

14. Close the cylinder valve as soon as thebubbles have all disappeared from thesight glass.

15. Turn the engine off and depress the com-pressor outlet Schrader valve for two sec-onds with a screwdriver to release any air.

16. Turn the engine and air conditioner onagain and check the sight glass for bub-bles. If bubble are present add more re-frigerant as previously.

9 REFERENCES 7

17. If no bubbles are present, make sure thegas cylinder valve is closed finger tightand turn the engine off.

18. Remove the charging hose from the com-pressor quickly to avoid loosing refriger-ant.

19. Remove the cylinder from the hood andall tools and equipment from beneath thehood.

20. Close the hood and check that the air-conditioner is functioning normally.

7.4 Further tests

If you have a pressure gauge set and ther-mometer and have replaced all or part of therefrigerant, you may check the pressures andsuperheat. The pressures should be similar toR12. The superheat should be over 6 K if allthe R12 has been replaced.

8 Conclusion

The total cost of the supplies purchased asdescribed above was $15.15. The quantity ofrefrigerant mixed was 1.2 kg so the cost was12.5 $/kg. This a quarter the cost of compet-ing ozone friendly refrigerants. There were noconversion costs. If sufficient interest is shownin Greenfreeze replacement refrigerant for carair-conditioners there are a number of suppli-ers who would be prepared to premix the re-frigerant and reduce the cost towards 2 $/kg.

9 References

ASHRAE 1988, 1988 ASHRAE HandbookEquipment, Chapter 37 Household Refrig-erators and Freezers, American Society ofHeating, Refrigerating and Air Condition-ing Engineers, Inc., Atlanta.

ASHRAE 1991, 1991 ASHRAE HandbookHVAC Applications, Chapter 8 SurfaceTransportation, American Society of Heat-ing, Refrigerating and Air Conditioning En-gineers, Inc., Atlanta.

ASHRAE 1993, 1993 ASHRAE HandbookFundamentals, American Society of Heat-ing, Refrigerating and Air Conditioning En-gineers, Inc., Atlanta.

Gallagher, J., Huber, M., Morrison, G., andMcLinden, M., 1993, NIST ThermodynamicProperties of Refrigerants and RefrigerantMixtures Database (REFPROP), Version4.0 Users’ Guide, NIST Standard Refer-ence Database 23, U.S. Department of Com-merce, National Institute of Standards andTechnology, Gaithersburg MD.

Gudgeon, M.C., 1990, Domestic Water Heat-ing Alternatives for Australia, BE thesis,School of Mechanical and ManufacturingEngineering, The University of New SouthWales.

Hoffman, J. S., 1987, Assessing the Risks ofTrace Gases that can Modify the Strato-sphere, Office of Air and Radiation, U.S.Environmental Protection Agency, Wash-ington DC.

Kuijpers, L. J. M., de Wit, J. A., Janssen, M.J. P., 1988, Possibilities for the Replacementof CFC12 in Domestic Equipment, Inter-national Journal of Refrigeration, Vol. 11,July, pp. 284–291.

Nowak, J., 1990, Replacements for Chloroflu-orocarbon Refrigerants, BE thesis, Schoolof Mechanical and Manufacturing Engineer-ing, The University of New South Wales.

Threlkeld, J. L., 1970, Thermal Environmen-tal Engineering 2nd ed., Prentice-Hall, NewYork, 1970.

Vidal, J., 1992, The Big Chill, The Guardiannewspaper, Manchester, Thursday, Novem-ber 19, 1992.