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OverviewHCFC-22 is the worlds most widely used

refrigerant. It serves in both residential andcommercial applications, from small windowunits to large water chillers, and everything inbetween. Its particular combination of efficien-cy, capacity and pressure has made it a popu-

lar choice for equipment designers.Recently, extensive use of HCFC-22 has

made it possible to reduce the use of CFCrefrigerants, because its Ozone DepletionPotential (ODP) is as much as 95% lower thanCFCs. Nevertheless, it does have some ODP,so international law set forth in the MontrealProtocol and its Copenhagen and Viennaamendments have put HCFC-22 on a phase-out schedule. In developed countries, produc-tion of HCFC-22 will end no later than the year2030. In intervening years, production isreduced in a series of specified steps.

Detailed phaseout schedules vary fromcountry to country. In the U.S., HCFC-22 pro-duction will be frozen at baseline levels onJanuary 1, 2010, and the production of virginrefrigerant will be banned unless it is used asa feedstock for other refrigerants, or in equip-ment manufactured prior to January 1, 2010.The countries of the European Communityhave adopted even stricter measures.

After the phaseout dates, supplies ofHCFC-22 should still be plentiful thanks toconservation and recycling techniques devel-oped for CFCs. For instance, CFC-11 hasntbeen produced since January 1996, butbecause of recycling, it is still widely available.Recycled HCFC-22 should be even more plen-

tiful, because it is more widely used than CFC-11. It is important to remember that the phase-out affects only production, not use.

Direct-expansion (DX) chillers are amongthe many products that have traditionally uti-lized HCFC-22. Therefore, owners and speci-

fiers of DX chillers have an obvious interest asto how the phaseout will impact such chillers.After all, chillers purchased today will have aservice-life well into the 21st century, when thephaseout will have begun to take effect.

The impact will vary from country to coun-try. In countries with a late phaseout date, DXchillers will be sold with HCFC-22 for sometime to come. In countries with an early phase-out date, existing DX chillers may never haveto switch refrigerants because of the plentifulsupply of recycled HCFC-22. However, fornew DX chillers to be sold in countries with an

early phaseout date, chiller manufacturers aredeveloping units which utilize refrigerants otherthan HCFC-22.

HCFC-22 Substitutes for DX ChillersObviously, new substitutes should possess

what HCFC-22 lacks from an environmentalstandpoint, while retaining its good thermody-namic characteristics. Environmentally, theideal candidate must have an ODP of zeroand a low Global Warming Potential (GWP).

Thermodynamic similarity is important whenretrofitting existing chillers; otherwise, capacityand efficiency may be lost. In new chillerdesigns, thermodynamic similarity is less of an

issue because the equipment can be specifi-cally designed for the replacement refrigerantsparticular characteristics.

Several HCFC-22 substitutes have beenidentified by the Alternative RefrigerantEvaluation Program (AREP). This internation-al, industry-backed program was developed bymajor refrigerant suppliers and HVAC manu-facturers to ensure a broad-based assessmentof HCFC-22 alternatives. Refrigerant data wasshared among the participants to speed test-ing and replacement recommendations.

Currently, there are four leading replace-ment candidates: HFC-407C, HFC-404A,

HFC-134a, and HFC-410A.As an AREP participant, YORK believes allfour HCFC-22 alternatives have merits. Its nosurprise, then, that each refrigerant has beenchosen by at least one manufacturer toreplace HCFC-22 in new DX chillers.

The Impact of the HCFC-22 Phaseouton Direct-Expansion Chillers

YORK believes

all four HCFC-22alternatives havemerits.

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Unfortunately, having made their refrigerantchoice, some chiller manufacturers are bad-mouthing the choices of others. At this earlystage of implementing HCFC-22 alternatives,these disparaging claims cause undue confu-sion and are a disservice to chiller owners andspecifiers. The evaluation that follows attemptsto give an even-handed analysis of the HCFC-22 alternatives, so chiller owners and speci-

fiers can make informed decisions.

Properties of HCFC-22 SubstitutesBecause all four replacement candidates

are HFCs, their molecules do not include chlo-rine, so their ODP is zero.

As far as GWP, however, the numbers dovary. According to the Dupont Internet site,the GWP ratings are:

HFC-134a: 1300 GWPHFC-407C: 1600 GWPHCFC-22: 1700 GWPHFC-410A: 1890 GWPHFC-404A: 3750 GWP

While there is a variance in these numbers,it is not significant. According to the TEWI(Total Equivalent Warming Impact) formulabeing proposed by GWP researchers, thereare two ways in which a water chiller canaffect global warming: refrigerant leaks andelectric-energy consumption. Of the two fac-tors, electric-energy consumption (or morespecifically, the CO2 created by the powerplant supplying the electricity) is far more sig-nificant, accounting for 98 to 99% of a chillersTEWI. So the refrigerant GWP differencesshown above have such a minuscule impacton TEWI that they can be effectively ignored.

According to refrigerant manufacturers, all

HCFC-22 substitutes will be available for the

long-term. All are non-flammable and have lowtoxicities like HCFC-22. However, their capaci-ties, efficiencies, and pressures vary, whichaffects their application.

Retrofitting Existing ChillersTo be successful in a retrofit situation, a

replacement refrigerant needs to have capaci-ty, efficiency, and pressure comparable to

HCFC-22. These thermodynamic characteris-tics will ensure satisfactory equipment capacityand efficiency.

How do the replacement candidates mea-sure up thermodynamically? Figure 1 showstheir efficiency, capacity, and pressure as com-pared to HCFC-22.

HFC-407C is very similar to HCFC-22 in allthermodynamic respects, which makes it agood retrofit candidate. Consequently, HFC-407C is being used for retrofits in some areasnow.

The capacity of HFC-134a is much lowerthan HCFC-22, so it is not a good retrofit can-didate.

The pressures of HFC-404A and HFC-410Aare much higher than HCFC-22, so they arenot good retrofit candidates either.

Designing New ChillersBecause new chillers can be designed

around a refrigerants properties, all of theabove refrigerants are candidates for use innew DX-chiller designs. Obviously, the chillerdesign will differ from HCFC-22 chillers to agreater or lesser degree, according to theproperties of the particular refrigerant choice.

For HFC-134a DX chillers, the design isaffected by the refrigerants lower capacity and

pressure. Lower capacity means more refriger-ant will have to be circulated, which necessi-tates larger or faster compressors. Lower pres-sure means that cost can be taken out ofsome chiller components because they donthave to be built as ruggedly.

For HFC-410A DX chillers, the designermust deal with much higher refrigerant pres-sure. As a result, heat exchangers and com-pressors will have to be designed to withstandthat pressure. The higher pressure also meansthe refrigerant gas will be more dense. Higherdensity means less gas will have to be circu-lated to provide the same amount of refrigera-tion. So compared to HCFC-22 chillers, small-

er or slower compressors can be used.For HFC-404A DX chillers, there is a lower

refrigerant efficiency and higher refrigerantpressure to deal with. To counter the lower effi-ciency, bigger heat exchangers may berequired. The higher pressure may require thatthe heat exchangers and relief devices beredesigned.

For HFC-407C DX chillers, the design pre-ferred by YORK, the refrigerants slightly high-er pressure is not high enough to require dif-ferent chiller components than used for HCFC-22 chillers. The refrigerants capacity and effi-ciency are very similar to HCFC-22. There are,

RelativePerformance

Refrigerant

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10

1.05

1.00

0.95

0.90

0.85

0.80

0.75

0.70

0.65

0.60

Figure 1: Thermodynamic Characteristics of HFC-134a, HFC-407C,HFC-404A, and HFC-410A Relative to HCFC-22

R-134a R-22 R-407C R-404A R-410A

Efficiency

Capacity

Pressure

Thermodynamic Performance Assumptions:Isentropic Compressor Efficiency = 0.65

Mean Condensing Temperature = 120F

Subcooling = 15F

Mean Evaporating Temperature = 38F

Superheat = 10F

Pressure Determined at the Mean Condensing Temperature

GWP differenceshave such aminusculeimpact on TEWIthat they can beeffectivelyignored.

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however, intriguing design implications for oneunique feature of HFC-407C the propertyknown as temperature glide.

Temperature Glide ExplainedHFC-407C, HFC-404A, and HFC-410A are

all blends of other refrigerants.HFC-407C is a ternary blend, comprised of

HFC-32, HFC-125 and HFC-134a, with a com-

position by weight of 23%, 25% and 52%respectively. HFC-404A is ternary blend ofHFC-125 (44%), HFC-143a (52%), and HFC-134a (4%). HFC-410A is a binary blend ofHFC-32 and HFC-125 in a 50%-50% ratio.

Each of these HCFC-22 alternatives is azeotropic blend, meaning that the resultingblend does not react as a single substance. Ata given pressure, they evaporate and con-dense over a range of temperatures, ratherthan at a single temperature. The expressiontemperature glide was coined to describe thisphenomenon.

HFC-410A and 404A have temperatureglides of 1F or less, which is small enoughthat we can overlook the effect. However,HFC-407C has a temperature glide of 7 to 8F.

Impact of Temperature GlideThe phenomenon of temperature glide,

when fully understood, holds tremendouspromise for chiller designers and customers asa means of improving chiller efficiency.Unfortunately, some manufacturers using otherHFCs are obscuring this benefit by spreadingseveral misconceptions.

Misconception # 1:Any refrigerant leakwill alter the blend percentages of the remain-ing HFC-407C and degrade chiller perfor-

mance.As stated above, the components of a

zeotropic blend evaporate at different tempera-tures for a given pressure. Consequently, it isperceived that an HFC-407C refrigerant leakwill cause the more volatile components HFC-32 and HFC-125 to escape first. Thisphenomenon is known as fractionation.

But it is wrongly thought that a refrigerantleak invariably changes the proportion of theremaining constituents, thereby degradingchiller performance. In real-world applications,there are few conditions where fractionation isa factor. During chiller operation, any refriger-

ant-gas or refrigerant-liquid leaks will not resultin fractionation because the refrigerant blend isstill thoroughly mixed.

Only if there is a refrigerant-gas leak duringchiller shutdown will the more volatile compo-nents escape first. But calculations and testsshow that the effect on performance is slight.

To empirically test the impact of refrigerant-gas leaks during shutdown, an independenttest laboratory (Intertek Testing Services, for-merly ETL) ran an experiment on a 100-tonchiller. During chiller shutdown, 35% of theHFC-407C gas was purposefully leaked fromthe point in the system where the fractionationeffect would be most pronounced.

The leaked refrigerant was replaced with amake-up quantity of fresh HFC-407C. Thisleakage/recharge cycle was repeated 4 times.In the end, the amount of gas lost andreplaced simulated a refrigerant leak of 140%of the original charge. While such repeated,massive leaks would be highly unusual in real-life, they do serve as an extreme test of frac-tionation.

What was the impact on chiller perfor-mance? In spite of massive refrigerant leakageand replacement, the laboratory found thatcapacity went down only 4.5%, while efficiencywent up 1.1%.

This test illustrates that it would take anear-catastrophic refrigerant leak to produceany discernable loss in capacity, at which pointthe seriousness of the leak would far over-shadow the performance issues.

Misconception # 2:The temperature glideof HFC-407C will result in refrigerant tempera-tures below 32F, which will freeze the chilledwater.

A typical DX evaporator has a 7F small dif-ference, which is defined as chilled-water tem-perature minus refrigerant temperature at theevaporator location where the temperature dif-ference is smallest (usually where the refriger-ant and water exit the evaporator, but notalways). Now charge this evaporator withHFC-407C, with its temperature glide of 7 to8F. At first glance, it would appear that thiscombination might expose the chilled water tonear-freezing temperatures. As shown inFigure 2, if the design leaving-chiller-watertemperature is 44F, then the HFC-407C refrig-erant might enter the evaporator at 33F.

But actual applications show there is nofreezing problem. Most major HVAC equip-ment suppliers already allow their HCFC-22DX evaporators to operate with refrigerant-inlettemperatures below 32F, and there are nofreezing problems.

Temperature(F)

Location in Evaporator

HFC-407CRefrigerant

HFC-407CRefrigerant

Water

54

33

37

41

44

Figure 2: HFC-407C Temperatures in a Two-pass Evaporator

Water InletRefrigerant Inlet & Outlet

Water Outlet

7F SmallDifference

Refrigerant

in Tubes

Water in Shell

Two-pass Evaporator

8F Temp.Glide

Temperature glidholds tremendouspromise as ameans ofimproving chillerefficiency.

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The reasons are simple. First, the coldestrefrigerant is typically in contact with thewarmest water, as shown in Figure 2.Secondly, ice-crystal formation is inhibited bythe high velocity and turbulence present in thewater side of the evaporator. If ice crystals didform on the tube or tubesheet surfaces, thescrubbing action of the turbulence would pullthem back into the warm bulk flow.

Benefit of Temperature GlideAt first glance, the phenomenon of tempera-

ture glide looks like an unwanted side effect inan HCFC-22 substitute. However, closerexamination reveals that the temperature glideof HFC-407C holds a promising benefit major improvement in chiller efficiency.

If the DX evaporator is designed as acounter-flow heat exchanger, then the refriger-ant and the water enter at opposite ends, asshown in Figure 3. In this configuration, theleaving refrigerant temperature is 45F.Compare this temperature with an HCFC-22chiller using the same evaporator. The leavingrefrigerant temperature would be 37F.

The higher leaving-refrigerant temperaturewith a counter-flow evaporator and HFC-407Cmeans the compressor does less work to raisethe refrigerant to the condensing temperature.And less compressor work means lower ener-gy consumption.

Thanks to temperature glide, HFC-407Cpromises to be an outstanding HCFC-22 sub-stitute, not just from the perspective of ODP

and GWP, but from an efficiency viewpoint aswell.

ConclusionA variety of HFC refrigerants have been

developed as alternatives to HCFC-22 in DXchillers. All are viable candidates, and all arebeing used by one or more chiller manufactur-ers. YORK has chosen HFC-407C because ofits performance characteristics in real-worldapplications. Its capacity, efficiency, and pres-sure similarities to HCFC-22 make it a logicalchoice for retrofits. And its temperature glidepromises significant efficiency improvements innew chillers.

When the HVAC industry eliminated its useof CFC refrigerants, some chiller manufactur-ers confused owners and specifiers withclaims and counter-claims as to which was thebest replacement refrigerant. In the end, sev-eral refrigerants turned out to be worthyreplacements, and the focus of chiller evalua-tions turned away from refrigerants and towardthe more important factors of value and perfor-mance. At YORK, we hope this paper hascleared up some misconceptions, and resultsin a speedy acceptance of all HCFC-22 alter-natives.

Temperature

(F)

Location in Evaporator

54

37

4445

Figure 3: HFC-407C Temperatures in a Counter-flow Evaporator

Water InletRefrigerant Outlet

Water OutletRefrigerant Inlet

7F SmallDifference

Refrigerant

in Tubes

Water in Shell

Counter-flow Evaporator

8F TemperatureGlide and ReducedCompressor Head

HFC-407CRefrigerant

HCFC-22 Refrigerant

Water

We hope thispaper resultsin a speedyacceptance ofall HCFC-22alternatives.