R-410A – Why is it such an Interesting Refrigerant Fluid (2024)

R-410A – Application Experience

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D. B. Bivens, J. R. Morley, W.Wells

DuPont Fluoroproducts

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Abstract:R- 410A is attracting a lot of interest among Air Conditioning systemmanufacturers because of its attractive properties as a refrigerant workingfluid. This paper discusses the thermophysical properties of R-410A, highlighting those aspectswhich contribute to its energy efficiency, as well as those which limit itsapplication range. The results oflaboratory testing of R-410A air conditioning systems over a wide range ofambient (condensing temperature) conditions are presented.

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Background:R-22 has been the “life blood” of the domestic and commercial air conditioningindustry for many decades. When its phase out was signalled by the CopenhagenAmendment to the Montreal Protocol in 1992 the refrigeration/air conditioningindustry was fully engaged in introducing alternative technologies for the CFCs(R-11, R-12, R-502, etc.). The publication, in 1994, of the European ODSregulation EC 3093/94 which imposed an earlier (than that of the MontrealProtocol) phase out for the supply of HCFCs (including R-22), and went one stepfurther by imposing a time-table of specific use bans for these substances,accelerated the development of alternatives for R-22. Refrigerant manufacturershad been developing alternatives for R-22 focusing on those substances whichmirrored as closely as possible the thermo-physical, chemical stability andsafety characteristics of R-22, within, obviously the constraints imposed byODS regulation.

The industry (refrigerant manufacturers and air conditioning system OEMs) initiallysettled on R-407C as being the preferred replacement for R-22 for airconditioning. However R-407C, being a zeotropic mixture with a significanttemperature glide, is not suitable for all (specifically certain chiller) airconditioning applications. The continuingemphasis on system energy efficiency provoked the industry to continueresearching other HFC fluids, and this led to the development of R-410A. R-410Ais not a like-for-like replacement for R-22 because it is a much higherpressure fluid (and also has a significantly higher volumetric refrigerationcapacity) than R-22 and thus cannot be used in refrigeration equipment ratedfor R-22 (without re-rating, if this is possible).

Figure 1 showsthe relative pressure (at 55°C) and typical volumetric refrigeration capacityrelative to R-22.

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Initial trials of R-410A showed that air conditioningsystems using this fluid exhibited an energy efficiency superior to that incomparable, un-optimised, systems using R-407C or R-22.

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R-410A: R-410A is a near-azeotropic mixture of HFC-32 and HFC-125. It has a very lowtemperature glide (around 0.1K), however it istruly zeotropic over its useable temperature range – the composition ofits vapour in equilibrium with the liquid at any temperature (below theCritical Point) is different from the composition of the liquid phase. Thismeans that, although R-410A has a very low temperature glide it should not behandled as an azeotropic fluid: transfers should always be made from the liquidphase. One potential draw-back withregard to the applications of R-410A is that its Critical Temperature issignificantly lower than that of R-407C or R-22 (see table 1)

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Table 1 Physical Property Comparison

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An analysis of the theoretical refrigeration cycle showsthat the theoretical cycle efficiency (COP) of R410A is significantly LESS thanthat of R-22 by around 4 – 6%. This is in disagreement with the earlylaboratory trials of R-410A in air conditioning systems which showed asignificant INCREASE in COP vs. R-22. The apparent anomalous behaviour ofR-410A has been shown to be due to its very favourable (opposite R-22, orR-407C, for that matter) transport properties.See Tables 2 and 3

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Table 2 TransportProperty Comparison

Saturated Liquid (10°C)

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Table 3 TransportProperty Comparison

Saturated Vapour (10°C)

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These differences in transport properties result in reduced viscous losses (i.e. pressure drop)in the system and within the compressor itself, and also give improved heattransfer characteristics in the evaporator and condenser. Thus the improvedenergy efficiency of R-410A systems over R-22 systems under normal airconditioning conditions.

Performance of R-410A in high temperature condensingambients:

As discussedpreviously R-410A has a relatively low Critical Temperature. This will impactit* performance in conditions where high condensing temperatures are required –in air condensing systems in hot climates,in heat pump applications, etc.

To evaluate the impact of condensing ambient temperatureson system performance a series ofperformance tests were undertaken in controlled laboratory conditions usingseveral commercial R-410A system configurations for air conditioning.

The results of these tests are presented below asperformance relative to the performance at 35°C Ambient for each refrigerantfluid, in order to discount absolute differences in performance between R-22and R-410A. In general there was an approximately 15°C approach temperature atthe condenser (the difference between the condensing temperature and thetemperature of the condensing ambient).The performance of both R-22 and R-410A is influenced by condensingtemperature – R410A is slightly more sensitive to condensing ambient temperature than is R-22 up to around 45°C.Above this temperature (equivalent to a condensing temperature of around 60°C)the refrigeration capacity of the R-410A system starts to fall off morerapidly. At this temperature therelative drop in capacity exhibited by R-410A systems is around 10% greaterthan that of an R-22 system.

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These results are summarised in Figure 1 and Figure 2:

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The effect ofcondensing ambient temperature is system dependent. Figure 3 compares a Windowunit and a ducted split system

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Conclusions: Trialswith R-410A under varying condensing conditions demonstrate that itsperformance (capacity and energy efficiency) does decrease with condensingtemperature in a manner somewhat similar to that of R-22, and there are noabrupt changes as the condensing temperature reaches and passes the CriticalTemperature. (This will be at condensing ambient temperatures of around 55 –60°C.) The system capacity at the Critical Temperature is around 60 – 70% ofthat 35°C (around a 10% greater drop than R-22 experiences over the sametemperature range). The rate of performance reduction with increasingcondensing temperature is a function of system design.

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