Performance of Alternative Refrigerants in Heat Pumps and Air Conditioners

In this paper the results of both modeling and testing a representative 3-ton air-to-air heat pump running with the baseline refrigerant (HCFC-22) and zero ODP alternative refrigerants will be presented. Alternative refrigerant simulation runs are made with two pure fluids (HFC-134a and HFC-152a) and an azeotropicmixture (60/40wt%) ofHFC-32 and HFC125 (Allied-Signal Inc. U.S. Patent 4,978,467). The expansion device, the heat exchangers, and line sizes are optimized for each refrigerant. Pre-optimized and post-optimized system performance is presented to demonstrate the impact of this process on the ranking of replacement refrigerants. System tests of the heat pump and compressor calorimeter tests were run with the 32/125 azeotrope and a 32/134a (25/75 wt%) blend. Introduction A move away from familiar refrigerants is currently in progress. This move is spurred on by concerns for the earth's protective ozone layer and accelerated global warming. Although the main focus in the near-term is the elimination of CFC's, HCFC's which are viewed as interim replacement candidates in many applications, will also be eventually banned from production. According to present domestic legislation, only refrigerants without any ozone depletion potential would be acceptable long-term replacements. However, a switch to refrigerants that do not deplete the ozone layer only addresses the first of two environmental concerns. The impact on global warming also requires attention, (although by switching to zero ODP HFC's, the direct greenhouse warming potential of the refrigerant is significantly reduced from that of the CFC's). Global warming will be impacted by both the direct greenhouse potential of the gas in the atmosphere and by the fossil fuel demands of the system the refrigerant is charged into. This makes energy efficiency a critical parameter that must be considered when selecting alternative refrigerants. However, too often refrigerants are ranked solely on the basis of simple thermodynamic cycle efficiencies. Factors such as heat transfer and pressure drop characteristics are ignored with this type of comparison. Even when a comparison is based on calorimeter testing, the results can lead