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Study on Alternative Refrigerants for Direct Expansion Solar Assisted Heat Pump System

This paper reports the investigation results of the possibilities for using pure and mixed refrigerants as working fluids to replace R22 for the DX-SAHP systems. Firstly, pure refrigerants are compared in terms of COP, discharge temperature and mass flow rate. Comparison results show that R290 is the most promising alternative to R22. Secondly, two kinds of mixed refrigerants are investigated as well. It indicated that the mixed refrigerant R290/R22 with more R290 performs better than the others in terms of COP. Meanwhile, the mixed refrigerants produce relatively low discharge temperatures and proper mass flow rates can be created due to appropriate mixture in suitable mass proportion. Further investigation indicates that R290 and R290/R22 show better system performance with relatively high superheating temperatures.