The off-design experimental performances of heat pump system using R125/R290 (25/75, mass fraction) blend are investigated by varying the mass flowrate of refrigerant blend. The influences of variable mass flowrate upon system coefficient of performance (COP), discharge temperature, temperature glide (GT) and temperature profile in condenser are analyzed, the system performance comparisons between R125/R290 and substituted refrigerant R22 are carried out. The results show that when the blend mass flowrate increases, compressor power increases linearly, the COP linearly increases at first and then gradually decreases, and an optimum COP of 3.04 is obtained when mixture mass flowrate reaches 1.12 kg/min. The compressor discharge temperature is almost decreased linearly whereas specific mass heating capacity is increased firstly and then it has a drop. The temperature differences between refrigerant and water at the inlet and in the middle of the condenser is gradually increased while the one at the outlet is decreased gradually with a heat transfer pinch point kept in the middle of the heat exchanger. Compared with that of R22, the overall performance has proved that the new refrigerant blend could be a promising substitute for R22, which are of significance for the application of the new refrigerant blends used in heat pump system.

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