Experimental Study on Characteristics of Trans-critical Heat Pump Water Heater Using Refrigerant HFC125

With continuous increase of energy consumption and constant strength of environmental protection, the moderate and high temperature heat pump technology has been paid more and more attention, and the study on it is one of the most attractive fields. Recently, the researches on moderate and high temperature heat pump have been concentrated on alternative refrigerants and system matching, where heat pumps using refrigerant HFC125 seem to be promising. In order to evaluate the performance of the heat pump using refrigerant HFC125, an experimental rig of dc-inverter heat pump water heater was designed and set up, and the experimental study on trans-critical heat pump water heater using refrigerant HFC125 was performed so as to investigate its system performance. The relationship between COP and frequency of compressor was analyzed. It is found that there is an optimum frequency when the system runs at 95Hz. Then, case study at 95Hz, the evaporation pressure, condensation water temperature rise, discharge temperature, were discussed. Finally, the COP of HFC125 trans-critical cycle was compared with R410 sub-critical heat pump at the same conditions. The results indicate that there is an optimum COP when the compressor runs at 95Hz; the system COP shows an increasing tendency with the decrease of condensation pressure and compressor ratio while the evaporation pressure keeps invariant, and the COP decreases rapidly when cooling water temperature rises over 47.5 degrees C. Compared with R410A sub-critical cycle, the COP of HFC125 trans-critical cycle significantly increases by an average of 12%.