An investigation on the efficient reverse cycle defrosting strategy for microchannel heat exchanger heat pump system

Microchannel heat exchangers (MCHX) are widely used in heat pump systems due to their high efficiency and lower refrigerant charge. However, during the defrosting processes, the MCHX heat pump system encounters some problems, such as longer defrosting duration and lower defrosting efficiency due to its poor drainage performance. To solve these problems, a new defrosting control strategy with indoor fan and electric heater turned on at the same time was proposed in this study. The defrosting characteristics of the new defrosting strategy and the conventional defrosting strategy were compared experimentally. Results indicate that the new defrosting strategy could shorten the defrosting time by 59.4% at Tamb = 2 °C and 65.9% at Tamb = −5 °C. Meanwhile, the defrosting efficiency of the new defrosting strategy was improved by 14.2% at Tamb = 2 °C and 18.0% at Tamb = −5 °C. In addition, as the relative humidity decreased, both defrosting duration and defrosting energy consumption would be reduced under different defrosting strategies, and it was more advantageous for conventional defrosting strategy. Due to the reduction of defrosting duration, the heating capacity of the heat pump system would increase during the periodic defrosting and defrosting cycles. In this study, the average heating capacity of the heat pump system with the new defrosting strategy was increased by 14.2% at Tamb = 2 °C and 18.0% at Tamb = −5 °C. Furthermore, for the conventional defrosting strategy, wet compression occurred in the late defrosting stage, which could significantly affect the reliability of the compressor. For the new defrosting strategy, wet compression was eliminated during defrosting due to the better heat transfer in the indoor coil, which was a reliable way for system operation. The contribution of this study can effectively guide the defrosting strategy design of MCHX heat pump system, improve the thermal comfort of occupants and promote the heat pump system energy saving.