Refrigerant substitution in household air conditioning has become a common concern in the global refrigeration and air conditioning industries. This study analyzes the specific clauses of the Kigali Amendment. Based on the GWP value of the R410A refrigerant, different equivalent factors were selected to calculate the regulatory limits of different countries and regions in different years. Under the restrictions of different national laws and regulations, three available refrigerants from R410A, R32, R454B, R161, and R290, have been selected to represent different usage scenarios. The refrigerant replacement process of HFCs was predicted and analyzed following Kigali′s revised Global Warming Potential (GWP) limit, and the influence of refrigerant charge reduction was discussed. The results show that to satisfy the Kigali Amendment, the proportion of R290 in Europe must exceed 30% and become the mainstream refrigerant in 2024, whereas the United States can realize the possibility of not using R290 by reducing the charge of R454B. China can meet the GWP limit by using either R290 or R161and there is no need to switch to both two refrigerants simultaneously.

An experimental system of an air-source heat pump with multiple outdoor units in parallel was designed and built. The outdoor units were defrosted in turn using hot subcooled liquid for defrosting. The heat pump heating performance variations in the course of frosting and defrosting under different outdoor temperature and humidity conditions were experimentally studied, and the heating performances of the hot liquid subcooling alternate defrosting system and hot gas bypass alternate defrosting system were compared and analyzed. The experimental results show that the hot liquid subcooling alternate defrosting can enable the heat pump to complete the defrosting under the condition of continuous heating and that the defrosting performance is good. When the outdoor air temperature is -10 ℃ and the relative humidity is 90%, the optimal time to start defrosting is 30 min. At this time, the system heating capacity decreases from 9.87 kW when there is no frost to 8.71 kW when the defrosting starts, and the heating COP decreases from 3.73 to 3.36. When the system operates defrosting under different humidity conditions, the minimum values of system heating capacity and heating COP can reach 5.42 kW and 2.28, respectively. Compared to the case of bypassing 20% of discharge gas for defrosting, the average heating capacity of hot liquid subcooling alternate defrosting is 13.8% higher, and the heating COP_C is 10.1% higher.