Abstract: Raises the minimum limit value of APF in accordance with GB 21454—2021 "Energy Efficiency Limits and Energy Efficiency Grades for Multi connected Air Conditioning (Heat Pump) Units" released by the National Standards Commission in 2021. Further research is needed on the influencing factors of multi connected APF and the methods for improving APF; Using a certain 16HP top-outlet air multi line, experimental tests were conducted to verify the impact of the size of the return oil capillary, the flow path of the outdoor heat exchanger, and the cycle time of low-temperature heating and defrosting on the APF. The experimental results showed that optimizing the flow path of the outdoor heat exchanger, the size of the return oil capillary, and the cycle time of low-temperature heating and defrosting is beneficial for improving the APF, with an increase ratio of 8.41%, 3.29%, and 1.68%, respectively; The main purpose of optimizing the size of the outdoor thermal exchange circuit and return oil capillary is to improve the energy efficiency ratio of the intermediate working conditions to achieve the goal of improving APF, while the main purpose of optimizing the cycle time of low-temperature heating and defrosting is to increase its circulating heat capacity and improve the overall APF.

Key words: APF, Return oil capillary, Heat exchanger flow path, Low temperature heating duration