Abstract: Air-source heat pumps typically use two defrosting methods during winter heating operation: reverse cycle defrosting and hot gas defrosting. Compared to reverse cycle defrosting, hot gas defrosting has the problem of longer defrosting time leading to poor thermal comfort in the room. Through theoretical analysis and experimental verification, the impact of the cold surface temperature of the outdoor heat exchanger on frosting and defrosting was studied. The results showed that the heat loss during the hot gas defrosting process is significantly higher than that of reverse cycle defrosting. At the same time, to evaluate the changes in frosting duration and defrosting duration more reasonably, an evaluation index for room temperature changes during the defrosting period was introduced. Using reverse cycle defrosting as a control, experiments verified the changes in frosting duration, defrosting duration, and room thermal comfort under different defrosting strategies. The results showed that under the same experimental conditions, by optimizing the hot gas defrosting strategy, the heating run time can be shortened by 2.5% to 14.9%, and the defrosting time can be reduced by 10.8% to 21.1%; the room temperature drop during the defrosting period can be reduced by 0.36 ℃ to 0.9 ℃, and compared to reverse cycle defrosting, the room temperature drop can be reduced by 1.76 ℃ to 1.88 ℃.

Key words: Heat gas defrosting, Defrosting length, Control method, Defrosting indoor-temperature drop