Abstract: An optimized defrosting control method based on the principle of hot gas defrosting is proposed to address the issues of reduced heating efficiency and operational stability caused by frost formation in heat pump air conditioners under low-temperature, high-humidity conditions. Compared to existing shutdown defrosting technologies, the hot gas defrosting technique significantly reduces system energy consumption and enhances indoor comfort by maintaining the four-way valve in a fixed position and optimizing the opening of the electronic expansion valve. Analyzed the effects of indoor fan airflow, outdoor fan speed, and compressor frequency on defrosting performance through psychrometric chart analysis and experimental validation. The results indicate that reducing the indoor fan speed can extend the defrosting duration by 14% to 40% and increase the outdoor unit coil temperature by 0.7 ℃; when the outdoor ambient temperature is above 0 ℃, activating the outdoor fan can utilize atmospheric heat sources to assist in defrosting; reducing the compressor frequency is more beneficial for defrosting performance, but indoor heating comfort should be considered when adjusting the above control parameters.

Key words: Hot gas defrosting, Control optimization, Defrosting effect, Energy efficiency improvement, Comfort