Experimental investigation on vapor injection defrosting performance of quasi-two-stage compression air source heat pump with flash tank

Abstract

Defrosting is one of the core problems affecting the performance of an air source heat pump. As the most common defrosting method, the reverse cycle defrost requires a stable and large amount of heat supply to improve defrosting performance. In order to improve the reverse cycle defrosting performance of quasi-two-stage compression air source heat pump with flash tank, this paper realize vapor injection by opening the vapor injection valve during defrosting and increase the refrigerant mass flow without changing the existing cycle structure of the unit. A test rig was built up and effectiveness of vapor injection to accelerate defrosting is verified by a series of defrosting experiments. The results show that vapor injection can effectively reduce melting frost stage time, thus effectively shorten defrosting time and reduce defrosting energy consumption by increasing the refrigerant flow through the outdoor finned heat exchanger. The lower the ambient temperature, the more significant the effect. In experimental conditions of −10 °C, −5 °C, and 2 °C, vapor injection defrosting shortened the defrosting time of the flash tank type unit by 40.48%, 28.30% and 23.73%, and reduced the power consumption of the unit by 45.90%, 26.15% and 17.75% during the defrosting period. The difference between flash tank (FT) system and intermediate heat exchanger (IHX) system was because of the difference in the production speed of injection vapor refrigerant caused by the different generation process.