Experimental investigation on a screw-type air source heat pump system with air heat absorption defrosting

Defrosting is crucial challenge for air-source heat pump operating in cold and humid climates due to its adverse impact on the heating efficiency. Conventional reverse cycle defrosting method has the disadvantages of reduced heating capacity, inefficient defrosting, and unstable heating temperatures. To address this issue, an Air Heat Absorption Defrosting method based on the reverse Carnot cycle principle was proposed to ensure uninterrupted heating during defrosting. To further validate the technical feasibility and energy-saving potential of the proposed system, a 710.0 kW screw-type air-water heat pump prototype was constructed to carry out control experiments under various conditions. Experimental results showed that, the proposed method achieved an average heating capacity of 315.7 kW during the defrosting process. The cyclic equivalent heating capacity and defrosting correction coefficient of the proposed method were 61.8 kW and 14.4 % higher in comparison with conventional reverse cycle defrosting method, respectively. Thus, the temperature fluctuation of supply water during the defrosting process was reduced by 69 %. In addition, the cumulative COP of Air Heat Absorption Defrosting method was 9.3 % higher than reverse cycle defrosting method, which could be attributed to the fact that the defrosting energy mainly came from air heat absorption. These findings highlight the potential of proposed Air Heat Absorption Defrosting method in addressing heat pump defrosting challenges while offering significant energy-saving benefits.