A modeling study on the revere cycle defrosting of an air source heat pump with the melted frost downwards flowing away and local drainage

Reverse cycle defrosting is widely used for air source heat pumps. When a multi-circuit heat exchanger is vertically installed in a heat pump as an outdoor coil, the melted frost could be kept downwards flowing or locally drained during defrosting by using water collecting trays. To analyze the performance differences of melted frost, two defrosting models were developed and previously reported by authors. In this study, the defrosting performance of an air source heat pump was numerically investigated based on the two models, with the melted frost downwards flowing away or local drainage considered. The following physical parameters are predicted and analyzed, including the thermal resistance of refrigerant, temperature of melted frost on tube and fin's surface, mass of melted frost and energy consumption from refrigerant during defrosting. As calculated, after the melted frost locally drained, the predicted total energy consumption could be decreased from 898.1 kJ to 727.5 kJ, and defrosting efficiency increased from 47.5% to 57.6%. This work is helpful to optimizing the intelligent control strategy of an air source heat pump unit, as well as saving energy for buildings.