A newly designed air-source heat pump system with liquid subcooling defrosting: Simulation and experiment

A new type of air-source heat pump system with liquid subcooling defrosting (ASHPSD) was proposed, in which a hot liquid refrigerant is used for defrosting; further, the outdoor unit of the system comprises multiple evaporators. In the process of frosting and defrosting, a finite-time, steady-state thermodynamic method was adopted to establish a simulation model of heat and mass transfer. Simulation results demonstrate that the defrosting performance of the heat pump system is optimal when the number of evaporators is four. Furthermore, the heat and mass transfer in the process of frosting and defrosting was calculated, particularly the variation in frost layer thickness with time. An experimental apparatus for the ASHPSD system was developed, following which its defrosting performance was experimentally investigated. Experimental results show that the energy efficiency ratio of the system can still reach 2.32 when the outdoor air temperature is - 10celcius.