The frost restraining effect of solar air collector applied to air source heat pump

The air source heat pump has been demonstrated to be an efficient clean space heating technology, but the frosting on the exterior surface of the evaporator will largely decrease its performance. In this paper, the triangular solar air collector is adopted for evaporator frost restraint of the air source heat pump, and the dynamic heat transfer model of the triangular solar air collector and quasi-steady-state frosting model of the evaporator were established and coupled. The effect of frost layer thickness variation on evaporator air flow is considered based on the resistance factor to improve the applicability of the model. The heat flux and water vapor diffusion flux at different frost time and frost thickness were calculated, and the frosting characteristics of the air source heat pump with the triangular solar air collector and the conventional air source heat pump were compared on varying working conditions and typical daily meteorological parameters. Results show that triangular solar air collector can effectively restrain the frosting of the air source heat pump, and when the solar irradiance is 500 W/m2, the triangular solar air collector can reduce the frost thickness by more than 15 %. The triangular solar air collector increases the total heat flux by 101.4 W/m2 under frosting conditions, which reduces half of the defrosting times and increases the heat exchange of the evaporator by 36.6 % during a typical day, indicating that triangular solar air collector significantly improved the energy efficiency of air source heat pump on frosting condition.