Experimental Investigation on Frost Growth and Dynamic Performance of an Air Source Heat Pump Unit under Frosting Conditions

摘要

The dynamic performance of an air source heat pump (ASHP) unit under frosting conditions was experimentally investigated considering the fan performance curves and variable evaporation temperature. The indoor air temperature is kept at 20°C, the experimental outdoor air temperature ranged from -15°C to 7°C and the relative humidity from 50% to 90%. The transient heating capacity, coefficient of performance (COP), and the frost accumulation mass on the outdoor heat exchanger surface were measured under frosting conditions. The effects of the outdoor air parameters on frost formation and the performance of the ASHP unit were analyzed. The experimental results indicate that the heating capacity and COP of the ASHP unit increase with the frosting time in the initial frosting stage, and they are more than these under non-frosting conditions in the period about 80% of the running time. In the later frosting stage the heating capacity, COP, and evaporation pressure decrease rapidly, i.e., there is a performance degradation point, after which the performance of the ASHP unit decrease rapidly. This is in good agreement with the author's simulation results. At the meantime, it was found that the frost accumulation rate is greatest when the outdoor air temperature is about 0-3°C without reference to the outdoor air relative humidity.