Experimental Study on the Defrost Characteristics of an Air Source Heat Pump Unit with Split Fin-tube Heat Exchangers

In this paper, the defrost characteristics of an air source heat pump (ASHP) unit with the split fin-tube heat exchangers was investigated experimentally. The dynamic heating capacity, input power, the wall temperature of outdoor heat exchanger and pressures of the heat pump system were measured. The defrost losses of the ASHP unit under the different frost conditions were analyzed. The experimental results indicate that the power consumption of the heat pump unit and the heat absorbed from the air-conditioned rooms in the defrosting process increase with the reduction of the outdoor air temperature and relative humidity, especially when the temperature is below 0°C, the total defrost losses increase faster. With the increase in the outdoor air relative humidity, the frost thickness grows faster, therefore, the proportion of the defrost losses to the total energy consumption and heating quantity in the frost/defrost cycle increases rapidly, and the average heating capacity and COP of the ASHP unit on the frost/defrost cycle decrease, correspondingly. The average performance on the frost/defrost cycle of the ASHP unit with the split fin-tube heat exchangers degrades much more faster with the increase in the outdoor air relative humidity than that of the ASHP unit with the plane fin-tube heat exchangers.