Influence of different defrosting cycles on operating performance of air-source heat pumps

To investigate the influence of different defrosting cycles on the operating performance of air-source heat pump (ASHP) and find out the optimal defrosting cycle under different frosting conditions, tests the performance of ASHP with five different defrosting cycles under four kinds of frosting conditions in Beijing. Conducts the field tests under the condition of -2.1 to 5.6 ℃ of environmental temperature with an average temperature of 1.8 ℃，48% to 88% of relative humidity with an average of 68% and 40 ℃ of return water temperature. The results show that there exists an optimal defrosting cycle under the same condition, and it changes with the different conditions. In the optimal defrosting cycles, nominal frosting-defrosting loss efficiency is in the range of 24% to 36%, nominal heating coefficient and average COP are between 0.69 to 0.78 and 2.06 to 2.30 respectively. The performance of ASHP can be significantly improved in optimal defrosting cycles.