A novel time-current-temperature difference (T-I-T) defrosting control method for air source heat pump based on outdoor fan operation characteristics in space heating

In space heating, air source heat pumps (ASHPs) always encounter mal-defrosting incidents, resulting in significant energy waste. To improve the defrosting accuracy of ASHP, this paper proposes a novel Time-Current-Temperature difference (T-I-T) defrosting control method based on the characteristic parameter of outdoor fan operation (current). Through theoretical analysis and experimental tests, the influence of frosting on the characteristic parameters of outdoor fan operation was revealed. Then, based on the optimal defrosting control point theory, a method for selecting the defrosting current threshold close to the actual ASHP was proposed. Ultimately, a novel Time-Current-Temperature Difference (T-I-T) defrosting control method was developed, using the current increment to control the defrosting operation. The results showed that, the defrosting current thresholds decreased as the severity of frosting decreases, from 1.52 to 0.78 A. The T-I-T defrosting control method enables the ASHP unit to operate stably and efficiently in space heating. The defrosting frequency decreased from 0.93 to 0.56 times per hour, a reduction of 39.80 %; the average duration of the frosting/defrosting cycle increases from 64.30 to 106.90 min (an increase of 66.25 %), and the average COP of the ASHP unit increases by 10.60 % compared to the T-T defrosting control method.