Determination of the defrosting duration ratio for defrosting performance evaluation of air source heat pump

Defrosting performance evaluation is an important aspect for pre-delivery inspection of air source heat pumps (ASHPs). According to GB/T 25127-2020 and ANSI/AHRI 550/590-2023, defrosting duration ratio (alpha) alpha ) should not exceed 20 % of the frosting-defrosting cycle. This value has remained unchanged for over 20 years. However, with the rapid iteration of defrosting technology, the alpha of new ASHPs has been decreased significantly. Hence, the applicability of this index value deserves to be deliberated. To solve this issue, a method for determining the optimal alpha was proposed firstly. Then, the alpha under different characteristic index ( CICO ) values at 2/1 degrees C and 2/0 degrees C were investigated at the optimal and original defrosting initiating time point ( t opt , t ori ), using twelve ASHPs from nine manufacturers. Results indicates the frosting duration (tf) t f ) is directly proportional to defrosting duration (tdf), t df ), at the same ambient air condition and CICO. . For Unit C, when t f is increased from 30.0 min to 60.0 min and 90.0 min at the CICO of 10.0 x 106, 6 , t df increases from 2.43 min to 3.20 min and 4.03 min at 2/1 degrees C, respectively. No matter at t opt nor t ori , the range of alpha is 1.4%-9.9 %. It is suggested that the 10 % is used as the new index for defrosting performance evaluation of ASHP.