A prediction model of the optimal defrosting initiating time for the air source heat pumps with different configurations and operations

Abstract

Frosting is a critical challenge that affects the energy efficiency of air source heat pumps (ASHPs). Defrosting periodically is the most widely used method to solve this problem. However, the rate of frosting varies considerably for ASHPs due to their configurations and operations (CICO) being different. This leads to the obvious differences in their defrosting initiating time. Defrosting too early or too late will both cause energy loss. To ensure the efficient operation of ASHPs, the variations of energy loss coefficient caused by frosting-defrosting (εNL) and the defrosting initiating time for ASHPs with different CICO values were investigated. Based on the theory of optimal defrosting initiating time (Topt) and experimental results under different frosting durations, the Topt for different ASHPs is found. Then, a prediction model for ASHPs with different CICO values is established. Results show that there is a Topt for ASHPs with different CICO values, respectively. Under the frosting condition of 2/1 ℃, the Topt increases with the rise of CICO values. When the CICO values increase from 3.14 to 22.44, the corresponding Topt increases from 22 min to 148 min. By fitting the Topt and CICO values, a cubic mathematical model for the prediction of the optimal defrosting time of ASHPs has been developed.