A novel defrosting initiating method for air source heat pumps based on the optimal defrosting initiating time point

Abstract

Air source heat pumps (ASHPs) have been widely used for space heating in recent years. When a space heating ASHP unit is operated in frosting conditions, periodic defrosting is necessary to ensure its safe and efficient operation. Therefore, it is important to develop appropriate defrosting initiating method for best possible operating performances and energy efficiency of ASHPs during frosting-defrosting operations. As a result, a study on the development of a novel defrosting initiating method for ASHPs based on the optimal defrosting initiating time point has been carried out and the study results are presented in this paper. Firstly, various existing defrosting methods for ASHPs are briefly reviewed. Secondly, the development of a novel defrosting initiating method based on the optimal defrosting initiating time point is detailed. Finally, field tests with a field ASHP unit using the novel defrosting initiating method have been carried out, and the tests results demonstrated that the novel defrosting initiating method can respond to the changes in frosting environmental conditions and correctly evaluate the optimal defrosting initiating time point of the field ASHP unit. It was further shown that the use of novel defrosting initiating method can help greatly improve the output heating capacity and COP of the field ASHP unit, by 36.79% and 27.85%, respectively, as compared with the use of T-T defrosting method, the most commonly used defrosting initiating method currently, during frosting-defrosting operations.