Experimental and theoretical research on evaluation criterion for defrosting initiation time accuracy of air source heat pump

Abstract

The defrosting control strategy plays a critical role in influencing the heating performance and reliability of air source heat pump (ASHP). However, there is still a lack of a practical criterion to evaluate the defrosting initiation time accuracy. To solve this problem, an experimental bench was built, and the frosting-defrosting experiments using twenty-one ASHPs from nine manufacturers were conducted. Based on the variation characteristics of energy loss caused by frosting-defrosting, a new testing method, double-cycle method, was developed, which can determine the optimal defrosting initiation time by only two frosting-defrosting processes. Then, utilizing this method, the operation performance distribution at the optimal defrosting initiation time was analyzed, and an evaluation criterion for defrosting initiation time accuracy based on the attenuation rate of heating capacity was proposed. Results showed that the proposed double-cycle method can determine the optimal defrosting initiation time quickly and accurately. It can reduce the experimental duration for determining the optimal defrosting initiation time by 47.56 –56.64 %, and the relative errors in 90% of the experiments were within 5%. Then, by analyzing the operation parameters using this method, a new evaluation criterion, the attenuation rate of 5–20% in heating capacity, was proposed for defrosting initiation time accuracy.