A novel index model for defrosting initiating time point of air source heat pump based on the cusp catastrophe theory

Abstract

In winter, the operating performance of air source heat pump (ASHP) units deteriorates due to the accumulation of frost on the outdoor coil surface. In order to reduce the impact of this disaster phenomenon, ensure stable operation and save energy, it is necessary to accurately determine the initiation of defrosting after a period of unit operation. Although some existing defrosting initiation control strategies are effective, too much data volume and accuracy are required. To address these issues, a different perspective on mutation from previous studies is taken. This study combines the cusp catastrophe theory with frost accumulation, and presents a defrosting initiation index model for ASHP. After a brief description of the cusp catastrophe theory, the discriminant index model based on the cusp catastrophe theory (DICC) is proposed, state variable and control variables of the index model are determined. Then, the unit was tested for 10-days. To solve and verify the DICC, 10-days experimental data was used and it was found that DICC can efficiently predict the heating capacity decreases. Consequently, the DICC-based defrosting initiation control strategy was compared with the existing strategies, and the unit’s performance improvement compared to the original strategy was evaluated, as the results show, a 3.9% improvement in coefficient of performance (COP) and a 4.9% increase in heating capacity. Therefore, the strategy proposed in this paper is suitable for ASHP units with limited data capacity and low data accuracy, also can ensure the accurate initiation of defrosting and efficient operation.