Theoretical study of a novel ejector-enhanced heat pump system with subcooling defrosting under cold conditions

Abstract

The two main barriers to using air source heat pumps in cold climates are low performance and the evaporator freezing up. To this end, this study proposes an ejector-enhanced heat pump system (EEC) with liquid subcooling defrosting, which combines scenario characteristics to switch different modes for efficient heating and uninterrupted defrosting. A mathematical model and a defrosting model of the novel system are developed. A novel performance evaluation coefficient is proposed. Theoretical study of the system’s heating and defrosting performance under different operating conditions. The heating coefficient of performance (COPh) of the system was 33.9 % and 17.7 % higher than the vapor compression cycle (VCC) under typical solar enhanced conditions and frost conditions, respectively. The COPh of the system during defrost is also 9.3 % higher than the VCC in normal operation under the same conditions. In comparison to R134a, the heating capacity of R290 and R600a has been observed to increase by 3.72 kW and 3.58 kW, respectively, with a 1.7 % increase and a 2.1 % decrease in COPh, respectively. Additionally, the pressure lift ratio of the ejector for the two in defrosting mode is found to be comparable to that of R134a. Therefore, the novel system, which employs the environmentally friendly refrigerant R290, is an appropriate means of providing domestic heating in cold regions. This study can theoretically support the popularization of air source heat pump systems.