Thermodynamic analyses of a novel ejector enhanced dual-temperature air source heat pump cycle with self-defrosting

Abstract

Previous studies have pointed out problems with the dual-temperature air source heat pump. Thus, this paper proposes a novel dual-temperature air source heat pump cycle with a self-defrosting method for simultaneous production of heat sources at different temperatures. An ejector was added to the novel system, which reduced the heat transfer temperature difference of the low-temperature condenser and the utilization of multiple heat sources. In addition, a new type of defrosting, which utilizes the heat from the hot liquid refrigerant to defrost the evaporator using two evaporators and a four-way valve, is used to reduce the energy needed for defrosting and decrease temperature fluctuations. Thermodynamic modeling using the energetic and exergetic analysis method was employed to evaluate the modified cycle performance and compare it with that of the basic heat pump cycle. Eco-friendly refrigerants, such as R134a, R600a, R290, and R1234yf, were adopted as the working fluid. The simulation results show that the heating coefficient and exergy efficiency in the proposed cycle were improved by 29.34% and 43.52%, respectively, compared with those of the standard cycle under typical operating conditions. Among the refrigerants, the eco-friendly refrigerant R600a exhibited the best performance under various operating conditions. Moreover, the COP in the new system was 20.72–44.47% higher than that of a traditional system, and the exergy efficiency improvement was 29.70–49.19% compared to the standard system. In summary, this study confirms the performance enhancement potential of an ejector-based dual-temperature air-source heat-pump cycle and provides theoretical support for its practical implementation.