Theoretical Performance Analysis of an Ejector Enhanced High-Temperature Heat Pump with Dual-Pressure Condensation and Evaporation

In this paper, an ejector enhanced high-temperature heat pump with dual-pressure condensation and evaporation is proposed to improve the system performance. Theoretical analyses of the system operation characteristics are conducted using energetic and exergetic methods. The performance comparisons among the basic cycle, parallel compression cycle, and ejector enhanced cycle are conducted with six different refrigerants, including R245fa, R600a, R1234ze(Z), R1336mzz(Z), R1224yd(Z), and R1233zd(E). The results demonstrate that environmentally-friendly refrigerant R1234ze(Z) would be a promising alternative refrigerant. Compared with the basic cycle and parallel compression cycle at selected operation conditions, 29.5% and 12.6% improvements in COP, and 16.7% and 11.1% higher system exergy efficiency are achieved in the ejector enhanced cycle on average. The volumetric heating capacity of the ejector enhanced cycle is increased by 15.7%–21.7%. The ejector enhanced cycle outperforms the other two cycles in high-temperature heat pump applications at the large temperature lift and temperature rise in the heat sink. The assessment offers an option to improve the energy utilization efficiency of the high-temperature heat pumps.