Thermodynamic analysis of a modified vapor-injection heat pump cycle using an ejector

This paper presents a modified sub-cooler vapor-injection (MSV) cycle with an ejector for air source heat pump applications. The added ejector is used to realize two condensation temperatures for the cycle by using its pressure lift ability and effectively improve cycle performance. The cycle performances are evaluated through thermodynamics methods and compared with those of a basic sub-cooler vapor-injection (BSV) cycle. The results show that compared with the BSV cycle, the heating coefficient of performance (COPh), the volumetric heating capacity and the exergy efficiency of the MSV cycle are increased by 10.1%, 6.3% and 14.1% under a typical operating condition, respectively. The COPh of the MSV cycle using three low-GWP substitutes (R1234yf, R1234ze(E) and R32) are compared with R134a. The results indicate that among them, R1234ze(E) is the most promising refrigerant for improving MSV cycle performance while replacing R134a. It can be concluded that the MSV cycle has a better heating performance by the introduction of the ejector, and thus could offer potential benefits for applications in air source heat pumps.