Comparative Analysis of Transcritical CO2 Heat Pump Systems With and Without Ejector: Performance, Exergy, and Economic Perspective

To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO2 double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key innovation of this work lies in the integration of an ejector into the dual-source system, aiming to improve system performance and energy efficiency. This study systematically compares the conventional circulation mode and the proposed ejector-assisted circulation mode in terms of system performance, exergy efficiency, and the economic payback period. Experimental results reveal that the ejector-assisted mode not only achieves a higher water outlet temperature and reduces compressor power consumption but also improves the system’s exergy efficiency by 6.6% under the condition of the maximum outlet water temperature. Although the addition of the ejector increases initial manufacturing and maintenance costs, the payback periods of the two modes remain nearly the same. These findings confirm the feasibility and advantage of incorporating an ejector into a transcritical CO2 compression/ejection heat pump system with integrated air and water sources, offering a promising solution for efficient and environmentally friendly high-temperature water heating applications.