Performance research on high temperature CO2 heat pump with supercritical enhanced gas injection

A novel high temperature CO2 heat pump cycle with supercritical enhanced gas injection was proposed to significantly improve heating performance under high temperature hydronic heating conditions. The numerical model of the high temperature CO2 heat pump system with supercritical gas injection was established, and the performance of the system was analyzed by EES (engineering equation solver) software. The influence of parameters such as evaporation temperature, middle pressure of compressor, gas cooler pressure, etc. on system performance at the high gas cooler outlet temperature was mainly studied. The results indicated that COP of 3.0 can be reached when the gas cooler outlet temperature was as high as 60℃. In comparison to common vapor injection system, the COP improved distinctly. As compared to conventional system without gas injection, the COP increased by 14.8%, 21.2%, 29.2% respectively with gas injection ratio of 0.3, 0.4, 0.5 at the gas cooler outlet temperature of 60℃. The influence of middle pressure and gas cooler pressure on COP have the same variation trend while the effect of gas cooler pressure is more significant. Besides, there exist an optimal gas cooler pressure and middle pressure. The optimal gas cooler pressure and middle pressure are 13.5MPa and 8.5MPa, respectively, when the gas cooler outlet temperature is 60℃ and the gas injection ratio is 0.4. © 2020, Chemical Industry Press. All right reserved.