Thermodynamic performance study on a novel trans-critical CO2 heat pump cycle integrated with expander and internal heat exchanger

This paper presents a novel trans-critical CO2 heat pump cycle with expander (TCCE) for increasing COP in the warm period and the suction preheating in the cold period. This cycle has two main operation modes. One is TCCEA for warm period and the other is TCCEB for cold period. Theoretical simulations are conducted to study energy efficiency and exergy efficiency of this novel cycle as well as the basic cycle. The results show that in the warm period TCCEA has an excellent COP and exergy efficiency and at low discharge pressure, the COP of TCCEA is improved by up to 31.49% compared with the basic cycle. Additionally, in the cold period, using TCCEB is helpful to avoid liquid suction. Compared with the basic cycle, the heating capacity of TCCEB can be improved by up to 12%. Taking the heating capacity into account, TCCEB is the best system under the warm period. According to the simulation results, this novel cycle is better suited for warm or cold weather.