Thermodynamic performance improvement and economic analysis of CO2 transcritical heat pump system

The optimization of the thermodynamic performance of the CO2 transcritical heat pump system often increases the initial investment cost of the equipment, and its impact on the overall cost during the equipment life cycle is unclear. In this paper, thermodynamic and economic models of conventional CO2 transcritical heat pump system (BASE), CO2 two-stage compression heat pump system (TSCHPS), and CO2/CO2 mechanical subcooling heat pump system (MSHPS), were established. In the economic model, the objective function was defined via considering the initial investment and operation cost of the equipment. The relationship between the thermodynamics and economy was studied through using three heat pump systems with small temperature difference fan-coil unit (STD-FCU), floor-coil radiator (FCR), and traditional designed radiator (TDR) as heat dissipation terminals. The economic change during the life cycle after the system upgrade was discussed. The results showed that the COP of TSCHPS and MSHPS were both improved by over 15% than that of the BASE system under the system nominal conditions of the three heat dissipation terminals, but their life cycle economy is not necessarily improved. There is a correlation between the thermodynamic performance and economy of the BASE system, but the correlation between the thermodynamic performance and economy of TSCHPS and MSHPS is not strong. The economic change after the system upgrade is related to the evaporation temperature and heat capacity, and the best economic system in different application ranges under three heat dissipation terminals is provided. © 2021, Chemical Industry Press Co., Ltd. All right reserved.