Thermodynamic, environmental, and economic analysis of a novel dual-mode ejector-enhanced CO2 cooling and heating system

The widespread use of hydrofluorocarbons in air conditioners poses a significant threat to the climate due to their high global warming potential. CO2 as an environmentally friendly and safe working fluid is considered one of the promising alternative refrigerants. However, its application in residential air conditioners suffers from low energy efficiency, necessitating performance enhancements for both cooling and heating modes. This study proposes a novel dual-mode ejector-enhanced transcritical CO2 cycle (DEEC), which employs two dedicated ejectors for the cooling and heating modes, respectively. The cycle functions as an ejector-enhanced dual-temperature evaporation refrigeration cycle in cooling mode and as an ejector-boosted heat pump in heating mode. A comprehensive comparative analysis of the DEEC and the conventional vapor compression cycle (CVCC) was conducted using energy, exergy, environmental, and economic models. The results demonstrate that the coefficient of performance (COP) and exergy efficiency of the DEEC are increased by 23.9 %–32.9 % and 16.3 %–20.3 % in cooling mode, and by 10.2 %–13.9 % and 10 %–13.6 % in heating mode, respectively. Additionally, the annual performance factor is improved by 11 %–18.5 % across the evaluated cities. Environmental analysis indicates that the life cycle carbon emissions can be reduced by 9.6 %–15.2 %. Economic analysis reveals that the lifetime energy consumption cost of the DEEC is 9.9 %–15.7 % lower than that of the CVCC, with lower annual costs in all seven cities. This study can serve as a reference for the enhancement and optimization of CO2 air conditioning systems for both cooling and heating.