Performance evaluation of a novel transcritical CO2 dual-mode ejector-enhanced cycle
The development of sustainable energy technologies is crucial for mitigating climate change. Currently, the widely used hydrofluorocarbons (HFCs) pose a significant climate threat due to their high global warming potential (GWP), making their substitution particularly urgent. CO2, as a natural, environmentally friendly, and safe working fluid, is considered one of the promising alternative refrigerants. To improve the performance of CO2 cooling and heating, this study proposes a novel CO2 dual-mode ejector-enhanced heat pump cycle (DEEC). This cycle operates as a dual-temperature ejector expansion refrigeration cycle in cooling mode and as an ejector-boosted heat pump in heating mode. Compared with the conventional vapor compression cycle (CVCC), the DEEC features two dedicated ejectors for the cooling and heating modes, respectively, which effectively reduces throttling losses and lowers the compressor pressure ratio, resulting in a significant improvement in cycle efficiency. Moreover, the optimized cycle configuration achieves effective thermal matching between the air and refrigerant, reducing irreversible losses during heat exchange. The performance of the DEEC was evaluated against the CVCC through energy and exergy analysis. The results demonstrate that across the studied parameter range, the DEEC shows an improvement in the coefficient of performance for cooling (COPc) and heating (COPh) of 22.9%-32.4% and 8.8%-13.9%, respectively, compared with CVCC. Furthermore, the exergy efficiency of the DEEC is 16.2%-20.7% higher under cooling mode and 10.6%-11.2% higher under heating mode. The proposed CO2 ejector-enhanced cycle demonstrates promising application potential in fields requiring efficient cooling and heating, such as building spaces and vehicles.