Thermodynamic analyses on an ejector enhanced CO2 transcritical heat pump cycle with vapor-injection

• An ejector enhanced vapor injection CO2 transcritical heat pump cycle is proposed.
• Energetic and exergetic methods are carried out to analyze the system performance.
• Component exergy efficiency is introduced to evaluate the ejector performance.
• The ejector could effectively improve system COP and volumetric heating capacity.

In this paper, an ejector enhanced vapor injection CO2 transcritical heat pump cycle with sub-cooler (ESCVI) for heating application in cold regions is proposed. The thermodynamic analysis using energetic and exegetic methods is carried out to predict the performance characteristics of the ejector enhanced cycle, and then compared with those of the conventional vapor injection heat pump cycle with sub-cooler (SCVI). The simulation results demonstrate that the ejector enhanced cycle exhibits better performance than the conventional vapor injection cycle under the specified operating conditions. The improvements of the maximum system COP and volumetric heating capacity could reach up to 7.7% and 9.5%, respectively. Exergetic analysis indicates that the largest exergy destruction ratio is generated at the compressor followed by the evaporator and gas cooler. Additionally, the exergy efficiency of the ejector is introduced to quantify the effectiveness of the exergy recovery process, which may be a new criterion to evaluate the performance of the ejector enhanced vapor compression cycle.