The application of thermoelectric and ejector in a CO2 direct-expansion ground source heat pump; energy and exergy analysis

The thermodynamic analysis of a horizontal CO2 direct-expansion ground source heat pump in transcritical cycle was performed to investigate the influence of using thermoelectric sub-cooler and the ejector on the performance parameters of the cycle. A comparative analysis was conducted between the Base cycle and the cycles with ejector and thermoelectric sub-cooler considering the pressure drops in the gas cooler and the ground heat exchanger. The effects of compressor inlet temperature, soil temperature, thermoelectric sub-cooler length, thermoelectric sub-cooler cooling water mass flow rate, and ground heat exchanger outlet temperature on different performance parameters of the cycles were studied. The results demonstrated that the application of ejector exhibits a more stable operation of the cycle and increasing its COP by 16.5% as compared to the Base cycle considering the same ground heat exchanger length. Also, the length of ground heat exchanger is considerably decreased by using the ejector considering the same COP for the Base and EJR cycles. Besides, thermoelectric sub-cooler decreases the irreversibilities of the cycle by generation more power, thereby COP is boosted by 16% as compared to the Base cycle. Furthermore, the major irreversibility in the cycle with thermoelectric and ejector is occurred in the compressor and followed by ejector, ground heat exchanger, gas cooler, thermoelectric sub-cooler, and the expansion valve, respectively.