Abstract
At present, the output water temperature of most CO2 heat pumps is below 95°C. Herein, the reverse-Brayton cycle is innovatively applied to the CO2 heat pump to increase its output water temperature. A numerical model of a two-stage reverse-Brayton cycle with refrigerant injection and internal heat exchanger is proposed. The effects of discharge pressure, suction temperature, injection mass ratio, and pressure of refrigerant injection on COP of this system at different heat source temperatures are analyzed. Simulation results show that the highest COP can reach 3.05 with a discharge temperature of 129.1°C. The highest discharge temperature is 157.1°C and the temperature lift is 87.1°C with a COP of 2.85 correspondingly. High temperature hot water or steam is supplied by the proposed cycle with a respectable COP, which will broaden the application scope of CO2 heat pumps in industries. Moreover, relationship between COP and the payback period is revealed under typical conditions to evaluate the benefit of the proposed system.
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