Energetic and exergetic analysis of a transcritical CO<inf>2</inf> air-source heat pump water heating system in the cold region: Fid-Bau Portal

Energetic and exergetic analysis of a transcritical CO2 air-source heat pump water heating system in the cold region

Yang, Yushen / Peng, Xu / Wang, Guanghui / Liu, Xinxin / Wang, Dingbiao

Highlights • The numerical model and simulation algorithm of the transcritical CO2 air-source heat pump water heating system are set up and verified. • The effects of operating parameters on the system performance are investigated under the low-temperature condition. • The optimal coefficient of performance and exergy efficiency exist in the system. • The system has a suitable operating condition.

Abstract To analyze the energetic and exergetic performance of the transcritical CO2 air-source heat pump water heating system in the cold region, the numerical model and simulation algorithm are set up and verified with the experiments. Under the low ambient temperature (−15 °C to 0 °C) and water inlet temperature (9 °C), the performance evaluation of the system is investigated using the developed numerical model at different compressor frequency (75, 80 and 85 Hz). The results show that Q gc, COP and η ex decrease by 14.47%, 12.78% and 20.83% respectively as the ambient temperature decreases from 0 °C to −15 °C. The CO2 outlet state of the gas cooler and corresponding slope of isotherms have significant effects on COP and η ex. The COP opt and η ex,opt exist in the system but at different compressor discharge pressures. With the compressor frequency increasing from 75 Hz to 85 Hz, the increase in Q gc is at the cost of a decrease in COP, and COP opt decreases by 5.31%. The effect of the compressor frequency on η ex is different as the compressor discharge pressure elevates. Thus, a suitable operating condition, considering different needs, should be selected in the system operation.