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

• Published in: Energy and buildings 2023-11, Vol.298, p.113558, Article 113558
• Main Authors: Yang, Yushen, Peng, Xu, Wang, Guanghui, Liu, Xinxin, Wang, Dingbiao
• Format: Article
• Language: English
• Subjects: Cold region; COP; Exergy efficiency; Heating capacity; transcritical CO2 heat pump
• ISSN: 0378-7788
• DOI: 10.1016/j.enbuild.2023.113558

•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. 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 Qgc, COP and ηex 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 ηex. The COPopt and ηex,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 Qgc is at the cost of a decrease in COP, and COPopt decreases by 5.31%. The effect of the compressor frequency on ηex is different as the compressor discharge pressure elevates. Thus, a suitable operating condition, considering different needs, should be selected in the system operation.