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Approaching optimal high pressure by charge management in transcritical CO2 heat pump water heater.

Number: No 117

Author(s) : HE Y. J., LIANG X. Y., CHENG J. H., SHAO L. L., ZHANG C. L.

Summary

Transcritical CO2 cycle has been widely applied in heat pump systems. Optimal high pressure is crucial to the performance of transcritical CO2 heat pump water heater (HPWH). However, current techniques for high pressure control cannot meet the requirements of easy-to-implement and low COP loss simultaneously. From the perspective of charge management, this work aims to approach optimal high pressure in CO2 HPWH without high pressure control. By modeling a running CO2 HPWH, we in-depth investigated the relationship between optimal high pressure and refrigerant charge. It was found that for practical systems, the essence of optimal high pressure control is to manage optimum refrigerant charge of the system. If the optimum charge of the system remains constant under any working conditions, the system can be guaranteed at optimal high pressure with fixed refrigerant charge. Then the influence of water inlet temperature, water outlet temperature and ambient temperature on optimum refrigerant charge was analyzed. Two system design methods with the aim of minimizing the change of optimum charge under different working conditions are presented, which are re-sizing heat exchangers and adding additional refrigerant reservoir. The minimum average COP loss of the redesigned system can be reduced to only 2.82% and 0.67%, respectively.

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Pages: 13 p.

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  • Original title: Approaching optimal high pressure by charge management in transcritical CO2 heat pump water heater.
  • Record ID : 30029992
  • Languages: English
  • Subject: Technology
  • Source: 13th IEA Heat Pump Conference 2021: Heat Pumps – Mission for the Green World. Conference proceedings [full papers]
  • Publication date: 2021/08/31

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