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Enhancing reverse-cycle defrosting performance in CO₂ heat pump systems for electric buses: experimental investigation of metal thermal storage and horizontal exchanger configuration.

Author(s) : LEI Q., ZHANG C., SONG X., SHI J., CHEN J.

Type of article: IJR article

Summary

The application of carbon dioxide (CO₂) as an eco-friendly refrigerant in electric bus heat pumps presents sig nificant advantages for low-temperature operations, yet frosting on outdoor heat exchangers severely compro mises heating efficiency, passenger comfort, and vehicle range in cold climates. The development of an appropriate defrosting method is therefore important to improve the operating performance of the CO2 heat pump system during operations involving multiple frosting-defrosting cycles. Currently, there is a lack of studies focusing on performance improvement of CO₂ heat pumps during continuous frost-defrost cycles within a single operational period, as well as investigations into utilizing the thermal storage capacity of the indoor heat ex changers’ metal components to enhance defrosting efficiency. This study addresses the critical challenge of optimizing defrosting performance in CO₂ heat pump systems under multiple frosting-defrosting cycles. An experimental investigation was conducted to evaluate a novel reverse-cycle defrosting (RCD) strategy integrated with thermal energy storage from indoor heat exchangers. Experimental results demonstrate that the proposed RCD method maintains stable heating capacity and coefficient of performance (COP) across multiple frost-defrost cycles, with no performance degradation observed during prolonged operation. The heating capacity and co efficient of performance do not decrease with increasing number of frosting-defrosting cycles, which ensures that the heat pump system can operate for long time durations in low-temperature regions. In addition, using metal storage energy of the indoor heat exchangers can provide more than 20 % of the total defrosting energy, significantly increasing the electric bus’s defrost efficiency. These findings establish a robust framework for implementing CO₂ heat pump technology in electric buses operating in sub-zero environments, providing critical insights into energy-efficient defrosting strategies for sustainable transportation systems.

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Pages: 16 p.

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Details

  • Original title: Enhancing reverse-cycle defrosting performance in CO₂ heat pump systems for electric buses: experimental investigation of metal thermal storage and horizontal exchanger configuration.
  • Record ID : 30034484
  • Languages: English
  • Subject: Technology
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 181
  • Publication date: 2026/01
  • DOI: http://dx.doi.org/10.1016/j.ijrefrig.2025.10.008

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