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Thermo-economic evaluation of low-GWP CO2-based zeotropic mixtures in space heating heat pumps with and without internal heat exchanger.

Author(s) : ZENDEHBOUDI A.

Type of article: IJR article

Summary

Transcritical CO2 heat pumps are commonly used for tap water heating in buildings; however, their performance is often limited in space heating applications. Low-GWP CO2-based mixtures can enhance subcritical operation and reduce irreversibility during transcritical processes. Promoting this technology requires a comprehensive understanding of its thermo-economic performance; yet, there is a lack of relevant studies. This paper develops thermodynamic models using energy, exergy, and exergoeconomic analyses to evaluate the performance of four CO2-binary mixtures (CO2/R41, CO2/R1234yf, CO2/R290, and CO2/R1270) in space heating heat pumps. These mixtures are compared against pure CO2 in two cycle configurations: with and without an internal heat exchanger (IHX). The evaluation is conducted in accordance with the EN 14511–2 standard across various heating temperatures. Results indicate that the CO2/R41 blend achieves significant COP improvements, exceeding pure CO2 by up to 17.1% at 30/35 ° and 8.3% at 47/55 °. CO2-based mixtures also significantly lower optimal discharge pressures, with reductions ranging from 24.4% for CO2/R41 to 52.9% for CO2/R1270. The inclusion of an IHX has a notable effect on COP, particularly for CO2/R41, where performance improves when the CO2 mass fraction exceeds 70% at lower temperatures. Exergy analysis demonstrates that the CO2/R41 mixture achieves the highest exergy efficiency up to and including a CO2 mass fraction of 80%, outperforming pure CO2 by up to 16.3%. Furthermore, CO2/R41 exhibits 16.3%–19.8% lower total exergy destruction cost rates compared to pure CO2, with significant cost reductions in the throttling valve (25.5%–42.5%). These findings highlight the potential of CO2/R41 as a highly effective and economically viable option for space heating heat pumps, offering superior performance and reduced operational costs compared to pure CO2 and other mixtures.

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Details

  • Original title: Thermo-economic evaluation of low-GWP CO2-based zeotropic mixtures in space heating heat pumps with and without internal heat exchanger.
  • Record ID : 30033749
  • Languages: English
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 173
  • Publication date: 2025/05
  • DOI: http://dx.doi.org/10.1016/j.ijrefrig.2025.01.036

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