Version 1
: Received: 23 July 2024 / Approved: 23 July 2024 / Online: 24 July 2024 (14:28:56 CEST)
How to cite:
Gambini, M.; Manno, M.; Vellini, M. Energy and Exergy Analysis of Transcritical CO2 Cycles for Heat Pump Applications. Preprints2024, 2024071879. https://doi.org/10.20944/preprints202407.1879.v1
Gambini, M.; Manno, M.; Vellini, M. Energy and Exergy Analysis of Transcritical CO2 Cycles for Heat Pump Applications. Preprints 2024, 2024071879. https://doi.org/10.20944/preprints202407.1879.v1
Gambini, M.; Manno, M.; Vellini, M. Energy and Exergy Analysis of Transcritical CO2 Cycles for Heat Pump Applications. Preprints2024, 2024071879. https://doi.org/10.20944/preprints202407.1879.v1
APA Style
Gambini, M., Manno, M., & Vellini, M. (2024). Energy and Exergy Analysis of Transcritical CO2 Cycles for Heat Pump Applications. Preprints. https://doi.org/10.20944/preprints202407.1879.v1
Chicago/Turabian Style
Gambini, M., Michele Manno and Michela Vellini. 2024 "Energy and Exergy Analysis of Transcritical CO2 Cycles for Heat Pump Applications" Preprints. https://doi.org/10.20944/preprints202407.1879.v1
Abstract
Heat pumps are recognized as a key tool in the energy transition toward a carbon-neutral society, enabling the electrification of the heating sector at least for low- and medium-temperature heat demands. In recent years, natural refrigerants have been reconsidered due to their low environmental impact: among them, CO2 is a safe option without impact on the ozone layer and low global warming potential compared to synthetic fluids. However, as a consequence of its thermophysical properties, its thermodynamic cycle is transcritical and is particularly suitable for specific end-user temperature profiles. This paper analyzes in a systematic and thorough way the most significant modifications to the reference cycle that have been proposed in the literature to improve the performance, finding how the optimum configurations change with a change in the rated operating conditions (inlet temperature and temperature glide of the heat demand, and ambient temperature). Exergy analysis explains why there is an optimal gas cooler pressure and why its trend with the average temperature is split into two distinct regions, clearly recognizable in all cycle layouts. The maximum coefficient of performance (COP) of the reference cycle varies in the 1.52–3.74 range, with a second-law efficiency of 6.436.1, for an optimal gas cooler pressure of up to 15.45MPa, depending on ambient temperature and end-user temperature profile. The most effective modification is the cycle with ejector and internal heat exchanger, which raises the COP to 1.84–4.40 (second-law efficiency 8.745.56). The presented results provide an extensive guide to understanding the behavior of a transcritical CO2 cycle and predict its performance in heat pump applications.
Keywords
Heat pump; natural refrigerants; CO2; thermodynamic cycle; transcritical cycle; energy analysis; exergy analysis; pinch point
Subject
Engineering, Energy and Fuel Technology
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
