AccScience Publishing / GTI / Online First / DOI: 10.36922/GTI025320011
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Experimental investigation on the heating characteristics of a transcritical CO2 heat pump

Lingxiao Yang1 ,  Zhenqian Chen1,2*
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1 Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu, China
2 Jiangsu Provincial Key Laboratory of Solar Energy Science and Technology, School of Energy and Environment, Southeast University, Nanjing, Jiangsu, China
GTI, 025320011 https://doi.org/10.36922/GTI025320011
Received: 8 August 2025 | Revised: 4 November 2025 | Accepted: 7 November 2025 | Published online: 24 November 2025
© 2025 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
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Abstract

Inadequately configured operating parameters can have a detrimental effect on the performance of a transcritical CO2 heat pump due to the unique thermophysical properties of CO2. This study investigates the heat transfer characteristics of the gas cooler (GC) and the effects of three operating parameters on the heating process of the system. The results showed that: The temperature distribution of CO2 and water in the GC exhibited typical “two-region” and “three-zone” patterns; and the increase in discharge pressure enhanced the thermal quality of the GC CO2 side, thereby improving the heat output temperature. Nevertheless, higher thermal quality on the GC CO2 side can exacerbate the heat capacity mismatch between the two fluids, thereby reducing the system coefficient of performance (COP). Furthermore, increasing compressor speed (ncom) mitigated the mismatch in heat capacity caused by elevated thermal quality. Taken together, ncom resulted in a 14.7°C increase in heating temperature within the experimental range, accompanied by an 18.4% decrease in COP, showing the best performance among the three parameters studied. This study offers a critical reference for both the theoretical analysis and the control strategy of transcritical CO2 heat pumps, directly supporting the pursuit of efficient heating.

Keywords
Transcritical CO2 heat pump
Gas cooler
Compressor speed
Heating performance
Funding
This study was funded by the National Key Technologies Research and Development Program of China (Grant No. 2024YFB4007400).
Conflict of interest
The authors declare that they have no competing interests.
References
  1. Dai B, Qi H, Dou W, et al. Life cycle energy, emissions and cost evaluation of CO2 air source heat pump system to replace traditional heating methods for residential heating in China: System configurations. Ener Conv Manag. 2020;218:112954. doi: 10.1016/j.enconman.2020.112954

 

  1. Ge TS, Weng ZC, Huang R, Hu B, Eikevik TM, Dai YJ. High temperature transcritical CO2 heat pump with optimized tube-in-tube heat exchanger. Energy. 2023;283:129223. doi: 10.1016/j.energy.2023.129223

 

  1. Liao SM, Zhao TS, Jakobsen A. A correlation of optimal heat rejection pressures in transcritical carbon dioxide cycles. Appl Ther Eng. 2000;20(9):831-841. doi: 10.1016/S1359-4311(99)00070-8

 

  1. Lorentzen G. Revival of carbon dioxide as a refrigerant. Int J Refriger. 1994;17(5):292-301. doi: 10.1016/0140-7007(94)90059-0

 

  1. Song Y, Cui C, Yin X, Cao F. Advanced development and application of transcritical CO2 refrigeration and heat pump technology-a review. Ener Rep. 2022;8:7840-7869. doi: 10.1016/j.egyr.2022.05.233

 

  1. Liu R, Gao F, Liang K, et al. Thermodynamic evaluation of transcritical CO2 heat pump considering temperature matching under the constraint of heat transfer pinch point. J Therm Sci. 2021;30(3):869-879. doi: 10.1007/s11630-021-1373-z

 

  1. Wang X, Yang L, Xu B, Chen Z. Analysis of coupled heat transfer and flow behaviors of supercritical CO2 in horizontal circular tube. Int J Heat Fluid Flow. 2026;117:110064. doi: 10.1016/j.ijheatfluidflow.2025.110064

 

  1. Zhao W, Zhang Y, Sun C, Li L, Li B, Xu J. Thermodynamic analysis of a transcritical CO2 heat pump for heating applications. Energy. 2025;318:134896. doi: 10.1016/j.energy.2025.134896

 

  1. Zou H, Li X, Tang M, et al. Temperature stage matching and experimental investigation of high-temperature cascade heat pump with vapor injection. Energy. 2020;212:118734. doi: 10.1016/j.energy.2020.118734

 

  1. Chen YG. Pinch point analysis and design considerations of CO2 gas cooler for heat pump water heaters. Int J Refriger. 2016;69:136-146. doi: 10.1016/j.ijrefrig.2016.05.003

 

  1. Chen YG. Optimal heat rejection pressure of CO2 heat pump water heaters based on pinch point analysis. Int J Refriger. 2019;106:592-603. doi: 10.1016/j.ijrefrig.2019.04.003

 

  1. Ye Z, Wang Y, Song Y, Yin X, Cao F. Optimal discharge pressure in transcritical CO2 heat pump water heater with internal heat exchanger based on pinch point analysis. Int J Refriger. 2020;118:12-20. doi: 10.1016/j.ijrefrig.2020.06.003

 

  1. Cui Q, Wei D, Gao E, Zhang X. Compressor control strategy for CO2 heat pump toward efficient and stable domestic hot water production: An experimental investigation. Therm Sci Eng Prog. 2023;38:101681. doi: 10.1016/j.tsep.2023.101681

 

  1. Cui Q, Wang C, Gao E, Zhang X. Pinch point characteristics and performance evaluation of CO2 heat pump water heater under variable working conditions. Appl Therm Eng. 2022;207:118208. doi: 10.1016/j.applthermaleng.2022.118208

 

  1. Kline S, McClintock F. Describing uncertainties in single-sample experiments. J Mech Eng. 1998;1:3-17. doi: 10.1016/0894-1777(88)90043-X

 

  1. Yang L, Qin X, Zhao L, Ye S, Wei X, Zhang D. Analysis and comparison of influence factors of hot water temperature in transcritical CO2 heat pump water heater: An experimental study. Energy Conv Manag. 2019;198:111836. doi: 10.1016/j.enconman.2019.111836

 

  1. Yang LX, Wei XL, Zhao LH, Qin X, Zhang DW. Experimental study on the effect of compressor frequency on the performance of transcritical CO2 heat pump system with regenerator. Appl Therm Eng. 2019;150:1216-1223. doi: 10.1016/j.applthermaleng.2019.01.091

 

  1. Badache M, Ouzzane M, Eslami-Nejad P, Aidoun Z. Experimental study of a carbon dioxide direct-expansion ground source heat pump (CO2-DX-GSHP). Appl Therm Eng. 2018;130:1480-1488. doi: 10.1016/j.applthermaleng.2017.10.159

 

  1. Rabelo SN, Paulino TF, Duarte WM, Maia AAT, Machado L. Experimental analysis of the influence of the expansion valve opening on the performance of the small size CO2 solar assisted heat pump. Solar Ener. 2019;190:255-263. doi: 10.1016/j.solener.2019.08.013

 

  1. Liu X, Wang D, Peng X, Wang G, Yang Y. Experimental study on performance and compressor characteristics of transcritical CO2 heat pump system. Appl Therm Eng. 2024;250:123524. doi: 10.1016/j.applthermaleng.2024.123524

 

  1. Baek C, Heo J, Jung J, Cho H, Kim Y. Optimal control of the gas-cooler pressure of a CO2 heat pump using EEV opening and outdoor fan speed in the cooling mode. Int J Refriger. 2013;36(4):1276-1284. doi: 10.1016/j.ijrefrig.2013.02.009
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