Thermal Performance of Borehole Heat Exchangers with Varying Borehole Depths in Cold Regions: Implications from In Situ Thermal Response Tests

Zezhou Yan, Qi Zhang, Ming Yang, Peiyu Zeng, Jin Luo () and Deshan Cui ()
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Zezhou Yan: Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China
Qi Zhang: Key Laboratory of Geotechnical Mechanics and Engineering of the Ministry of Water Resources, Changjiang River Scientific Research Institute, Wuhan 430010, China
Ming Yang: Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China
Peiyu Zeng: Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China
Jin Luo: Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China
Deshan Cui: Faculty of Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China

Energies, 2025, vol. 18, issue 21, 1-18

Abstract: In cold regions, performance reduction in a Ground-Coupled Heat Pump (GSHP) system has been frequently reported. Many operational strategies have been adopted to mitigate such an undesirable phenomenon. However, these strategies have limited effects because the specific heat rate of Borehole Heat Exchangers (BHEs) is usually treated as constant. In this study, eight BHEs were installed in typical loess areas in Northwestern China to investigate how borehole depth affects its thermal performance. Thermal response tests (TRTs) showed that deeper boreholes led to a higher fluid outlet temperature. Compared to 150 m and 100 m boreholes, the energy coefficient factor (η) for a 200 m borehole increased by 18.02% and 45.0%, respectively. Numerical simulation also confirmed that deeper BHEs perform better. In addition, the initial ground temperature influences the thermal performance sensitively, but in the opposite way for heating and cooling modes. These findings offer valuable insights for installing GSHP systems to achieve sustainable and high thermal performance in cold regions.

Keywords: shallow geothermal energy resources; Ground Source Heat Pump (GSHP); Borehole Heat Exchanger (BHE); thermal sustainability; borehole depth; cold regions (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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