Heat transfer performance and dynamic effects of middle-shallow U-tube ground heat exchangers under geological stratification

Chang-zhe Wang; Feng Liu; Li-juan Yuan; Hua-jun Wang

doi:10.26599/JGSE.2026.9280101

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Wang CZ, Liu F, Yuan LJ, et al. Heat transfer performance and dynamic effects of middle-shallow U-tube ground heat exchangers under geological stratification. Journal of Groundwater Science and Engineering doi: 10.26599/JGSE.2026.9280101

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Heat transfer performance and dynamic effects of middle-shallow U-tube ground heat exchangers under geological stratification

doi: 10.26599/JGSE.2026.9280101

Chang-zhe Wang^{1, 2},
Feng Liu^{3, 4},
Li-juan Yuan²,
Hua-jun Wang^{1
,
,}

1.
School of Energy and Environment Engineering, Hebei University of Technology, Tianjin 300401, China
2.
Key Laboratory of Shallow Geothermal Energy, Ministry of Natural Resources of PRC, Beijing 100195, China
3.
Institute of Hydrogeology and Environment Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China
4.
Technology Innovation Center of Geothermal and Hot Dry Exploration and Development, Ministry of Natural Resources, Shijiazhuang 050061, China

More Information

Corresponding author: huajunwang@126.com
Received Date: 2025-08-11
Accepted Date: 2026-04-23

Available Online: 2026-06-26

Abstract

Abstract

Previous research has lacked sufficient attention to the heat exchange performance of middle-shallow U-tube ground heat exchangers (GHEs), particularly regarding the impact of vertical lithology heterogeneity. In this study, a heat transfer model of GHEs coupling vertical lithological variations and ground temperature distribution is established, based on field test data of middle-shallow boreholes in Langfang, Hebei Province. The heat transfer characteristics of GHEs within the depth of 200–300 m and their influencing factors are analyzed. Results show that the flow velocity and wall thickness strongly affect the heat transfer of middle-shallow GHEs. Increasing the flow rate helps to enhance heat transfer, but is not conducive to improving energy efficiency of the system due to higher power consumption of circulating pumps. There is an optimal flow rate range of 2–3 m³/h for PE-RT GHEs. Furthermore, reducing the wall thickness from 8 mm to 3 mm can significantly improve the heat transfer per unit depth by 10–12% for PE-RT GHEs. The thermal influence distance (TID) of GHEs exhibits significant lithological differences and seasonal variations along the depth. As the depth increases, the TID in winter and summer exhibits increasing and decreasing trends, respectively. Especially, the TID of sandy layers due to a high thermal conductivity is greater than that of clay layers under the same conditions. For 250–300 m deep GHEs, the maximum TID reaches 5.8 m in winter and 7.3 m in summer, respectively, after running for five years. The heat transfer performance of middle-shallow GHEs has an attenuation risk of up to 33–35% during long-term operation, which can be alleviated using an intermittent operation strategy. The present findings can offer a useful reference for the design and optimization of middle-shallow GHEs in similar geological conditions.
- Middle-shallow U-tube ground heat exchangers,
- Heat transfer performance,
- Thermal influence distance,
- Long-term performance

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References(29)

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