Influence of operational parameters and intermittent start-stop strategy on thermal storage performance of ground heat exchangers

doi:10.19799/j.cnki.2095-4239.2025.0373

Abstract

Abstract:

Efficient regulation of charging parameters in borehole thermal energy Sstorage (BTES) systems is crucial for ensuring system efficiency and long-term stability. This study investigates the influence of key operational variables and intermittent start-stop strategies on thermal storage efficiency during the charging phase. A full-scale, three-dimensional transient simulation model is developed and validated using field data from a BTES demonstration project at Shenyang Jianzhu University, where initial ground temperature and soil thermal conductivity were 10.94 ℃ and 1.72 W/(m·K), respectively. The analysis examines the influence of inlet flow velocity, inlet temperature, and intermittent operation patterns on the heat storage process. Results reveal four primary findings: (1) The heat exchange ratio per borehole depth between double U-tubes and single U-tubes decreases from 2 to 1.4 over time, indicating that the structural advantage of double U-tubes diminishes with prolonged thermal storage. (2) As inlet flow velocity increases (0.07—1 m/s), the temperature difference between U-tube inlet and outlet declines, with double U-tubes exhibiting lower temperature differences than single U-tubes due to thermal short-circuiting effects. Optimal flow velocity ranges for single and double U-tubes are determined as 0.4—0.6 m/s and 0.2—0.4 m/s, respectively, based on the ratio of heat transfer to pressure drop. (3) Increasing the fluid inlet temperature from 30 ℃ to 80 ℃ elevates the soil temperature around the borehole, expanding the thermal influence radius from 0.4 to 0.85 m (a 112.5% increase). Heat exchange capacity and temperature difference exhibit linear growth with rising inlet temperature. (4) When the start-stop time ratio increases from 1 to 2, soil temperature at r = 0.2 m rises from 26.62 ℃ to 29.81 ℃, while recovery rate decreases from 17.53% to 7.65%. Intermittent operation reduces total heat storage by 13.38%—26.31% compared to continuous operation but improves heat exchange efficiency by 29%—47%, demonstrating its effectiveness in mitigating thermal accumulation and enhancing storage efficiency. These findings provide theoretical and practical insights for optimizing BTES operational strategies, supporting the design of more efficient seasonal thermal energy storage systems in cold regions.

Key words: buried pipes, seasonal thermal storage, operational parameters, intermittent operation, thermal response test, numerical simulation

CLC Number:

TK 52

Guohui FENG, Weidong LU, Xiru WANG, Kailiang HUANG, Xiaoke TIAN. Influence of operational parameters and intermittent start-stop strategy on thermal storage performance of ground heat exchangers[J]. Energy Storage Science and Technology, 2025, 14(10): 3785-3795.

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地层编号	地层名称	层底高度/m	层底深度/m	分层厚度/m	地层描述
1	土层	73.00	7.00	7.00	以粉质黏土为主，混较多碎石
2	泥沙	71.00	9.00	2.00	含有机质及粉细砂、石英质砂
3	米卵石	46.00	34.00	25.00	卵石为主，石英砂次之
4	粗砂	20.00	60.00	26.00	多为粗颗粒岩石如石英、长石等
5	岩石	0.00	80.00	20.00	全风化花岗岩

材料	导热系数/[W/(m·K)]	比热容/[J/(kg·℃)]	密度/(kg/m³)
土壤	1.72	1500	2500
回填	1.76	1500	2000

方案	运行模式	启停比
1	运行6 h，停机6 h	1
2	运行6 h，停机4 h	1.5
3	运行6 h，停机3 h	2
4	连续运行	ꝏ