Influencing factor analysis and optimization of heat extraction performance of moderately deep coaxial borehole heat exchangers in northern Shaanxi, China

Authors

ZOU Haijiang, Shaanxi Hancheng Tianjiu Grouting Exploration Co., Ltd., Weinan 715499, China; School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, ChinaFollow
LI Yongpeng, School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
ZHANG Lin, Shaanxi Hancheng Tianjiu Grouting Exploration Co., Ltd., Weinan 715499, China
HUI Peng, Shaanxi Hancheng Tianjiu Grouting Exploration Co., Ltd., Weinan 715499, China
LIU Houning, Shaanxi Hancheng Tianjiu Grouting Exploration Co., Ltd., Weinan 715499, China
SHEN Fang, Shaanxi Hancheng Tianjiu Grouting Exploration Co., Ltd., Weinan 715499, China
WANG Fenghao, School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, ChinaFollow

Abstract

The geothermal heating technology utilizing moderately deep coaxial borehole heat exchangers (MDCBHEs) has emerged and found extensive applications in urban heating in northern China. Despite abundant geothermal resources, northern Shaanxi exhibits slightly low geothermal gradients and distinct thermophysical properties of rocks and soils. Therefore, geological parameters influence the heat transfer performance of MDCBHEs in this area. Using OpenGeoSys, an open-source numerical simulation platform, this study established a three-dimensional calculation model for heat transfer between a MDCBHE and surrounding strata. Based on typical geological parameters in northern Shaanxi, the study investigated the influence of various design parameters on the heat transfer performance of MDCBHEs, as well as their techno-economic feasibility during their life cycle. Finally, this study selected the optimal parameters of MDCBHEs for geothermal engineering. Results indicate that increasing the outer diameter of outer pipes and the burial depth can both enhance the heat extraction capacity of a MDCBHE. Notably, compared to the outer diameter of outer pipes, the burial depth produced more significant effects on the capacity. Specifically, the nominal heat transfer capacity increased by 77.3% when the burial depth rose from 2500 m to 3500 m. Engineering practices reveal that when the outer diameter of outer pipes exceeds 177.80 mm × 9.19 mm, the average energy cost will increase due to a sharp rise in drilling costs. Under the specific operating parameters, this study recommends that the optimal design parameters of MDCBHEs should comprise an outer diameter of outer pipes of 177.80 mm × 9.19 mm and a burial depth of 3200 m. In this case, the average energy cost is 0.524 CNY/(kW·h), suggesting the optimal economic benefits.

Keywords

moderately deep, coaxial borehole heat exchanger, heat transfer performance, numerical simulation, economy, burial depth, pipe diameter, OpenGeoSys

DOI

10.12363/issn.1001-1986.23.06.0365

Recommended Citation

ZOU Haijiang, LI Yongpeng, ZHANG Lin, et al. (2024) "Influencing factor analysis and optimization of heat extraction performance of moderately deep coaxial borehole heat exchangers in northern Shaanxi, China," Coal Geology & Exploration: Vol. 52: Iss. 1, Article 15.
DOI: 10.12363/issn.1001-1986.23.06.0365
Available at: https://cge.researchcommons.org/journal/vol52/iss1/15

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