陕北地区中深层同轴地埋管取热性能影响因素分析及优化

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 2 500 m to 3 500 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 3 200 m. In this case, the average energy cost is 0.524 CNY/kWh, suggesting the optimal economic benefits.