Investigation of the horizontally-butted borehole heat exchanger based on a semi-analytical method considering groundwater seepage and geothermal gradient

Goaf treatment and comprehensive utilization of geothermal energy are great significance to the restoration of land resources and sustainable development of energy in coal mining subsidence areas. In this paper, goaf treatment technology and geothermal energy development technology are reviewed in detail. Among them, the goaf treatment technology mainly includes: caving treatment method, filling treatment method, support method, closed isolation method and joint treatment method. Geothermal development technology mainly includes: shallow ground source heat pump technology, coaxial casing development technology, pumping and reinjection technology, directional drilling technology, U-type precision docking drilling technology. The systematic idea of filling treatment and geothermal comprehensive utilization in coal mining subsidence area is proposed, and the technology is described in detail through three cases. The research results can provide innovative inspiration for subsidence control and comprehensive utilization of geothermal energy in coal mining subsidence area, and has broad application prospects.

Section: U-type Precision Docking Drilling Technologymentioning

confidence: 99%

Research on goaf treatment and geothermal comprehensive utilization technology in coal mining subsidence area

Yang

2022

“…In the past few decades, many studies on clean energy have been conducted [2,3]. Geothermal energy and solar energy have achieved significant development due to the advantages of wide distribution and large reserves [4,5]. The medium-deep geothermal energy can avoid some drawbacks of shallow geothermal energy.…”

Section: Introductionmentioning

confidence: 99%

Performance prediction and analysis of a solar assisted medium-deep geothermal heating system

Zhang,

Tao,

et al. 2024

The solar assisted medium-deep geothermal heating (SAMGH) system is a novel kind of heating system that can combine the benefits of geothermal and solar energy. However, the variations in borehole heat exchanger (BHE) performance and the intermittency of solar energy pose challenges for predicting the overall performance of the coupled system and designing the operational strategies. To conduct simulation on the SAMGH system for performance prediction and analysis, a coaxial medium-deep borehole heat exchanger coupled with the solar energy heating system for an office building in Xi’an was developed. The TRNSYS software was employed to establish the model of the coupled system. A ground source heat pump (GSHP) heating system was used for comparison. The simulation results showed that with the introduction of the solar energy and heat storage modules, the annual operating time of the geothermal system only accounts for 32.06%. The energy consumption of the coupled system can be reduced from 63585 kW to 44586 kW, and the energy consumption proportion of the geothermal system in total value decreased from 69.10% to 40.58%. Therefore, the average coefficient of performance (COP) of the heat pump and the system were improved by 63.71% and 91.77%, respectively. Moreover, because the solar energy is beneficial to the ground heat recovery, the average ground temperature increased from 42.5 °C to 43.88 °C after ten years of operation. The proposed design method and simulation results can serve as a reference for design method and performance analysis of the geothermal and solar coupled system.

“…The ground heat exchangers (GHEs) are extensively employed in geothermal systems for building cooling or heating. Compared with shallow GHEs, the deep GHEs can be used for heating with higher performance, because they utilize the geothermal energy in the high-temperature soils and rocks in IOP Publishing doi:10.1088/1755-1315/1074/1/012001 2 deep strata [2,3]. Due to this point, the deep GHE has been regarded as a superior solution for building heating in China [5,6].…”

Section: Introductionmentioning

confidence: 99%

A case study on long-term performance optimization of a geothermal heating system

Jia

Duan²,

Xue

et al. 2022

The optimal use of geothermal energy necessitates the performance evaluation and economic analysis of the geothermal heating systems. This work presented a field study of the long-term operating performance of a geothermal heating system in Xixian New Area, China. Nine deep coaxial ground heat exchangers (GHEs) with depths of 2,500 m were adopted for space heating to the residential buildings, with a total heating area and heating load of 136,097.71 m2 and 6,082 kW, respectively. The system’s 30-year running performance at various volumetric flow rates and operating modes was simulated. Through response surface analysis and multi-objective optimization, the levelized cost of energy (LCOE) and payback period were obtained based on the thermal performance analysis. It is concluded that the operating parameters have a significant impact on the system economy. When the daily operating time reduces from 24 hours to 8 hours, the payback period will be lowered from more than 25 years to approximately 11 years. When the volumetric flow rate is 35 m3·h-1, the examined system achieves the lowest LCOE. The minimum values of LCOE are 13.2 $/GJ, 11.6 $/GJ, 9.4 $/GJ, 7.8 $/GJ and 5.6 $/GJ when the system operates 24 hours (continuous operation), 20 hours, 16 hours, 12 hours and 8 hours a day, respectively. With the optimal flow rate, the average heat exchange rate of the single GHE increases from 295 kW to 519 kW after 30 years of operation when the daily operating time is reduced from 20 hours to 8 hours. The proposed method and findings can be used to guide the high-efficiency operation, which is conducive to reducing operating costs of geothermal heating systems.