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In the context of reducing carbon emission, Deep Borehole Heat Exchanger (DBHE) array has a large potential in extracting geothermal energy to provide building heating in densely populated urban areas. To investigate the thermal interaction among the DBHE, a comprehensive numerical model has been built with the OpenGeoSys software, and it is validated by monitoring data from a pilot project in Xi'an, China. The long-term simulations manifest that the outlet temperature of the DBHE array has a noticeable draw-down of 4.70 ° C over 20 years in comparison to the single borehole setup. The maximum difference of outlet temperature among individual DBHE can reach up to 0.88 ° C over 20 years, which will lead to a shifted thermal load of 23.35 kW (12.25 % of the designed average value). Based on the predicted subsurface temperature distribution, a non-linear correlation can be established between the drawdown in working fluid temperature and the accumulated amount of extracted heat. The finding of work implies that the thermal interaction among individual DBHE is of significance for the sustainability of the system, and comprehensive numerical modeling should be considered in the designing procedure. • A numerical model for depicting the interaction among multiple DBHEs is established. • The model is validated against the monitoring data within one heating season. • DBHE array suffers more attenuation than single DBHE in heat extraction performance. • Load shifting behaviors caused by thermal interaction in DBHE array are not severe. • Energy analysis could be another perspective for studying the sustainability of DBHE. [ABSTRACT FROM AUTHOR]

To meet the prospect of carbon neutrality, Deep borehole heat exchanger (DBHE) shows good potentiality in extracting deep geothermal energy for building heating, especially in densely populated urban areas of northern China. To investigate the influence on different soil thermal properties and system layouts of the DBHE array, a comprehensive numerical model has been established by OpenGeoSys software coupled TESPy toolkit and a series of scenarios are simulated. Results show that thermal conductivity lay a more important influence on heat extraction performance for DBHE array, rather than volumetric heat capacity. The thermal plume of DBHE array will grow larger along with higher thermal diffusivity. For typical geological parameters in Xi'an, the inter-borehole spacing should not be set below 15 m or it will bring a risk of freeze in circulation. The heat extraction performance and long-term sustainability of single-line layout are obviously better than other layout patterns, also with a smaller ground area needed to deploy the boreholes. This study implies that soil thermal conductivity is the core factor in determining the heat extraction performance of DBHE array and also gives suggestions for the system design of DBHE array in the aspect of borehole spacing and system arrangement. • Long-term performance evaluation under different soil thermal properties for DBHE array. • The level of soil thermal conductivity has a crucial impact on the heat extraction of DBHE array. • Radius of thermal plume after long-term operation increases with soil thermal diffusivity. • Proper inter-borehole spacing and arrangement geometry are suggested for DBHE array. [ABSTRACT FROM AUTHOR]