Heat extraction and recover of deep borehole heat exchanger: Negotiating with intermittent operation mode under complex geological conditions

The geothermal heat pump system based on deep borehole heat exchanger (DBHE) is one of the important systems to realize cleaner heating. It is key to ensure that DBHE can make full use of the dynamic characteristics of deep heat extraction and recovery (HER) in a long period of time to maintain the stability of geothermal field as well as sustainable development of DBHE and geothermal energy. This study mainly has made contributions in the following four aspects: (1) Through numerical analysis with a “stratified segmented finite line source method” (S2-FLS) and its model analytical expression, the impacts of heating duration and heating load distribution on the long-term operation performance of DBHE is revealed, which provides a theoretical basis for the optimal operation of DBHE. (2) The numerical analysis explained how complex geological conditions affect the dynamic heat extraction and heat recovery of DBHE in intermittent operation mode, which provides a theoretical basis for DBHE drilling site selection. (3) The model robustness is fully checked and an initial investigation on DBHE array with HER is presented, which may lead to massive application of deep geothermal systems. •A robust, efficient and easy implemented model is proposed for deep borehole heat exchanger.•The long-term heat extraction/recovery ability of deep borehole heat exchanger is verified.•Analysis on geological conditions can provide guides for drilling site selection.•The deep borehole array with heat extraction and recover is demonstrated.