A novel enhanced deep borehole heat exchanger for building heating

Deep borehole heat exchanger (DBHE) technology can be used in various regions due to without dependence on the hot water reservoir. However, its performance can hardly be improved due to poor thermal conductivity of rocks and cement. Here a novel enhanced deep borehole heat exchanger (EDBHE) is first proposed, which applies composite filler, cement and well tube. To depress thermal resistance, graphene is used to mix with ordinary mud and cement respectively to prepare composite filler and composite cement. Especially composite filler is controlled deliberately to flow into leakage formation by adjusting its density, viscosity and back pressure in order to improve the thermal conductivity of surrounding rocks. We find that the extracted thermal output from EDBHE is 1002.34 kW, which is 2.36 times that of DBHE (424.45 kW). EDBHE can be used in low water output zone and difficult recharge zone even dry hole zone with leakage formation, which will increase geothermal heating area substantially