Influence of hydrogeological parameters on temperature variations due to borehole heat exchangers

Extracting heat from and input of heat into sediments using shallow ground-source heat pumps, so called Borehole Heat Exchanger (BHE) causes cold or hot plumes of anomalies of groundwater temperature different in all directions from the BHE. The simulations shown in this paper emphasize the significance of ground-water flow to the heat extraction from unconsolidated rocks. The simulation results show a large influence of the flux extracted heat and the sediment properties, especially the hydraulic conductivity, on the dimension of cold plumes. Groundwater flow is the main factor of influence on the spreading of cooled water as well as supply of warmer water masses. The results of modelling can help to predict the dimension of these plumes growing under the given conditions of various grain sizes, ranging from clay to coarse sand, and ground-water flow velocities between 5 center dot 10(-11) to 1 center dot 10(-5) m/s. Furthermore different heat capacity values, ranging from 3,600 to 10,800 kWh a year were simulated. Converting the heat capacity of a BHE into a specific heat extraction capacity per meter allows the transfer of our results to other boreholes.