Estimating thermal conductivity from lithological descriptions: A new web-based tool for planning of ground-source heating and cooling

It is the overall policy of the Danish Government that by 2050 electricity, heating and transport will be 100% based on renewable energy. In order to reach this goal a number of different green technologies will have to interact. In areas with no district heating, ground-source heating by heat pump technology (Sanner 2011) could well be one of the solutions. The potential energy extraction from closed-loop boreholes for ground-source heating depends to a large degree on the thermal conductivity of the surrounding geological formations, although other parameters such as the thermal gradient and the extent of groundwater flow also affect the transport of heat to the borehole. Initial estimates indicate that in Denmark there may be as much as 40% difference between the most and the least favourable geological conditions, determined by the thermal conductivity of the different sediment or rock types alone (Vangkilde-Pedersen et al. 2012). Therefore specific knowledge of the thermal conductivity of the geological formations is essential when estimating the optimal drilling depth and the number of boreholes required for a specific plant. In co-operation with research and industrial partners, the Geological Survey of Denmark and Greenland is conducting a three-year project with the title ‘GeoEnergy, tools for ground-source heating and cooling based on closed-loop boreholes’ (www.geoenergi.org). The objective of the project is to acquire knowledge and develop tools and best practices for the planning, design and installation of shallow geothermal energy systems. This paper describes a web-based tool developed to estimate the thermal conductivity in the area surrounding a potential new plant. The tool was developed within the GeoEnergy project and can be used by administrators, energy planners and drillers of closed-loop boreholes.