Potential Mapping of Geothermal Heat Pumps with GIS in Southern Germany

Abstract

Although the amount of sold heat pumps in Germany as well as the interest in using shallow geothermal energy grew enormous within the last years, a better knowledge of the factors influencing the efficiency could lead to a more effective and widespread application of the shallow geothermal energy source.

Potential estimations of a special site are based on geological, hydrogeological and lithological studies of the area. With the resulting informations a 3-dimensional model of the underground can be constructed with the software GIS, dividing the model into several layers with similar thermal properties. Depending on the depth of analysis, parameters like heat conductivity or specific heat extraction can be assigned to the relevant thickness of the layer. The resulting maps show the distribution of the weighted mean values.

Such potential maps were created for the region called Donau-Iller in southern Germany, which includes parts of the Swabian Mountains and the Molasse Basin.

The resulting maps are based on three different parameters: thermal conductivity, specific heat extraction and cold extraction, which are projected for the analysis depths of 100 m, 150 m and 200 m. The choice of the assigned thermal conductivity values is mainly influenced by lithological and hydrogeological aspects.

If the heat demand of a building is known, the map shows the potential specific heat extraction which can be used to estimate the needed length of a borehole heat exchanger. The third and last map of the cold extraction potential shall point out, that borehole heat exchangers present a simple and cost-effective possibility for cooling of buildings without an additional heat pump (Geo-Cooling).

The constructed potential maps shall show the difference of geothermal heating and cooling potentials in dependency on local changing geological conditions with respect to different considered depths.