Thanks to the slight seasonal temperature fluctuations of the soil, geothermal heat pumps also operate stably at low outdoor temperatures and when there is a high demand for heating. Horizontal geothermal collectors make this technology usable for a large number of consumers, although to operate they do require a large surface area. A research project, involving the participation of Bundesverband Wärmepumpe (BWP) e.V., the Institut für Solarenergieforschung GmbH and tewag Technologie - Erdwärmeanlagen - Umweltschutz GmbH, analysed the possibility of reducing this surface area through the combined use of geothermal and solar thermal collectors.

Together, the project partners developed a simulation model for geothermal collectors. This numerical model provides a two-dimensional representation of the dynamic thermal processes in the soil and thus forms the basis for calculating the performance of a geothermal collector. The results of the simulation were validated by the researchers on the basis of a test facility specifically built for this purpose.

The conclusion drawn was that the accompanying use of unglazed solar thermal collectors for warming up the soil prevented the formation of frost. This means that a 50% smaller geothermal collector was used without any loss of efficiency. This vastly increases the possibilities for using this technology on a larger scale in the private and public building sector.

An information sheet with simplified rules of interpretation for planners will be published on the FIZ Karlsruhe website in the third quarter 2018.