Modern geothermal systems use a simple construction in which the inlet and outlet are not thermally insulated from each other and are arranged so narrowly that part of the heat obtained in the deep is lost again during its return to the surface. The aim of this subproject was therefore to improve the thermal insulation of the return flow in geothermal probes and to optimize the fluid flow in the probe. Among other things, a technically improved geothermal probe was to be developed and integrated as part of the planned new building on the Minden campus. In addition, another goal was to implement a special measuring and logging toolset for precise measurements in this context. Finally, the advantages of the improved system should be proven in field studies.
First, the technical system requirements were defined. Subsequently, an insulation concept was designed, which focused on the question of how the geothermal probes should be insulated. Then two probes and three injection pipes were assembled. Before final installation, the measuring chains were carefully and systematically checked and the testresults documented in detail, in order to avoid possible pitfalls. The hole for the geothermal system at Minden campus was finally drilled in September and October of 2015. Two 90 meter deep holes were prepared and two probes were installed. In addition, three other holes were drilled for temperature measurement circuits. The effectivity of the insulation has been proved by the measuring results.
In addition to the originally planned project further insights could be optioned. In a phase without operation of the heat pump during winter 2016/17 a difference of temperature between the supply line and the return line was measured resulting in a free convection in the insulated borehole heat exchanger. This self-induced flow can be used to increase the effectivity and economic efficiency of ice-avoiding systems in traffic surfaces.