Pilot area activities – #7 New construction of a shallow geothermal installation in Prague, Czech Republic

How to build a borehole heat exchanger for a single family house

The Czech Geological Survey documented the construction process of a shallow geothermal installation in Slivenec municipal district of Prague in January 2020. Owners of a single family house chose to install a closed loop system, more precisely a borehole heat exchanger, as heating source for their home. A local drilling company constructed the underground part while subcontractors delivered the heat pump and other equipment.

Two boreholes of diameter 12 cm were drilled by rotary percussion drilling in limestone bedrock to depths of 105 m each. The top layer of bedrock was heavily weathered and sand filled pockets were encountered during the course of drilling due to host lithology. The distance between the boreholes is 10 meters.

After completing the drilling, double U-tube probes (outside diameter of tube 3,2 cm) were inserted into the boreholes. Last step for the underground installation was to fill empty spaces between the probe and the underground with a bentonite-cement mixture (grouting) to enhance the heat transport to the tubes.

In operating mode, a mixutre of water and refrigerant circulates inside the double U-tube probes and carries heat from the underground to the surface, where a heat exchanger is installed. The heat exchanger transfers the fluid’s heat to a heat pump. In this way the geothermal system provides a heat output of around 10 kW.

For more information about this project, please contact:
Jaroslav Rihosek, jaroslav.rihosek@geology.cz

Drilling of the borehole with rotary percussion.
Bottom end of the geothermal probe ready to be installed.
Installation of geothermal probe and tubing into the borehole.

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