Geothermal probes are a key element in near-surface geothermal energy and play a central role in the efficient utilisation of renewable energies. The NanoGeoTherm network is dedicated to optimising this technology.

Geothermal probes, also known as borehole heat exchangers, are part of heat pump systems and serve as heat exchangers. They usually consist of plastic pipes and are designed so that a heat transfer fluid can circulate in order to extract (heat) or store (cool) thermal energy from the ground. The exact composition and shape of the probes varies depending on the manufacturer and the specific application.

Requirements

• Tightness: The materials used must be tight to prevent uncontrolled ingress of water or other substances into the probes
• Resistance: The materials must be resistant to the heat transfer fluid and the groundwater in order to ensure long-term and reliable use
• Thermal conductivity: The materials must have good thermal conductivity to enable efficient heat transfer between the ground and the heat transfer fluid.

Types of geothermal probes

There are different types of geothermal probes that are used to extract heat from the ground. The most common types are

• Double U-probes: four parallel polyethylene plastic pipes, two of which are connected at the lower end via a U-shaped base section. There are a total of 2 supply and 2 return pipes.
• Coaxial probes: two pipes fitted into each other. The flow of the heat transfer fluid takes place in the inner pipe, the return flow in the annular space (between the inner and outer pipe of the coaxial probe)
• Multi-tube probes: consist of several tubes. As with coaxial probes, the flow is via a central pipe. The return flow is via several circular pipes.

Environmental compatibility

Safety and environmental compatibility are top priorities in our research. For example, extensive ecotoxicological studies with MWCNT have shown that there are no negative effects on organisms such as green algae, luminescent bacteria, water fleas and freshwater shrimps.

Outlook

Thanks to the combination of heating and cooling functions and the possibility of integration into energy storage systems, geothermal probes offer enormous potential for the sustainable energy supply of buildings. The optimisation of geothermal probes using nanotechnology opens up new possibilities for the efficient use of this sustainable energy source.