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Geothermal probes for brine/water heat pumps

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Photo: © mylisa /

In addition to geothermal collectors, many system owners rely on geothermal probes to extract the heat stored in the ground for their brine/water heat pumps. There are several reasons for this.

Geothermal probes have a very limited footprint

One of the main reasons for using geothermal probes is the very low installation footprint. The individual probe itself is scarcely wider in diameter than a CD. The only thing that needs space is the vehicle that does the drilling. A further advantage of geothermal probes is the high efficiency all year round, which is achieved by the consistently warm temperature deeper in the ground.

How geothermal probes work

To access this thermal energy, one or more boreholes need to be drilled beforehand. Double U-pipes are inserted into the boreholes and sealed with a concrete mixture. A brine medium (frost-proof liquid) circulates in the pipes, which absorbs the thermal energy stored in the ground and passes it on to the ground source heat pump. The latter uses this heat to evaporate a refrigerant.

What then follows is the compression process typical of heat pumps. In the process, the evaporated refrigerant is compressed until it reaches the required temperature to be used for heating and domestic hot water heating. You can learn more about how the process works in detail in the section entitled How a heat pump works.

Finding the right geothermal probes

At a depth of around 15 metres, the temperature is a constant ten degrees Celsius and continues to increase, the further down you drill. For a brine/water heat pump to work efficiently, the source should provide the highest possible temperatures. In practice, geothermal probes are sunk to a depth of 40 to 100 metres. The ultimate length of the geothermal probes depends on heat demand and on the thermal conductivity of the soil. Alternatively, several geothermal probes can be used instead of one. Care must be taken to ensure that not too much heat is extracted from the soil at certain points, otherwise there is a risk of icing up.

Subject to approval – look out for certified drilling companies

Official approval is required by anyone who wants to extract heat from the ground using geothermal probes for brine/water heat pumps. Local water authorities are responsible for approval. In the private sector, the competent water authorities may order expert tests if necessary. In that case, it is advisable to contact an expert before starting construction. This will ensure that verifications and checks can be coordinated during the construction process.

Since improper drilling poses a risk to the environment, the drilling company contracted must meet stringent standards. Specifically, when looking for drilling companies, one should ensure that they are certified according to the quality requirements of the DVGWW120-2 technical rule. This proof is also necessary to receive government subsidies of up to 35 percent of the eligible costs for a heat pump. For more information on this topic, see the section on financing for brine/water heat pumps.

Benefits of geothermal probes for brine/water heat pumps summarised

In addition to the economic benefits already mentioned, there are other factors in favour of using geothermal probes. The most important are:

  • Constant and high heat all year round
  • Can be used for passive cooling in summer
  • Safe and durable operation
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