Initial position
A geothermal solution was sought for the renovation of a complex with several holiday apartments in Clavadel near Davos in the canton of Graubünden. The property is located on 1660 metres above sea level and is embedded in a mountainous landscape.
Originally, it was planned to install several double U probes with 40 millimeter pipe diameter and a depth of 200 metres each. However, the first drilling already showed that due to artesian groundwater from about 42 metres depth a conversion in this dimension was not feasible.
It had to be reacted quickly. In cooperation with separatus, MR Erdwärme was able to quickly and easily provide a practical alternative. Using the system specialising in short probes, the project was successfully adapted and realised. The planning and implementation was converted to 40 metre-deep separatus borehole heat exchangers.
Implementation of ground-source heat pump system
TRT test separatus
In order to specify the required number of 40 metres deep separatus borehole heat exchangers for the project, a separatus probe with a borehole grouting with a thermal conductivity of 2 W/(mK) was installed at the first drilling. Eight days after installation, a thermal response test (TRT) was carried out in July 2025.
In the first part of the test, an undisturbed average soil temperature of 9,8 degrees Celsius was measured. In the second part, the probe was operated with a specific heat output of 76 watts per metre. The thermal stress phase lasted 139 hours, exceeding the internationally recommended minimum requirements.
During the test, the average heat output was 3,8 kilowatts. The measured flow rate was on average 617 litres per hour. The effective thermal conductivity of the subsurface has been determined with 2 W/(mK) and is consistent with the locally known hydrogeological structure (moraine deposits). In addition, Darcy underground water drain velocity of 2,1 × 10−6 metres per second was detected.
Dimensioning
The geothermal system was dimensioned using the design software GHEtool. The soil parameters determined in the TRT were used as a basis for the simulation.
The building has an annual heating requirement of 27’200 kilowatt hours. The demand for hot water is additionally 2’800 kilowatt hours per year. For the summer months, an annual cooling requirement of 3’900 kilowatt hours was calculated. A heat pump with a maximum heating capacity of 25 kilowatts is used.
Based on this information, a long-term simulation over a period of 50 years was carried out. This resulted in a minimum average fluid temperature of –1,31 degrees Celsius.
Drill field configuration and implementation
On the property, a total of 30 drilling with a depth of 40 metres was distributed and implemented.
The bores were made with a tubing having an external diameter of 132 mm. Due to the geological conditions, continuous piping was required. The drill rod used had an external diameter of 89 mm, the hammer drill 108 mm.
The borehole grouting was carried out via a 25 mm injection tube which was introduced into the borehole together with the probe. The high-performance geothermal mortar K Zeo-Therm 2.0 with high thermal conductivity was used for maximum thermal transmission.
The follow-up work was carried out by Bruno Brunner AG. A separatus head with a connection piece of 40 millimeters was welded onto each probe. Three probes were connected in series so that a total of ten probe circuits were formed and brought together via two distribution shafts.
The distribution shafts were mass-produced by Geser Erdwärme GmbH. They used a four-fold and a six-fold ECO 650 manifold chamber with A-35 cover, inline-setters with 5 to 42 litres per minute and D40-EWS connections.
Conclusion
This project impressively demonstrates how, with thoughtful planning, technical expertise and innovative technology, an economical and reliable geothermal solution is realised under challenging geological conditions. Thanks to many years of experience and the solution-oriented approach of MR Erdwärme, a viable alternative could quickly be found. In combination with the separatus system specialising in short drill depths, an efficient geothermal solution was implemented. MR Erdwärme not only took over the operational implementation, but also demonstrated high competence in project coordination and system integration.
The plant meets all the energy requirements of the building and at the same time shows that geothermal systems can be realised even with reduced space requirements and lower drilling depths without losses in efficiency or operational safety.
This reference is a convincing example of how modern geothermal energy can be planned and implemented in a sustainable way through expertise, flexibility and innovative system solutions in sensitive Alpine regions. Despite difficult framework conditions, it has been possible to realise a functioning and sustainable ground-source heat pump system for the client.
