With the first geothermal plant in Trimmis, we're celebrating two premieres. It's our first project in the Swiss market and the first plant we've planned using the GHE tool.
The software is just as intuitive to use as our geothermal probe. We'll give you an insight into how easy it is to plan and implement a system with separatus.
Project environment and geological conditions
The project concerns a new single-family home in the Chur Rhine Valley, which will be built to the Minergie standard. The building's energy efficiency is correspondingly high, and thus the demand for a sustainable and appropriate heat supply is high.
The building has a heating capacity of 10.6 kW and an annual heat demand of 14 MWh. In summer, the building can be cooled with a maximum cooling capacity of 7.6 kW and an annual cooling demand of 3.4 MWh. The heat pump's SCOP is 4.5.
The geological location is a particular challenge for the use of geothermal energy. The building is located on a scree cone consisting of moist gravel, stones, and earth. A layer of hard-packed moraine begins at a depth of approximately 80 meters.
The geological conditions were assessed based on borehole profiles from the Graubünden Office for Nature and the Environment and subsequently validated together with the drilling company MR Erdwärme. The company is part of the separatus network and is highly familiar with the region's geology.
Based on this geological assessment, the thermal conductivity of the subsurface was defined in the GHEtool. Two soil layers were used: 80 meters of moist gravel (λ = 1 W/mK) as the upper layer and 20 meters of molasse rock (λ = 1.8 W/mK) at depth. The inputs were made according to the specifications of SIA Standard 384/6.
Drilling field configuration and hydraulic design
The planned drilling field comprises three separatus boreholes, each 100 m long. They will be positioned in a triangular arrangement with a probe spacing of 10 m and connected in parallel. The boreholes have a diameter of 132 mm and will be filled with a thermally enhanced backfill (λ = 2 W/mK).
For the simulation in the GHEtool, a brine fluid with a glycol content of 25% and a volume flow of 1 m³/h was used. This results in a Reynolds number of 2936, which places the flow in the transition zone close to the turbulent regime.
Results
The simulation was conducted over a period of 50 years. It resulted in an effective borehole resistance of 0.13 mK/W. The calculated maximum average fluid temperature is 20.27 °C, and the minimum average fluid temperature is -1.45 °C.
The temperature curve shows a stable development throughout the entire simulation period and is shown in the diagram below. The results confirm that the project is feasible with separatus under the given conditions.
Findings:
The GHEtool proved its worth in this project as a user-friendly and powerful software for dimensioning separatus geothermal probes. However, for a sound design in the challenging local geology, the expertise of local experts is essential. In our case, the drilling company MR Erdwärme was a key partner – experienced, regionally rooted, and intimately familiar with the geological conditions. We are proud and grateful to have MR Erdwärme, a strong separatus installation partner for the cantons of Graubünden and Ticino, at our side.
The simulation with the GHEtool clearly confirmed the feasibility of the separatus system under the given conditions. Thanks to the close collaboration with our two network partners presented in this article, we are eagerly anticipating the upcoming installation of the first separatus system in Switzerland.
Originally, the use of single-U probes with a diameter of 40 mm was planned. Using a scenario comparison, this configuration was easily converted to separateus and compared. The clear graphical presentation of the simulation results from multiple scenarios helps to transparently communicate the technical design and engage project managers early on.
Implementation with MR Geothermal Energy
Three separate geothermal probes, each 100 meters long, were installed on the old Trimmis cone. The geological conditions required a hammer borehole with continuous casing to the final depth. This is not easy terrain and requires considerable drilling expertise.
All the more remarkable is how smoothly the implementation went: The first probe was installed in under five minutes. A new record, made possible by the well-coordinated collaboration of our drilling partner, MR Erdwärme. The graphics and videos demonstrate how intuitively our probe is installed and how the required tools are used.
Can we even surpass this record? We're ready for new challenges. Anyone who wants to explore new avenues in geothermal energy with us is welcome to join us; we look forward to more exciting projects.
