With the first geothermal plant in Trimmis, we are celebrating two premieres. It is our first project in the Swiss market and the first plant we have planned with the GHEtool.
The operation of the software is just as intuitive as our borehole heat exchanger (BHE). We give an insight into how easy it is to plan and implement a plant with separatus.
Project environment and geological framework conditions
The project concerns a newly built single-family house in the Churer Rhine Valley, which is realised in the Minergie standard. The energy efficiency of the building is correspondingly high and thus the demand for a sustainable and suitable heat supply.
The building has a heating power requirement of 10.6 kW and an annual heating requirement of 14 MWh. In summer, the building can be cooled, with a maximum cooling capacity of 7.6 kW and an annual cooling requirement of 3.4 MWh. The seasonal coefficient of performance (SCOP) of the heat pump is 4.5.
The geological location is particularly challenging for the use of geothermal energy. The building is located on a debris cone consisting of damp gravel, stones and earth. At about 80 metres depth, a layer of permanently stored moraine begins.
The geological conditions were estimated on the basis of drilling profiles of the Office for Nature and Environment Graubünden and subsequently validated together with the executing drilling contractor MR Erdwärme. The company is part of the separatus network and is very familiar with the geology of the region.
Based on this geological assessment, the thermal conductivity of the subsurface was defined in the GHEtool. Two soil layers were used: 80 metres of wet gravel (λ = 1 W/mK) of as upper layer and 20 metres of molasses rock (λ = 1.8 W/mK) at depth). The inputs were made according to the specifications of the SIA standard 384/6.
Drill field configuration and hydraulic design
The planned drill field comprises three separatus borehole heat exchangers, each with 100 m length. They are positioned in a triangular arrangement with a probe spacing of 10 m and connected in parallel. The bores have a diameter of 132 mm and are filled with a thermally improved borehole grouting (λ=2 W/mK)).
For the simulation in the GHEtool, a brine liquid with a glycol content of 25 % and a volumetric flow rate of 1 m3/h were used. This results in a Reynolds number of 2936, whereby the flow in the transition zone is close to the turbulent region.
Results
The simulation was performed over a period of 50 years. This resulted in an effective borehole resistance of 0.13 mK/W.. The calculated maximum average fluid temperature is 20.27 °C, the minimum average fluid temperature is −1.45 °C.
The temperature curve over the entire simulation period shows a stable development and is shown in the diagram below. The results confirm that the project with separatus is well feasible under the given conditions.
Findings:
The GHEtool has proven itself in this project as a user-friendly and powerful software for the dimensioning of separatus borehole heat exchangers. For a well-founded design / system sizing in the demanding geology on site, however, the know-how of local experts is indispensable. In our case, the drilling contractor MR Erdwärme was a central partner – experienced, regionally anchored and well-acquainted with the geological conditions. We are proud and grateful to have with MR Erdwärme a strong separatus installation partner for the cantons of Graubünden and Ticino at our side.
The simulation with the GHEtool has clearly confirmed the feasibility of the separatus plant under the given conditions. Thanks to the close cooperation with our two network partners presented in this article, we can look forward to the upcoming installation of the first separatus plant in Switzerland.
Originally, the use of single U probes with 40 mm diameter was planned. Using a scenario comparison, this configuration was easily converted to separatus and compared. The clear graphic presentation of the simulation results from several scenarios helps to communicate the technical design / system sizing transparently and to pick up project managers at an early stage.
Reaction with MR Erdwärme
Three separatus borehole heat exchangers à 100 metres were installed on the old burrow cone of Trimmis. The geological conditions required hammer drilling with continuous piping to final depth. This is not easy terrain and requires a lot of drilling expertise.
All the more remarkable how smoothly the implementation went: The first probe was installed in less than five minutes. A new record, made possible by the established cooperation of our drilling partner MR Erdwärme. The graphics and videos show how intuitively our probe is installed and how the required tool is used.
Can we surpass that record?We are ready for new challenges. Anyone who wants to go new ways in geothermal energy with us is cordially invited, we look forward to further exciting projects.
