How do you decarbonize a hillside village with narrow streets, traditional homes, and no space for a heat plant? Across Switzerland, many small municipalities face this dilemma. They want to move away from oil and gas, but classic district heating is often too bulky, disruptive, or costly.
In Grandvaux, part of Bourg-en-Lavaux, CSEM and its partners are demonstrating a new way to tap into low-temperature heat. In 2026, a low-temperature anergy loop, a closed circuit of buried pipes that circulate liquid, will carry heat beneath the village roads and become a model for similar communities. Most people have never heard the word anergy. It refers to low-temperature heat that is usually wasted, such as the mild warmth stored in the ground or the air. On its own, it cannot heat a house, but it is present all year. In Grandvaux, this shared underground circuit will turn that warmth into a local, renewable heat source for the village.
With seven partners in the ANERGYCAD pilot, CSEM co-designed and validated this heating-network concept. Traditional systems circulate water at 80–100°C through heavy, insulated pipes connected to large plants. For small villages, running kilometers of network to distant plants is too expensive and impractical.
The ANERGYCAD network is fully localized. A single, low-anergy loop carries a cool liquid beneath village roads and parking areas, where geothermal probes and compact heat-recovery elements collect heat from the ground and surrounding structures. Each building’s heat pump then upgrades this low‑temperature heat to a usable level, ensuring comfort without fossil fuels.
As Max Boegli, Senior R&D Engineer, CSEM, explains: “Our role was to turn a promising idea into a fully engineered solution. We simulated how this underground loop would behave over 50 years, studied ground temperature changes, heat pump performance, and defined geothermal probe placement to keep the system in thermal balance.”
Grandvaux provided the real-world test. Working with Planeto, a University of Geneva spin-off, CSEM modeled 67 buildings in the village with an annual heat demand of 2.3 GWh. The simulations confirmed that village roads could host the necessary geothermal probes and identified an efficient layout. Clusters of six to ten buildings are connected in series, with geothermal probe groups placed between them. This configuration uses one borehole per building and fits within the underground space already available.
To assess efficiency, the team compared this design with conventional alternatives. Individual systems would require 33% more probe length, while a centralized system would need 25% more boreholes, 65% more pumping energy, and 30% more electricity. As Yves Stauffer, Project Manager, CSEM, notes: “This design delivers the same comfort while using fewer resources across the board. It’s a major step toward practical, low-carbon heating for small communities.”
ANERGYCAD was co-funded by the Swiss Federal Office of Energy (SFOE), with Bourg‑en‑Lavaux involved from the start. Construction of the low-temperature network in Grandvaux is planned for 2026 under the supervision of Ström SA, the engineering company of the project. As Dr. Thomas Söderström, Director of Ström SA, emphasizes: “This approach enables every village to achieve decarbonization while storing excess energy from summer to winter.”
Switzerland has more than 1,000 municipalities with fewer than 2,000 inhabitants each where hot water from a central plant cannot be justified. By combining localized field hardware such as geothermal probes, compact heat-recovery elements, and a low-anergy loop with advanced modeling, CSEM and its partners have turned Grandvaux into a repeatable blueprint for villages wanting to tap the energy beneath their feet, cut emissions, and keep both streets and budgets manageable.
Through its innovative project, the ANERGYCAD consortium has exemplified Swiss collaboration and generated invaluable new insights for Switzerland’s energy transition. The novel anergy heating network could deliver an ingenious solution to a challenging field, by enabling an energetically, economically, and spatially efficient concept for a local heat network that could be transferred onto countless similar communities nationwide. SFOE is looking forward to the next milestones in the development of this technology that shall confirm its potential and relevance for our national climate and energy goals.
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