CO₂-neutral at 2,100 metres above sea level

Can a building at more than 2,000 metres above sea level be heated in a CO₂-neutral way? The Pro Natura Aletsch Centre in Riederalp puts this to the test and proves that it can. Air/water source heat pumps from CTA play a key role in this process. The power comes from a self-powered photovoltaic system.

The installed heat pumps from CTA

  • Villa Cassel: CTAexklusiv air/water source heat pump with a 89.5 kW output and a coefficient of performance (COP) of 2.36 at A-5/W55

  • Chalet Cassel: CTAexklusiv air/water source heat pump with a 28.7 kW output and a COP of 2.28 at A-5/W55

  • Haus Bellevue: Aeroheat Inverta All-in-One air/water source heat pump with an output of 2.7-7 kW and a COP of 4.1 at A2/W35

A different climate

The Alps make up around 60 percent of Switzerland’s surface area. Those living in the Alpine region have to adapt to specific climatic conditions. Living there means buildings are exposed to more intense climatic stresses than in the lowlands. One such building is Villa Cassel in Riederalp, in the canton of Valais. Here, at around 2,100 metres above sea level, the Pro Natura Aletsch Centre was built over 40 years ago. Making conscious, environmentally friendly use of the available resources is a key concern of Pro Natura. “When we started planning the renovation of our building seven years ago, one thing was clear: we were looking for a CO₂-neutral operation, from an energy perspective,” explains centre manager Laudo Albrecht, who, together with his five-person team, runs the Pro Natura Aletsch Centre, which employs more than 20 people each summer.

The challenge of heritage conservation

Even though the Pro Natura Centre is open to visitors ‘only’ during the summer months, from the start of June to mid-October, it quickly became apparent that CO₂-neutral operation would be anything but simple. This is because the main building, the villa built in around 1900 on behalf of the German-English banker Sir Ernest Cassel, is poorly insulated. Furthermore, the villa is a listed building. On the one hand, this made the redevelopment works complicated, and, on the other, the building envelope can only be insulated or used for photovoltaics to a certain degree.

Wood, geothermal probe or air as a heat source?

The building was last renovated when Pro Natura took over Villa Cassel in the mid-1970s and built the Aletsch Nature Conservation Centre on the site. “At the time, the only option was between oil-fired and electric heating systems,” explains Laudo Albrecht. “Today, it’s not at all clear what the most suitable alternative is. We all agreed, though, that a fossil fuel heating system was out of the question. For a CO₂-neutral operation in energy terms, we considered various options: a geothermal heat pump, a wood chip or pellet heating system, and an air/water source heat pump.” The corresponding discussions showed that CO₂-neutral operation can only be achieved using an air/water source heat pump. With wood, the time-consuming transport and necessary compensation costs associated with this proved to be a hurdle; in the case of geothermal heating, there was barely enough space available for a geothermal probe field. The situation was complicated by the fact that there is a water tunnel underneath the property, so, in the end, the effort and risk would have been too high. Accordingly, the choice was made to go with the air/water source heat pump.

An optimal solution thanks to internal power

During the summer and autumn of 2019, an important part of the renovation works, which cost around three million Swiss francs, was completed. Inside each of the three buildings—in addition to the villa, the nature conservation centre also includes the smaller Chalet Cassel and Haus Bellevue—an air/water source heat pump from CTA was successfully installed. Transporting the external register for Villa Cassel proved to be challenging. The register, which weighs more than a tonne, was transported to the villa via cable car and a specialised vehicle. However, to position it exactly on the inaccessible northern side of the building, a helicopter was still necessary. For energetically CO₂-neutral operation, the heat pumps also needed CO₂-free electricity. Pro Natura recognised this and wanted the power to be generated using its own photovoltaic system. However, this was not possible for the listed Villa Cassel. In a collaboration with Pro Natura’s partners, a photovoltaic system was installed on the school building and on neighbouring residential homes. With 450 square metres of solar panels, this covered the centre’s entire electricity needs of 72 kW peak power over the year. The electricity is fed into the local grid, and the centre in turn purchases the electricity from the local grid operator. This prevents any potential ‘power shortages’.

Customised and “off-the-peg”

In addition to two custom-made large heat pumps for Villa Cassel, an Aeroheat Inverta All-in-One output-regulated air/water source heat pump in Haus Bellevue provides heat. One major benefit of this product is its compact design—all components are pre-installed. Installation is therefore simple and inexpensive. The Silent Mode setting provides even quieter operation.


Reliable partners make it possible

“We’re proud of our flagship project”, says Laudo Albrecht. “It shows that, with a quality heat pump and reliable partners, it’s possible to operate heating and buildings in an energetically CO₂-neutral way, even in the Alps. We’ll specifically bring our experience into the educational work done at our centre to raise visitor awareness of renewable energy projects and generate enthusiasm for them."




  • Design: Lauber IWISA AG

  • Installation: Walker A&M Haustechnik AG

  • Heat pump supplier: CTA AG


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