Lake Annecy, sometimes nicknamed "Blue Lake" is located in the Alps, in Haute-Savoie. - ALLILI MOURAD / SIPA

The city of Annecy will begin in spring the underground installation of a reversible pump system which will heat and cool, using lake water, some 1,500 homes currently under construction.

This hydrothermal system will make it possible to lower the CO2 emissions linked to the heating needs of apartments in winter, at the rate of 1.5 million kg avoided per year, but also the consumption of electricity to cool them in summer, says the municipality.

Already tested in Switzerland

Successfully tested for several years in Switzerland around Lake Geneva, this underground technology will be calibrated with the ambition of eventually connecting other buildings in the Haut-Savoy capital.

According to the municipality, the 400 meters of network of this "water loop" whose route will pass, starting from the lake and to return there, under the road which separates it from the center of Annecy, will be completed and put into service at during winter 2020.

The water will be captured through a network buried 20 meters deep in the lake, where its temperature is stabilized at six degrees all year round. Once pumped and then cooled, it will be returned to the lake in the same volume and without treatment, thus limiting the impact of the process on the level and quality of the Annecy water body.

Less than 1% of the millions of cubic meters of the lake

“For comparison, we pump ten times more into the lake each year to supply the drinking water distribution network. This will represent less than 1% of the millions of m3 it contains each year, ”explains Thierry Billet, municipal councilor for sustainable development in Annecy. "The interest is also that it will be much more profitable for the inhabitants because water costs nothing and its price will remain stable over the years", he underlines.

The first connected buildings will be those of a building project of 1,500 apartments on the shores of the lake, some of which are still under construction. The total cost of installing the heat pump and its connection network is five million euros. The project was funded to the tune of 1.7 million euros by the Environment and Energy Management Agency (ADEME).


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  • Environment
  • Global warming
  • Heater
  • Planet
  • Annecy
  • Water