- Réseau de chaleur et de froid
In Annecy, Idex develops France's first lake-source heating and cooling network
Following a complete renovation, the district of Trésums on the shores of Lake Annecy is now heated and cooled by France's first lake-source network: ali énergie.
Learn more about how this 2.5 km water loop was designed, and how it will be able to generate up to 13 GWh of heat per year.
A unique heating and cooling network for a new district
Trésums transformed
Following the transfer of the regional hospital (CHRA) to Metz-Tessy, Trésums has undergone a major transformation, initiated by Crédit Agricole Immobilier: 570 homes have been built, with stunning views of the lake. The Marquisats hotel and water sports centre have been rebuilt.
Drawing on its experience with lake-source heating networks in Geneva and Saint-Gingolph, on the shores of Lake Geneva, design office SGI Groupe asked Idex to take up the challenge of developing France's first lake-source heating network.
An optimised heating and cooling network
The district of Trésums was chosen for its proximity to the lake, and more specifically the Boubioz spring, which descends to 83 metres below the surface. The network descends to a depth of 20 meters, where the temperature of the lake remains at a steady 7°C all year round – the ideal temperature for a heating and cooling network.
With its heat pumps and heat exchangers, the water loop covers 95% of heating and domestic hot water requirements, up to 13 GWh/year.
To meet the air-conditioning requirements of the hotel and a future serviced residence for seniors, an aqua-cooling system will generate 500 MWh/year. This will avoid 2,600 tonnes of CO2 emissions per year.
Key figures
€10 M for the total investment
€1.7 M in grants from ADEME (agency for the ecological transition)
95% of energy requirements produced by heat pumps (5% by gas back-up)
13 Gwh of heat and 500 MWh of cold energy
2,600 tons of CO2 emissions avoided per year
570 lhomes heated by the water loop
Up to 20% in savings for residents on their energy bills
Timeline
November 2016
ADEME feasibility study
November 2017
ADEME financing agreement
May 2019
Building permits
October 2019
Environmental approval
May 2023
Inauguration
A virtuous loop
A number of environmental studies were conducted in cooperation with the Direction Départementale des Territoires (DDT) planning office in order to protect flora and fauna. One of the main aims during works was to protect the seagrass beds used by many types of fish for reproduction.
Note that 100% of the water used by the network is discharged at a depth of 7 meters, where it has no impact on water quality.
The network is authorised to pump up to 420 l/s from the lake. The Thiou River discharges between 4,000 and 40,000 l/s into the lake.
A word from the people best placed to talk about the project
When we bought our home, we knew it would be heated by this water loop. We liked the ecological approach and the promise of lower energy consumption. It was also attractive from a financial standpoint!
In response to the many warnings issued by the IPCC (Intergovernmental Panel on Climate Change), cities need to act responsibly and take urgent action. The first step is to reduce our greenhouse gas emissions.