- Tertiaire privé
First French-developed lake-water heating and cooling network enters service
In Annecy, the Idex Group recently opened the first French-developed lake-water heating network. The new network, named “ali énergie”, entered service on 7 April 2023. It uses lake water with heat pumps and thermal exchangers to heat and cool buildings in the Les Trésums district, including a hotel and the future municipal swimming pool.
Backed by the City of Annecy, this innovative water-loop system uses 15 times less electricity than a conventional climate control system and will ultimately make it possible to eliminate 2,600 tonnes of CO2 a year.
The installation is based on a water loop supplied from Lake Annecy and covers 95% of the district’s heating and domestic hot water needs (13 GWh per year) using heat pumps, with the remainder provided by gas boilers, which take over during maintenance of the heat pumps. Air-conditioning needs (500 MWh per year) are fully met (100%) from the water loop.
65% renewable energy using lake water
The water used is extracted from 20 metres beneath the lake’s surface, where the temperature is a constant 7 °C all year round. It supplies three heat pumps connected to an urban heating network serving 570 homes in Les Trésums. All extracted water is later returned to the lake. For every 100 MWh of heat produced, the system will use 35 MWh of electricity and 65 MWh of renewable energy sourced directly from the lake.
In summer, the lake water is cooler than the ambient temperature and is injected directly into a cold distribution network. It is then used to cool buildings via heat exchangers using the free cooling method.
By avoiding the installation of individual air conditioning units, which contribute to the creation of heat islands, the “ali énergie” water loop reduces electricity consumption by a factor of 15 compared with a conventional system.
The total cost of the pumping installations and underground network connections was €10 million, €1.7 million of which was covered by a grant from ADEME. The project was initiated by Crédit Agricole Immobilier as part of the Les Trésums property development programme. The water loop was designed, built, and financed by Idex, which appointed the engineering consultants SGI to manage the project. Construction began in September 2020 and took two-and-a-half years. Idex will maintain and operate the network for the next 25 years.
