In a warming world, "urban cooling networks" on the scale of neighborhoods or entire cities, still very marginal in the world, aim to offer a more environmental alternative to the proliferation of individual air conditioners that are problematic for the climate.
"Heating and cooling networks are extremely efficient. A centralization of energy production means better distribution performance, better competitiveness and better performance for the environment", assures AFP Frédéric Joseph , director of Idex La Défense, which refreshes more than 3 million m2 of the largest business district in Europe, at the gates of the French capital.
On the Courbevoie site, two systems complement each other. First, several giant refrigeration units connected to the chilled water network: a closed circuit where the water (initially pumped from the Seine) is cooled to 4°C thanks to the refrigerant fluid from the giant refrigerators, sent to customers and returned then at 10-11°C before being cooled again.
At the same time, the building houses 12-meter deep swimming pools in its basements, crisscrossed with tubes where glycol water circulates (so that it does not freeze) at -7°C, which gradually freezes the water in the basins.
"This ice storage facility is the largest in Europe", underlines Olivier Fleck, director of operations. But ice, "less efficient", is mainly used as a backup, in the event of a forecast of peak consumption, like this week with the heat wave.
"We prefer to avoid any risk for our customers, we have chosen to store half of the basins", he notes.
"Sobriety"
As heat waves multiply and intensify due to global warming, experts point to the "vicious circle" linked to the proliferation of individual, energy-intensive air conditioners, emitting greenhouse gas refrigerants more powerful than the CO2 and which reject hot air amplifying urban heat bubbles.
According to the International Energy Agency, around 2 million air conditioners, mostly inefficient models, were installed worldwide in 2020, making them one of the drivers of electricity consumption. And the increase in demand is likely to continue.
In this context, "implementing district cooling networks in dense environments provides the same cooling service" as individual air conditioning units "but with up to 50% less energy and emissions", estimates UN Environment in a recent report.
Highlighting the advantage of also avoiding reinforcing the phenomenon of "urban heat island" which transforms concrete cities into radiators, the report nevertheless notes the limits to a generalized deployment of such systems, underlining in particular the difficulty of integrating them in already built-up areas.
"The cooling network must be considered in urban development, when the district is created", also believes Frédéric Joseph.
According to Via Sèva, a French association for the promotion of heating and cooling networks, there are 32 cooling networks in France, with approximately 1.400 buildings connected.
That of Paris, the largest in Europe with tens of kilometers of pipes installed under the capital, supplies customers such as the Louvre, the National Assembly or department stores such as Galeries Lafayette with cold.
Another limit of these centralized systems, to produce the cold, you necessarily need electricity, produced in a more or less carbon-free way depending on the country.
So to reduce emissions, "we have to move towards sobriety. The best kilowatt hour is the one we don't consume", pleads Frédéric Joseph.