Under the streets of Paris, a 75-mile labyrinth of pipes is at work trying to keep the parts of the city cool. They’re carrying water that’s been chilled in special plants before being sent across the French capital, to offices, malls and museums including the Louvre.

In a country where air conditioning is rare, the district cooling network offers just that. Operator Fraicheur de Paris, part of Engie SA, says it’s more environmentally friendly, using 50% less electricity than a standalone system and cutting emissions by half.

The network, which uses water from the Seine as part of the cooling process, is under intense strain right now from record high temperatures that have taken hold across the continent. Managing Director Marie Carlo said chilling plants are working round the clock, and huge demand as well as occasional power outages means sometimes they can’t get the water as cold as usual.

Despite the stresses on operations, Carlo says district cooling is going to become even more important as a response to climate change and more extreme weather patterns.

The latest heatwave in Europe arrived before the usual summer temperature peak in July. In Paris, it forced the Louvre and the Eiffel Tower to close earlier than usual this week. Across the continent, transport was disrupted, crops were damaged, and schools and nurseries had to shut.

It’s also been linked to a number of deaths, something that’s become a recurring theme in Europe. More than 60,000 people were likely killed by scorching temperatures in the summer of 2022, and about 47,000 people in 2023.

“What used to be seen as a comfort solution is now becoming a health issue,” Carlo said this week while presenting a tour of Fraicheur de Paris’s operations. “We have a lot of demand for connections these days.”

District cooling is being used in a number of cities, including Zurich, Singapore and Chicago. The basic process is to use refrigerants to chill water to as low as 4 degrees Celsius (39.2F). The water, in a closed loop system, is pumped to the buildings of clients to produce fresh air. As it warms, it’s circulated back to plants for cooling again. Water from a local source is tapped via heat exchangers as part of the cooling process.

It’s been used on a small scale in Paris since the 1970s, but started to really grow in the 1990s. Since then, Fraicheur de Paris has expanded to 14 chilling plants, as well as large reservoirs and ice tanks.

One facility, under the banks of the Seine near the Place du Canada, is a hive of pumps, pipes and machinery. There’s a loud permanent buzz as “chillers” — deep underground — cool large volumes of water before sending it via scores of pipes to serve air conditioning systems of clients. Above them, as part of the cooling operations, heat exchangers use water from the Seine, which is regularly flushed back slightly warmer into the river.

Fraicheur de Paris, which operates under a concession from the city, supplies more than 900 clients, from offices buildings to landmarks like the Opera Garnier. It aims to add more plants and almost 100 miles of pipes to triple the number of premises connected by 2042, when its concession expires.

The company says there are calls to accelerate its planned expansion. And requests for connections are coming in from a range of businesses and public services, including commercial landlords, department stores, entertainment venues and hospitals.

Carlo said one of challenges with expansion is space for new cooling plants. To expand the pipe network, about half requires ripping up sidewalks, while the rest can be installed in the existing sewage grid, meaning that new clients can sometimes be connected in less than a year.

Paris Mayor Emmanuel Grégoire says district cooling is now vital for the city.

“It’s strategic to develop this cooling network, which doesn’t use individual air conditioning, which has huge drawbacks in terms of overuse of energy and heat emissions,” he said. “The heatwaves must no longer be managed as crisis situations but as recurring phenomena.”