As heatwaves intensify across Europe, most cities resort to a common solution: using more air conditioning. But Paris has chosen a different path: in the ’90s, it began planning one of the largest centralized cooling networks in the world.
It consists of 120 kilometers of underground pipes that distribute cold water to museums, offices, hospitals, schools, and other public buildings, including the Louvre, Grand Palais, some luxury hotels, and office districts. Instead of thousands of individual air conditioning units, cooling is done centrally and distributed throughout the city, as reported by The Guardian.
How centralized cooling works
- The system circulates cold water through a network of pipes: cold water from the Seine is pumped through a pipeline that runs alongside a secondary pipe carrying hot water from the city's buildings.
- A thin metal wall separates them, and a heat exchanger allows heat from the hot water to enter the cold water without the fluids ever touching. It is a process similar to holding a hot tea cup in a bowl of cold water - the liquids do not touch, but the tea cools down.
- The colder water is then circulated through the buildings connected to the system, and the water from the Seine is discharged back into the river slightly warmer than before.
The plan was conceived in the '90s by a subsidiary of the electricity company Engie, which started conceptualizing and building one of the largest centralized cooling networks in the world to combat the urban heat island effect and improve energy efficiency.
In 2022, with the help of the Paris City Hall, the company Fraîcheur de Paris, translating to "The Freshness of Paris," took over the contract and began a massive expansion, over several years, of the existing underground infrastructure.
"It's a kind of miraculous solution in the era of global warming," says Thibauld Voïta, an energy and climate expert and advisor at the Jacques Delors Institute.
Paris remains the owner of the network, and it is operated by the transport company RATP and Engie through a 20-year concession contract, which was renewed in 2022.
The company aims to triple the size of the network by 2042, expanding it to all districts and reaching over 3,000 buildings, including critical infrastructure units such as hospitals, schools, nurseries, and nursing homes.
"Not all (buildings in Paris) have the same cooling needs, nor are they all suitable for connection to the network. The figure of 3,000 reflects a realistic development trajectory. The ambition is to move from a historic network focused on large tertiary buildings to city-wide infrastructure," said Tim Guigon, spokesperson for Fraîcheur de Paris.
Air conditioning does not fully solve the heat problem
Beyond city-wide cooling effects, the municipality hopes that the "Fraîcheur de Paris" system will convince at least some of the 2.1 million Parisians to forgo buying air conditioning units, which work by absorbing heat from indoors and expelling it outside.
"Anything that consumes energy emits heat, and that heat needs to go somewhere," explained Sophie Parison, a Paris-based researcher specializing in urban heating phenomena and cooling solutions.
"Fraîcheur de Paris" does not completely eliminate this problem - the system discharges slightly warmed water back into the Seine. However, to date, there is no clear evidence that this affects the river's ecosystem. Studies and monitoring generally indicate that the thermal exchanges of the system generate only small and regulated temperature variations that fall within acceptable ecological limits.
Pauline Lavaud, director of the climate transition department at the municipal administration, states that "Fraîcheur de Paris" offers "energy and environmental performance far superior to individual cooling systems."
This view is also supported by experts. "Energy consumption should be much lower than if the same cooling were provided by modular systems," said Charles Simpson, a senior researcher in climate change at University College London, referring to air conditioning units.
Why this system is not feasible everywhere
Paris is not the only city adopting this strategy. Stockholm uses water from the Baltic Sea to reduce electricity consumption during heatwaves, and Toronto utilizes a cooling system that draws water from Lake Ontario.
Experts say such a solution could work in a metropolis like London, but the model cannot simply be copied and applied identically.
Costs pose a major obstacle. The total value of the 20-year contract for the "Fraîcheur de Paris" project amounted to 2.4 billion euros. Implementing a similar structure in London would involve at least the same costs.
For developing economies, centralized cooling systems could radically change the situation. However, high interest rates and existing, often chaotic infrastructure could make city-wide modernization financially unattainable. Instead, in areas with less congested underground infrastructure, such a project might be easier to accomplish.
Another obstacle is geographical factors. In the case of London, the flow rate and temperature of the Thames water are not ideal for such a project, and the city's underground is already crowded with utility networks and metro lines.
"Measures must always be tailored to the specificities of the city and local issues," explained Emmanuel Gendreau, an ecologist and environmental specialist at Sorbonne University. "It is essential not to directly apply adaptation solutions that have already worked in one city to another."
T.D.