Paris is using Seine water to cool buildings

Since the 1990s, Paris has been using a vast underground network of pipes to cool public buildings using water from the river Seine.

According to an article by Jesse Chase-Lubitz in The Guardian, "The system circulates cold water through a network of pipes: cold river water from the Seine is pumped through one pipe, which runs right next to a secondary pipe carrying warm water from the city’s buildings. A thin metal wall separates them and a heat exchanger allows the heat from the warm city water to enter the cold Seine water without the fluids ever touching."

The system was started in the 1990s by Fraîcheur de Paris, a subsidiary of the city's electric utility. "The city of Paris remains the owner of the network and it is operated by the transportation company RATP and Engie through a 20-year concession contract that was renewed in 2022." Paris plans to triple the network's size by 2042 to reach over 3,000 buildings. 

As Chase-Lubitz explains, "Beyond the city-wide cooling effects, the hope is that Fraîcheur de Paris will stop at least some of the 2.1 million people who live in Paris from buying an air conditioner, which works by taking the heat inside and sending it into the streets outside."

Although the system sends slightly warmer water into the Seine, there is so far no evidence that it is harming the river's ecology.