In the suburbs of northeast Paris, there is a giant terra-cotta-colored warehouse with a labyrinth of windowless corridors inside. A deafening whir emanates from behind rows and rows of anonymous gray doors, and under white striplights, disposable earbuds are available to protect passersby from the noise.
These are the uncanny innards of one of France’s newest data centers, completed earlier this year, which is now being used to heat the new Olympic Aquatics Center—visible from the data center’s roof. When US swimming star Katie Ledecky won her ninth Olympic gold medal last week, she did it by speeding through water heated, at least in part, by the data center’s machinery.
Known as PA10, this noisy site belongs to the American data center company Equinix—the whirring sound is the company’s cooling systems trying to lower the temperature of its clients’ computer servers. “PA10 is especially made for high-density racks,” says the site’s data center engineer Imane Erraji, pointing to a tower of servers capable of training AI.
For the past month, the data center has turned its hot air waste into water and piped it to a local energy system run by French utility company Engie. Once it runs at full capacity, Equinix expects to export 6.6 thermal megawatts of heat out of the building—the equivalent of more than 1,000 homes.
As projections suggest AI is about to turbocharge the amount of electricity data centers need—Equinix predicts power consumption per rack could rise by as much as 400 percent—PA10 reflects a European phenomenon whereby officials attempt to mitigate the environmental impact of the coming AI energy crunch and transform data centers into part of the infrastructure keeping cities warm.
Erraji describes the project as a “win-win situation” for both Equinix and the local suburb of Seine-Saint-Denis. Equinix can pipe the heat out of the building so its cooling devices don’t have to work so hard, she explains, while the city gets a cheap source of heat produced locally. After the project received a €2 million ($2.1 million) investment from the city of Paris, Equinix has committed to providing the energy free-of-charge for 15 years. In June, the mayor of Seine-Saint-Denis, Mathieu Hanotin, also called attention to the environmental benefits, claiming that using the data center as an energy source will spare the region 1,800 metric tons of CO2 emissions per year.
Yet France has a “very low-carbon electricity mix,” according to the International Energy Agency (IEA), with 62 percent of its electricity generated by nuclear power. And critics say multiplying heat-reuse projects are a distraction from the real issue: the amount of land, water, and electricity data centers consume. “When the data centers are already here, of course it’s better to reuse the heat than do nothing,” says Anne-Laure Ligozat, computer science professor at France’s National School of Computer Science for Industry and Business (ENSIIE). “But the problem is the number of data centers and their energy consumption.” There would be less of an environmental impact to to have a basic electricity heating system without the data center, she adds.
Recently, projects capturing and reusing heat to warm homes, offices, or universities have sprung up across the region, as data centers face increasing pressure to help the European Union meet ambitious environmental targets, such as reducing emissions by 55 percent by 2030, says Simon Hinterholzer, researcher at Germany’s Borderstep Institute for Innovation and Sustainability. Over the past two years, these projects became more popular as European energy prices spiked, prompting local governments to look around for cheap sources of heat to replace Russian gas. “There’s definitely a correlation with the war in Ukraine,” Hinterholzer adds.
Once data centers are built, researchers agree these heat reuse projects make sense. “It makes a significant difference,” says Shaolei Ren, an associate professor specializing in sustainable computing at the University of California, Riverside. Ren estimates that cooling technology can contribute up to 50 percent of a data center’s total energy consumption. “If companies reuse the heat, essentially, they are slashing the energy required for cooling.”
But in order to claim there are benefits to heat-reuse projects, there has to be scrutiny of where data centers source their power to start with. Equinix says PA10 energy demands are 100 percent “covered” by renewable energy sources, including using power purchase agreements (PPAs), where tech companies pay wind or solar farms for the equivalent power they produce, even if that power is not directly connected to the data center.
“At this point, there’s no data center that’s running entirely on renewables,” says Ren. “When tech companies claim to be running their data centers on renewables, or say they’re carbon neutral, they’re referring to carbon offsetting, which means they plug their data center into the power grid and they are doing some offsetting methods elsewhere.” Companies that rely on PPAs, for example, do not always buy renewable energy from the same country where their data centers are based.
Over the past nine days, the roar from the crowds at the Olympic pool may have eclipsed the whirring of the nearby Equinix data center. But in Paris, as in other parts of Europe, skepticism remains toward this booming industry and the disruption AI is set to introduce. The major issue, according to Ligozat, is the debate about the continued building of data centers and what applications they should be used for. “To me the main question is, should we continue building data centers?” she says. “And not, should we reuse the heat?”
