As more of our lives move online, power-hungry data centers are multiplying. Already, the servers that run weather models, fuel financial markets, and store Facebook statuses soak up about 1% of the world’s electricity. By the end of the decade, they could use as much as 20%.
A big chunk of that power—about 40%—goes toward keeping the machines cool. Operators spend billions of dollars (and billions of gallons of water) each year on cooling systems that shed heat from the computers into the atmosphere.
There’s a better use for that all wasted heat: heating homes and businesses that would otherwise burn gobs of fossil fuels. For the past decade, researchers have called on cities to close the loop and recycle waste heat from server farms to cut costs and carbon emissions.
Some towns listened. In 2010, Helsinki installed a massive data center in a disused bomb shelter and piped enough hot water into the city’s district heating system to warm 1,000 apartments. That year, Parisian computer servers began heating a nearby arboretum. The Winnipeg Sun began using heat from a downstairs data center to warm its offices in 2011.
So far the idea has been slow to catch on, as falling fuel prices and logistical barriers have crimped the economic incentive to reuse waste heat. But renewed corporate commitments to sustainability and imaginative efforts to bring servers directly into the buildings that need to be heated could hasten adoption.
Heat is hard to transport. It’s easier to reuse waste heat in countries like Finland, where district heating systems are common and the infrastructure for pumping hot water around town already exists. Many cities, however, don’t provide heat as a municipal utility. Even in Seattle, which does have district heat in some areas, Amazon had to lay new pipes connecting its campus to a nearby data center when it launched its own heat reclamation project in 2017.
That kind of infrastructure investment can be tough to justify, especially in the US, where the rise of fracking has driven down fossil fuel costs over the past decade. “These days natural gas is so cheap that space heating isn’t that big a burden,” said Clinton Andrews, a Rutgers urban policy professor who heads the university’s Center for Green Building. “That means your strategy for capturing the waste heat has to be extra cost effective… and there’s a more limited margin for making it profitable than there was 10 years ago.”
Rather than trying to figure out how to make money selling heat to nearby businesses or municipal utilities, many data center operators have simply figured out how to build their servers in frigid places, like the bottom of the sea or the Arctic Circle. These developments have curbed the economic incentive to reuse computers’ heat—unless fossil fuel supply shocks or aggressive carbon taxes raise energy prices and make waste heat a hotter commodity.
But as corporations face increasing scrutiny over their environmental impact, designing a data center to dump heat directly into rapidly melting Arctic ice sheets may not be the best PR move. More companies might follow the lead of Facebook, which just completed a project to heat 6,900 homes in Odense, Denmark using hot water from a server farm it built nearby. In a press release, Facebook said the scheme was part of its efforts to meet its sustainability goals.
Meanwhile, some startups have sought to sidestep the problem of transporting waste heat to end users. French firm Qarnot installs small servers directly into customers’ homes and businesses. The so-called “data furnaces” and “data boilers” can warm a room or heat water to any temperature by running a set number of calculations. So far, Qarnot has installed 1,500 heaters and 10 boilers, which act as a distributed data center. The company rents out its computational power to banking clients like BNP Paribas and animation studios like Despicable Me maker Illumination Mac Guff.
Qarnot’s business model was intriguing enough to gin up a $6.5 million round in March—but it’s not likely to replace hulking, centralized data centers, which tend to be built in remote areas wherever electricity is cheapest. These servers are too far from major cities to vent warmth into district heating systems. But even there, Andrews says, savvy entrepreneurs might find ways to put waste heat to profitable use.
“I think you could come up with some good industrial symbiosis ideas, like how about doing some fish farming next to your remote server?” he said. Aquaculture requires heat to keep fish tanks at the right temperature, and might get it at a low cost from a neighboring data center. Until someone figures out what to do with it, Andrews points out that waste heat will always be a form of inefficiency.
“That means there’s money left on the table for other people to figure out how to do it better,” he said. “Waste heat is waste, and it ought to be in everyone’s interest in a competitive market to reduce waste.”