Our bodies, machines, and buildings are emitting a lot of heat. Can we use it?
Robyn Phelps/Insider
Heat is an unused energy source that’s all around us, from our bodies to our infrastructure.
Recycling waste heat to warm homes and businesses could save money and reduce fossil-fuel use.
Projects in Europe and Canada are learning to use heat from sewage, data centers, and underground.
This article is part of “Gains in Green Tech,” a series showcasing some of the most transformative solutions to the climate crisis. For more climate-action news, visit Insider’s One Planet hub.
Heat is energy, and we waste a lot of it every day. As our machines, buildings, and bodies burn fuel to function, they emit heat into the atmosphere.
Cities are throbbing with this thermal byproduct; they get up to 7 degrees Fahrenheit hotter than the surrounding countryside, according to the US Environmental Protection Agency. The so-called urban-heat-island effect can aggravate health issues and lead to mechanical failures as the world gets hotter.
On top of the dangers, all that heat is unused energy. The EPA has estimated that more than 60% of energy in the US is lost as heat. By recovering those losses, businesses and governments could secure a reliable, local source of energy that doesn’t require fossil fuels.
Projects in Europe and Canada are already capturing and using what’s known as waste heat. In a Glasgow nightclub, sweaty partiers’ body heat gets funneled to colder rooms. A London district is capturing heat from subway tunnels and channeling it to nearby homes. Pipes beneath a German road circulate fluid that absorbs the asphalt’s heat in summer, which then warms and deices the road in winter.
Meanwhile, scientists are surveying the heat that escapes underground for possible future use.
These projects are small, but they’re paving the way for other governments and businesses to tap into the heat all around us.
A Vancouver neighborhood recycles heat from the sewers
The sewage-pumping station in Vancouver’s Olympic Village is also a heat-recovery plant.
City of Vancouver
When you wash dishes, shower, or do laundry, hot water flows down the drain and into the sewers. If you live in the False Creek neighborhood in Vancouver, British Columbia, the heat in that water may eventually come back to warm your home.
In most neighborhoods, sewage goes to a pumping station that pushes it to a wastewater-treatment plant. But in False Creek, the pumping station is also a heat-recovery plant.
Green pipes in the Neighbourhood Energy Utility energy center divert sewage to heat pumps.
City of Vancouver
Some sewage gets diverted to heat pumps that extract heat, transfer it to water in another system of pipes, and concentrate it to raise the water temperature as high as 80 degrees Celsius. The pipes then carry that hot water to homes in the area, where the heat is transferred once more to the buildings’ furnaces and boilers.
The project, called the Neighbourhood Energy Utility, began in 2010 when the city built a sustainability-centric village for the Winter Olympics. To heat new homes with minimal fossil fuels, the city turned to the sewage system.
“That was a bold decision, and one that turned out to be a very good decision,” Derek Pope, who manages the NEU project, told Insider.
The project started out heating nine residential buildings. Today NEU delivers recycled sewer heat to 44 buildings including more than 6,000 residential units, a university campus, a science museum, and commercial facilities.
Pope said the heat pumps have 300% efficiency: For every unit of electricity that powers them, the utility gets three units of thermal energy. By contrast, Pope said, when the system has to top off the heating supply with natural gas in periods of high demand, that has efficiency below 100%.
The NEU energy center is beneath a bridge. The “fingernails” — LED panels at the top of the boiler stacks — change color depending on how much energy is being pulled from the system.
City of Vancouver
The system delivers a “modest return on the city’s investment,” Pope said, because it’s run like a public utility for a slight profit.
In a 2022 report to the City Council, the utility found that for customers the cost of the recycled heat was in line with that of other local energy and heating options.
NEU’s upgrades have expanded its customer base, adding buildings to its network. Now the utility is tripling its heat-recycling capacity by installing two more heat pumps.
Workers gently lowering a new heat pump into the NEU energy center.
City of Vancouver
NEU’s success indicates that sewage-heat recovery may be a sustainable and cost-effective option when building new urban areas, like an Olympic Village.
Data centers can heat homes too
Across the ocean, Stockholm is tapping into a major heat source: data centers.
The world needs more and more of these warehouses of computer servers to process and store information. All that computing, concentrated in one building, gets hot.
“It seems very strange that we should let out excess heat when we can actually buy it,” Johanna Nerell, a project manager at the utility Stockholm Exergi, told Insider. “We can make money for the company who delivers it.”
The company buys captured waste heat from nearby data centers and funnels it to homes. It’s part of what Exergi calls an “open district heating” system, which draws waste heat from different businesses in the city, including a yeast-production plant and a supermarket, as well as sewage. Data centers contribute the lion’s share, accounting for 90% of open district heat, Nerell said.
A chart showing how Stockholm Exergi funnels heat from data centers, at the bottom, to homes.
Stockholm Exergi
All in all, Nerell said, this heat-recycling network accounts for 1.5% of the heat Exergi delivers throughout Stockholm.
“Most likely we will never get much higher than that,” Nerell said. “That would’ve been different if we had industries surrounding Stockholm that produce a lot of excess heat.”
Without heavy industries, only a few types of businesses can make the up-front investment to install the heat pumps and pipes needed to sell their heat, she said, adding, “That’s where data centers are ideal.”
There’s more untapped heat underground
The urban heat island — the churn of activity that makes cities hotter — extends underground too.
A man using a newspaper as a fan on the subway in central London during a heat wave.
Yui Mok/PA Images via Getty Images
Excess heat can harm river ecosystems fed by groundwater, since fish and other life-forms there generally prefer cool water flowing from underground.
Overheated groundwater also affects drinking-water quality, since the warmth can breed bacteria or cause more heavy metals to leach from the surrounding soil.
But it’s possible to cool the underground and cut fossil-fuel use by capturing the heat beneath the surface, researchers found in a study published in Nature Communications in 2022.
“It’s like two birds with one stone,” Susanne Benz, an author of the study who researches subsurface heat, told Insider. “Carbon-free energy, and at the same time we get to reduce the impact of climate change and urbanization on our environment.”
Benz and her colleagues assessed over 8,000 locations where measurements of groundwater temperature were available, mostly in Europe. They found that in about 25% of those places there was enough heat underground to recycle for energy.
That percentage will surely increase as the planet’s average temperature rises, heating up the underground even more. The study’s authors estimated that by the end of the century, 73% of the locations could fulfill all their heating needs with underground heat.
A staff member standing at the underground Oyu Tolgoi copper mine in the Gobi Desert in Mongolia.
B. Rentsendorj/Reuters
Tapping into flowing groundwater would allow municipalities to access that heat. Regions without flowing groundwater would have to lay pipes underground and cycle fluid through them to absorb the heat and bring it to the surface.
Benz says it’s worth considering adding those underground pipes as part of new construction, especially building new streets, which absorb extra heat. Subway tunnels could also be an easy place to start. In 2020, the Islington neighborhood of London built a system in its subway to funnel heat from those underground tunnels to homes.
Of course, underground heat builds up the most in summer, when people don’t need to heat their homes. But Benz said the ground would hold on to the heat until it’s needed.
“Heat takes a little bit to travel in the underground. So if you time it right and put your heat pump or your pipes at exactly the right depth, all the heat from the summer reaches it in winter, when you actually need the heating,” she said. “The ground is the battery in this case.”