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Using a City’s Excess Heat to Reduce Emissions

A district in London has developed an innovative way to divert subway heat for buildings to lower carbon emissions. Other cities are getting creative, as well.

The London Underground is the oldest subway system in the world, so it might seem an unlikely source of innovation for one of the thorniest problems facing humanity in the 21st century: climate change.

While public transit is usually more environmentally friendly than other methods of travel, the Underground is playing a more direct role in a groundbreaking experiment to reduce greenhouse gas emissions from buildings.

The local council for the Borough of Islington in London has developed, planned and installed a way to provide heat and hot water for several hundred homes, a school and two recreation centers, all using otherwise-wasted thermal energy generated mostly by the electric motors and brakes of the Underground’s trains.

With world and national climate change efforts lagging, cities are taking responsibility for helping reach goals of net-zero carbon in the next decade. Islington’s project is just one of many innovations by cities around the world to provide heat to residents and businesses while reducing greenhouse gas emissions, improving efficiency and saving people money.

Andrew Testa for The New York Times

A neighborhood in Vancouver is also recovering waste heat, but from sewage. Stockholm is also using heat from sewage, as well as tapping data centers and other sources to supply heat for much of the city.

Buildings are also a major source of urban greenhouse gas emissions, largely because heating, cooling, cooking and electricity largely rely on fossil fuels.

“If you can start to use a whole array of waste heat streams, you’re taking out a big chunk of greenhouse gas emissions,” said Jon Gluyas, a professor of earth sciences at Durham University in Britain who specializes in geoenergy, carbon capture and storage.

“We don’t really need to burn gas at 1,000 degrees centigrade [1,832 degrees Fahrenheit] to get your bath to 30 degrees centigrade,” Dr. Gluyas added. “What we need to do is work with nature to optimize the use of heat.”

The concept of district heating networks is not new and may, in fact, date from 14th-century France or even, some say, the Roman Empire. Throughout the 20th century, geothermal energy, biomass or fossil fuels such as natural gas were commonly used to distribute heat and hot water from a centralized location through insulated pipes — a far more efficient system than individual furnaces and other localized heating sources, yet still a major producer of greenhouse gas emissions.

New York City has one of the world’s largest district systems to provide heat, cooling and, in some cases, even electricity to many buildings in Manhattan. However, the program, run by the local energy provider, Con Edison, uses natural gas and some fuel oil to heat water and produce the steam that powers the systems. (Venting of that steam, funneled through the energy company’s orange- and white-striped safety towers, have become an image of the city.)

Though perhaps less wasteful than having a boiler in every single building, it is not the most efficient district heating system, as it was designed to heat a building on the coldest day of the year with all the windows open — partly a public health legacy of the 1918 pandemic.

Local governments, like the Islington borough council, are hoping to improve on the district heating model by using excess heat from other sources.

Andrew Testa for The New York Times

“Local councils are in the strongest and best position to be able to lead on this sort of project,” said Keith Townsend, the Islington council’s director of environment and regeneration.

Islington, which stretches from north London to the London’s city center, was already partly served by a district heat and power network, which came online in 2012. But the innovation — which took more than five years to plan and build, and began operations in March 2020 — was to feed in heat from the Underground.

Typically, the hot air from the Underground is released into the air through stations and ventilation shafts. In this case, however, air is drawn from a ventilation shaft at an abandoned Underground station into an energy center where a series of heat transfers take place, eventually leading to delivery of the heat into the buildings in the network.

The fans in the shaft can also run in the other direction to send ambient air into the Underground to cool it in the summer months.

The system, known as the Bunhill 2 Energy Center, is centered at the former City Road station in Islington. The network now serves about 1,350 homes, with capacity to serve about 900 more.

Islington is a dense, urban area, and while construction was not easy, Mr. Townsend said he hoped it would serve as a model of what cities can achieve.

“For our residents, locally, this is absolutely the right thing to do,” because it saves money in an area where many residents struggle to afford heat, Mr. Townsend said. “And this is a perfect solution for big cities across the world.”

Andrew Testa for The New York Times

In Vancouver, British Columbia, buildings account for 57 percent of the city’s emissions. The False Creek Neighborhood Energy Utility, the city’s sewage and wastewater heat recovery system, serves several densely populated, centrally located neighborhoods yet produces 60 percent less emissions than typical buildings in the city.

Heat from wastewater and sewage now provides about 70 percent of the space heating and hot water for the 43 buildings connected to the network, with the remaining 30 percent coming from natural gas, though the goal is to end that by 2030. The electricity powering the heat pumps is 97 percent zero-carbon, supplied by hydroelectric dams.

“Every time we take a shower, do the dishes or do a load of laundry, the water is still hot when it goes down the drain,” said Ashley St. Clair, Vancouver’s senior renewable energy planner.

“It’s flowing under our streets, and we’re already collecting it through the traditional infrastructure of wastewater pipes, and to be able to tap into that waste heat is really the ultimate circular economy.”

The project came online in 2010, just in time to heat the Olympic Village for the 2010 Winter Games, and it was the first utility-scale sewage waste heat recovery system in North America. Since then, it has expanded, with plans to further scale up to provide space heat for 22 million square feet in the coming decades.

And it cannot come soon enough: This year alone, Vancouver has experienced several bouts of extreme weather, made more likely and intense because of climate change: heat domes, wildfires and catastrophic flooding, which recently cut the city off by road and rail from the rest of Canada. Having its own heat and hot water supply has been an additional benefit of the project, Ms. St. Clair said.

Stockholm, on the other hand, has used a district heat network since the 1950s, according to Erik Rylander, the head of heat recovery for Stockholm Exergi, a heating and cooling company. Much of the city’s heat is already provided by trash incineration and wood waste from Sweden’s extensive forestry industry, but data centers are increasingly becoming part of the energy mix, he said.

Since starting in 2017, Stockholm Data Parks, a collaboration between the city and Exergi, has offered companies different locations to build new data centers and participate in the heat recovery system. The companies are paid for the heat they provide to the network.

Stockholm, Mr. Rylander said, has particularly good connectivity to Northern Europe, Finland and Russia, which makes it attractive to data center companies, as does Sweden’s relatively clean power mix. However, they use biomass to produce a significant amount of heat and power, the renewable classification of which is debated by experts.

Amazon, Facebook and Microsoft have built data centers in Sweden over the last several years, but not close enough to Stockholm to sell their waste heat to the network, Mr. Rylander said.

Many companies have looked to put data centers in cold climates because they can use ambient air for cooling, which is more efficient than air-conditioning. But Mr. Rylander said that actually reusing the heat makes more sense: “If you establish a data center in a cold place like Sweden, it’s stupid to waste the heat, because heat has power and value in a cold country.”

Because of the heat from data centers and other sources, Stockholm was able to close the city’s last coal-fired power plant, Mr. Rylander said.

The coordinators in all three cities spoke of the importance of sharing their hard-won knowledge and adding to a growing body of urban climate solutions.

“To try and tackle the climate emergency will absolutely come with shared learning,” said Rowena Champion, the Islington council’s member for environment and transport.

“We’re very clear that we are an experiment, and we are doing the work that will enable others to benefit from it.”

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