Another cold snap swept the fields in Cornwall, in the southwest of England. But on a windy country road, Keri Simmons’ house is blazing with heat. Her living room is a jungle of hanging plants, while the wood-paneled studio, peeking through the kitchen, shows Simmons’ work as an aerial yoga teacher. “A warm home not only appeals to me, but is also important to my clients,” she said.
The remote village of Stitians, near the southwesternmost tip of mainland Britain where the Simmons family lives, has become an unlikely frontier in the race to decarbonize heating. He is testing a new low-carbon heating method that could be the key to the rapid scale-up the world needs.
The project addresses the barriers faced by individual homeowners and develops a heat pump system that can be delivered at scale to streets, cities and towns. In doing so, it can provide urban spaces around the world with a model for thinking about how to quickly and efficiently decarbonize their heating systems.
In the UK today, 74% of people heat their homes with gas-fired boilers, with the remainder mostly using electric heaters and oil heaters. This has resulted in the heating sector accounting for a third of the UK’s greenhouse gas emissions – as much as all petrol and diesel vehicles in the UK. Similar figures can be found in the United States, where about half of all heating comes from natural gas.
To limit global warming, a radical change must be made, and in many places that means installing more heat pumps. According to the UK government’s climate advisory body, they should heat about a quarter of buildings in the UK by 2030 and rise to 52% by 2050. Electric heating will also be key to decarbonizing buildings in the US, said Melissa Lott, director of research at Columbia University’s Center for Global Energy Policy. A San Francisco study called heat pumps “the single most powerful lever” for reducing emissions.
Instead of burning fuel, a heat pump concentrates heat energy already in the air, ground or water and pumps it through the building’s pipes and radiators.
They do this with incredible efficiency, converting 1 kilowatt (kW) of electricity into 3-5kW of heat, compared to 1kW for direct electric heaters and 0.9kW for gas boilers. This means they actually provide “free heat,” Lotter said. However, as with all heating systems, efficiency depends on how well the building is insulated to minimize heat loss, she noted.
If the electricity source is renewable, the heat pump itself emits no carbon. In the UK, nearly half of the electricity supplied to the national grid comes from renewable sources, compared to 20% in the US. Both countries are aiming to significantly increase these percentages.
The Keri Simmons heat pump that can be seen outside her house now provides her with all the heat and hot water from a pipe network under the street (Image: Evie Townend)
The Stithians Heat the Streets project is a new example of how geothermal heat pumps work.
Geothermal heat pumps are more efficient than air source heat pumps. This is due to the fact that the soil has a constant temperature. Most ground source heat pumps have a vertical pipe that must be drilled in an expensive well 60–200 meters (200–650 ft) underground. Or they could use a horizontal loop, which is much smaller at ground level but requires a lot of surface area that most people don’t have, especially in cities.
What’s more, installing a heat pump is often the responsibility of the individual homeowner. Despite incentives such as the UK boiler retrofit program and US federal tax credits under the Biden Inflation Reduction Act, significant barriers remain to widespread adoption. Often, a lack of understanding and awareness of the technology, combined with significant upfront costs and multiple trained installers, can deter homeowners from making changes. Architecture can also be a hindrance: houses also have enough outdoor space just for a heat pump, which is clearly lacking in apartments and dense urban environments.
However, instead of each house having one well for one heat pump, Heat the Streets uses more than 200 wells drilled 100 meters (330 ft) below street level that connect to a huge public network, a public network made up of horizontal underground pipes under the street, called the heat source.
Glycerin, a non-toxic, odorless, viscous liquid, absorbs heat vertically through wells and then circulates in these horizontal pipes, which in turn provide heat pumps for individual properties along entire streets and, ultimately, entire blocks.
Heat pumps – no larger than a conventional gas boiler – are installed inside or outside individual residences, depending on the size of the property, suitability and owner preferences.
Max Bridger, Project Manager at Heat the Streets, says that meters below the ground in Cornwall, heat pipes collect this temperature at a constant temperature of around 11°C (52°F) due to absorbing sunlight for thousands of years. .
View image Heat pumps work more efficiently when buildings are insulated to minimize heat loss (Source: Credit: sturti/Getty Images)
The heat pump then performs another series of exchanges, compression and evaporation, bringing the temperature up to about 50°C (122°F). Finally, this heat is transferred to water, which is pumped through the house’s specially upgraded plumbing and radiators.
Kensa Utilities, the company responsible for installing the network at Stithians, will remain the owner of the infrastructure. For residents, connecting to a heat pipe is like connecting to any other utility, such as broadband or water. Residents have their own personal heat pumps and pay for connection when they are ready.
“When a [gas] boiler fails, there is now an alternative to replacing it. But this system also means people don’t have to pay big upfront infrastructure costs or plug everything in at once,” Bridger said.
Geothermal heat pumps provide all the heating and hot water needs of a home and reduce greenhouse gas emissions by 70%. Residents have full control over heating and can change their energy supplier at any time.
Simmons’ house has a heat pump installed and shares a heat pipe with several neighbors. The interior and exterior work took about a week and “wasn’t really too disruptive or noisy,” she said. The water tank was hidden in an old linen closet and was almost the size of an ordinary boiler.
Ultimately, she plans to use her solar panels to directly power a heat pump, which she says will make her home almost completely self-sufficient.
Drill rig workers in Enfield, London, install ground source heat pumps in apartment buildings (Photo: Kensa Utilities)
This concept of burying heat pipes under public streets is by no means limited to single story buildings like Simmons. Another Kensa project in Enfield, London is the installation of ground source heat pumps in apartment buildings.
Under each of the eight towers (400 apartments in total) heating ducts are laid, using their car parks to drill the necessary wells.
Shafts used to transport other utilities throughout the building, known as service risers, allow Stithians technology to be adapted to multi-story buildings, Bridger said. He added that for small spaces, installing a “shoe box” type heat pump in each apartment can provide enough heat while minimizing the space occupied inside.
The future of heat pumps in high-rise buildings is attracting more and more attention around the world. In New York City, air source heat pumps have become the focus of an effort to decarbonize the city’s 6,000 high-rise buildings.
Nowadays, most of them have a large gas boiler to control heating throughout the building. Each individual apartment also uses an air conditioner connected to the exterior windows, which operates separately from the heating system.
In 2021, the New York City Housing Association launched the Clean Heating for All competition, a competition designed to encourage industry innovation in line with future local laws that will limit greenhouse gas emissions from buildings starting in 2024. The winner was an air source heat pump, which according to Lott hangs “like a saddle bag” at the bottom of the apartment’s window without blocking light or taking up space inside the apartment.
“The beauty of heat pumps is that they can both heat and cool a space using the same process instead,” Lotter added. “It’s a modular device that does two things.”
The design will also allow apartments to control their own heating and cooling. “It’s more efficient because you can set up your apartment to suit your comfort level, so there’s no more window opening from an overheated apartment in winter,” Lotter said.
The new heat pumps will be tested this year at Woodside Residences, a complex of 20 brick buildings in Queens where residents were left without heat and hot water after Hurricane Ida last winter.
Although an immediate upgrade of the local network infrastructure is not expected, the increase in electricity demand is an important factor for the wider use of heat pumps in general.
Director of the European Regulatory Assistance Project (RAP) Jan Rosenov said that the load on the UK energy system could double or even triple over the next 20-30 years. “There must be other ways to store electricity other than large batteries in people’s homes,” he said. He added that there are a number of promising technologies such as flow batteries and green hydrogen. (Learn more about whether gravitational batteries can solve our energy storage problems).
Stockholm’s district heating network uses industrial heat pumps and other heat sources to power 800,000 homes (Source: Credit: Christine Olsson/Getty Images)
In a way, Heat the Streets uses another important home heating solution in a low-carbon world: district heating.
Essentially, district heating networks are “just banging on the empty containers that hold properties together,” said David Barnes, a thermal decarbonization expert at the University of Leeds. “How heat is injected into the heating network is a related but separate issue.”
During the oil crisis of the 1970s, district heating flourished in the Nordic countries, but these systems were mainly powered by large fossil fuel-fired combined heat and power plants. However, Barnes said the design of this single centralized system could make it easier for large numbers of households to switch to low-carbon heating without “removing” thousands of boilers.
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For example, Stockholm’s 3,000-kilometer (1,860-mile) piped district heating network currently powers 800,000 homes with industrial-scale heat pumps that draw energy from domestic wastewater, data centers and sea water, as well as incinerated non-recyclable waste and forests. biofuels get heat.
The Stithians “Heat the Streets” model uses “fifth generation district heating” – a localized network combined with heat pump technology. Caroline Haglund Stignor, an energy technology researcher at the Rise Research Institute in Sweden, said the benefit of a project like this across the streets is being able to focus on any nearby energy source for the best fit. “You start small and build up gradually,” she said.
This could allow for more innovative approaches to heat sources such as the Islington grid using heat flow from the London Underground tunnels or flood water from old mines.
However, a lack of awareness and regulation of district heating in the UK is hindering its expansion, Barnes said.
The UK Government has committed to dedicate heat grid zones by 2025 at the latest, place heat grids in the best possible location and force people to connect to these zones. Barnes explained that this would help make the heat grid business model more financially viable, as private investors would be more confident that people would use it.
This type of large-scale work could be coordinated with other infrastructure work, such as cables for electric vehicle charging points, to reduce disruptions, Rosenov said. But he added that these local deployments would require “fundamental changes” in planning that have not yet been reflected in policy or framework.
Air source heat pumps are more commonly used in private homes than in multi-family homes (Photo: Mark Morgan/Alamy)
However, central heating is not always the right answer. It is best used in densely populated areas due to the high heat loss associated with transporting high temperature water over long distances.
District heating already exists in some US cities such as Milwaukee and Baltimore, Lotter said, but with a few exceptions, the country’s population density is not the same as in the UK and much of Western Europe. “For most of the US, we’re talking about individual building heating, so a district heating network doesn’t make sense. [Personal] heat pumps, whether air source or ground source, are the best option for us.”
The path to decarbonizing heating will not be easy, but heat pumps are a technology that is more or less ready if the price barrier can be overcome. But even as issues of energy security, fuel prices, and climate-related extremes hang in the balance, Simmons’ yoga studio still seems like an attractive place to deal with uncertainty.