Communal heat pump networks, from New York City to rural Cornwall, could be the answer to decarbonizing heat in both city high-rises and other difficult-to-heat homes.

Another cold spell has hit Cornwall, in south-west England, and the fields are blanketed in snow. Ceri Simmons’ house, however, is toasty warm down a windy lane. Her living room is a jungle of hanging plants, and glimpses of a wood-lined studio through the kitchen reveal Simmons’ job as an aerial-yoga instructor. “Having a warm house isn’t just nice for me; it’s also important for my clients,” she says.

The Simmons family’s home in the remote village of Stithians, near the most south-westerly tip of the UK mainland, has become an unlikely frontier in the race to decarbonize heating. It is testing a new approach to low-carbon heating that could be critical to the rapid scale-up required globally. The project looks beyond the challenges that individual homeowners face and creates a heat pump system that can be delivered at scale across streets, towns, and cities. As a result, it could serve as a model for cities around the world considering how to quickly and effectively decarbonize their heating systems.

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Today, 74% of people in the UK heat their homes with gas boilers, with the remainder primarily using electric heaters and oil. As a result, the heating sector accounts for one-third of the UK’s greenhouse gas emissions, which is comparable to the emissions of all petrol and diesel cars combined. Similar figures are seen in the United States, where gas accounts for roughly half of all heating.

To limit global warming, this must change dramatically, which means installing many more heat pumps in many places. According to the UK government’s climate advisory body, around a quarter of UK buildings should be heated using them by 2030, rising to 52% by 2050. According to Melissa Lott, an architect, electrifying heating will be critical to decarbonizing buildings in the United States. Columbia University’s Center on Global Energy Policy’s director of research. According to one San Francisco study, heat pumps are the “single most impactful lever” for reducing emissions.

If the source of electricity is renewable, heat pumps themselves emit no carbon

Rather than burning a fuel, heat pumps concentrate heat energy that is already present in the air, ground, or water and pump it through the pipes and radiators of a building.

They do so with incredible efficiency, converting 1 kW of electricity into 3-5 kW of heat, compared to 1kW for a direct electrical heater and 0.9kW for a gas boiler. This translates to “practically free heat,” according to Lott. However, as with all heating systems, efficiency is determined by how well the building is insulated to prevent heat loss, she adds.

Heat pumps emit no carbon if the electricity source is renewable. In the United Kingdom, nearly half of the electricity supplied to the national grid comes from renewable sources, compared to 20% in the United States. Both countries want to see significant increases in these percentages.

The Heat the Streets project in Stithians establishes a completely new model for how ground source heat pumps can function.

Ground-source heat pumps are more efficient than air-source heat pumps. This is because the ground maintains a constant temperature. Most ground source heat pumps have vertical piping, which necessitates drilling a deep, expensive borehole 60-200m (200-650ft) into the ground. They can also use a horizontal loop, which is much shallower in the ground but requires a large surface area, which most people, especially in cities, do not have.

Furthermore, installing heat pumps is typically the responsibility of the individual homeowner. Despite incentives such as the UK’s Boiler Upgrade Scheme and US federal tax credits under Biden’s Inflation Reduction Act, widespread adoption faces significant challenges. There is frequently a lack of understanding and awareness of the technology, which, when combined with high upfront costs and a scarcity of trained installers, can deter homeowners from making the switch. Architecture can also be a barrier: houses simply require enough outdoor space to install heat pumps, which is clearly lacking in flats and dense urban settings.

When a [gas] boiler breaks, there’ll now be an alternative to simply replacing it – Max Bridger

Heat the Streets, on the other hand, uses over 200 boreholes drilled 100m (330ft) beneath the street linked to a massive communal network of horizontal, underground pipes just below street level known as a heatmain, rather than each home drilling a single borehole for a single heat pump.

Glycerol, an odourless, non-toxic, viscous liquid, is passed vertically through boreholes to absorb heat and then circulate it in these horizontal pipes, which supply heat pumps in individual properties along the street and, eventually, the entire neighbourhood.

The heat pumps, which are no larger than a standard gas boiler, are installed either inside or outside individual homes, depending on the size, suitability, and owner preference.

Just a few metres beneath Cornwall’s surface, According to Max Bridger, project operations manager of Heat the Streets, the ground has a constant temperature of around 11C (52F) from absorbing sunlight for millennia, and it is this heat that is harvested by the heatmain.

The heat pumps then perform another round of exchange, compression, and evaporation, raising the temperature to around 50 degrees Celsius (122F). Finally, the heat is transferred to water, which is then pumped through specially upgraded pipes and radiators in a home.

The infrastructure will continue to be owned by Kensa Utilities, the company in charge of installing the network in Stithians. Connecting to the heatmain works similarly to connecting to other utilities such as broadband or water. Residents own their own heat pumps and pay a connection fee to participate whenever they want.

“When a [gas] boiler fails, there will now be an option other than simply replacing it. However, this system eliminates the need for people to finance large upfront infrastructure costs or connect all at once “Bridger explains.

Ground source heat pumps provide all of the house’s heating and hot water while reducing greenhouse gas emissions by 70%. Residents retain complete control over their heating and can change energy suppliers at any time.

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