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The era of the gas boiler is almost over. That much is clear. What isn鈥檛 so clear is what will replace it.
There are a variety of competing technologies vying for the prize: infrared radiators, air source heat pumps, district heating systems and even hydrogen boilers.
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A new kid on the block could outshine them all. For years, ground source heat pumps have been written off as a niche heating solution, suitable to install only for those with plenty of land and money.
But a new model for ground source heat pumps, using shared pipework dug into public streets, could bring this technology to the masses.
Why ground source?
Home heating is responsible for a hefty chunk of greenhouse gas emissions in most nations 鈥� in the UK, for example, it accounts for around 14 per cent of the country鈥檚 total emissions. That is because most houses in the UK rely on a gas-fired boiler for their heating and hot water. To reach net-zero emissions, that will have to change.
Air source heat pumps are perhaps the most obvious replacement. These machines act like refrigerators in reverse, extracting heat from outside air and amplifying it so it can be used to warm water for piping through radiators.
But although many millions of UK households will be able to switch with little hassle to an air source heat pump, there are drawbacks to the technology. One is that it requires a chunky outside unit, which current English and Scottish rules say must be situated at least 1 metre away from the boundary of the property. For many homes with small back gardens, that could mean right in the middle of the patio or back yard. Plus, air source heat pumps require a hot water tank inside the home, taking up more space than the common combi-boiler.
Enter ground source heat pumps, also known as geothermal heat pumps. These machines require cabling to be laid underground, from where they can draw up warmth stored in the earth. They are 30 to 40 per cent more efficient than an air source heat pump because they don鈥檛 have to fight against cold winter air. And the consumer units that sit inside the home are more compact.
Usually, ground source heat pumps can only be installed in homes where there is plenty of surrounding land to drill the boreholes and run the required cabling, but Kensa, a firm based in Cornwall, UK, has different ideas.
鈥楴etworked鈥� heat pumps
Kensa has pioneered the concept of networked heat pumps, where a shared network of pipes, boreholes and cabling supplies warmth to multiple households within a single neighbourhood. This makes more sense than having individual households pay for their own boreholes and cabling, says Kensa鈥檚 Lisa Treseder.
鈥淭he biggest barrier to ground source heat pumps is the high upfront cost of the infrastructure,鈥� she says. 鈥淭hat infrastructure is plastic pipework that sits in the ground 鈥� it鈥檚 got no moving parts, and it lasts for 100 years. So, it鈥檚 perfect for private investment.鈥�
Last month, Kensa wrapped up a pilot project in Cornwall dubbed Heat the Streets, where it tested this networked approach to heat pumps in three different communities: a new-build development, a public housing development and a private street.
Boreholes were drilled to 110 metres below ground and connected by horizontal pipework. A mixture of cold water and antifreeze is pumped through the pipes, where it absorbs heat from the ground, raising its temperature to between 10 and 12掳C (50-54掳F). This fluid is piped into the heat pump inside a customer鈥檚 house, where its energy is used to evaporate a refrigerant. The refrigerant gas is then fed into a condenser, which heats up the water that flows through the home鈥檚 heating system.
For the private homes in the pilot project, all the infrastructure was installed in the public street, in what Kensa believes is a world first. Under this model, homeowners own the consumer unit inside their property, while Kensa owns and manages all the infrastructure outside the house. Residents pay a standing charge of around 拢60 a month to access this infrastructure.
Rolling out clean heat in this way means you can decarbonise almost an entire street at once, in denser suburban areas, says Treseder. 鈥淭he best place that we see this for is the forgotten middle of UK housing, which is medium-density areas,鈥� she says. 鈥淧erhaps terraced streets where you鈥檝e maybe not got much green space, and there鈥檚 not much room in the back garden for an air source heat pump.鈥�
The residents seem happy. Vicki Spooner received a heat pump as part of the trial in private homes. her family home is now warm and cosy: 鈥淲hen we come in after a dog walk, we can dry coats on the radiators, or if the boys have dunked their boots in the sea we can dry them too.鈥�
Private home challenge
Heat the Streets has already shown that it is financially viable for Kensa to install networked heat pumps in new-build developments. 鈥淲e started selling it before we鈥檇 even finished the project,鈥� says Treseder. The company says it is now talking to all the UK鈥檚 major housebuilders, with three schemes already up and running at new developments in the Midlands and London 鈥� and more in the pipeline.
Installing new state-of-the-art infrastructure is relatively easy when building a neighbourhood from scratch. It鈥檚 trickier when you are navigating an existing spaghetti of pipes, cables and other infrastructure, and dealing with multiple homeowners all at once, says Treseder.
鈥淔or new-builds and social housing, you have a single decision maker. They have access to capital funding. So, you can make a sale for 100 houses, and you do everyone in that group,鈥� she says. 鈥淲hen you are working on a private retrofit, you鈥檝e got to work with every individual household in that area, and you have to make a sale to every individual household.鈥�
At the moment, the Heat the Streets model isn鈥檛 likely to take off for private housing in the UK, says Treseder. Part of the problem is getting permission from local authorities to dig up public highways, which is often far from straightforward. The other issue is cost 鈥� installing aheat pump and equipment into a home would cost around 拢10,000 per household, plus the monthly standing charge. And given the high cost of electricity in the UK 鈥� more than three times the price of gas 鈥� savings on energy bills would be minimal. 鈥淲e don鈥檛 really think that is attractive enough right now,鈥� she says.
There may be scope to bring down the upfront cost by tweaking the scale of the underground pipe work and fine-tuning the in-house installation process, she says. The UK government could help by shifting green levies from electricity bills to gas to make electricity cheaper, she says, boosting the potential for savings on long-term energy costs.
But more work is still needed to optimise the offer to households so that enough homes on a single street can join and make a new project viable. To that end, Kensa is working with the innovation charity Nesta to explore ways of making the proposal more attractive for private homeowners. This could include providing financial help with the upfront cost of the initial installation, or offering community incentives such as free on-street electric vehicle chargers, bike racks and 鈥減ocket parks鈥� if enough households on a single road sign up. 鈥淚f you can get 50 to 60 per cent of the people on the street signing up in one go, then it鈥檚 a really attractive model,鈥� says Nesta鈥檚 Andrew Sissons, who is leading the project.
Beyond the UK
Kensa is focused on making Heat the Streets a viable proposition for the UK. Elsewhere in the world, others have a similar idea.
In Massachusetts, of a networked ground source heating system. The $10 million scheme, which broke ground in June, will provide heating and cooling to 37 buildings in the city of Framingham, fed by fluid-filled pipes running under the streets between homes. The project includes apartment complexes, residential homes, a fire station and a college building.
Eversource says it will monitor the pilot closely to ensure it delivers carbon emission savings, customer satisfaction and the potential to scale up.
