London's Underground is heating homes

Waste heat from the London Underground is being recycled to heat the London Borough of Islington | By Sophia Saleem

London's Underground is heating homes
Photo by Maarten Deckers / Unsplash
Poster by Federick Charles Harrick, 1926

This isn’t a satirical take on rising temperatures. Nor is it mocking the sweaty Londoner determined to keep cool on their journey home. This is an advertisement from 1926 when the Tube could be used as a cooling ground for locals to escape the city heat. Nearly a century later, you only have to ride the Tube once to know it’s the last place you want to be on a sunny day.

A Community Project

Today, some of that infamous heat is being used to warm homes. The Bunhill 2 Energy Centre is part of a district heating network located in the London Borough of Islington. In line with Islington's goal to be net carbon zero by 2030, the network provides low-carbon heating to 1,350 council homes, two leisure centres and Moreland Primary School.

The aim of the network is to reduce carbon emissions and provide cheaper energy by utilising waste heat energy produced by the London Underground. The recent expansion of this project, Bunhill phase 2, reduces carbon emissions by 500 tonnes per year. Residents whose homes are connected to the network will save 10% of their energy bill each year.

Transport for London, who worked closely with the Bunhill project, spend a portion of their budget on ‘cooling schemes’. By giving the waste heat a new pathway, less is absorbed and stored in clay earth surrounding the underground. This means a cooler tube; improved safety and comfort for passengers in the face of rising temperatures.

As public transport is a carbon-efficient way to commute, providing monetary savings and service improvements for TfL is conducive to a more environmentally-friendly London. Additionally, by providing cheaper energy to schools, more money can be spent on educational facilities as well as helping local low income households with bills.

Original illustration by Louise Scriven

Breakdown - how it works

The site of the Bunhill 2 Energy Centre at the disused City Road Underground station (between Angel and Old Street) already functions as part of the Northern Line ventilation system. Using a pre-existing fan, rising hot air is blown up the ventilation shaft through a Heat Pump. This air heats a gas, which is then put into a compressor, turning the gas into a hot liquid. This liquid is then used to heat the water inside the pipes that run through the Bunhill network to heat the buildings connected.

District heating networks, such as the Bunhill 2 Energy Centre, then take advantage of highly efficient technologies such as heat pumps which can achieve energy use efficiency levels of over 300%.

So not only is this idea novel, but it works. The Greater London Authority (GLA) estimates that there’s enough heat energy wasted in London to meet 38% of the city's heating demand. Additionally, with an expansion of district heating networks, it could rise to 63% of demand by 2050.

Who’s behind it?

The energy centre was funded by the London Borough of Islington and the EU CELSIUS Project, as well as other London project partners such as the Greater London Authority. Aided by TfL, the project was completed by engineering companies Ramboll and Colloide and the architecture firm Cullinan Studios. The Bunhill 2 Energy Centre was originally estimated at £10m but ultimately cost £16.3m.

Leaving the EU has created some uncertainty around the UK's ability to meet its climate goals. The EU’s extensive legislation on environmental standards and commitment to funding climate innovations such as the CELSIUS project allowed for initiatives like the Bunhill 2 Energy Centre to come true.

However, since leaving the EU, the UK has established its own independent climate policies including targets to reduce greenhouse gas emissions to net zero by 2050, as advised by the Climate Change Committee. Could more projects like the Bunhill scheme appear in the future?

Expansion of District Heating

As the pandemic came to an end the demand for gas rose, then came the Russian invasion of Ukraine, having extreme inflationary effects on the price of natural gas and oil. Now more than ever, this successful example of the decentralisation of energy is pointing the way forward. Using heat that is readily available to London increases Britain’s energy security.

London’s Underground is an extensive network. If every underground station were to be adapted to recycle waste heat energy, all boroughs would benefit.

Lucy Padfield, District Heating Director at Ramboll, said “We believe that the use of large scale heat pumps in this way connected to urban district heating systems will play a major role in decarbonising the UK’s heating energy demands”.

This seems to be a widespread opinion. According to this EU level survey, 98% of respondents believe "the role of district heating and cooling networks in future energy systems, especially in cities, will increase”. The only respondent who believes it ‘Will remain the same’ is from Denmark, where 65% of citizens are already served by District Heating.

In fact, Ramboll, the design firm responsible for ensuring the feasibility of the Bunhill project, also played a role in the 160km transmission network supplying heat in Copenhagen, Denmark. Supplying heat with 3 times fewer carbon emissions than boilers to more than 500 million square metres. Perhaps this is just the start for the UK.

Sophia Saleem is a journalism student at the London College of Communication, UAL.