Bunhill 2 District Heating Network - Heating up London

Bunhill 2 Energy Centre Construction - Preparing foundations at top of vent shaft. Image courtesy of Transport for London

Bunhill 2 Energy Centre Construction - Preparing foundations at top of vent shaft. Image courtesy of Transport for London


Ramboll. Crispin Matson. Image courtesy of Paulina Sobczak Photography

Crispin Matson

Business Development, District Energy
T: +44 20 7631 5291

Lucy Padfield

Director, Energy
T: +44 7967 799 431

Ramboll was commissioned by Islington Council in London to design and deliver a district-wide heating network to provide cheaper and greener heat to 1,350 homes plus community buildings in north London, using unwanted heat from the London Underground. 

The Northern Line, the oldest deep level metro line in the world, will heat 21st century homes, offices and leisure centres. The project will be a European first of its kind, extending what is possible when using waste energy to make for a more liveable, more sustainable society. 

Ramboll has been instrumental in bringing this highly innovative low-carbon solution to the people of Islington. Producing first a detailed study into the feasibility of using heat from the London Underground to supply district heating, and subsequently further design development and overseeing procurement and delivery. 

The Greater London Authority (GLA) estimate there is enough heat wasted in London to meet 38% of the city’s heating demand. With the expansion of district heating networks this could rise to 63% of demand by 2050. The heating network at Bunhill is one of the most innovative in the UK; recycling waste heat from the London Underground to provide a low carbon, low cost heat source for local homes and businesses, largely existing council housing and leisure centres built in the 1930-1980s. Northern Line passengers also benefit from cooler tunnels, while London residents as a whole benefit from lower carbon emissions and improved air quality as gas combustion is displaced.

As well as being financed by the London Borough of Islington, the award-winning Bunhill Heat and Power Network was partly funded by the EU CELSIUS Project, and is supported by other London project partners including the Greater London Authority, TfL and UK Power Networks. Our work on the extension of the Bunhill heating network project is split into 2 phases. 

Stage 1 - Feasibility and scoping

Islington had already built the first phase of the Bunhill heat network, delivering efficient heating to 850 homes through a gas combined heat and power (CHP) scheme at Bunhill Energy Centre 1, but they wanted to do more. Islington Council appointed Ramboll to find out how to supply heat to an additional 500 dwellings in north London using low grade waste heat from the London Underground. Our ground-breaking study confirmed that Islington Council could in fact extend the district heating network to 1350 homes by adding an innovative low-carbon heat source. 

Extracting waste heat from ventilator shaft

The proposed low-carbon heat source was a London Underground ventilation shaft, located on City Road, where 18-28 degrees Celsius air is exhausted to the atmosphere from a long abandoned tube station (City Road, between Old Street and Angel), now part of the Northern Line tunnel ventilation system. Ramboll’s feasibility study confirmed that this source of waste heat could be exploited by heat pumps, which would capture the waste heat and upgrade it to approximately 80 degrees Celsius, as opposed to the original design temperature of 95 degrees Celsius.

Bunhill district heating schematic


Connecting the heat network to established housing stock 

Islington Council wanted the scheme to supply the cheapest, greenest heat possible, so the heat pump design temperature was lowered further to 70 degrees Celsius to increase the systems efficiency. Ramboll investigated the impact of lower temperatures for the connected buildings’ heating and domestic hot water loads to ensure demands could be met and end user comfort wasn’t compromised. Our investigations proved the heat pump concept was financially and technically viable.

Another design innovation was to incorporate two smaller gas-fired CHP engines which, as well as providing heat, also supply electricity directly to the heat pump when the power from the grid is most expensive, helping reduce the cost of the heat.  Funding for this innovative feature was supplemented by a grant from the GLA. A second thermal store also enhances system technical and economic performance.

“We believe that the use of large-scale heat pumps in this way connected to urban district heating systems will play a major part in decarbonising the UK’s heating energy demand”, says Lucy Padfield, District Heating Director at Ramboll. “The use of heat pumps utilising industrial waste heat sources is more carbon efficient than gas-fired CHP, the usual source of heat for district energy schemes. I am convinced that with the increasing use of renewable power sources, large-scale heat pumps connected to district heating systems will play a major role in the future heating of cities in the UK.”

Stage 2 - Delivering the Solution

On completion of the feasibility study, Ramboll was appointed to act as the Owner’s Engineer on the project. This role involved developing the design of the complete system to enable planning permission to be obtained and for it to be tendered.  

As part of the design development, discussions were held with London Underground with respect to the size and function of the fan serving their ventilation shaft and how heating and cooling solutions can be integrated, resulting in further environmental savings. These discussions resulted in them upgrading the fan’s capacity and enabling it to be reversed, opening up the potential for the district heating scheme to supply cooler air during warmer weather.

All district heating works are now complete and work on Energy Centre 2 is well under way. The main heat generation equipment is containerised and vertically stacked within the Energy Centre structure which is clad in a striking, perforated anodised aluminium façade.  

Continuing innovation

Reports from the Committee on Climate Change (CCC), published February 2019, called for new homes to be banned from connecting to the gas grid. Whilst these proposed changes will undoubtedly have a positive effect on carbon emissions with over 80% of the building stock that will exist in 2050 being built already, a significant challenge will be to de-carbonise existing properties. 

The Bunhill district heating scheme is a revolutionary example of how linking waste heat resources to existing buildings, and new high-density developments, using district heating can provide low carbon and affordable heat alternatives.

Applying our vast experience from Copenhagen, home to one of the most sophisticated systems in the world where a 160km district energy network supplies over 1 million people, Ramboll is leading the district heating revolution in the UK. We are identifying opportunities and providing solutions on how to maximise efficiency and reduce carbon and energy costs. We are currently investigating ways to provide buildings on the same district heat network with a tailored heat temperature supply to match that building’s requirements.

With 300,000 new homes needed every year to meet our housing demand the opportunities to establish district energy networks is vast. Our ground-breaking solutions implemented at Bunhill and our ongoing investigations show that by using waste heat as a core part of our energy mix, we can deliver cheaper and de-carbonised energy to thousands of people in existing buildings and new build developments simultaneously from the same district heating network. Another UK first.

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