Heat from the London Underground recycled for homes and businesses

london underground sign

A disused tube station in Islington, North London, is now home to the Bunhill 2 Energy Centre, from Colloide Engineering Systems.

This project, for which Danfoss Heating is providing the plate heat exchangers and substations, will recycle the heat produced by the tube to be used by nearby housing estates.

As Martyn Neil from Danfoss says:  ‘The Bunhill 2 Energy Centre is a world-first scheme where they are capturing the heat from the underground train network, and utilising it to heat homes and a primary school. This is an excellent way to reduce hot air in the underground and at the same time support the CO2 reduction in London.”

The new energy centre uses state-of-the-art technology. This includes a 500kW ammonia heat pump driven by the heat recovery from a heat exchanger coil within the London Underground shaft, recovering the warm air lost throughout the northern line tube.

The scheme recycles the wasted heat to provide heating and hot water to more than 1,350 homes, a school and two leisure centres in Islington. It has been described as a blueprint for decarbonising heat in potential future schemes in London, reducing heating bills and carbon emissions while improving air quality.

Bunhill Heat and Power Network links together the existing Bunhill phase 1 heat and power network with this new Bunhill phase 2 extension. A third phase could see more homes connected in the future.

Project challenges

During the course of this project, Colloide Engineering Systems identified a number of challenges that needed to be overcome:

  • working with existing plant rooms, all of which needed to be upgraded to accept heat from the district heating network
  • engineering the communication network between the energy centres and the plant rooms
  • engineering associated with an ammonia-based heat pump in the centre of London
  • working on very congested, tight sites
  • the number of different partners involved and ensuring all parties worked cohesively together
  • the complexity and uniqueness of the project, with no similar previous projects to refer to.

In addition to these challenges, Colloide had to consider the many residents in close proximity whilst working in a very busy part of London. During the construction period, the already heavily congested roads had to be dug up and a lot of work had to be carried out around the site in order to install the Energy Centre and new district heating network.

How it works

To help control the temperature on the tube network there are a series of ventilation shafts that carry hot air from the tunnels up to ground level. Warm air created by trains and machinery in the underground network goes up the ventilation shaft and is pushed by a two-metre fan through a heat pump.

The heat pump captures heat from the warm air, via a closed loop water circuit in the ventilation shaft. This is used to heat a gas, which is then put through a compressor, converting it into a very hot liquid and making the pipes that hold it very hot as well. These hot pipes are used to heat the water that runs in the pipes of the Bunhill Heat Network so that they can heat the buildings connected to the network.

The pipe network is very well insulated to minimise the amount of heat lost on the way to the buildings. As a bonus, the fan can also be reversed to help with cooling the tube tunnels in the summer months.

The utilisation of two natural gas CHP units, with a combined output of 700Kw and district heat pipework of 1800m, allows a further 550 homes and a primary school to be connected to the existing Bunhill Heat and Power district heating network, which was launched in 2012, with the potential to supply up to 2,200 homes.

A Colloide spokesperson said: “The kit was packaged, the equipment well engineered and designed specifically for this project. It was a plug and play system designed to operate under old and new temperature regimes on a skid that has been pressure tested off-site and fabricated in modular sections, that can be split and reconnected on-site to work around difficult access arrangements and mean minimal on-site work.”

Bespoke substations

Thanks to the new Energy Centre, the heating bills for council tenants connected to the network will be cut by 10% compared to other communal heating systems, which themselves cost around half as much as standalone systems heating individual homes.

The units to connect the buildings were bespoke substations from Danfoss, designed and specified in conjunction with the designers, 3D models, built and delivered as pre-fabricated units and the Sondex PHE were also used elsewhere in the system as separation of circuits.

Martyn Neil from Danfoss says: “For this project, Danfoss supplied eleven Sondex plate heat exchangers, and five substations to connect the four housing blocks and the school. ”

Colloide chose Danfoss as it was ‘by far the most engaged response we received and it was clear that we were going to get the right involvement in design and testing of the project that we needed, and within budget.’

For further information, check out colloide.com/bunhill-2-energy-centre-innovative-district-heating