How a shuttered London Underground station became a model for green energy

Bunhill 2 Energy Centre in north London. (Credit: Paul Raftery)

This article appears on CityMetric courtesy of Blueprint magazine.

On the corner of a north London street, a world-first energy centre provides a blueprint for decarbonising heat in London and major cities around the world.

Bunhill 2 Energy Centre reuses waste heat from the London Underground system to power 550 homes, a primary school and a leisure centre. What’s more, this groundbreaking facility tucks neatly into the urban landscape, with a compact structure devised by Cullinan Studio, which signals its arrival and its civic intentions with a cladding of copper-hued, perforated aluminium panels.

Bunhill 2 was funded by Islington Council and developed in collaboration with Transport for London and the Mayor of London, with research assisted by a grant from the European Union’s CELSIUS project. The newly completed energy centre is a key part of Islington’s strategy to be zero carbon by 2030. Islington-based Cullinan Studio was in on the project from its gestation, having heard about the proposal in 2014 at a meeting of Islington’s Sustainable Energy Partnership, of which it is a member. Having just completed the University of Warwick’s Cryfield Energy Centre (2014), the practice volunteered its expertise, and was enrolled to work with the Islington Energy Team to help bring this project to fruition.

The scheme entailed the refitting and repurposing of an old London Underground station, City Road, which closed in 1922. Flanked by roads and social housing, the energy centre had to be housed within the existing footprint of the old station and its ventilation shaft, which now houses a huge underground fan that extracts warm air from the Northern Line tunnels below. This air is used to heat water that is then pumped to neighbouring buildings through 1.5km of underground pipes. 

“We were very restricted on where we could put anything – on this building everything had a purpose and a specific requirement,” says Cullinan Studio partner Alex Abbey.

The design evolved over the better part of a year and, as the Islington team got up to speed with the new technologies, different elements were tweaked and added – for example, a thermal store, so hot water could be retained and then distributed as needed.

Every element required adjustments, says Abbey: “We always knew there was a gas turbine going in, but then there were heat pumps going on to the roof and they were noisy, so we had to get acoustic advice, and then right to light issues meant we had to adjust the profile of the building, so it wouldn’t affect the adjacent residents… It was very much form following function in the end.”

However, the client was enthusiastic that the building should make a civic statement – unlike many urban energy structures which either hide their purpose behind large walls or within a boring box.

“They want it to be a celebration of how our cities will function,” says Abbey. “It’s about local providers producing power, reducing carbon, pollution and the energy losses from the grid – there is a huge amount of power lost just from transporting it along the wires.”

The resulting structure is a trapezoid shape, wrapped around three shipping containers placed on a steel shelving system. These house the above-ground plant and machinery and need to be easily accessed at any time; the containers can even slide out and be replaced as technology and maintenance requires. So the exterior facades comprise removable, anodised aluminium perforated panels, with stairs and access points neatly incorporated into the frame.

Credit: Paul Raftery

The perforations follow both an aesthetic and engineering logic: the engineering requirement was to provide greater ventilation the higher up the building you go.

“The panels get more and more perforated, because the chillers on the top need lots of air around them,” says Abbey. “That dictated the patterning. We could have done it in a very rudimentary fashion with a rising amount of perforations, but we wanted to make it more interesting… We had to look at loads of precedents. It came down to an idea of thermal currents, trying to get across the idea of warm air or heat rising. If you look at it closely, it starts off quite chunky and in a diamond pattern and then it interlaces and gets smaller and then gets smaller again, kind of tree-like.”

At the corners, the panels switch to an expanded metal mesh, “purely to differentiate between the corner and the flanks,” says Abbey.

In inserting the building into the street, the Cullinan team adhered to good urban planning principals. “We were trying to respect the building lines of the original station along the street,” Abbey explains. “We tried to give it some scale on the street corner, and stacked it higher there, so it has a bit of presence”.

With a large social housing block immediately behind it, and residential towers (at the time unbuilt) scheduled to arrive across the road from it, “we knew it would be a little thing surrounded by giants”, says Abbey, “but as a result, we wanted to have quality, and give it a quiet sense of purpose and power from the street corner”.

Islington’s brief stipulated a base that was vandal-proof but also attractive. “That set us up with the idea of a plinth and a top,” Abbey says. “So we had some fun with the client looking at old precedents for the site – for example, the original underground station had the classic oxblood tiles on it, and there are a lot of buildings in the London Underground with vitreous enamel panels, which are really tough and good against graffiti.” In the end, Cullinan came up with a two-part base: There is a skirting board of black glazed brick, and above that, black vitreous enamel panels. Set within these are Scottish artist Toby Paterson’s work – his cast aluminium panels with coloured enamel insets are based on the internal layout of flats in the nearby King’s Estate.

Credit: Paul Raftery

With the design finally finished and approved in 2015, the project was handed over to executive architect McGurk Architects. The finished building is “pretty much as we proposed,” Abbey says.

This energy centre substantially boosts the capacity of the existing Bunhill Heat and Power district heating network, which was launched in Islington in 2012. Between them they provide power to 1,350 homes, with the potential to heat up to 2,200, plus the primary school and two local leisure centres. Furthermore, the two-metre fan can be reversed to draw cooler air from above and funnel it into the underground system in the summer months. Heating bills for connected council tenants will be cut by 10% compared to other communal heating systems, which apparently already cost half as much as standalone systems heating individual homes.

“We are very proud to be part of it,” Abbey says. “As a practice we have pushed the agenda of sustainable design for decades. But you can only do so much with a building. The usual power station typology is something that sits on its own, and takes rather than gives. Whereas this building gives, which is great. And it’s providing real change socially, helping to eradicate fuel poverty.”

He concludes: “Hats off to Islington: they went with it and were prepared to pay for high-quality materials. They now have a little jewel on the corner there.”

Veronica Simpson is a senior contributing editor at Blueprint Magazine.


What's actually in the UK government’s bailout package for Transport for London?

Wood Green Underground station, north London. Image: Getty.

On 14 May, hours before London’s transport authority ran out of money, the British government agreed to a financial rescue package. Many details of that bailout – its size, the fact it was roughly two-thirds cash and one-third loan, many conditions attached – have been known about for weeks. 

But the information was filtered through spokespeople, because the exact terms of the deal had not been published. This was clearly a source of frustration for London’s mayor Sadiq Khan, who stood to take the political heat for some of the ensuing cuts (to free travel for the old or young, say), but had no way of backing up his contention that the British government made him do it.

That changed Tuesday when Transport for London published this month's board papers, which include a copy of the letter in which transport secretary Grant Shapps sets out the exact terms of the bailout deal. You can read the whole thing here, if you’re so minded, but here are the three big things revealed in the new disclosure.

Firstly, there’s some flexibility in the size of the deal. The bailout was reported to be worth £1.6 billion, significantly less than the £1.9 billion that TfL wanted. In his letter, Shapps spells it out: “To the extent that the actual funding shortfall is greater or lesser than £1.6bn then the amount of Extraordinary Grant and TfL borrowing will increase pro rata, up to a maximum of £1.9bn in aggregate or reduce pro rata accordingly”. 

To put that in English, London’s transport network will not be grinding to a halt because the government didn’t believe TfL about how much money it would need. Up to a point, the money will be available without further negotiations.

The second big takeaway from these board papers is that negotiations will be going on anyway. This bail out is meant to keep TfL rolling until 17 October; but because the agency gets around three-quarters of its revenues from fares, and because the pandemic means fares are likely to be depressed for the foreseeable future, it’s not clear what is meant to happen after that. Social distancing, the board papers note, means that the network will only be able to handle 13 to 20% of normal passenger numbers, even when every service is running.

Shapps’ letter doesn’t answer this question, but it does at least give a sense of when an answer may be forthcoming. It promises “an immediate and broad ranging government-led review of TfL’s future financial position and future financial structure”, which will publish detailed recommendations by the end of August. That will take in fares, operating efficiencies, capital expenditure, “the current fiscal devolution arrangements” – basically, everything. 

The third thing we leaned from that letter is that, to the first approximation, every change to London’s transport policy that is now being rushed through was an explicit condition of this deal. Segregated cycle lanes, pavement extensions and road closures? All in there. So are the suspension of free travel for people under 18, or free peak-hours travel for those over 60. So are increases in the level of the congestion charge.

Many of these changes may be unpopular, but we now know they are not being embraced by London’s mayor entirely on their own merit: They’re being pushed by the Department of Transport as a condition of receiving the bailout. No wonder Khan was miffed that the latter hadn’t been published.

Jonn Elledge was founding editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.