Fresh from the Depths

By Amanda Birch

Building Design

4 May 2007

James Bond eat your heart out. I’m standing in a vast, 12m x 12m x 13.4m, brick-built bascule chamber 5m below water level and a 420-tonne counterweight is slowly moving towards me.

London’s Tower Bridge is being raised and like Bond, I will manage to get out of this fix in the nick of time. When the bridge is fully raised, the counterweight will stop with inches to spare.

I am watching this dramatic event unfold in the underbelly of the grade I listed 1894 structure with Justin Bere, director of Bere Architects. We aren’t here just to witness a wonder of Victorian engineering: Bere has identified the bascule chamber as a source to provide cool air passively into Tower Bridge’s ticket office.

Bere Architects was commissioned in 2005 by the City of London to upgrade Squire & Partners’ 1993 entrance and ticket office building. “Our brief was to make the ticket office a pleasant place to work,” says Bere.

Its fully glazed construction and lack of insulation have made the structure vulnerable to extremes in temperature, so Bere Architectshas had to find ways of cooling and thermally improving the building. This has involved a number of alterations to the structure, including infilling the existing roof light to prevent overheating in summer while reducing heat loss in winter; applying solar reflective paint to the exterior to prevent excessive heating of the space above the new ceiling; and installing solar control blinds to shade the building from intense sunlight. A new revolving entrance doorway has also been inserted, which along with the new toughened glass panels - six times stronger than those they are replacing - should make the building more airtight and remove cold air draughts.

The refurbishment package also entailed upgrading the interior, primarily replacing the existing glass ticket booth with a circular, more open, reception desk made of oak, composite board and stainless steel.

Bere admits that he has made the brief more ambitious by actively searching for ways to make the ticket office more environmentally friendly, a particular passion of his. “I probably do go beyond the call of duty,” he confesses. As well as altering the building’s fabric, Bere was keen to find a passive way to cool the ticket office instead of using the existing energy-greedy air-conditioning unit.

Bere’s curiosity was aroused by the discovery of a duct running from the bascule chamber up to the ticket office. He immediately saw an opportunity to use the existing reservoir of cool subterranean air in the chamber, which is generally below 20 degreesC.

“I was thrilled to find this, but I didn’t know what the duct was for,” he says.

Max Fordham, senior partner at Max Fordham Consulting Engineers, had been informally consulted on the viability of using the duct as a tool for passively cooling the ticket office. Bere says Fordham was equally excited by the duct and said he “had always wanted to work on a project like this”. However, because Fordham couldn’t commit to attending the regular client meetings, Fulcrum Consulting was appointed to advise on the services.

It was discovered that in the event of an electrical fire in the plant rooms, once carbon dioxide had been used to extinguish the fire, the duct would be used to blow air from the bascule chamber to remove the carbon dioxide.

Health and safety concern

Bere then learned of plans to relocate the electrical switch room, which had the fortunate outcome of making the duct redundant.

But a health and safety representative at the Tower Bridge management team committee raised concerns that the air in the chamber might be contaminated. Bere appointed environmental consultancy Enviros Consulting to establish whether the air quality would be acceptable.

Its three-month testing programme measured the amounts of fine particulate matter or very fine dust, microorganisms (fungal spores and bacteria) and nitrogen dioxide in the air.

The results were surprisingly good. The government standard for particulate matter is a maximum of 40 micrograms per cu m. Mark Broomfield, Enviros Consulting’s technical director, says no very fine dust was detected. The government guideline for microorganisms is no more than 1,000 colony-forming units per cu m, while the highest level recorded in the bascule chamber was 440. And the nitrogen dioxide tests detected levels below the government maximum of 40 micrograms per cu m. These findings showed that the air quality in the chamber was actually better than that on the bridge because of an absence of traffic fumes, and meant Bere’s proposal could be implemented.

Richard Shennan, senior director at Fulcrum, describes the “extremely simple” proposal for cooling the ticket office: “Air is drawn from deep inside the bascule chamber using a recycled fan previously used for other purposes. The air is distributed by ductwork with sound attenuation, to a system of purpose-designed ducts incorporated into the bespoke reception desk.

“Air outlets are incorporated into the staff side of the desk, comprising individually designed nozzles, and air is also distributed to the public side at low level. The system has automatic controls which enable it to continue running at night to cool down the internal elements, and sensors prevent overcooling.”

Shennan adds that the fan power is “significantly lower” than that required for a mechanical cooling system. This has led to a reduction in electrical energy consumption and is estimated to save 500kg of carbon dioxide over a year.

“Perhaps a small quantity in global terms,” says Shennan, “but a perfect example of how determination to identify and implement simple and low-cost opportunities to reduce emissions at a micro level can deliver compatible benefits in terms of cost, comfort and carbon dioxide emissions.”

The whole project was completed in December last year, and at £196,000 came in significantly under the original budget of £234,000. Bere has to be credited for working against the odds to see his proposal through, but the real test will be whether the more sustainable solution will keep both staff and visitors to the Tower Bridge ticket office cool enough this summer.

Client: City of London, Architect: Bere Architects, Contractor: Killby & Gayford, M&E engineer: Fulcrum Consulting, Environmental consultant:
Enviros Consulting, Structural engineer: Whitbybird, Quantity surveyor: Ernest Pasterfield & Partners, Art consultant: Futurecity Arts

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