An old publicity poster claimed that the Bakerloo Line was “the coolest place in hot weather” and at the time it was true. However, as commuters know, these days’ summer temperatures can frequently touch 30 degrees Celsius, and as a result London Underground has started a comprehensive upgrade of the existing tunnel and station ventilation fan network.
Under a contract to upgrade the ventilation systems on the Tube, Fläkt Woods has been commissioned to produce a mix of bespoke ventilations products that are designed to help improve the airflow on many of the station concourses and in the tunnels.
Research has identified that around three quarters of the energy used on the network is a result of train operation, which includes the energy required to move the train and losses occurred through friction braking. The rest is accounted for by the operation of the station and tunnel services, which includes lighting and communication . This energy generates a significant amount of heat and subsequently ventilation of the stations and tunnels is essential to help remove this heat and reduce temperatures.
Here, Fläkt Woods’ expertise is crucial, with 100 years experience in the ventilation business the Colchester based Company knows about all there is to know about moving air. “Trains moving through the tight deep-level tunnels push air forward through the tunnels” explains Paul Wenden Engineering and Marketing Director of Fläkt Woods “This is called the piston effect. This effect can produce a strong wind blowing though the tunnels and stations but so far it has proven difficult to use this air movement to expel warm air and bring in cooler air to provide sufficient cooling.”
Currently, there are various ventilation shafts around the London area which open out onto street level and were built during the Victorian era to provide some airflow, while this 'piston effect' of trains entering tunnels and exiting into stations is relied on to pull in fresher air to platforms and extract stale air.
Over the past 3-4 years, a lot of unseen work has been going on. One of the main things was simply cleaning up and repairing the existing ventilation shafts, many of which had been left untouched, some for over 40 years. There are 160 ventilation shafts throughout the underground parts of the system, and Fläkt Woods is currently supplying fans for 8 of these mid Tunnel Ventilation Shafts on the Victoria Line. These shafts exist all around London and many have been incorporated into London’s architecture.
One unique aspect of Fläkt Woods’ contract is how the Company has overcome the problem of physically positioning the fans in the shafts deep underground. The replacement fans although similar in size to those previously installed can often no longer be lifted into place in through the same route as before as other equipment or building work has filled in this space since the original fans were so Fläkt Woods engineers have had to change the rules and devise an unusual way to surmount the associated difficulties of installation.
In some stations, fans measuring over 2.24 metres have had to fit through service doors no wider than 1 metre. The shafts, like the doors are narrow and extremely restrictive, “No matter what shape we started with; we had to find a way of fitting our fans through” says Paul Wenden “Our engineers have had to go back to the drawing board to find a way of fitting a square peg through a round hole.”
The answer was as complex as it was simple. Fans that can be disassembled into segments, and then reassembled again once engineers have the space to work. Computer modelling of every made-to-order fan has ensured that what is delivered is a practical solution.
Every resolution is as individual as the stations, and work at each station is a carried out under a separate contract, so the fans, 1 or 2 per station, have to be factory tested for acoustics, airflow etc, before they are installed. Each fan segment is three dimensionally analysed before it leaves the factory to ensure that it will work, once in-place and put together.
Before fixing work can start, the existing fans and all the old steel work has had to be stripped out. The new steelwork is calculated to take the weight of the fixed vertical fans and the associated silencers, diffusers and inlet cones, making certain that the fans sit within their new metal frames and can operate to the maximum capacity.
“It’s a challenging contract because every station is different” concludes Paul Wenden “but that is also the attraction of the project, you can never become complacent because we don’t know what we’ll find next week”
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