London Underground

Transport for London (TfL) knows commuters have had some unfortunate experiences – crammed like sardines and sweltering onboard a tube during peak hours, praying for the doors to open and fresh air to flood in. For the general population, introducing air-conditioning seems a frustratingly obvious solution. Despite spending years searching for a solution, for TfL the challenge remains a complex one due to the set of environments and solutions unique to each line and location that must first be solved.

"The Tunnel Cooling programme hopes to mark the transition of a cooler London underground network from an 'if' into a 'when'."In an attempt to crack the solution to cooling London's underground network, which comprises 268 stations and approximately 400km of track, the Tunnel Cooling programme was launched. It hopes to mark the transition of a cooler London underground network from an 'if' into a 'when'. Over the last few years the programme's team has been conducting extensive research into the exact conditions of each underground line and developing possible solutions to combat rising temperatures.

By 2010, TfL and its supply-chain partner Metronet expect to deliver the first air-conditioned carriages to the London Underground's subsurface lines, namely the Metropolitan, Circle, Hammersmith & City and District lines. Tunnel Cooling Programme director Kevin Payne says the team is more than aware of the scale of the challenge it must face to reach this.

"These are not new challenges – they were being worked on 30 years ago," he says. "In fact, searching through our archives, we even discovered that a prototype air-con system on a Northern line cart was first trialled in 1935."

"It was already recognised back then, even with lower traffic densities, that the extra heat energy caused by the air-conditioning unit would cause a problem when the train stopped in a tunnel." Thirty years on the challenge remains the same – how to cool the tunnels, without effectively making them hotter.

Climbing climates in the underground

It is not only climate change that has caused temperatures in the underground to rise. Increasing passenger numbers have also caused a rise in traffic frequency, in turn meaning an undeniable rise in temperatures. In 1900, temperatures in the Bakerloo line were recorded at about 14°C. By 2007, that figure had more than doubled.

"In 1900, temperatures in the Bakerloo line were recorded at about 14°C. By 2007, that figure had more than doubled."The challenge for TfL, however, has not so much been the incremental rise in passenger numbers but the consumption of energy in the confined environment, particular on the narrower single-track deeper-ground lines. "There is a widespread perception that the heat in the underground is a result of the people using it which is false," says Payne.

The local government body has identified that 80% 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. A further 15% is accounted for by the operation of the station and tunnel services, which includes lighting and communication services. The remaining 5% is attributed to customers and staff.

The rise in energy consumption on the network coupled with 7% year-on-year passenger growth means the situation is one TfL cannot afford to leave unresolved, particularly given the fierce customer demand for journeys in comfort.

"We are on the brink of a line-up programme that will progressively tackle each of the deep tube lines in turn and in doing so will offer more trains, more capacity and ultimately more energy will be consumed," says Payne. "We need to ensure the more is as small as possible."