The hot ticket – keeping the London Underground cool

12 September 2016



Over 100 miles of the London Underground network runs through tunnels, which are difficult to cool effectively. François Maurin, Hesop product manager at Alstom, explains how the company is working with TfL to reduce the network’s temperature and carbon footprint.


As recent weeks of UK summer have proved, temperatures on the London Underground can rise to unbearable levels. On parts of the network – particularly the smaller deep-level tube lines – temperatures have reached as high as 34°C in recent years, forcing Transport for London to hand out 250,000 bottles of water on one particularly sweltering day in July 2015.

With climate change contributing to globally rising temperatures, plus a growth passenger numbers and train frequencies, the tunnels of London’s metro system are likely to become even hotter as the years pass. Transport for London (TfL) is already tackling the problem, though, with several subsurface lines having benefitted from the introduction of air-conditioned trains over the past few years.

The biggest challenge is cooling the deep-level lines, which have neither adequate space nor ventilation to install air-conditioning units on trains, and whose hot exhausts cannot be removed from tunnels and platform areas. The use of air-conditioning units is also not a particularly environmentally sound solution.

Take the heat off

So, what can TfL do to cool down the tube network and use less energy, thereby reducing its environmental impact and contributing less to global temperature rise? In partnership with rail-transport company Alstom, it may have found a solution that kills both birds with one stone, in the form of the Hesop reversible substation technology, which is currently operating at the Victoria Line’s Cloudesley Road substation.

“London Underground selected Hesop in 2013 for its high energy savings,” explains Alstom’s François Maurin, Hesop product manager. “Thanks to the dynamic voltage regulation, Hesop is able to capture 99% of the available braking energy and use it to help cool down the tunnels.”

The technology works by recovering energy that would otherwise by wasted during braking, and returning it to the grid. According to TfL, after just one week of operation, enough energy had been recovered to power a station as large as Holborn for two days.

“The initial trial started in March 2015 and the technology has been running ever since. In fact, the average energy saving during the last year and a half is around 800kWh a day” says Maurin.

But energy saving is not the only goal of Hesop. “The Victoria Line runs almost fully underground and so there is a need to control tunnel temperatures while simultaneously improving energy efficiency,” explains Maurin. The energy normally wasted during braking would otherwise be dissipated through resistor grids mounted on the underside of carriages. With Hesop installed and these resistor grids removed, the heat generated during braking no longer ends up in the tunnels and also creates space beneath the carriage, where cooling systems could be installed or, on future carriages, new designs could improve space and passenger comfort inside.

As it stands, Hesop is currently only installed at the Cloudesley Road substation, but were it to be rolled out across the network, London Underground (LU) could reduce its energy bill by as much as 5%, allowing it to reinvest the money in further green technologies across the capital’s transport network. In fact, this installation forms part of a much larger drive to decrease energy consumption in London’s mass transport systems.

Chris Tong, LU’s head of power and cooling, said: “This trial follows a number of other measures put in place by the mayor and Transport for London to ‘green’ the capital’s Tube system. In January 2016, it was announced the historic Greenwich Power Station would be revamped to transform it into a low-carbon power generator for the Tube network. Its six new gas engines will replace existing boilers and provide cheaper, cleaner power for the Tube, with waste heat being channelled into a new local heat network that will also benefit residents.”

Matthew Pencharz, deputy mayor for environment and energy, added: “The results of this project are really exciting and show huge potential for harnessing some of the immense energy in our Tube trains. The trial puts London at the cutting edge of this kind of technology and clearly demonstrates how energy from trains can be recovered to power Tube stations, making the network more environmentally friendly and cost-effective. This complements our wider work to make other forms of public transport cleaner and greener, including our buses, where we have introduced hybrid and zero-emission technology.”

The logistics of legacy

How easy would it be to install Hesop across one of the world’s largest metro systems? After all, parts of the London Underground are more than 150 years old; a legacy that makes the installation of some new technologies more difficult than others.

According to Maurin, “Hesop technology can be adapted to any existing infrastructure. The system is designed to be flexible and, as it is real-time controlled, the system adapts itself to line behaviour.” Any new parts of the network would also benefit as “it also reduces infrastructure investment on new lines thanks to the reduction in substation numbers compared with the classical solution”, he adds.

Should this rollout come to fruition, tube passengers could be allowed some respite from the heat on their daily commute, and give the UK’s notoriously grumpy travellers one fewer thing to complain about. Still, overcrowding, above-inflation price hikes and increasingly frequent strikes on the wider rail network will still provide them with plenty of fodder. The heat will be one fewer worry, though, thanks to TfL and Alstom’s partnership.

The Hesop system captures energy from braking and uses it to help cool the tunnels and stations.


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