Fighting heat in the Underground

RTM looks at the successes of the Cooling the Tube programme so far and what TfL hopes to achieve in the coming years.

Despite what was a relatively mild summer, in this year’s June/July edition we decided to take a look at the reasons behind the sweltering temperatures in London’s underground rail network. For the millions of residents and tourists jumping on-board jam-packed Tube trains, temperatures in the Underground are often hotter than those outside, even at season’s peak.

As RTM explained then, the London Clay, through which deep-level tunnels were bored, is largely to blame for this. It originally provided such a cool environment that the network was advertised as a refuge from the warmth. But over time, the thick clay began soaking up the heat generated from the braking trains to the point where its temperature rose from an average of 14° to a whopping 26°.

To prevent this situation from becoming untenable, TfL launched its long-running Cooling the Tube programme, created specifically to address the problem of excessive heat in the Underground.

A number of ‘quick wins’ were achieved at first, such as temporary summer fans across stations; platform-level supply ventilation, where fresh air was pumped via existing shafts; impulse fans to circulate air along platforms; a variable refrigerant flow system to reduce the heat in ticket halls and staff areas; and chiller units at Euston, one of the capital’s most-used stations. Already from these measures, TfL learned that improving temperatures could have a considerable impact on customer satisfaction.

But as passenger demand grew and temperatures continued climbing, more intricate solutions were required. In a presentation at the IET earlier this year, Sharon Duffy, head of station systems engineering, said that despite challenges – such as having to deal with historical assets, or the fact that adding more ventilation is often difficult and expensive – key solutions have already been delivered.

As well as the new air-conditioned S-Stock trains, 50 ventilation fans have been restored so far, doubling the capacity of the fan network, whilst 10 long-term out-of-service fans were brought back into use. Fourteen of the Victoria Line shafts were upgraded and many portable summer fans were deployed.

London Underground (LU) also completed a ground water cooling trial at London Victoria, which sourced water from an underground supply to chill the air in the station.

A permanent version of this was then installed in Greek Park, where LU began abstracting water from, and re-injecting it back into, the deep-level chalk aquifer at the station. Water is pumped up to the surface level and circulated from five boreholes – all with water temperature, conductivity and level sensors – to the station plant room. And because the aquifer is a source of potable water, the system does not have any negative environmental impact.

Another pioneering experiment has been capturing waste heat from Underground tunnels and an electrical substation to warm homes in Islington. The scheme, which runs through Islington Council’s Bunhill Heat and Power energy network, has been successfully delivering greener and cheaper heating to hundreds of homes in the area.

Other new technologies are currently being studied, including in-train hybrid cooling – a fancy way of saying using air-conditioning to turn water packs into ice while trains are above ground, which then melts and cools the environment when the train is back in the tunnel.

TfL has also been trialling the benefits of regenerative braking, which converts heat loss back into electricity. A successful 2015 pilot in the Victoria Line showed the energy captured could power Holborn station for more than two days per week. The technology also lessened the amount of heat generated by trains braking in tunnels, thus reducing the energy required to operate cooling systems. In a similar vein, a feasibility study looked at the possibility – and cost – of removing tunnel heat through pipes and then using it in Trigeneration plants to create electricity.

Over the next 20 years, TfL wants to renew existing tunnel ventilation systems, install a chilled supply ventilation system at Oxford Circus and Bond Street, and look at the opportunity of hybrid waste heat utilisation and cooling schemes during station upgrades. It will also press ahead with cooling and draught relief enabling works as part of its major Deep Tube Upgrade programme, which aims to replace life-expired trains and signalling systems across four lines.




Andrew Gwilt   25/11/2017 at 00:17

At least new tube stocks are to be manufactured to replace the older stocks such as the 1972 and 1973 stocks used on the Bakerloo and Piccadilly Lines that new air-conditioning walk-through tube trains are likely to replace these oldest tube stock in the 2020's. Aswell as replacing the 1992 Stocks used on the Central and Waterloo & City Lines with new air-conditioning walk-through tube stocks.

Boris   28/11/2017 at 22:56

Will the “1992 Stocks” be cascaded to the Marks Tey-Sudbury line then?

Andrew Gwilt   28/11/2017 at 23:10

Enough with the same old joke Boris ok.

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