Rail Industry Focus


Keep cool and carry on

Source: RTM Jun/Jul 17

RTM’s Luana Salles looks at the reasons behind the scorching summer temperatures on the Underground’s rolling stock – and what TfL is doing to change this.

Ah, summer in London – a time to have a drink at Covent Garden whilst watching comedians perform live in the Piazza; take a stroll through Greenwich Park before settling for some food and jazz at the Pavilion Café; dance like nobody’s watching at the British Summer Time Hyde Park festival; shop around for a new summer wardrobe at Oxford Circus; satisfy your Shakespeare cravings at the Globe’s open-air theatre. 

The only downside is that the journey to get to these places often feels more like summer than the destination itself. Catching a train on the jam-packed Piccadilly Line towards Hyde Park can prove to be a sweltering experience, whilst riding on the Central Line towards the shopping district can expose you to temperatures of over 30°. For comparison purposes, the average temperature in the capital for the month of August is just 23°, according to the Met Office. 

The experience of passengers this summer has been no different. Twitter has been inundated with complaints of what the Daily Mail described as “hot and bothered” commuters stuck in Tube carriages with sweat dripping from places where it shouldn’t – not exactly the best look for a day at the office. And every friendly TfL tweet reminding people to drink water has been met with criticism over the lack of air-conditioning onboard the trains. 

It doesn’t help that a recent Freedom of Information request released by TfL confirmed passengers’ worst fears: that they are, indeed, effectively trapped in underground tunnels with climates far hotter than the outside parks. Data for 2016 revealed that the Jubilee, Northern, Piccadilly, Victoria and Waterloo & City lines all hit temperatures of at least 26° in August and September, whilst the Central and Bakerloo lines topped the list with sizzling highs of 30° and 31° respectively. 

In a statement, Mark Wild, London Underground’s managing director, told RTM: “We completely understand that travelling can be uncomfortable during periods of hot weather and are investing millions of pounds to make the Tube cooler for customers. 

“We now have 192 new air-conditioned trains covering 40% of the network, have doubled the number of fans on the network since 2012, are installing chiller units to pump in cold air and are constantly working on new ways to keep the temperature down.” 

It is warmer below - Frederick Charles Herrick (1927) editBy Underground to fresh air - Maxwell Ashby Armfield (1915) edit

Blame the clay 

To understand the crisis that plagues the Tube every summer, we first need to look at where the network was built: the deep-level tunnels were bored through the London Clay, which originally provided such a cool environment that the Underground was actually advertised as a refuge from the heat. Yet over time, the thick clay began soaking up the heat generated from the trains to the point where its temperature has now risen from 14° to a whopping 26°. Around 79% of heat generated underground is still absorbed by the tunnel walls, with just 10% removed by ventilation and the other 11% remaining in the tunnels. 

The primary source of heat comes from trains braking, so it’s no wonder that TfL has focused much of its efforts on developing regenerative braking technology. In 2015, it teamed up with Alstom to trial the use of a world-first inverting substation system capable of sending unused power back into the grid. A five-week trial on the Underground that collected waste energy from train brakes captured enough power to run a large station, as well as decreased the amount of heat generated in the first place. 

Other solutions have been focused on removing the heat itself, such as through mechanical ventilation shafts, installing fans, using ground water to cool stations, and capturing tunnel heat to warm housing estates in Islington. 

And while it’s highly unlikely that TfL will be able to remove all the heat from the tunnels, future projects are designed to ensure heat doesn’t get there in the first place: specifications for both the New Tube for London and the Elizabeth Line include air-conditioned carriages, more energy-efficient technology and, importantly, lighter trains running for a much shorter time – thus making for a much happier journey.




James Miller   24/07/2017 at 20:22

The Class 345 train running to Shenfield is certainly cool, although it is not in the tunnel. I'm suspicious that these trains have batteries to take care of the regenerating brake energy. The Japanese do this and I wouldn't be surprised if the 345s use batteries. To return the current would need to transform the electricity up to 25 KVAC. Batteries would also be very useful ater a complete power failure, due to hackers.

David   15/08/2017 at 17:12

We must not forget that the air-cond units on the trains reject a significant amount of heat from the condenser coils which is then blown into the tunnels so we need to remove even more hot air from tunnels with air-cond trains running through them !

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