Why is London’s Central line so hot? Science has the answer

Posted: June 28, 2018 by oldbrew in News, Temperature, Travel

Bank station on the Central Line

This has little or nothing to do with the weather. Ingenious engineers needed to find ways to take some of the heat off London’s perspiring Central Line travellers.

The London Underground is hot. But nowhere is hotter than the Central line, which is routinely so hot that it exceeds the EU limit at which it is legal to transport cows, sheep and pigs, says Wired UK.
. . .
Cooling the Central line in particular presents an almost impossible puzzle for TfL [Transport for London] to solve.

In the late 1800s and early 1900s, when many of London’s tube tunnels were carved out of its subterranean clay, engineers didn’t leave a lot of extra space. In fact, they left none.

That makes installing air-con units on trains that run through deep level tunnels impossible. The tunnels are too small to allow the heat to escape, effectively turning the Tube into a giant underground oven.

Gaze absent-mindedly out of the window on the Central line and you’ll see cables and panelling whizzing past just inches from the train itself. Above them, London’s cloying clay keeps all that heat locked in.

And that clay has been heating up. When much of central London’s Tube network opened in the early 1900s, temperatures in tunnels and at stations were recorded at around 14C.

But with nearly 80 per cent of energy dissipated by trains, people and related infrastructure seeping out into London’s clay, it’s been slowly heating up. So much so that the ambient temperature of the clay is now between 20C and 25C.

Unlike the Victoria and Jubilee lines, London’s oldest tube lines, and the Central line in particular, suffer from having very few ventilation shafts. And with the Central line cutting a path through some of London’s most densely-populated and expensive post codes, there are few options for introducing shafts now.
. . .
So while other parts of the London Underground benefit either from investment in cooling technology or the luxury of not being surrounded by rapidly-heating clay with nowhere for hot air to escape, the Central Line keeps on cooking.

It’s the perfect, sweaty storm and one that TfL is nowhere close to solving.

Full report here.

  1. Phoenix44 says:

    So London has lots of openings from underground that spill heat into the atmosphere…

    Presumably that means past temperatures from the countryside should be adjusted downwards.

  2. Graeme No.3 says:

    Send wagons loaded with ice through the tube lines. Could be done late at night when there are less services. Plenty of ice will be available as the Eddy Solar Minimum takes hold. Otherwise mine the arctic floating ice** and cause lots of Greens to die in anxiety attacks.

    ** The Russians would probably be happy to keep the NW passage open and sell the ice.

  3. oldbrew says:

    The builders couldn’t have foreseen today’s 24-30 trains per hour at peak times.


  4. cognog2 says:

    Seems to me to be an ideal heat pump opportunity to warm the shops and offices above and provide an income. Small modular units dotted along the line should do the trick.

  5. oldbrew says:

    cognog – no room. That’s the problem for any tech solution.

    Gaze absent-mindedly out of the window on the Central line and you’ll see cables and panelling whizzing past just inches from the train itself.

  6. stpaulchuck says:

    cognog2 and oldbrew, what about anywhere NEAR the line but in the clay? It sounds like the clay can act as a heat source for geothermal type BTU sourcing for heat pumps on the surface. Sounds like a fantastic winter heat source.

  7. oldbrew says:

    Various ideas have been floated.


    Cheapest solution – carry a bottle of water.
    Beat the heat

    Not very likely these days, especially on the deep lines (original steam lines were sub-surface with vents)…

  8. Ian W says:

    Having used the Central Line for many years in the past. I often tried to calculate what the probability was of the coincidence of 3 apparently random events:
    * A hot day in London
    * A signal failure leading to a long wait in the tunnel in rush hour
    * The person crushed up against me apparently having had an anchovy and garlic curry

    As – contrary to what one would have expected, the first two events seemed to be inexplicably linked to the third.

  9. oldbrew says:

    From IanVisits website:
    Something which has been built into Crossrail station designs, and where possible may be retrofitted to some London Underground stations is under platform air systems.

    Knowing that more than half the heat in the tunnels comes from the brakes and motors, blowing cool air onto them when they are in the stations, or sucking away hot air, will help reduce the heat dumped into the tunnels when the trains leave the stations.

    The warm air is then removed from the station by ventilation systems.


  10. pochas94 says:

    Bore a new parallel tunnel to supply ventilation to the working tunnel.

  11. oldbrew says:

    pochas – tunnelling in London nowadays is complex and horribly expensive.

    20 of the line’s 49 stations are below ground and at 46 miles it is the longest and second busiest line in the London Underground.

  12. Anoneumouse ( disappeared by Guido) says:

    Lack of circulation!

  13. ivan says:

    There ae ways of removing the heat from the tunnels but they all require money and the closing if the tunnels to public use.

    From memory (my days at Imperial College and using the central line) there should be enough space to allow retro fitting heat pipes (think of CPU cooling on high end notebooks and workstations) on the walls to conduct the heat to the vents and/or stations. Using the same idea it should also be possible to drill small holes down to the tunnels and fit high capacity heat tubes that pick up from the wall mounted ones. It just requires the engineers to think out of the box – something that is not taught in engineering degree courses today.

  14. nickreality65 says:

    Science does not care about credentials.

    Science does not care how many initials are in front and behind your name.

    Science does not care about the number of your publications and citations.

    Science cares that the rules are followed.

    Science does not waive those rules based on who you are, who you know or your noble cause.

    (What follows is for those who actually did the homework.)

    288 K – 255 K = 33 C warmer with an atmosphere does not follow the rules.

    396 W/m^2 LWIR upwelling from a BB surface powering a GHG energy loop does not follow the rules.

    These two broken rules invalidate RGHE theory.

    RGHE theory failure negates any role for CO2 and mankind in the behavior of the climate.

    [mod] this is off topic

  15. E.M.Smith says:

    The heat pipe solution is a good one. These can be made as small as a mm diameter tube, so clearance is very easy to find. I’d likely try to lay it between the two tracks in the tunnel with piping at the station taking the heat up and out.

    Now, a quicker and easier solution:

    Add a specialized car at the end of each train. In it, have a few ton of ice. Flow the air via the shape and vents of the car through the ice leaving a trail of cold air behind it. At the last station (maintenance yard) or open space, swap that car for a fresh one. The “spent” ice car gets hooked to a large chiller that freezes the ice again and dumps the heat “outside”.

    No clearance issues. Only impact is modest cost (chillers and tanks of ice pretty simple tech) and a logistical issue of changing out a car (that is already standard operating procedures on subways) along with a minor increase in energy used to haul the ice car around.

    Not as elegant as a long term solution using heat pipes, but you could implement it rapidly and relatively easily in a modular manner.

  16. p.g.sharrow says:

    EM is right, sort of.
    Eutectic plates on an open car and fast freeze barn at end of lines. Attach cold car to end of train and swap out with fresh car as needed. Technology that is over 100 years old. no muss&fuss with Ice or plumbing.or maintenance of extensive systems. Just a standard fast freeze rail barn and some extra carriage frames…pg

  17. oldbrew says:

    Add a specialized car at the end of each train.

    Platforms aren’t long enough on most of these old stations. Driver would be in the tunnel after stopping.

  18. From the distant shire of Huntingdon where attepts to get into London are now almost impossible – thank you GOVIA and DafT – there should surely be room for pipes under the track?

  19. Calvin Barrows says:

    If we keep rewriting the laws of physics we’ll never solve the problem! I like to share my thoughts and temperature measurements.
    Has anyone else noticed the correlation between the extreme summer weather conditions and the heat on the tube? All the mechanical and electrical systems don’t know it’s summer! My car hadn’t moved all day yesterday but the temperature on the gauge was registering 32 degrees.
    Cars and trains are fundamentally constructed of similar material so why wouldn’t the summer weather make the trains super-hot? The trains carry all the summer heat into the tunnels and discharge some of it. Please think about it!
    It may surprise you that the numerous temperature readings I have taken all indicate that the trains gain much more heat in the summer when on the surface than they do underground. These tests could easily and cheaply be replicated and verified.
    Overheating wasn’t a problem in the winter – you probably kept your coat on in the tube then? Perhaps not surprising when the annual temperature range varies from say minus 5 to 35 degrees!
    Cooling stations is not addressing the real danger. That of being stuck in an overheated train in a tunnel when one is unable to escape. From the point of view of comfort, most passengers spend more time in a train than on a platform. So, what has been achieved does not, I believe, address the real issues.
    This would be part of my suggested solution.

  20. oldbrew says:

    Calvin Barrows says:
    July 27, 2018 at 7:44 pm

    There’s a lot more glass on tube train carriages than on warships 😐

  21. Calvin Barrows says:

    It has everything to do with the weather! How can they claim otherwise when summer temperatures can be 40 degree higher than winter temperatures and the overheating problem clearly only happens in the summer. And the clay overheating is an effect, not a cause!