How hot can it get?

[Russel]

It's common knowledge that the underground is hot because the clay the tunnels are dug through retains heat generated through the daily operation of the network and poor ventilation, but how hot can it physically get, will the network keep getting warmer or will it/has it got to the point where the heat generated vs absorbed will reach equilibrium?

I was stood on the Vic line platform at Warren Street at about 7pm tonight and the air the train was pushing through the tunnel felt like someone had switched on a fan heater, how much of that is normal background heat and how much is down the the recent heatwaves I'm not sure.

 

[dch82]

It's common knowledge that the underground is hot because the clay the tunnels are dug through retains heat generated through the daily operation of the network and poor ventilation, but how hot can it physically get, will the network keep getting warmer or will it/has it got to the point where the heat generated vs absorbed will reach equilibrium?

I was stood on the Vic line platform at Warren Street at about 7pm tonight and the air the train was pushing through the tunnel felt like someone had switched on a fan heater, how much of that is normal background heat and how much is down the the recent heatwaves I'm not sure.

I doubt the heatwaves would have much effect considering that a) the tube is very deep underground and the ground tends to keep a constant temperature after a certain depth, and b) tube trains will dissipate a fairly significant amount of energy as heat with little room to escape

 

[deltic]

TfL publish data on temperature on the underground so you can see how it changes with the seasons. https://data.london.gov.uk/dataset/...rage-monthly-temperatures/?q=tube temperature

 

[Magdalia]

I doubt the heatwaves would have much effect considering that a) the tube is very deep underground and the ground tends to keep a constant temperature after a certain depth, and b) tube trains will dissipate a fairly significant amount of energy as heat with little room to escape

This isn't correct. Heatwaves have a huge impact on temperatures at platform level in the deep tube. Traditionally the tube lines are ventilated by the movement of the trains through the tunnels. When a train departs a station, it draws in air behind that is sucked down from the surface. During hot weather the movement of the trains drags in hot air from surface level. During heatwaves this builds up, especially when the temperature remains high at night.

TfL publish data on temperature on the underground so you can see how it changes with the seasons. https://data.london.gov.uk/dataset/london-underground-average-monthly-temperatures/?q=tube temperature

This link shows that the following lines had average monthly temperatures above 30C in these months:

Victoria: July and August 2019, July-September 2022, July-October 2023, July-September 2024.
Central: July and August 2019, August 2020, July and August 2022, July-October 2023, August 2024.
Bakerloo: July-September 2019, August 2022.

 

[Watershed]

I find the Victoria line unbearably hot in the summer months nowadays. Unless I'm only going for a stop or two, I generally avoid it , even if it means a longer or less convenient journey. Just not worthwhile sweating for the next 30 mins just to save a few minutes. Perhaps I'm just particularly sensitive to the heat.

 

[Mawkie]

TfL publish data on temperature on the underground so you can see how it changes with the seasons. https://data.london.gov.uk/dataset/london-underground-average-monthly-temperatures/?q=tube temperature

I couldn't find where they take the data from (what station or stations). Do they average under ground and above ground temperatures (for those lines that do go outside?) Would be interesting to see the methodology.

I find the Victoria line unbearably hot in the summer months nowadays. Unless I'm only going for a stop or two, I generally avoid it , even if it means a longer or less convenient journey. Just not worthwhile sweating for the next 30 mins just to save a few minutes. Perhaps I'm just particularly sensitive to the heat.

I have the cab aircon on virtually all year round on the Piccadilly Line in tunnel sections, so maybe I am sensitive to heat as well. I don't recognise the 20C figure for mid winters in the data.

 

[Nym]

I couldn't find where they take the data from (what station or stations). Do they average under ground and above ground temperatures (for those lines that do go outside?) Would be interesting to see the methodology.

Methods have included;

Temperature monitoring probes just above head height on platforms. (Air temperature)
The same, in mid-tunnel ventilation (MTVF) assets (including pressure relief shafts)
MTVF SCADA data.
Inter-station monitoring points with either tags or remote monitoring
Other remote condition monitoring equipment which may or may not be public, or still in operation.
Other CTP (Cooling the Tube Programme) SCADA assets, most of which legacy items do not include remote SCADA.

It generally does not include;

On train (Train Data Recorder) or TCMS data.

EDIT:
(Sorry, tired mode with the TLAs and FLAs)

MTVF - Mid Tunnel Ventilation Fan
SCADA - Supervisory Control And Data Acquisition
TCMS - Train Control and Monitoring System
CTP - Cooling the Tube Programme

 

[Russel]

I find the Victoria line unbearably hot in the summer months nowadays. Unless I'm only going for a stop or two, I generally avoid it , even if it means a longer or less convenient journey. Just not worthwhile sweating for the next 30 mins just to save a few minutes. Perhaps I'm just particularly sensitive to the heat.

I find the temperature doesn't really feel like it drops though all year round, especially on the Victoria.

 

[Islineclear3_1]

At least the trains have air-con these days. I used to travel on the Victoria/Central line in the 1970s - no aircon back then. Plus you could smoke on the tube back then ... When the new Central line trains came into service, the difference was literally night and day...

 

[rebmcr]

At least the trains have air-con these days. I used to travel on the Victoria/Central line in the 1970s - no aircon back then. Plus you could smoke on the tube back then ... When the new Central line trains came into service, the difference was literally night and day...

None of the tube lines mentioned here have air conditioning nor air cooling.

 

[whoosh]

Sub-surface lines do have air con (S stock on Circle, Hammersmith & City, Metropolitan and District Lines), but deep tubes don't.

Some deep tube driving cabs may have air cooling, or maybe (?) proper air conditioning, but the passenger area does not.

I believe new Piccadilly Line stock has one or the other for passengers too.


Notably, 1990 Central Line stock has tinted windows, which may be why there was a perceptible difference when they were introduced.

 

[Wilts Wanderer]

I might be wrong, but doesn’t air-conditioning the trains just vent more hot air into the tunnels? The heat has to go somewhere surely.

 

[rebmcr]

I might be wrong, but doesn’t air-conditioning the trains just vent more hot air into the tunnels? The heat has to go somewhere surely.

Yes, though there is some marginal gain by bringing in 'pre-cooled' carriages from their open-air sections. The primary reason it's possible for the first time with the upcoming 2024 Tube Stock is a big reduction in waste heat from both traction and braking systems, plus some investment in station cooling.

 

[Watershed]

I might be wrong, but doesn’t air-conditioning the trains just vent more hot air into the tunnels? The heat has to go somewhere surely.

Yep, which means that in New York you end up with the opposite problem to London. The trains are pleasantly cool but the stations are roasting hot due to the heat given off by the trains' A/C over decades.

Regardless of which approach you take, ultimately heat is being added to the environment all the time (by motors, brakes and humans(!) amongst other sources) so you need some form of cooling for the stations and tunnels to offset that. Otherwise it just keeps on getting hotter as time goes on which isn't sustainable. More modern lines like the Elizabeth line have active cooling IIRC - I think it's done through cold water which gets piped through the tunnels.

I wonder if TfL have done modelling to establish when the heat on the deep Tube lines will become so bad it will start to materially affect passenger flows and revenue. Perhaps they'll then be able to make a case for substantial investments into cooling infrastructure.

 

[Wilts Wanderer]

Yep, which means that in New York you end up with the opposite problem to London. The trains are pleasantly cool but the stations are roasting hot due to the heat given off by the trains' A/C over decades.

Regardless of which approach you take, ultimately heat is being added to the environment all the time (by motors, brakes and humans(!) amongst other sources) so you need some form of cooling for the stations and tunnels to offset that. Otherwise it just keeps on getting hotter as time goes on which isn't sustainable. More modern lines like the Elizabeth line have active cooling IIRC - I think it's done through cold water which gets piped through the tunnels.

I wonder if TfL have done modelling to establish when the heat on the deep Tube lines will become so bad it will start to materially affect passenger flows and revenue. Perhaps they'll then be able to make a case for substantial investments into cooling infrastructure.

I have friends who actively avoid the Central line in particular on even remotely warm days, so I imagine it does have an impact, yes.

I remember reading that certain central stations had been fitted with a water-jacket cooling system so I imagine that’s what you’re referring to? One wonders if the Tube could even be used as a source of heat for buildings / amenities up on the surface.

 

[Nym]

I have friends who actively avoid the Central line in particular on even remotely warm days, so I imagine it does have an impact, yes.

I remember reading that certain central stations had been fitted with a water-jacket cooling system so I imagine that’s what you’re referring to? One wonders if the Tube could even be used as a source of heat for buildings / amenities up on the surface.

Ground water source air cooling and yes it can, but it's rediculously expensive to capture the heat at a usable temperature delta without using heat pumps, which are again, expensive.

Much cheaper and more energy efficient to just suck the air out of the tunnels and in through the stations as fast as is permissible. Or use ground water and air handling units on the platforms, but I don't think that ever got past the first tranche of installations.

 

[Russel]

I wonder if TfL have done modelling to establish when the heat on the deep Tube lines will become so bad it will start to materially affect passenger flows and revenue. Perhaps they'll then be able to make a case for substantial investments into cooling infrastructure.

How hot will/can it get down there though, will the heat just keep increasing indefinitely or is there a point where the heat given off by the trains/passengers matches that already stored in the clay and temperature plateaus?

 

[Mawkie]

One wonders if the Tube could even be used as a source of heat for buildings / amenities up on the surface.

You are thinking about Bunhill in Islington.

Bunhill, world-first scheme uses waste heat from London Underground
The state-of the-art energy centre that uses heat from London’s underground adds 550 homes and a primary school to the existing heat and power district energy network with the potential to support up to 2,200 homes with cheaper, greener heat every day of the year.