I don’t know if you’ve been to london, but if you’re a standard “modern” height for a man you can barely to not even stand straight in the deep tube trains. They are very very small, and limited by the tunnels which are absolutely tiny. I’m not surprised fitting air conditioning is a challenge, even ignoring the ventilation issues which are also massive.
It's a huge achievement considering both the technical challenges (which other comments explain) but also that anything actually got done considering the UK's economic and political disaster.
Well fortunately New Tube for London (this new train design) all got signed-off a decade ago. Buuuuuut, TFL only bought the trains necessary for the Piccadilly line, with "options" to buy trains later for the other lines. However, post-Covid they don't have enough money to buy them anymore, and would need the government to pay for them, which it likely won't. So I won't be holding my breath for any further improvements :-(
Here in Hamburg the S-Bahns are only just being replaced by air conditioned models. I don't think there are even plans for an air conditioned U-Bahn yet
Where would the waste heat go? Air Conditioning units dump the heat "outside" into the air. But there is no "outside" in deep tunnels. Worse, Air Con has to work to move heat, which creates more heat. You can't even break even. See the 2nd law of Thermodynamics.(1)
It's not so much "air con on trains" but "air con in deep tunnels without a vent". There is nowhere for the heat to go, and the tunnels have already warned up over the decades. (2)
> Conventional air conditioning was initially ruled out on the deep lines because of the lack of space for equipment on trains and the problems of dispersing the waste heat these would generate.
Every solution is a costly compromise. e.g. drilling a new vent to the surface is theoretically possible, but very hard in a densely populated and built-up area.
A lot of comments talk about tunnel size, which is a minor factor: Everything's easier to engineer when you have more space. But fundamentally the issue is where to send the waste heat, not "tunnel too small".
Air conditioning in a busy 19th century underground tunnel system is absolutely an achievement.
Air conditioning an underground train means pumping that hot air into the tunnels. The tunnels have insufficient ventilation because this wasn't conceived of as a problem when many of them were built, and that's a challenge to rectify.
There's also the issue that the trains are already making the tunnels too hot. 4000 trains running back and forth generates a lot of heat from both the engines and braking friction. That heat goes into the clay of the tunnel and is very slow to dissipate due to the high heat capacity of the clay. The trains are never stopped for long enough for the temperature to drop, and so the temperature of the clay has slowly risen 5-12 degrees depending on the line from when the first line was dug in 1863.
Air conditioning the carriages of the new trains didn't result from any developments in air conditioning technology, but from breakthroughs reducing the thermal output of the engines and brakes. This gives them a heat "budget" letting them air condition the carriages without outputting any more heat into the tunnels than a standard train.
Yes, given the size constraints of the deep-level Tube tunnels, which are much smaller than those for mainline trains; apparently developments in small air con systems have helped a fair bit here, fifteen odd years ago apparently it just wasn’t feasible.
Arguable the more fundamental problem is this. Air-con is a negative-sum game because it not 100% efficient. As well as moving heat from one place to another, it creates extra heat.
Turn air-con on in an enclosed space, with nowhere to vent the exhaust, and that space just gets hotter. A small, deep tunnel is close to being an enclosed space. You might be able cool the train interior a bit, but the tunnel will get hotter. Meaning the air-con has to work harder. Meaning it generates more heat.
The Picadilly line is already uncomfortably hot for a good part of the year (but far from the worst [1]). This includes the platforms.
What this article says is that the trains themselves are lighter and more efficient, so less heat is generated by the motors and brakes. They argue that that gives them some heat budget to use on air-conditioning. As a whole, the new trains will generate roughly the same amount of heat as the old ones. So the tunnels and platforms will stay around the same (ie, too hot!), but the train interior will be comfortable.
Adding AC units to trains which travel through tunnels with minimal clearance is the achievement - Can't make the trains any bigger and there's no room in the old ones to just tuck an HVAC in without make them even more cramped.
Headroom is not an issue - there is plenty of room underneath the trains between the wheels. They then pump the cooled air up through the walls to where they want vents. Sometimes trains use the space between the wheels for passengers, but that has significant disadvantages and so should be avoided for subways (it is worth it for street running trams!),
It is here; they're small trains and the tunnels are very warm already, so the AC isn't as efficient, and adding more heat to the tunnels (which all comes from the running trains) will make it more inhospitable.
There are some projects underway to try and cool the tunnels, but they're deep underground and have accumulated heat over decades.
The challenge here is specific to this line - other lines (like Circle) already have AC on the trains - mainly because they’re absolutely huge trains by comparison
London 2 main types of underground line: Subsurface (Circle, District, Metropolitan and Hammersmith and City lines), and tube. The subsurface lines were constructed by cut and cover and were made for steam engines. They are much larger than the tube lines. The Tube lines are tunnelled, and designed for electric power only.
It's not really the size of the trains that allows AC on the subsurface lines, it the fact that the lines are well ventilated to allow steam and smoke from steam engines to escape.
Of all the things TFL could do to improve the tube, cell service would not even be close to top of my list. We've had WiFi on the platforms for about 10 years which is enough to send/receive whatsapp messages while the train is stopped.
I'm not sure it's fair to dig out TFL for being backwards. They introduced the Oyster in 2003, something NYC didn't get until 2019.
masklinn|2 years ago
kmlx|2 years ago
arethuza|2 years ago
Nextgrid|2 years ago
chilmers|2 years ago
kmlx|2 years ago
i really don’t understand where this myth is coming from. do people seriously think the UK is an “economic disaster”?
https://data.worldbank.org/?locations=DE-GB-FR
and here are the numbers for 2023: https://commonslibrary.parliament.uk/research-briefings/sn02...
globular-toast|2 years ago
It's London...
bowsamic|2 years ago
anonymous_sorry|2 years ago
SideburnsOfDoom|2 years ago
It's not so much "air con on trains" but "air con in deep tunnels without a vent". There is nowhere for the heat to go, and the tunnels have already warned up over the decades. (2)
> Conventional air conditioning was initially ruled out on the deep lines because of the lack of space for equipment on trains and the problems of dispersing the waste heat these would generate.
Every solution is a costly compromise. e.g. drilling a new vent to the surface is theoretically possible, but very hard in a densely populated and built-up area.
A lot of comments talk about tunnel size, which is a minor factor: Everything's easier to engineer when you have more space. But fundamentally the issue is where to send the waste heat, not "tunnel too small".
1) https://en.wikipedia.org/wiki/Laws_of_thermodynamics
2) https://en.wikipedia.org/wiki/London_Underground_cooling
zeristor|2 years ago
I’m guessing water would be creating more problems. But it’s a train line, bringing in large blocks of ice should be simple.
DoughnutHole|2 years ago
Air conditioning an underground train means pumping that hot air into the tunnels. The tunnels have insufficient ventilation because this wasn't conceived of as a problem when many of them were built, and that's a challenge to rectify.
There's also the issue that the trains are already making the tunnels too hot. 4000 trains running back and forth generates a lot of heat from both the engines and braking friction. That heat goes into the clay of the tunnel and is very slow to dissipate due to the high heat capacity of the clay. The trains are never stopped for long enough for the temperature to drop, and so the temperature of the clay has slowly risen 5-12 degrees depending on the line from when the first line was dug in 1863.
Air conditioning the carriages of the new trains didn't result from any developments in air conditioning technology, but from breakthroughs reducing the thermal output of the engines and brakes. This gives them a heat "budget" letting them air condition the carriages without outputting any more heat into the tunnels than a standard train.
unknown|2 years ago
[deleted]
thejsa|2 years ago
anonymous_sorry|2 years ago
Turn air-con on in an enclosed space, with nowhere to vent the exhaust, and that space just gets hotter. A small, deep tunnel is close to being an enclosed space. You might be able cool the train interior a bit, but the tunnel will get hotter. Meaning the air-con has to work harder. Meaning it generates more heat.
The Picadilly line is already uncomfortably hot for a good part of the year (but far from the worst [1]). This includes the platforms.
What this article says is that the trains themselves are lighter and more efficient, so less heat is generated by the motors and brakes. They argue that that gives them some heat budget to use on air-conditioning. As a whole, the new trains will generate roughly the same amount of heat as the old ones. So the tunnels and platforms will stay around the same (ie, too hot!), but the train interior will be comfortable.
[1] https://www.standard.co.uk/news/london/tube-underground-lond...
benjijay|2 years ago
SideburnsOfDoom|2 years ago
It's not primarily about headroom.
bluGill|2 years ago
Cthulhu_|2 years ago
There are some projects underway to try and cool the tunnels, but they're deep underground and have accumulated heat over decades.
bombcar|2 years ago
dwroberts|2 years ago
rjmunro|2 years ago
It's not really the size of the trains that allows AC on the subsurface lines, it the fact that the lines are well ventilated to allow steam and smoke from steam engines to escape.
londons_explore|2 years ago
They only recently got cell service for example. 20 years after most of the rest of the worlds railways.
Some lines don't even have that yet either!
walthamstow|2 years ago
I'm not sure it's fair to dig out TFL for being backwards. They introduced the Oyster in 2003, something NYC didn't get until 2019.
kmlx|2 years ago
globular-toast|2 years ago
jjgreen|2 years ago