5 ms·

Looking at the temperature chart and the significant drop in 2020 during the pandemic, the source is certainly the trains and people themselves. (fewer trains m

by chiph 1y ago

Looking at the temperature chart and the significant drop in 2020 during the pandemic, the source is certainly the trains and people themselves. (fewer trains moving, less heat added back then). At this point I expect the infrastructure is heat soaked and will need a prolonged period of cooling to bring temps down. i.e. don't expect instant results. Moving more air through the tunnels, adding A/C systems - both have a problem of needing room up on the surface for blowers and compressors, something that is hard to do in modern London. Tough problem.

meindnoch 1y ago
This. Brake friction pumps heat into the ground at a higher rate than it could dissipate away.
- eternauta3k 1y ago
  Aren't they using regenerative braking?
  - Zigurd 1y ago
    Some parts of the London underground use passive energy recovery by locating stations nearer to the surface than most of the tunnel between them. Trains start by rolling downhill and when they approach a station, uphill.
  - blipvert 1y ago
    Yes. https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3010-2223 https://tfl.gov.uk/corporate/transparency/freedom-of-informa...
    - altairprime 1y ago
      > If the line is unreceptive, braking energy is dissipated in on-board resistors How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week? Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? > Regenerated braking energy is transmitted to the London Underground high voltage distribution network If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need. (Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)
      - cranky908canuck 1y ago
        To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids. I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes. If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques! Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
      - avianlyric 1y ago
        > Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons. 1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid. 2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely. 3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions. As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
  - zeristor 1y ago
    Believe regenerative breaking is used to supplement Oxford Circus’ electricity supply
  - avianlyric 1y ago
    The trains in London can be up to 50 years old at this point. Where the technology was available during the building of the trains, you can generally expect regenerative breaking. But it’s far from universally available unfortunately.
netsharc 1y ago
I wonder if they can carry hundreds of opened barrels of ice on open-bed trains through the tunnels at night, go slowly and let them melt to water (but kept in the buckets, because you don't want to flood the tunnels)...
- thyristan 1y ago
  They could flood the tunnels with an appropriate amount of liquefied air.
- Andys 1y ago
  Ice blocks were trialed in the past. https://en.wikipedia.org/wiki/London_Underground_cooling#cite_note-13 https://en.wikipedia.org/wiki/London_Underground_cooling#cit...
- tgsovlerkhgsel 1y ago
  I would expect them to already have some kind of drainage system, so if the line has some connection to some line that goes outside, just pulling cargo trains full of ice down there and dumping them might work. That said, a typical shitty single-hose monoblock air conditioner has 9000-12000 BTU/h of rated cooling capacity. 12000 BTU/h is also known as "one ton". Sometimes, stupid units can be helpful, because "one ton" of cooling is what you get if you dump one ton of ice (short ton, of course) per day in the place. So you'd need a lot of ice, many tons per station, to make a significant difference. Either way, since this is such an obvious idea, and they had a competition to solicit solutions, I'm sure this was evaluated and discarded - although it would be interesting to read the official analysis of the idea and learn why it wouldn't work.
euroderf 1y ago
Big fans to pull surface air down into the tubes when the tubes are warmer than surface ambient ? Cool the tunnels, warm the surface.
- avianlyric 1y ago
  Where there’s space, this has already been done. Unfortunately for many lines there simply isn’t space. Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible. TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.
  - mike_hearn 1y ago
    The problem isn't so much space, iirc. It's that the blowers make a lot of noise and upset the residents, so they can't be run at full speed all the time.
  - looofooo0 1y ago
    The trains probably push a lot of air around. Wonder whether closing off sections with doors would help to push air out at one point and pull it in at others.
    - Cthulhu_ 1y ago
      Possibly, but the pressure difference would pop people's ears, moreso than they do already. I'm sure the piston-like effect of moving trains is considered too to help move air around. Question is whether that's enough air movement to offset the heat generated by the trains, after all (and this is secondary school level understanding of thermodynamics), the energy needed to move the train is the train weight itself, plus track friction, plus air resistance. That is, in my head, it costs more energy to move the train than the amount of air that is moved around, so it in itself wouldn't be enough.
- 1y ago

by chiph 1y ago

meindnoch 1y ago

This. Brake friction pumps heat into the ground at a higher rate than it could dissipate away.

eternauta3k 1y ago
Aren't they using regenerative braking?
- Zigurd 1y ago
  Some parts of the London underground use passive energy recovery by locating stations nearer to the surface than most of the tunnel between them. Trains start by rolling downhill and when they approach a station, uphill.
- blipvert 1y ago
  Yes. https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3010-2223 https://tfl.gov.uk/corporate/transparency/freedom-of-informa...
  - altairprime 1y ago
    > If the line is unreceptive, braking energy is dissipated in on-board resistors How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week? Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? > Regenerated braking energy is transmitted to the London Underground high voltage distribution network If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need. (Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)
    - cranky908canuck 1y ago
      To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids. I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes. If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques! Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
    - avianlyric 1y ago
      > Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons. 1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid. 2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely. 3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions. As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
- zeristor 1y ago
  Believe regenerative breaking is used to supplement Oxford Circus’ electricity supply
- avianlyric 1y ago
  The trains in London can be up to 50 years old at this point. Where the technology was available during the building of the trains, you can generally expect regenerative breaking. But it’s far from universally available unfortunately.

netsharc 1y ago

I wonder if they can carry hundreds of opened barrels of ice on open-bed trains through the tunnels at night, go slowly and let them melt to water (but kept in the buckets, because you don't want to flood the tunnels)...

thyristan 1y ago
They could flood the tunnels with an appropriate amount of liquefied air.
Andys 1y ago
Ice blocks were trialed in the past. https://en.wikipedia.org/wiki/London_Underground_cooling#cite_note-13 https://en.wikipedia.org/wiki/London_Underground_cooling#cit...
tgsovlerkhgsel 1y ago
I would expect them to already have some kind of drainage system, so if the line has some connection to some line that goes outside, just pulling cargo trains full of ice down there and dumping them might work. That said, a typical shitty single-hose monoblock air conditioner has 9000-12000 BTU/h of rated cooling capacity. 12000 BTU/h is also known as "one ton". Sometimes, stupid units can be helpful, because "one ton" of cooling is what you get if you dump one ton of ice (short ton, of course) per day in the place. So you'd need a lot of ice, many tons per station, to make a significant difference. Either way, since this is such an obvious idea, and they had a competition to solicit solutions, I'm sure this was evaluated and discarded - although it would be interesting to read the official analysis of the idea and learn why it wouldn't work.

euroderf 1y ago

Big fans to pull surface air down into the tubes when the tubes are warmer than surface ambient ? Cool the tunnels, warm the surface.

avianlyric 1y ago
Where there’s space, this has already been done. Unfortunately for many lines there simply isn’t space. Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible. TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.
- mike_hearn 1y ago
  The problem isn't so much space, iirc. It's that the blowers make a lot of noise and upset the residents, so they can't be run at full speed all the time.
- looofooo0 1y ago
  The trains probably push a lot of air around. Wonder whether closing off sections with doors would help to push air out at one point and pull it in at others.
  - Cthulhu_ 1y ago
    Possibly, but the pressure difference would pop people's ears, moreso than they do already. I'm sure the piston-like effect of moving trains is considered too to help move air around. Question is whether that's enough air movement to offset the heat generated by the trains, after all (and this is secondary school level understanding of thermodynamics), the energy needed to move the train is the train weight itself, plus track friction, plus air resistance. That is, in my head, it costs more energy to move the train than the amount of air that is moved around, so it in itself wouldn't be enough.
1y ago