> indeed, the use of regenerative braking now converts about half the heat loss back into electricity. However, that can only work where trains are accelerating and braking at the same time, on the same electricity sub-station loop.
Besides that, Tube tracks often rise slightly at stations, so that trains get a small gravity assist to both stopping and starting off again. (Unfortunately it also means that hot air from the tunnels tends to collect there, but you can't win 'em all.)
That is a pretty cool way to implement regenerative breaking that I honestly never thought of (even though the tram in my hometown feeds energy in the grid when driving downwards)
Correct me if i'm wrong, but it seems that regenerative braking is a bit troublesome because it is a third rail direct current system: a "regular" AC system can simply feed power back through the transformers to the power grid, but this is not possible here, so power must be consumed by another train fed by the same rectifier.
1) modern railway is fully IGBT powered. In this case it is trivial to inject current.
2) with DC current you need a substation capable of converting AC to DC (easy: bridge rectifier) but also DC to AC (to given tolerances) which is much more cumbersome.
You're not wrong:
However, that [regeneraative braking] can only work where trains are accelerating and braking at the same time, on the same electricity sub-station loop.
The first generation of Munich subway trains (manufactured from 1967-1983) uses resistor banks for braking, so the energy from braking goes right into heat.
Only the later generation B and the new C generation can move brake energy back into the grid.
I'm wondering if fitting the station with a wall or glass curtain between the tracks and the platform (with sliding doors to let people in/out) could help mitigate this effect. See the MTR in Hong Kong for an example of what I'm talking about.
Subway system in Seoul also has glass partition between the platform and the tracks.
This offers 2 distinct improvements for passengers.
1. noise/dust mitigation: One can sweep the platform floors all you want, but dust from the track will always get to the platform. By installing the glass partitions, general atmosphere of the platform is just more pleasant.
2. less space for AC to cool: It's impossible to cool ALL of the space of a subway system, from miles of tracks to the platform. By installing the glass partitions between tracks and platforms, AC at the subway stations only has to cool the platform.
I heard NYC subway engineers say they can't install the glass partitions because the subways are not capable of stopping at a particular spot. This is required for the glass partitions to be installed.
I think they're referring to cooling of the train cars.
The deeper tube cars running on older lines have serious space constraints to deal with that make integration of things like cooling equipment difficult and expensive. We're talking about trains that have comically small proportions relative to what you would see anywhere else in the world.
That said, last I had read, the deep line cars are supposed to get AC sometime within the next decade or so.
>I think they're referring to cooling of the train cars.
Don't think so. That is a fixable problem. (e.g. convert the space of 1 seat per car for an AC unit).
The fact that everyone is so stumped by the problem says it's the actual tunnels that are overheating. The fact that some lines don't have AC just exasperates this.
> offered a prize of £100,000 to anyone who could come up with fresh ideas
Too late now, but I wonder if they considered district cooling, where e.g. cold water from rivers is used as an alternative to air conditioning. Seems to be used successfully in my hometown of Munich: https://www.swm.de/english/m-fernwaerme/m-fernkaelte.html
> Elsewhere, they’ve been using cool ground water to cool some of the stations. An experiment at Victoria station was the first, as water from the River Tyburn was used to cool the air in the station. This was only an experiment, but at Green Park, a permanent version was installed in 2012.
> Elsewhere, they’ve been using cool ground water to cool some of the stations. An experiment at Victoria station was the first, as water from the River Tyburn was used to cool the air in the station. This was only an experiment, but at Green Park, a permanent version was installed in 2012.
Per https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube... there already is regenerative braking on some cars, the issue is that regenerative braking can't happen if there's no train on the same section of DC bus that can accept the power. There needs to be some sort of inverter to sink the higher DC voltage and send it back into the grid.
why not incorporate storage in the car and discharge it when launching from a stop. I am sure there has to be a little onboard storage but it appears they need more if they cannot discharge it. Isn't this ideal for ultra capacitors?
it really reads like the cars must be changed to fix the problem as they are the heat source. so unless an economical means can be found to store/discharge it between stations their only solution is to cool the tube itself.
So isolate the passenger area from the tube area at all stations and force cool air from points where you have easy access to cooling. the air flow would of course move in the direction of trains. can that work?
Adding stuff to trains ("cars"?) increases the weight, which means more energy is needed to move the thing. It also takes up space, which is very limited.
Some storage system near a station (where there is more ventilation) could make sense, but probably costs more than the system mentioned in the IanVisits blog to return power to the city (i.e. convert the DC the trains use back to AC for the city).
I don't think the isolation idea would work. Where does the air for people on trains to breath come from?
Or you can just convert that energy into heat, but do that on the surface. Have large resistor banks on the surface that you connect to the DC grid when the voltage is too high.
Because you can use it for something else other than heating, like, putting it back into the grid, storing (either battery, flywheel or supercapacitor).
Why? Stopping the trains wastes energy regardless of whether you dump the extra power into the wheels with friction brakes or into a resistor bank. Dynamic brakes on diesel trains already sink the power into resistors.
That would work, but a large flywheel would also be a good solution. You could spin up the flywheel to store energy and if it reaches maximum speed then use the resistors. You'd also need to detect load on the grid and then run the flywheel system in reverse to assist vehicles that are moving.
Given that regenerative braking is ~60% efficient, we're talking about 1.2 kWh. That's really not that much; a typical Tesla battery pack is in the range of 65-100 kWh depending on model. Now, granted, I don't know if you can feed that much energy into a battery pack on the order of ~20 seconds, but using multiple packs would suffice.
So it does seem feasible to do it either by installing battery packs connected to the tracks, or in the cars themselves. I wonder which would be better.
There's no need for storage nor batteries at all, though. It suffices to convert the energy from the DC rails (where the train dumps it) to a bus where every other accelerating train can draw current from -- since there's lots of trains, there'll always be one willing to accept the load.
The only issue is that each third rail section is fed by its own set of independent rectifiers, and the third rail sections are not paralleled together. This means that if there's no other currently-accelerating train on the section of rail that you're on, it's just you and the rectifier substation -- and those rectifiers can't accept your regenerative braking current.
Adding inverter circuitry to the substations would introduce a path for energy flow to go from the DC third rails into the AC grid (opposite of the normal direction of flow, hence the term "reversible substation"). Since the AC grid is connected to all the rectifier substations and since there's many trains on the rail network, there'll always be a source for regenerative braking current that's dumped onto the AC bus.
The question is what's cheaper -- adding inverters to every substation, or adding battery packs on the trains? I don't know enough about the prices of things to be able to guess.
If storage makes sense (if a consumer for the electricity can't be found), battery storage (or flywheel storage) will almost certainly be kept on the wayside and not on trains; that way you don't have to care about weight / volume / heat dissipation concerns. SEPTA has such a system -- a large battery array at a station that captures regenerative braking energy.
You can do that, but you can also use it to power accelerating trains that live on every other track section / DC bus -- by inverting it back into AC and dumping that onto the AC grid that's used to supply your rectifiers.
>The future of the cooling the tube project will be judged not so much by how they cool the hot tunnels, but by how they stop tunnels becoming hot in the first place.
For one thing I'm surprised they're not using regenerative brakes. It sure will cost some of the profit but refurbishing the trains with these will cut somewhat on that 80% of heat
TfL isn't a private organisation, they are a government body. In 2015/16 only half of their costs were covered by ticket sales and other income (advertising, sponsorships, etc). The rest comes from government funding, so taxes.
Subways in NYC are not fun in the summer either. I always assumed it was because when they were designed they didn't consider a future state where air conditioners on the trains dump their heat into the tunnel.
I tried searching for a similar study for NYC but all I found was old articles from years back.
there is no way that the NYC Subway's AC's dumping heat into the tunnels contributes in any meaningful way to the temperature inside the stations - the tunnel system is enormous relative to the trains. much more it's simply NYC summers are sweltering and the stations aren't well ventilated at all.
Did you read the linked article? The heat of the London Underground tube tunnels is directly caused by heat released by trains (though primarily from brakes and friction, not AC), and has nothing to do with season. It's swelteringly hot down there in winter.
I don't see why it'd be any different for NYC, where I live.
Many NYC subway tunnels are not 'tubes' and are shallow enough to have surface access. So part of the answer is probably that the NYC subway is a more open system.
The same is true of London (also mentioned in the linked article). The linked article is explicitly only talking about the deep tunnels, which NYC also has.
Yeah, NYC is a very different system. The deep tunnels are very well ventilated. Go to a station at the end of a deep section, like High Street and you can feel the wind blowing out because of the forced-air ventilation system. You can also see daylight from the subway trains throughout the system, because it's that close to street level and there are ventilation grates every hundred-ish feet.
Actually it is related to the air conditioning. Prior to AC, the subway and its platforms were cooler than the outside. Still not pleasant on a 100 degree day, but certainly not as it is today: the platform will be significantly hotter than outside. Just gotta survive long enough to board the train.
The Montreal subway system has a very clever way of somewhat saving energy (and emitting less heat): the section of the track at the station stop is higher than the rest of the track.
This means that the train's kinetic energy is converted to/from potential energy whenever the train arrives/leaves the station stops.
I feel like in the long term, this may become a liability compared to regenerative braking and level tracks.
For example the Montreal metro currently only allows a train to leave a station when the platform of the next one is free, limiting the frequency of this very crowded system. With modern signaling, trains can creep up to the ones before them and reduce the time between them down to 40 seconds - but it's more difficult with all those slopes around.
It's also making extending platform lengths or moving/adding stations nearly impossible.
In Australia when it's flat, there were still collisions. Trains are very very heavy. The collision report recommendations had been to keep a long distance between trains. For trains ahead, the coming train would slow down and would come to a stop, if it's probably one train length ahead.
I'm not sure how long the distance is though. 40 seconds is really really hard to estimate with very very heavy trains and no weight sensors. Even AI/ML cannot predict this (re: no weight sensors).
Why would a computer need weight sensors? It knows exactly how hard the electric motor worked when it was accelerating the train and exactly how quickly the train accelerated. It should be able to come up with an entirely usable estimate of the train's weight.
Just as an aside, modern transit trains have weight sensors anyway which adjusts the pressure in the air suspension to make sure the train is exactly level with the platforms.
If there were collisions the signalling was crap. Train intervals below one minute are definitely possible. For example the new Thameslink line in London will have (or already has?) intervals well below one minute.
Trains know their position very precisely, with errors less than 20cm, and their braking characteristics and error margins are well known, especially in tunnels where there are now wet leaves or snow on the tracks. Automatic train operation makes trains stop at precisely the same spot each time (for example to match train doors to gates), to the point where increased track wear becomes a concern.
I don't understand why lack of space above ground is a hindrance to building new ventilation shafts. Surely these aren't going to be wider than a sidewalk, and in central London the distance between any two roads on a block is rarely more than 50-100 meters.
You'd end up with lots of ventilation grates on the sidewalks on the surface, but that seems like an easy and space efficient solution.
A substantial part of the problem is the sheer age of central London; people have been digging beneath it and piling more buildings on top of it for nearly 2000 years, so given any particular spot in the Tube network, there's every chance that if you try and drill upward from it, you'll hit part of the sewer system, a buried river, someone's wine cellar, something top-secret belonging to the state, a lost graveyard, a plague-pit...
... utilities too. There are probably not many spaces a vertical shaft could go.
You probably don't want a direct vertical grate either, you'll need to catch water, rubbish, people from falling down. An S-bend is going to effect flow.
No. I doubt anything less than a decade would make much of a difference.
It's taken a century or so to raise the temperature in the tunnels by around ten degrees C. That already includes the cooling effect of cold air being pushed into the tunnels for most of the year, balanced by the relatively small number of days a year when the air temp in London is more than 14C.
Without that cooling heat has nowhere much to go. It will radiate out into the air, which will make its way up and out rather slowly. And it will diffuse into the clay/soil around the tunnels, even more slowly.
A fully passive cooling-off period would take years - at least.
The problem isn't impossible to solve. All kinds of active cooling solutions are possible.
The problem is that it's impossible to solve affordably. You effectively have to build a heat exchanger the size of central London, which is never going to be cheap.
I never got why the heat in the tube was not being used as a heat source. You could extract the heat and supply it to surrounding buildings at a cost, thereby cooling the tube. The tech is readily available. It would be a win win situation. Plus it'd be be very environmentally friendly.
The problem is that the heat isn't a point source, it's diffused across hundreds of kilometers of tunnel. The amount of infrastructure you'd have to build to extract it at scale would simply cost way too much. It's cheaper for any reasonable timeframe to simply continue burning natural gas at the surface for heat than to invest all of this into infrastructure at a very long-term ROI.
Thermodynamics also makes this really hard. The tube is at most 40 degrees celsius. The air outside is perhaps 20 degrees celsius in summer. There's just not enough of a temperature gradient to run any kind of efficient engine.
It could be useful for low-grade thermal applications -- heating (or pre-heating) hot-water supplies, or space heat.
Even simply ducting warm air to street level for outdoor dining (in winter), presuming (against other information, I'm aware) that the ducting could be provided. If you're wasting the heat anyway, put it to some use prior to final venting.
How much heat are we talking about? I'm guessing it wouldn't be enough to use for district heating, the way some industrial waste heat is converted to hot water for homes?
The original source [1] has a graphic at the bottom where it says about 300m kWh per year currently, so about 34MW on average if I didn't miscalculate.
Interesting article. However I can't recall tube stations being much warmer than outside temperatures in winter (on non-windy days). If that's right then how is the heat dissipated better in winter?
I don't live in London so anyone with regular riding experience please correct me if I'm wrong.
The Tokyo (and Japan in general) underground/subway is actually quite fresh and amazing in the hot summer. How do they do it? It might be interesting to learn from them and a good question for the Underground of London Engineers.
In fairness the London Underground is from the 1860s, Singapores if from the 1980s.
That said, London's system was designed for coal, so imagine how bad the air must have been back then.
As the article states, there are two distinct types of underground rail in London: the older sub-surface lines, and the newer tunnels. The coal trains were never used in the tunnels.
I'm not sure what the difference is between the two. Aren't they both underground?
Here's a video of a steam train going thru the underground to celebrate 150 years of the tube:
https://www.youtube.com/watch?v=a3_rxuOFTm8
The sub-surface lines were built by digging trenches and then covering parts of them back up with roads, buildings, etc. This technique is called cut and cover. They're just beneath the surface and large stretches of them are actually open to the air, many were built for coal powered trains. These can be built without tunnelling. They're below-ground but not usually "under ground". The trains are rectangular shapes since that is the traditional shape for a train.
The deep lines (originally called "the tube" although that now refers to the whole system) were built by tunnelling, the trains and tunnels are cylindrical and the trains just fit into them. In many cases the tunnels are 30+ metres underground.
There are differences in loading gauge (things like maximum train height)--you can't run the subsurface trains on the deep tunnels because they're too big. Also, like many subway systems, there's a mixture of surface and underground sections (surface segments primarily on outskirts).
I don't think I get your point. Presumably ventilation is easier to engineer near the surface, but air quality is always going to be bad if oil/coal/coke/smokeless coal are burnt (or are you saying that these fuels weren't used, which would be incorrect).
The claim is that the air in the cut-and-cover lines would be no worse than around a surface coal-burning train. Which could still be pretty bad, though probably not uncomfortably hot.
Here is an idea that I sent to the Underground in 2006 when they solicited suggestions from the public.
Add cool to the tunnels, rather than taking heat out.
Build liquid air plants above ground, 2 or 3 floors up in the air so that the heat of the pumps is released above street level and the noise can be kept away from the street. Feed the liquid air into the tube tunnels through insulated pipes which takes up far less volume than air vents. Let gravity bring the liquid air down the pipes. Release the liquid into the tunnels near platforms where the air pump effect of moving trains caused lots of air circulation. Also the car doors open on the platforms.
Since you are liquifying the air, not just the oxygen, it can be safely released anywhere in the tunnels. And if your air intakes are high up you will actually be improving the air quality in the tunnels as well, i.e. cleaner air flows in.
For those who also didn't know about liquid air: "Liquid air is air that has been cooled to very low temperatures (cryogenic temperatures), so that it has condensed into a pale blue mobile liquid. To protect it from room temperature, it must be kept in a vacuum insulated flask." (c) Wiki
The flask is for small amounts in a lab. An ore processing plant liquifies gases on an industrial scale and if the temperature is low enough, you can keep it in large vats like any other liquid. Of course I am suggesting something in between where you only make enough to keep the pipes full. Of course it might make sense to make it in big vats overnight and drain them down throughout the day.
This could be tested with a single installation in a single tunnel because it requires no change to the tube system or the cars.
This is a terrible idea. First lets ignore the thermodynamic efficiency losses compared to a regular chilled water cooling system. Liquid air is a potent oxidizer and the Underground has myriad sources of ignition and flammable things like people. Plus the risk of frostbite from exposure is very real. A control failure could kill people and ignite a raging fire underground.
Liquid air is the same as normal air. During its liquid stage it would be entirely enclosed in pipes. It can be safely expanded using the technology used in mine rescue suits like those from Draegerman.
You are confusing it with liquid oxygen which is just as dangerous in its gas form as it is when liquid. Air has some 70+ percent nitrogen in it, whether gas or liquid, and that prevents it from being any more corrosive or flammable than plain air.
This is the correct answer! Tied to the spot price of power in London, it could be very inexpensive if run only at night (as well as using power delivered back into the grid by trains using regenerative instead of friction braking).
Air use not very good at transferring heat. To have effective air cooling you need to pump lots of air. The current ventilation shafts certainly have their limits and especially night time the noise may become an issue if you put serious jet engines there.
You'd pipe chilled coolant down into The Tube and perform the heat exchange below ground (cooling the air below). The energy intensive chillers would run on the surface.
But first, regenerative braking; you must stop adding more energy into the system before you consider a method to extract the existing thermal energy.
The heat from the trains etc. heats the surrounding clay over a period of years. You can add less heat, or you can remove heat from the surrounding clay, or both.
Removing:
Run ventilation on high during winter and keep temps quite low in the tunnels.
Run ventilation on high on cooler nights.
Install cooling tubes in the surrounding clay and cool it directly. Either from above, or from the tunnel itself, a ground-source heat pump (geothermal heat pump) to pull heat from the clay. These can be powered by the cheapest available power, likely solar on sunny days in the future.
Adding less:
Upgrade motors to highest efficiency available. This could halve the waste heat from the motors.
Regenerative braking: if it is too complex to put the power back on the grid, build large "electric kettles" and dump it into a vat of water with resistance heaters. The water vat could be part of a water main so it would be constantly refreshed, and result in slightly warmer water for water users.
Instead of ice in the cars, cool brakes and motors that exceed 100C with water, by boiling the water. This absorbs terrific amounts of heat per kg water.
>cool brakes and motors that exceed 100C with water, by boiling the water.
While this would cool the trains and solve the heat problem over the long term, I doubt most passengers would think that being sprayed with boiling water from arriving trains (and the resulting damp) would improve perceptions of traveling comfort
Long-term heat buildup was known in the design stage to be a problem for Eurotunnel.[1] Huge chilled water plants were built to prevent that from happening. It's a surprise, though, that it would be a problem for the London Tube, which has so many connections to the surface.
It says in the article they convert some of the heat caused by braking, but I thought regenerative braking meant you also didn't have to brake as much.
Your don't have to engage friction-based brakes as much, yes. And since friction-based brakes work by converting movement to heat, that's why regenerative braking helps with heat.
Is it feasible to increase the distance into surrounding clay that heat can be conducted? Could metal be used to conduct heat from clay surrounding tunnels to clay that is presumably cooler, further away? I could imagine that if a material exists that insulates electricity but conducts heat very well, the track itself might be useful in transferring heat to cooler clay, making the track colder and cooling tunnels.
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[ 4.7 ms ] story [ 209 ms ] threadBesides that, Tube tracks often rise slightly at stations, so that trains get a small gravity assist to both stopping and starting off again. (Unfortunately it also means that hot air from the tunnels tends to collect there, but you can't win 'em all.)
1) modern railway is fully IGBT powered. In this case it is trivial to inject current.
2) with DC current you need a substation capable of converting AC to DC (easy: bridge rectifier) but also DC to AC (to given tolerances) which is much more cumbersome.
Only the later generation B and the new C generation can move brake energy back into the grid.
Newer units on the subsurface lines do have AC fitted.
This offers 2 distinct improvements for passengers.
1. noise/dust mitigation: One can sweep the platform floors all you want, but dust from the track will always get to the platform. By installing the glass partitions, general atmosphere of the platform is just more pleasant.
2. less space for AC to cool: It's impossible to cool ALL of the space of a subway system, from miles of tracks to the platform. By installing the glass partitions between tracks and platforms, AC at the subway stations only has to cool the platform.
I heard NYC subway engineers say they can't install the glass partitions because the subways are not capable of stopping at a particular spot. This is required for the glass partitions to be installed.
Mines quite successfully manage to cool air 2+ miles under ground, so I'm finding it a rather hard to believe that nothing can be done about this.
The deeper tube cars running on older lines have serious space constraints to deal with that make integration of things like cooling equipment difficult and expensive. We're talking about trains that have comically small proportions relative to what you would see anywhere else in the world.
That said, last I had read, the deep line cars are supposed to get AC sometime within the next decade or so.
Don't think so. That is a fixable problem. (e.g. convert the space of 1 seat per car for an AC unit).
The fact that everyone is so stumped by the problem says it's the actual tunnels that are overheating. The fact that some lines don't have AC just exasperates this.
1. http://londonist.com/2015/07/itd-be-illegal-to-transport-cat...
According to Wikipedia, it's a groundwater based cooling system.
https://en.wikipedia.org/wiki/London_Underground_cooling
On deep level trains there is no good place for the trains to dump the heat.
On deep level trains there is no good place for the trains to dump the heat.
Too late now, but I wonder if they considered district cooling, where e.g. cold water from rivers is used as an alternative to air conditioning. Seems to be used successfully in my hometown of Munich: https://www.swm.de/english/m-fernwaerme/m-fernkaelte.html
I'd assume they did, especially if it's something that's done elsewhere.
Unfortunately only a couple of stations have an appropriate water supply, and enough free vertical shaft space to fit the pipes.
There was also this, from 1938, although i don't know where they got the water:
https://en.wikipedia.org/wiki/Tottenham_Court_Road_chiller
> Elsewhere, they’ve been using cool ground water to cool some of the stations. An experiment at Victoria station was the first, as water from the River Tyburn was used to cool the air in the station. This was only an experiment, but at Green Park, a permanent version was installed in 2012.
> Elsewhere, they’ve been using cool ground water to cool some of the stations. An experiment at Victoria station was the first, as water from the River Tyburn was used to cool the air in the station. This was only an experiment, but at Green Park, a permanent version was installed in 2012.
And instead of ventilation shafts you would probably need active heat pumps
it really reads like the cars must be changed to fix the problem as they are the heat source. so unless an economical means can be found to store/discharge it between stations their only solution is to cool the tube itself.
So isolate the passenger area from the tube area at all stations and force cool air from points where you have easy access to cooling. the air flow would of course move in the direction of trains. can that work?
Some storage system near a station (where there is more ventilation) could make sense, but probably costs more than the system mentioned in the IanVisits blog to return power to the city (i.e. convert the DC the trains use back to AC for the city).
I don't think the isolation idea would work. Where does the air for people on trains to breath come from?
Just to be clear, you wouldn't actually run the flywheel in the opposite direction.. You'd take energy out of the flywheel versus putting it in?
0.5 x 29 tons x (50 mph)^2 to kWh
h)^2 -> kW·h So a Victoria line train at top speed has 2 kWh of kinetic energy.So it does seem feasible to do it either by installing battery packs connected to the tracks, or in the cars themselves. I wonder which would be better.
The only issue is that each third rail section is fed by its own set of independent rectifiers, and the third rail sections are not paralleled together. This means that if there's no other currently-accelerating train on the section of rail that you're on, it's just you and the rectifier substation -- and those rectifiers can't accept your regenerative braking current.
Adding inverter circuitry to the substations would introduce a path for energy flow to go from the DC third rails into the AC grid (opposite of the normal direction of flow, hence the term "reversible substation"). Since the AC grid is connected to all the rectifier substations and since there's many trains on the rail network, there'll always be a source for regenerative braking current that's dumped onto the AC bus.
That's a very good metaphor for our planet.
All profits are re-invested with TFL so I don't think cost (within reason) would be a major concern.
https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube...
TfL isn't a private organisation, they are a government body. In 2015/16 only half of their costs were covered by ticket sales and other income (advertising, sponsorships, etc). The rest comes from government funding, so taxes.
http://www.mayorwatch.co.uk/govt-funding-changes-will-force-...
I tried searching for a similar study for NYC but all I found was old articles from years back.
It doesn't look like the MTA shares any measurements of temperature in their data feeds: http://web.mta.info/developers/download.html
Does anyone have ideas on how we could get this sort of data for NYC subways?
I don't see why it'd be any different for NYC, where I live.
https://cityroom.blogs.nytimes.com/2008/08/08/complaints-abo...
For example the Montreal metro currently only allows a train to leave a station when the platform of the next one is free, limiting the frequency of this very crowded system. With modern signaling, trains can creep up to the ones before them and reduce the time between them down to 40 seconds - but it's more difficult with all those slopes around.
It's also making extending platform lengths or moving/adding stations nearly impossible.
I'm not sure how long the distance is though. 40 seconds is really really hard to estimate with very very heavy trains and no weight sensors. Even AI/ML cannot predict this (re: no weight sensors).
Trains know their position very precisely, with errors less than 20cm, and their braking characteristics and error margins are well known, especially in tunnels where there are now wet leaves or snow on the tracks. Automatic train operation makes trains stop at precisely the same spot each time (for example to match train doors to gates), to the point where increased track wear becomes a concern.
And according to this Wikipedia list: https://fr.wikipedia.org/wiki/Liste_des_accidents_de_métro
The last collision in Paris metro was in 1981
You'd end up with lots of ventilation grates on the sidewalks on the surface, but that seems like an easy and space efficient solution.
You probably don't want a direct vertical grate either, you'll need to catch water, rubbish, people from falling down. An S-bend is going to effect flow.
It's taken a century or so to raise the temperature in the tunnels by around ten degrees C. That already includes the cooling effect of cold air being pushed into the tunnels for most of the year, balanced by the relatively small number of days a year when the air temp in London is more than 14C.
Without that cooling heat has nowhere much to go. It will radiate out into the air, which will make its way up and out rather slowly. And it will diffuse into the clay/soil around the tunnels, even more slowly.
A fully passive cooling-off period would take years - at least.
The problem isn't impossible to solve. All kinds of active cooling solutions are possible.
The problem is that it's impossible to solve affordably. You effectively have to build a heat exchanger the size of central London, which is never going to be cheap.
Natural gas burns at around 2000 degrees celsius.
Even simply ducting warm air to street level for outdoor dining (in winter), presuming (against other information, I'm aware) that the ducting could be provided. If you're wasting the heat anyway, put it to some use prior to final venting.
1: https://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube...
I don't live in London so anyone with regular riding experience please correct me if I'm wrong.
The deep lines (originally called "the tube" although that now refers to the whole system) were built by tunnelling, the trains and tunnels are cylindrical and the trains just fit into them. In many cases the tunnels are 30+ metres underground.
Add cool to the tunnels, rather than taking heat out.
Build liquid air plants above ground, 2 or 3 floors up in the air so that the heat of the pumps is released above street level and the noise can be kept away from the street. Feed the liquid air into the tube tunnels through insulated pipes which takes up far less volume than air vents. Let gravity bring the liquid air down the pipes. Release the liquid into the tunnels near platforms where the air pump effect of moving trains caused lots of air circulation. Also the car doors open on the platforms.
Since you are liquifying the air, not just the oxygen, it can be safely released anywhere in the tunnels. And if your air intakes are high up you will actually be improving the air quality in the tunnels as well, i.e. cleaner air flows in.
Plan sounds great and very expensive.
This could be tested with a single installation in a single tunnel because it requires no change to the tube system or the cars.
You are confusing it with liquid oxygen which is just as dangerous in its gas form as it is when liquid. Air has some 70+ percent nitrogen in it, whether gas or liquid, and that prevents it from being any more corrosive or flammable than plain air.
But first, regenerative braking; you must stop adding more energy into the system before you consider a method to extract the existing thermal energy.
The groundwater system in the article more or less does what you suggest, without the expense of the chillers.
https://en.wikipedia.org/wiki/Hydraulic_hybrid_vehicle
Much more of the power would be preserved, leading to less heat.
Removing:
Run ventilation on high during winter and keep temps quite low in the tunnels.
Run ventilation on high on cooler nights.
Install cooling tubes in the surrounding clay and cool it directly. Either from above, or from the tunnel itself, a ground-source heat pump (geothermal heat pump) to pull heat from the clay. These can be powered by the cheapest available power, likely solar on sunny days in the future.
Adding less:
Upgrade motors to highest efficiency available. This could halve the waste heat from the motors.
Regenerative braking: if it is too complex to put the power back on the grid, build large "electric kettles" and dump it into a vat of water with resistance heaters. The water vat could be part of a water main so it would be constantly refreshed, and result in slightly warmer water for water users.
Instead of ice in the cars, cool brakes and motors that exceed 100C with water, by boiling the water. This absorbs terrific amounts of heat per kg water.
While this would cool the trains and solve the heat problem over the long term, I doubt most passengers would think that being sprayed with boiling water from arriving trains (and the resulting damp) would improve perceptions of traveling comfort
[1] http://www.nytimes.com/1991/05/01/business/business-technolo...
As the train arrived it gets slowed by a spring or similar system which is then used to propel the train forward once it needs to depart.
Also, what about just slower trains? The heat produced while acccelerating or braking is probably not exactly linear with the speed of the train.