[HN Gopher] Cooling the tube - Engineering heat out of the Under...
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Cooling the tube - Engineering heat out of the Underground (2017)
Author : pkrecker
Score : 66 points
Date : 2022-06-10 14:08 UTC (8 hours ago)
(HTM) web link (www.ianvisits.co.uk)
(TXT) w3m dump (www.ianvisits.co.uk)
| cogman10 wrote:
| Makes me wonder if we can do something more productive with the
| heat.
|
| They mention energy generation, but what about heat pumps and
| water heaters for the above ground buildings? Probably cost
| prohibitive, but wouldn't it be neat if the waste heat from the
| brakes ended warming a building or hot water heater?
| Havoc wrote:
| I suspect a big part of the problem is that while the heat is
| there in adundance its not particularly concentrated. Just
| ambient everywhere.
|
| Any kind of capture heat and use it because much more workable
| if concentrated
| interestica wrote:
| I think the Montreal metro faces a lot of these same issues. It
| works out in the winter where you don't need to actively heat the
| space. In the summer, it can be unbearable. I'm not sure if the
| type of rolling stock (rubber tires + tunnel track) has a major
| difference from other typical subway cars.
| bombcar wrote:
| It really doesn't matter much - any amount of heat going into
| the underground system that is not able to be dispelled in a
| year-round cycle will heat the ground eventually.
|
| Reducing the heat entering the system slows it down, but at
| some point you have to cool it again.
| colechristensen wrote:
| Every amount of heat generated will have an equilibrium
| average temperature.
|
| Reducing input heat will lower this equilibrium temperature.
| mountain_peak wrote:
| I personally don't find Toronto or Montreal subways unbearable
| (warm, but not crazy), while my time in the London Underground
| was absolutely miserable - I'm not sure how locals handle that
| kind of stifling heat. Actually, there was one time I was in
| the old Toronto Osgoode (pre-opera house) station with a -30
| degree wind blowing through - that was chilly!
|
| Actually, I'm kind of sad that Montreal has so few cars left
| that play "Fanfare" [0]
|
| [0]
| https://web.archive.org/web/20090823173621/http://observator...
| willyt wrote:
| The underground gets quite a lot hotter than the legal
| temperature limit for transporting livestock in the UK.
| Supposedly the record is 47degC
| Havoc wrote:
| >I personally don't find Toronto or Montreal subways
| unbearable
|
| tbh London is fine too. Problem is if it is the main form of
| transport then the at-risk members of society use it too.
| Very old & frail etc.
| londons_explore wrote:
| The main cause of heat is the inefficiency of the trains. All the
| brake energy is converted to heat. The motors and controllers are
| pretty inefficient too - modern electric motors+controllers are
| 95-98% efficient, whereas most tube trains are more like 40-60%
| efficient. For example, to go slowly, they simply put a big
| resistor in the circuit and waste 50+% of the energy!!
|
| Perhaps not coincidentally, the inefficiency also has a massive
| carbon and budget impact... Or it would, if the train system had
| to pay for the electricity it used - which it doesn't! Trains in
| the UK are given free unmetered electricity, so there is no
| reason to conserve energy. Hot tunnels are just an extreme
| symptom of that.
|
| If they had to pay for usage, at todays wholesale electricity
| rates, it would cost nearly a billion pounds a year. Which is
| ~20% of their revenue! I can see why they don't want to pay that
| bill!
| tobylane wrote:
| Source on 40-60%? As some trains are from the early 70s, and
| others were introduced 10, 5 years ago, which are you referring
| to?
| londons_explore wrote:
| I'm referring to the oldest ones.
|
| The new ones are much better, although they still recover
| very little braking energy.
| TheOtherHobbes wrote:
| TFL does pay for electricity, but it pays for it as part of the
| Crown Commercial Service which aggregates procurement for many
| large public services in the UK. [1]
|
| TFL used to have its own generating stations, which helped keep
| costs manageable and also meant the trains kept running during
| power cuts.
|
| That ended around 2000. Now it has at least four separate
| connections to the National Grid, and is supposed to be moving
| to 100% renewables within the next decade.
|
| [1] https://content.tfl.gov.uk/fc-20171205-part-1-item08-tfl-
| ene...
| acta_non_verba wrote:
| This is categorically not true.
|
| In fact, the level of effort required to estimate electricity
| uses for multiple franchises on one physical section of railway
| has resulted in nearly all British rolling stock having built-
| in electricity metering.
| toss1 wrote:
| >>put a big resistor in the circuit and waste 50+% of the
| energy
|
| That Is Insane!!
|
| Rail needs a complete rethink of design from the ground up.
| There are certainly vast efficiencies from rolling steel wheels
| on steel rails. But I've seen little evidence of light-
| weighting and indeed active resistance to steps like making
| cars using composites, which would save enormous amounts of
| energy and cost over the lifetime, as well as reduce
| maintenance costs. Yet their approach to everything seems to be
| sticking with an approach of 'brute force and ignorance'. Sure
| that works in the 19th century when you're just starting to put
| some carbon in iron and make it stronger than pig iron, but
| materials are sooo far past that now, yet it's still the same
| old approach. (&yes, I strongly support the Chesterton's Fence
| checking but this seems way beyond that)
| Symbiote wrote:
| I don't think it's anywhere near 50% that is wasted, since if
| I understand correctly the resistors are used only during
| initial acceleration.
|
| But anyway, the affected trains are the oldest in use in
| Britain, from 1972 (Bakerloo Line, 36 trains) and 1973
| (Piccadilly Line, 87 trains), out of 620 passenger trains
| across the whole system. New trains have been ordered and
| should be introduced in 2025.
|
| There's been a 10 year delay, due in part to the 1990s
| attempt to privatize chunks of the system.
| alar44 wrote:
| Yeah, it's insane because it's 100% not true.
| londons_explore wrote:
| Surprising then that a company sells resistors just for
| rail speed control applications:
|
| https://www.cressall.com/applications/rail-traction-
| dynamic-...
|
| (scroll down to "MOTOR STARTING AND SPEED CONTROL
| RESISTORS")
| fredoralive wrote:
| That section starts with "This was the traditional
| approach...". I guess the Bakerloo and Picadilly line
| trains from the 1970s might still use them on London
| Underground? Wikipedia mentions stuff like GTO thyristers
| and IGBTs on descriptions of stuff like the 1992 (Central
| line) and 1995 (Northern) stock trains, so the next
| oldest trains from the 1990s seem to have modern(ish)
| power control. And new trains are coming to the Picadilly
| line, and presumably must come to the Bakerloo at some
| point before the old ones fall apart.
| alar44 wrote:
| That doesn't mean that's all that's used. It would also
| imply that it only has 2 speeds or something. Use your
| head. Or learn some basic electronics.
| s0rce wrote:
| Thats not to "go slower" but to slow down:
|
| Whenever possible regenerative braking is used. In this
| case the drive motors convert the kinetic energy of the
| train into electricity, which is fed back into the power
| supply and used elsewhere on the network.
|
| If it cannot be absorbed by the system the energy may
| have to be dissipated with braking resistors. These
| braking resistors can be either mounted on the rail
| vehicle or as a fixed (trackside) installation connected
| to the third rail or overhead catenary via Automatic
| Assured Receptivity Unit (AARU) systems.
| aaaaaaaaaaab wrote:
| Regenerative braking would improve a lot with not just the heat
| issue, but also air quality. Commuters on the London Underground
| get a characteristic grey/black snot from the brake dust they
| inhale. If you stare into the tunnel after a train left you can
| literally see a haze of brake dust in the air.
| na85 wrote:
| >Commuters on the London Underground get a characteristic
| grey/black snot from the brake dust they inhale.
|
| Well that's horrifying. Is there no health and safety
| monitoring being conducted?
| fredley wrote:
| It's already got a primitive version of regenerative braking!
| The deep-line tubes--those that have the heating problem--are
| designed so that the stations are at peaks in the line. As the
| train is approaching the platform the uphill slope helps it
| decelerate, and the downhill helps it accellerate again.
| andbberger wrote:
| hardly primitive, it's by far the most efficient form of
| regenerative braking
| pbhjpbhj wrote:
| I wonder if you could fit a magnetic braking system mainly at
| platforms, when engaged trains would be slowed. That could
| reduce weight on the trains themselves?
|
| Thinking wildly, tube trains are like pistons (they're actual
| plungers, I guess) if you had a smooth walled section of tunnel
| then you could have a seal at the head of the train that fans
| out and provides pneumatic braking, you could maybe use the
| pressure to drive the ventilation system. Unlikely to be
| practical (you'd have to have a pre-platform door to prevent
| all the passengers from getting exposed to the pressure
| increase, I think).
| jaywalk wrote:
| Magnetic (eddy current) brakes work by converting kinetic
| energy into heat, which doesn't really solve the problem
| here. I'm not sure if anyone has devised a system that
| actually captures electrical energy from the braking action,
| or if such a thing is even plausible.
| zorlack wrote:
| You could put the braking resistors above ground, no?
|
| Or if the braking resistors have to be close the the coils,
| then you could use a heat-exchanger to move the heat
| somewhere else...
| bushbaba wrote:
| It'd at least solve the dust break-pad dust issue
| jamincan wrote:
| Regenerative braking generates electricity and there's
| really no reason modern trains wouldn't use them.
|
| Another approach that can be used when initially building
| the system is to have a slope leading into/out of stations
| so that energy can be stored as gravitional potential. I
| know the Montreal Metro was built this way.
| dtgriscom wrote:
| Your second point was stated exactly in the parent of
| your parent comment.
| jamincan wrote:
| I don't think that's correct. @pbhjpbhj talks about
| magnetic braking and some sort of pneumatic braking. The
| sibling to his comment by @fredley mentions it, but I
| don't recall seeing that yet when I posted mine.
| namibj wrote:
| Yes. It's called "electric generator" and can be performed
| by almost all electric motors.
| andbberger wrote:
| piston effect already does a lot of ventilation work
|
| the more elegant solution in use around in the world is to
| put the stations on hills
| konschubert wrote:
| It seems they have been testing it out?
| https://arstechnica.com/cars/2015/09/london-tube-gains-regen...
| Symbiote wrote:
| The new trains on the deep lines should also bring a big
| improvement, from 2025.
|
| https://en.wikipedia.org/wiki/New_Tube_for_London
| bombcar wrote:
| Yeah, they mention it with a "grid balancing issue" but it
| seems that could be solved by adding under-floor battery packs
| to the trains or the stations themselves - store braking energy
| to restart the train afterwards.
| msandford wrote:
| Less batteries and more ultra capacitors. You might need to
| handle power requirements in the range of 5-20MW, albeit for
| just a minute or so.
| mnw21cam wrote:
| Definitely. The bonus is that they wouldn't have to be on
| the train. And the tube electric system is DC already as
| well. This sounds like an engineering problem that is
| largely already solved.
| christkv wrote:
| Could using magnets to break and start be a solution to reduce
| the heat generation ?
| CorrectHorseBat wrote:
| Using magnets will release exactly the same amount of heat
| since energy cannot be destroyed (unless you mean by that using
| regenerative braking, that does work since you can "recycle"
| the energy)
| giomasce wrote:
| I love this complex-engineering-thing-you-thought-it-was-trivial-
| but-it-doesn't-even-try-to-be kind of articles!
| spenrose wrote:
| "Over the years, the heat from the trains soaked into the clay to
| the point where it can no longer absorb any more heat. Tunnels
| that were a mere 14 degrees Celsius in the 1900s can now have air
| temperatures as high as 30 degrees Celsius on parts of the tube
| network."
| bombcar wrote:
| Similar issues can happen with geothermal heating/cooling if
| it's unbalanced - eventually the ground temperature changes and
| you have to dig deeper or stop using it.
| SoftTalker wrote:
| I wondered about that. I know a few people with GT systems
| and it has never been an issue, perhaps because we have real
| summer and winter here, so the heat dumped underground in the
| summer would be offset by the heat extracted in the winter?
| Havoc wrote:
| You know people that have a personal geothermal system?
| na85 wrote:
| They're quite common in some parts of the world.
| frabert wrote:
| https://en.wikipedia.org/wiki/Ground_source_heat_pump
| tomohawk wrote:
| If they added hydraulic hybrid braking to the trains, they could
| capture 80% or more of the kinetic energy and reuse it to
| accelerate again. This would drastically cut down on heat. By way
| of comparison, electric batteries can capture maybe 20-25% of the
| kinetic energy.
|
| Uncaptured energy is likely turned into pure heat.
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