7 ms·
Cooling the tube – Engineering heat out of the Underground (2017)
- spenrose 4y ago"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 4y agoSimilar 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 4y agoI 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?
- aaaaaaaaaaab 4y agoRegenerative 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.
- bombcar 4y agoYeah, 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 4y agoLess 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 4y agoDefinitely. 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.
- pbhjpbhj 4y agoI 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).
- 4y ago
- giomasce 4y agoI love this complex-engineering-thing-you-thought-it-was-trivial-but-it-doesn't-even-try-to-be kind of articles!
- londons_explore 4y agoThe 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!
- acta_non_verba 4y agoThis 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 4y ago>>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)
- alar44 4y agoYeah, it's insane because it's 100% not true.
- interestica 4y agoI 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 4y agoIt 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 4y agoEvery amount of heat generated will have an equilibrium average temperature. Reducing input heat will lower this equilibrium temperature.
- ClumsyPilot 4y agoBut that equilibrium could be a lethal temperature.
- mountain_peak 4y agoI 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://observatory.designobserver.com/entry.html?entry=7487 https://web.archive.org/web/20090823173621/http://observator...
- interestica 4y ago
- christkv 4y agoCould using magnets to break and start be a solution to reduce the heat generation ?
- CorrectHorseBat 4y agoUsing 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)
- advisedwang 4y agoThat's effectively what motors and regenerative braking are (just the magnets are in a circle!)
- tomohawk 4y agoIf 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.
- cogman10 4y agoMakes 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 4y agoI 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
- eptcyka 4y agoConverting heat into useful amounts of energy usually requires a temperature gradient that'd be unbearable for humans.
- toomuchtodo 4y agoHeat pump extraction into hot water distribution pipes for district use.
- ClumsyPilot 4y ago> The difficulty of adding more ventilation is the lack of space above ground to put new ventilation shafts. This is always going to be a problem for the older tube tunnels except on rare occasions when a surface development takes place at just the right location and agreements can be made to include a shaft down to the Underground Sounds like we need to knock down a few houses. This isn't unreasonable for critical infrastructure. Also sounds like giving people free ground source heat pumps along the tube line would be best - they would be pumping out the heat thats in the clay. The article talk about a scheme, but this needs to be done at scale