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Comment by t43562 | Hacker News Reader

I wonder if future tube lines could have some sort of cooling system to pump heat into some underground reservoir in summer which could then be the source for a district heating system above ground in winter.

I'm just wondering about how to make the problem a benefit.

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They do use the excess heat for some public buildings in Islington https://www.islington.media/news/bunhill-2-launch-pr

I never knew this existed before and can't help thinking it's absolutely incredible. Thanks for sharing!

The ground around the deep tunnels already is a heat reservoir, over decades it heated up. https://en.wikipedia.org/wiki/London_Underground_cooling

That is interesting because it suggests that we could grab some of that heat in winter and pump it into houses and businesses on the surface. In the long term that would help summer heat in the tube to be less of a problem.

The idea of "Grab that heat and pump it into businesses and apartment blocks above" requires actual physical infrastructure, and so suffers from the same issues as drilling new ventilation shafts to simply vent waste hot air into the air above: It's a densely inhabited area, and has been for a long time. It is neither cheap nor easy to find room for those ventilation shafts, both below and above ground.

If venting was easy, it would have been done long ago, well before the idea of re-using waste heat rather than just venting it was a thing.

They don't have to vent air though, for the same reasons we don't need to vent air for geothermal heat pumps. It doesn't seem all that crazy to drill minimally for some coolant lines and run a mini-split style heat pump system into the hottest stations.

I'm not saying this is easy per se, but far from impossible, or impossibly expensive.

This has been done to some degree at Green Park station, which still very much is quite warm in places, for ~£9M about a decade ago.

But when TfL has had its budget slashed, and such projects are competing for financing with other projects with more direct operational benefit… it's hard to justify. And it's still not necessarily easy to drill at all!

Agreed that drilling isn't easy, but this does seem more like a budgetary and political issue than an engineering challenge.

Not much (if any) drilling may even be necessary, as there's also the option of running coolant lines directly into the train tunnels. Existing water infrastructure could also be used as coolant — especially if it's otherwise sitting idle for a fire that hopefully never happens!

> seem more like a budgetary and political issue than an engineering challenge.

Science is about proving that something can be done at all.

Engineering is about taking that result and productionising it - doing it reliably, safely, effectively and on a budget. On the right site, even if that's in a busy city. "time and budget issues" are part of any engineering challenge. Very few engineering projects are "Money no object".

An also, there currently isn't the political will in the UK to invest in expensive infrastructure and engineering projects. London actually gets more investment than the hinterlands. See https://www.reuters.com/world/uk/whats-happening-hs2-britain...

It seems like we're in agreement here? Geothermal heat pumps aren't particularly novel, so it doesn't seem like engineering a solution is the blocker here. It's mainly politics.

Exactly, budget is an engineering concern, and in this case it's nigh impossible to engineer a solution, given the space and budgetary constraints.

The budgetary constraints are purely political though. Stuff like this has been engineered before at a reasonable cost (eg the Green Park station for 9M according to a poster above). So while yes things have to be engineered to a cost, it’s clearly not some impossibility high number.

It would need to be made so that it uses more heat than needs to be disposed of throughout the year though. Plus, digging heat pumps like that is a huge and complicated undertaking, with all the existing underground infrastructure.

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