Underground line to heat up north London homes | Hacker News Reader

Underground line to heat up north London homes

bbc.co.uk

23 pointsmonkeydust12 comments

Heat is becoming a real problem, note that most of it is from the brakes which is why the station is commonly higher than the main track to try and take advantage of GPE.

Great use of all the hot air we have to suffer, more info here: http://cullinanstudio.com/project/bunhill-2-energy-centre

Is this actually efficient?

I've read before that this kind of low-temperature heat (low-grade heat) is not very useful. This is why district heating water is running at 90C+.

Can the mentioned heat pump use this low-grade heat to raise water to high-grade temperatures?

Heat pumps become less efficient as the temperature differential across them increases, around 2% less efficient for every 1°C increase. If it's 5°C at street level and 19°C in the tunnels, that's a 14°C difference or around 28%.

Isn’t it more efficient to extract heat from a 19C environment vs a 5C environment for domestic heating?

This seems unintuitive. Why does it happen? I'd assume, it's faster to move heat from one source at very high temperature Vs one source at very low temperature.

I think he's a bit mixed up. That rule of thumb is for when you're pumping from cold area to warm area, which is what you usually do. For instance from outside (10 degrees C air) to inside (21 degrees C air). Then you can see how the performance would drop as the differential changes.

A heat pump should perform really well when the place it's pumping from is high temperature like this. Pumping from 19 degrees C to a house that's 21 degrees C is going to be great.

Obviously things will be much less efficient if the heat pump were being used to warm the Underground from outside air (5 degrees C) but no one's going to do that! The Underground air is going to go into the home (which is at 21 degrees C). The street air isn't in the picture at all.

After 100 years the Tube has basically used up it's heat sink of cool earth around it, making it impossible to keep as cool as it should be for passengers.

I assume this will serve two purposes, even if it runs at a loss the cooling of the tube might make it financially viable.

https://www.citymetric.com/transport/londons-tube-has-been-r...

Couldn’t you use the River Thames as a heat sink for the Tube? Similar to how power plants use rivers and other bodies of water for cooling.

A quick google search shows its often below 60F, so with the proper heat exchanger and cheap renewable power, you could slowly pump all of the heat (built up over 100 years) out of the surrounding Tube earth into the river for disposal.

If you can use the heat for a useful purpose, great! But it seems like there’s lots of ways to get rid of it and get the Tube temp down.

This has been talked about in the past.

I don't think the problem is finding somewhere to put the heat, but to get it out in the first place. The article says the heat is currently vented into the street.

They've used Tyburn

>I am sure readers will have heard of the ground water project at Victoria Station – and it has been a success. No questions – it works, and works well. The system currently draws most of its cool water from the Tyburn river, which slightly leaks into the circle line – and is drained into a sump. That cool water is used to cool systems in the station at Victoria and is very efficient in how it cools the air for minimal electrical effort in pumping water.

I think using the Thames would involve a lot of plumbing and pumping.

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