
Underground line to heat up north London homes - monkeydust
https://www.bbc.co.uk/news/uk-england-london-49482840
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LiamPa
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.

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

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thermonot
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?

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thescriptkiddie
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%.

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gingabriska
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.

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scarejunba
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.

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aaron695
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...](https://www.citymetric.com/transport/londons-tube-has-been-running-
so-long-its-literally-raising-temperature-earth-around-it)

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toomuchtodo
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.

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tim333
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.

