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The London Underground is, for some reason I don't
understand, quite a bit warmer than the streets above it.
There is also a lot of it. It's four hundred kilometres
in total and over 3.5 metres in diameter everywhere.
Assuming this to be semicircular, that gives it a volume
1900000 cubic metres. This volume of air seems to
heated to around five degrees K above the atmosphere
above ground. I can't do the maths because I don't know
enough about heat capacity and stuff, but it seems to me
that the energy required to heat such a huge volume of
must be considerable. Most people travelling on the
don't seem to enjoy the warmth, although in the winter
I've found it quite nice.
So: why not install Stirling engines, in the tubes to
refrigerate them down to the ambient temperature and
transfer the heat onto the streets while generating
power or mechanical energy? The ground surface can be
warmed in winter to melt snow and ice, which can then
run off into the water supply, generating further
hydroelectric power as it goes and providing a grey water
source for cisterns. Meanwhile the energy can either be
added to the underground rail system mechanically,
perhaps in the form of wheels between the tracks which
accelerate the trains, or used to provide electrical power
for the underground itself.
I'm almost certain they already air condition the
Underground, so the system is already partly in place to
I'm pretty sure this is by no means a negligible
[hippo, Apr 27 2017]
||amazed at how small those tubes are. I had to look it up.
||Me too. I think that's the minimum size though, and I
they have smaller trains running through them. Also,
is more space elsewhere on the system such as above
platforms and in station concourses.
||Assuming the tunnels are three-quarters of a circle in
cross-section, that they are 3.56 m in diameter and 402
km long rather than doing all my rounding down, that
makes the volume of the system over three million cubic
metres, and that's still ignoring all the extra bits. But
what's the volume of all the trains added together?
||The trains are mostly hollow shells, so the volume they
occupy is possibly more ignore-able than the volume of all
the passengers (body heat from the passengers would
explain some of "mystery" warmth --each person's body
produces about the same total warmth as a 100-watt
incandescent light bulb, radiating from a larger surface
||In addition to body heat, is it not also heat given off by the
trains as they move, and by electric motors and the like?
||And being closer to the centre of the Earth - that's
why deep mines are always hot places.
linked article says that the heat comes from trains,
and that the clay surrounding the tube has heated up
from 14C since the tube was built to 19-26C now. It
also discusses the use of heat pumps.
||Examining the map, the obvious solution to cooling is to drill vertically up from the tunnels at selected locations. This would ensure that the temperature of the system was rapidly lowered to that of the Thames.