John Alexander:
I agree, the idea of cooling the trains on the tube lines is ridiculous
until you extract heat from the stations and tunnel system first...

Any sort of air-conditioning, to provide effective relief, would have
to work no matter whether the train was on a surface, subsurface, or
deep tube section. Therefore it would be necessary to air-condition
the trains *as well* as applying measures to extract heat from the
tunnels and stations.

What is the problem with having a heat pump to suck heat out of a deep
tube platform to a liquid (water?) and then to pump the liquid to the
surface and chill the liquid there for return to the platform?

As someone else said, it's just a matter of money. You either need to
do something like that, or you need to move enough additional air through
the tunnels and stations to ameliorate the heat buildup. The Channel
Tunnel has a cold-water pipe running through each bore to absorb heat
from the trains; the subway systems in New York and Toronto, on the
other hand, without the deep and narrow tunnels that London has, run
air-conditioned trains and let normal air circulation deal with the heat.

Incidentally, a new air-conditioning system http://www.enwave.com
is now coming into use for major downtown buildings here in Toronto,
taking advantage of our location on Lake Ontario. Heat from these
buildings is transferred into water being drawn from the lake for the
city's drinking water system; the drinking water won't get significantly
warmer than it now does in summer, because the water used for this
purpose is coming from a new feed deeper in the lake where the temp-
erature is always 4 Celsius (at which water is densest). Unfortunately,
London doesn't have a Great Lake next to it...
--
Mark Brader "That's what progress is for. Progress
Toronto is for creating new forms of aggravation."
-- Keith Jackson

My text in this article is in the public domain.