There's a BBC report at
http://news.bbc.co.uk/2/hi/uk_news/england/leicestershire/6466501.stm
that the test track at Asfordby will be used to test the next generation
of tube trains which will be fitted with air conditioning.

Surely using energy to pump heat out of the trains into the tunnels will
just increase the temperature there. Has a solution to the problem of
cooling the system as a whole been found? I have heard groundwater
mentioned as a possible heat sink but building and running a full system
would be horribly expensive.
--
Goalie of the Century