Robin9 wrote:

I certainly hope this turns out to be feasible. Now, if only they can
find a way of extracting surplus heat from inside tube trains and
pumping that into domestic heating systems! Central Line trains
should be the first. It has always puzzled me that eastbound Central
Line trains arrive at Stratford where the platforms are above ground
level, the doors open . . . . . . and the heat remains in the carriages!

I read a recent article, I think in MR, that pointed out,
counter-intuitively, that underground trains are hot not because of the
heat they pick up in the tunnels, but because of the solar heat they absorb
before entering the tunnel. Apparently experiments have proved that
underground trains that never emerge into sunlight stay cooler (eg, the
Drain). Even being stabled in open sidings (eg, the Victoria line)
pre-heats them.

So just ventilating the hot air in the carriages in a station actually
releases very little of the stored heat in the carriage body.