Marratxi wrote:

As I suggested some months ago, long low water tankers at front and back of
every train. The one at the rear sprays out a very fine mist of water which
will cool the air and then be drained out, taking the heat with it, just as
with any other water which gets into the underground system. I claim the
prize.
Cheerz,
Baz

That would only work because of cooling effect of evaporating the water.
Once enough water has evaporated to raise humidity to near dew point
little more water would evaporate, AND you'd have an even more humid
sticky atmosphere. (It's evaporating the water that absorbs energy not
heating it from say 10degC to 15degC) (Hundred times as much!- I'll not
quote units as I'm sure to get cgs, MKS, & SI units muddled)

I'd suggest even with IDEA of using water pumped from sumps to cool air
you might need some sort of 'heat pump' in the circuit to enable waste
water to be at higher temperature than returned 'cooled' air.

Jim Chisholm