Where there’s space, this has already been done. Unfortunately for many lines there simply isn’t space.
Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible.
TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.
The problem isn't so much space, iirc. It's that the blowers make a lot of noise and upset the residents, so they can't be run at full speed all the time.
The trains probably push a lot of air around. Wonder whether closing off sections with doors would help to push air out at one point and pull it in at others.
Possibly, but the pressure difference would pop people's ears, moreso than they do already. I'm sure the piston-like effect of moving trains is considered too to help move air around. Question is whether that's enough air movement to offset the heat generated by the trains, after all (and this is secondary school level understanding of thermodynamics), the energy needed to move the train is the train weight itself, plus track friction, plus air resistance. That is, in my head, it costs more energy to move the train than the amount of air that is moved around, so it in itself wouldn't be enough.
Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible.
TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.