Take a look just to left of the station entrance in the grass in the photo above and you'll see the circular plant room at Green Park. The cooling is provided by groundwater drawn up
from 80m-deep boreholes in the park. Morgan Sindall carried out the Green Park
project, which also involved installation of eight air-handling units (AHUs as they are known in the trade)
on the platforms.
Here comes the science bit from Engineering and Technology Magazine "These are fed by cool water abstracted from two of the newly-drilled boreholes and piped to the station. The warmer return water is put back into the aquifer through two more boreholes at some distance from the abstraction points."
was the first installation of this type on the London, although at Victoria there are
two platforms are cooled by groundwater that would in any case have to
be pumped out of the station.
@IanDeeley noticed some huge air conditoning units had recently been installed at Victoria Line platforms at Oxford Circus. There are
already air-cooling units in the ticket hall there and Birse Metro expanded the
scheme with 14 AHUs in the platform areas. Air-cooled water chillers are in the roof of a building next door.
London Underground has introduced air-conditioned Tube trains on its shallower sub-surface
lines, but has always found it a challenge to cool the deep-level Tubes,
which do not have much clearance between tunnel and the train. The lack of space for air conditioning equipment inside or outside the trains, and for heat to escape is a long term problem for the system.
Back in 2003 when Ken Livingstone was mayor, he ran a competition with a £100,000 reward for anyone who could successfully cool the London Underground. At the time the reward went unclaimed, I wonder if anything like borehole air con had been suggested?