Station cooling works at two of London's busiest Tube stations was completed ahead of the London 2012 Games.
At Green Park the cooling is provided by groundwater drawn up from 80m-deep boreholes in the park, which is next to the station, while Oxford Circus relies on air-cooled water chillers on the roof of an adjacent building.
Morgan Sindall carried out the Green Park project, which involved installation of eight air-handling units (AHUs) on the platforms.
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.
This was the first installation of this type on the Tube, though at Victoria two platforms are cooled by groundwater that would in any case have to be pumped out of the station.
At Oxford Circus, where there were already air-cooling units in the ticket hall, Birse Metro expanded the scheme with 14 AHUs in the platform areas.
Existing rooftop plant was removed and structural steel-strengthening works carried out to accommodate new chiller units.
London Underground managed both projects using tight controls to ensure disruption was minimised and the accelerated schedule was met.
LU is introducing air-conditioned trains on its shallower sub-surface lines, but faces considerable challenges cooling the deep-level Tubes, which do not have much clearance between train and tunnel.
That means there is very little space for air-conditioning equipment inside or outside the trains, or for heat to escape.