From Richard Durrant
The engineering ideas for cooling subways, particularly the London Underground, did not address the impact of the late afternoon rush hour, when temperatures peak (6 August, p 38).
I suggest a modified train sent to the hottest station carrying coolant – tanks of compressed air at about 20 megapascals. The expansion of this air would cool the surroundings and displace hot air from the station.
Technology for transporting compressed gas in lightweight containers is viable. The containers could be charged by compressors at a suburban depot at night using cheaper electricity. The heat of compression could be removed by cooling with water.
St Albans, Hertfordshire, UK
