How to Keep Subways and Trains Cool in an Ever Hotter World

As global temperatures rise, cooling underground trains and subway systems has become a pressing challenge, with existing infrastructure often exacerbating heat issues. Jonathan Paul, a researcher at Royal Holloway, University of London, highlights that London’s Tube tunnels, carved through dense clay, retain heat generated by trains, sometimes reaching temperatures as high as 42°C (107.6°F). Traditional air-conditioning on trains risks worsening tunnel temperatures by releasing warm air into these confined spaces. To address this, Paul is developing a novel cooling system that leverages groundwater, which remains at a cool 10°C, to absorb and carry away excess heat from underground stations. This approach involves pumping water from subterranean aquifers through heat exchangers installed above platforms, where hot air transfers its heat to the water, which is then gently circulated away. Paul and his team are testing this technology in a chalk quarry near Reading, simulating the conditions of the Tube tunnels. Their prototype has demonstrated the ability to reduce room temperatures by about 10