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

TfL, to its credit, has made many efforts over the years to try to deal with the problem of hot tunnels, including attaching cooling panels to tunnel walls. The panels, which circulate water to remove heat from the air, were deployed in a trial in 2022, though they are not currently in use. Paul argues that such a system could be prohibitively expensive.

Hassan Hemida at the University of Birmingham says Paul’s water-cooling technology is a “good idea,” though it remains to be seen how much heat it could really remove from a real-life, busy Tube station full of people.

Certain railways simply push the boundaries of our ability to cool things down, says Hemida. He gives the example of super-high-speed trains traveling at, say, 400 kilometers per hour. They force air out of their way at high velocities, meaning the air pressure surrounding heating, ventilation, and air-conditioning (HVAC) equipment on the roofs of those trains can drop significantly. “Then, you cannot suck air into the HVAC system,” he says. Ultimately, that could cause the air-conditioning unit to fail. “I have been contacted by colleagues from China, and they want to find a solution for this problem,” Hemida adds.

More and more train operators are adopting air-conditioning systems as standard, though. London’s still relatively new Elizabeth Line features air-conditioning, for example. And a spokesman for Škoda Transportation, which recently rolled out air-conditioned metro trains in the capital of Bulgaria, says: “Generally, every vehicle we produce now is equipped with AC.” Sharon Hedges, senior engagement manager at Transport Focus, an industry watchdog, adds: “As people think about procuring new rolling stock, these are the kind of things that need to be uppermost in minds now.”

Heat waves are one thing in Britain. What about the Egyptian desert? German tech company Siemens is supplying Egypt with a new set of high-speed trains that can travel at speeds of up to 230 kilometers per hour. The firm’s Velaro trains are used in many places around Europe, but for Egypt, Siemens has really put them through their paces. Last summer, the company took one of the trains to a test facility in Austria and exposed it to unpleasant conditions, including temperatures as high as 60 degrees Celsius and high winds. “We are achieving 26 degree inside temperature at the hottest outside conditions,” says Björn Buchholz, head of HVAC and door systems.