Hot, stuffy Tube trains will carry blocks of ice to cool down overheated commuters, under plans unveiled yesterday.

Engineers from London Underground are attempting to design the world’s first train carriages that will have ice units to ensure a supply of cold air when underground.

The “phase change” cooling system is one of several technologies that Tube managers hope will bring an end to hot journeys on the Underground network by 2012.

Adequate heat control has been a longstanding problem, and many passengers regard travelling on the Tube during the summer as an ordeal. A build-up of heat in the carriages, tunnels and stations is caused by the energy consumed by the trains and the warming effect of millions of passengers passing through the network each day. With the effects of global warming intensifying the problem of rising temperatures in cities, the Tube network has been under pressure to find new solutions.

Professor Geoffrey Liver-more, of the University of Manchester, told a media briefing in London yesterday that by the end of the century London can expect to be up to 11C warmer than surrounding areas.

London Underground’s £150 million Cooling the Tube programme has, over the past two years, attempted to identify new ways of preventing the trains and stations becoming so hot. The “phase change” system is one of several technologies that are being developed, and a trial carriage is to be built next year. If successful, the units will be installed on trains on the Piccadilly Line.

Instead of using conventional air-conditioning units that, while keeping carriages cool, pump hot air into the tunnels and stations, the ice-block system would emit heat only when the train was in the open air. It is based on a chemical process called phase change, in which a substance alters form from solid, liquid or gas, and absorbs or emits more heat that a simple rise or fall in temperature would account for.

Mark Gilbey, of London Underground, said that water, which converts to ice, was under consideration, but that another substance, perhaps a salt hydrate, could be selected instead.

When the train was under ground, whichever frozen substance was selected would be used to cool water, which in turn would cool the air. This cooler air would be blown through vents alongside every block of four or six seats.

Once back above ground, the substance, by now melted, would be refrozen and the heat extracted from it would be ejected — outside the Undergound network.

Mr Gilbey said yesterday that the cooling system would work best on trains that spent short periods, perhaps 20 minutes at a time, deep underground. For this reason the Piccadilly Line, which runs through North and West London, was identified as ideal.

He said: “We will make the trains a little cooler with this technology, but we aren’t promising the big chill. It’s not been done before — it’s pretty ground-breaking. We hope that over the course of the next year we will get the thing into a train and then on to the main railway.”

Conventional air-conditioning units will be incorporated into new trains that are introduced on lines that both run close to the surface and have ventilation shafts built originally for steam trains. The number of fans has also been increased.

At Victoria station a heat-exchange system is being tested in which air is cooled by water. If the trial is a success, surface water and water from bore holes is likely to be used for such systems at up to 25 of the network’s stations.

Kevin Payne, the director of Cooling the Tube, said that he was confident of significant improvements in heat control over the next five years.

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