The system will be fitted first at Victoria, one of the busiest Tube stations, and is expected to reduce summer rush-hour temperatures on Victoria Line platforms by between 5C and 6C.

Tube trains will push the cooler air along the line, bringing relief to the hundreds of thousands of passengers who endure sweltering conditions on the Underground.

With Tube passenger numbers approaching a billion a year, it is hoped that the cooling system will help to cut frequent cases of people suffering heat exhaustion on overcrowded trains.

The cooling system takes advantage of the Underground’s existing pumps, which prevent the capital’s rising water table from flooding the network. Water will be extracted from boreholes at a temperature of 14C and pumped to heat exchangers located in rooms between platforms. Fans will blow hot air from the stations across water pipes. The water temperature will rise by a few degrees as it extracts heat from the air.

The cooler air will then be blown back on to the platforms and the warmer water will be pumped into the Thames. At Victoria, where a trial of the system will begin before next summer, more than 200 litres a second will be drawn from the underground River Tyburn.

The system has been developed by London South Bank University, working with London Underground. Graeme Maidment, a senior lecturer in engineering at the university, said that the system was ideally suited to the Tube because ground water was most readily available in the deepest parts of the network, which suffered the worst overheating.

“London’s rising groundwater is the natural solution to the problem of cooling the Tube,” he said. “The water has to be pumped out of the system anyway and it might as well take with it some of the heat.”

Tube engineers have struggled for decades to find a way of introducing air conditioning on its deep, narrow tunnels, many of which were built in the Victorian and Edwardian periods.

Modern metro systems, such as lines recently opened in Singapore, have much larger tunnels. This allows air conditioning systems to be built into the ceilings and under the floors of trains.

Ken Livingstone, the Mayor of London, announced a competition last summer to find ways of cooling the Tube. He offered a prize fund of £100,000 for the most workable solutions.

However, nearly all the 3,400 entries from 60 countries were dismissed as either impractical or too expensive.

A London Underground spokesman said: “A lot of the suggestions involved passengers entering the Tube in various states of undress.”

In the short term, London Underground is giving away thousands of bottles of water at stations on hot days in the hope of keeping passengers hydrated during hold-ups.

Temperature rises in the deep tunnels because of the body heat emitted by thousands of passengers and heat from the brakes of trains. The heat cannot escape because there are too few ventilation shafts and the tunnels are surrounded by clay, which is a good insulator.

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