Taking the heat

A low-cost air conditioning system could be the answer to London Underground’s overheating problems in the summer, its developers have claimed.

The system, which is being developed at Warwick University, comprises a tubular module with a generator at one end and a condenser and evaporator at the other. Inside the tube is a layer of carbon, capable of adsorbing gases such as ammonia at ambient temperatures, and storing them. When the generator section is heated, the gas trapped inside the carbon is released, and moves down the tube to the condenser, which rejects any heat in the gas turning it into a cool liquid that chills air flowing over it.

‘If you keep heating up the generator, it will drive out and condense as much gas as possible, and you will end up with the bottom section of the tube full of cool liquid,’ said Dr. Zacharie Tamainot-Telto, a research fellow in the civil and mechanical engineering department of the University.

If the generator heating is stopped, and heat is applied at the other end of the tube instead, the liquid will boil and release gas which will end up in the generator section again.

But as this would mean the system would only be able to cool the air intermittently, the researchers have developed a rotational device made up of around 30 modules, which allows continual cooling at one section and continual rejection of heat at another.

Since the device can use any heat source to produce a cooling effect, the researchers have been looking at developing a solar-powered unit for use in developing countries. And they have had interest from the car industry in an air conditioning system partly powered by heat recovered from an engine.

The team is currently developing a compact system that will be suitable for use in the limited space available on underground carriages.

London’s mayor, Ken Livingstone recently offered a £100,000 reward to anyone who could come up with a simple and effective way of cooling the carriages of the tube trains in the London Underground.

A spokesman for London Underground said the company had received a great deal of interest in Livingstone’s offer, but could not comment on individual suggestions. ‘We will be issuing more information shortly,’ he said.

But Professor Roger Kemp, the technical and safety director of Alstom Transport, which manufactures underground trains, said the answer to London commuter woes is simple – end unnecessary delays between platforms and improve ventilation of the system.

‘Installing air conditioning units on carriages in the deep Tube lines where the overheating problem is at its worst would be prohibitively expensive, while there is very little room to shoehorn in any more equipment’, he said.

‘The solution lies with the aerodynamics of tunnels and stations rather than anything you can do on the train.’