Keeping cool in the underground

It’s summer, and by the afternoon it’s often sweltering in London’s Underground.

In 1906 the tube was hailed as being “The Coolest Place in Hot Weather”. It had the ambient temperature of the surrounding subsoil, which was about 15 to 16 degrees Celsius. However the movement of rolling stock, working equipment and people using the lines emitted heat over time. This went into the walls and then into the subsoil, raising the ambient temperature and drying out the clay which reduced its ability to conduct heat away. Thus it was noticed after 20 to 30 years of operating the early deep level lines that the ambient temperature had slowly but steadily increased over that time. Since then, more passengers, more frequent trains and London’s role as a “heat island” haven’t helped. I have this from a talk by Kevin Payne, who in 2007 was appointed Director of the Cooling the Tube programme.

The situation is not just uncomfortable, it’s potentially dangerous. In 2003 a competition was launched by then London mayor Ken Livingstone for a solution. The prize was £100,000. None of the 3,500 entries were judged to be both original and workable. The more unusual suggestions included handing out ice-lollies, turning the Tube into an oasis, and using posters of snowmen to make people think of winter.

Offered solutions included fans, pumping cool water and melting ice. Trevor Bayliss, of wind-up radio fame, suggested a system where the two escalators from platforms were separated by glass and an extractor fan sucked hot air up one escalator while other fans blew cool air down the other one. Solar power would be used to power the fans. I wonder if the in-coming air would in fact also be warm in hot weather.

Heat pumps on the Underground were trialled as long ago as 1938. In 2005 a special team was set up by the underground authorities to investigate solutions. A trial was carried out at Victoria station where natural groundwater (which normally has to be pumped out of the tunnels) was pushed through a network of pipes into heat exchange units on the platforms, which sucked in warm air and pumped out cooler air. This would apparently only work in deep stations, and only if the water was uncontaminated (in case there was a leak).
New S-stock trains for the Circle, District, Hammersmith and City and Metropolitan lines will have an air cooling system when they begin running in 2009. These tunnels are large enough to displace the exhausted hot air. “Chillers” have been installed in the ceilings of some large ticket halls close to the surface, such as at Oxford Circus.
As might be expected, a number of (mostly private) applicants have offered solutions in published patent documents. I have no idea if they actually work, but it is interesting to see what sort of solutions they involve.

In 1940 Budd, an American manufacturer of railway cars, suggested in their US2251230 that the very motion of the carriages should be used to force air into ducts. The action of the movement of the trains moving through the tunnels pushing air is called the piston effect and can produce a strong wind, but apparently it has proved difficult so far to use this air movement to expel warm air and to bring in cooler air. Just opening the window at the end of a carriage has a useful effect, surely. An experimental carriage on the Central line was rebuilt with smaller windows on its sides with large air vents instead, and users apparently find it very comfortable.

In 2003 Thomas and Jonathan Ma of South Woodham Ferrers, Essex, applied for their “Method for cooling an underground rail network”, published as GB2404245. Their method uses fans in stationary trains at ends of tunnels after the system closes down for the night. Warm air would be extracted which would cause cooler air to enter from station entrances. This would surely give the same problem as in Bayliss’ solution: the air sucked in from station entrances would also be warm. Nor does it deal with the problems in the evening rush hour.
Armines, a French company, has applied for two patents which involve using a roof heat exchanger containing soft ice, in GB2421785 and GB2440290. London Southbank University is working on similar technology. Vivian Amourgam of West Hampstead has applied for a variation on the heat exchanger idea, by using liquid oxygen, with GB2406902.

Along the same lines, I have chosen as my Patent of the Month – without pretending that I understand the scientific principles, or how well it works  – a patent by Brian Stratford of Derby, who in 2003 applied for his “Air-conditioning for underground tube trains”.

This patent has been granted and is still in force. He has obtained numerous patents since 1953, at first on jets but later on such topics as solar energy, streamlined cars and trying to prevent volcanic explosions. Rather than trying to describe the invention, here is the inventor’s own summary on the front page:

An air-conditioning system for an underground tube train uses spherical pellets of ice 3 held in an ice box 4 for cooling the air. The ice is replenished at each station without delaying the train by delivering it through a pipe loop 2 in a carrier flow of water from the front end of the platform. Air from inside the railway coaches is cooled by the ice 3. This air is then mixed with air taken from outside the coach, either from the tunnel or from a station. The air taken will to a degree be heated. Ice enters the box 4 through an entry 5. When the box is full, bolts 6 close off the entry 5 and the water level is then lowered to the level of entry 5. The inlet air arrives at entry 7 and passes through a perforated plate 9. After travelling directly through the ice to be cooled, the air passes through a perforated plate 10 and an exit 8, and then on to various personal nozzles located in the railway coach. The ice box is below floor level. The rising air ducts each include a water trap to prevent water being sprayed into the coach. The ice may be covered by a flexible sheet.

Incidentally, what may be an urban myth suggests that those trains that are left outside on hot days before being run through the tunnels – or perhaps also those trains that run in the open as well as in tunnels – absorb so much sunshine that they cause much of the problem. If so, let us be grateful that the tops of tube trains are not painted black, which would increase the problem significantly.

Our Patent of the Month is provided courtesy of Steve Van Dulken from the British Library.  Steve is a patent specialist at the British Library and has his own blog at http://britishlibrary.typepad.co.uk/patentsblog/

Steve has worked since 1987 as a patents librarian at the British Library. Author of Inventing the American Dream, Inventing the 19th century and Inventing the 20th century, both popular science, and of British patents of invention, 1617-1977: a guide for researchers and editor of Introduction to patents information.