Can you keep Tube passengers cool? If you have a good idea London's mayor will give you £100,000. We asked inventor Trevor Baylis for his solution. Can you do better?
Where in the UK can you virtually guarantee it will be 32.5C (90F) every summer? On the Central Line of the London Underground.
Keep me cool and claim 100 grand
Temperatures regularly top 30C in the deep tunnels of several of the Tube's dozen lines, according to a survey conducted by Liberal Democrat shadow transport minister Tom Brake last summer.
If the rush-hour trains travelling through such temperatures were crammed with sheep - rather than sweating human commuters - such conditions would break European livestock regulations, Mr Brake said.
During the summer, signs are erected outside Tube stations warning passengers of the hazards of travelling in such temperatures and what they should do if they begin to feel unwell.
Since the flow of air around a moving train is the only existing means of cooling passengers, when carriages become stranded in deep tunnels, the ambulance service attends prepared to treat any victims of heat exhaustion.
99% perspiration requiring 1% inspiration
In mid-September 2002, 2,000 people were trapped on two Central Line trains for an hour, during which time three passengers fainted. A similar incident in July 2001 was described in an official report as a "near-miss" which could have turned into a "disaster".
London Underground has long grappled with the problem of how to cool narrow tunnels - some built more than a century ago - which lie up to 60 metres below London's busy streets. So far, no solution has been found.
Now a £100,000 prize is being offered to anyone present Mayor Ken Livingstone with an answer to tube passengers' summer woes. "But so far it has stumped everyone," says the mayor.
Trevor's on the case
Existing escalator shafts could carry cool air down to the tunnels and bring warm air up
A see-through barrier would separate the up and down escalators
A fan would push cooled air down with passengers descending the escalator
Cold air is heavy and would sink into the deep tunnels
Warm air is light and would rise out of the tunnels
A fan would draw warm air up the ascending escalator and push it out of the station
Solar panels could power the fans and air conditioning units
The main problems are; that the Tube tunnels are only just large enough to accommodate the train carriages with no room left for bolted on air conditioning units; and that even if the carriages were cooled down this could dangerously transfer the heat to the tunnels.
Sinking huge ventilation shafts would be prohibitively expensive and unpopular with people living above the Tube.
So what to do? BBC News Online asked inventor Trevor Baylis what he would do to give Tube passengers some relief.
"You don't need new ventilation shafts. You have escalators at many stations, you can use them."
Some of your ideas so far:
I suggest a practical, cheap and enterprising method of cooling the tube which would also work as a promotional tie-in with a frozen food company. The result - happy, chilled commuters, environmentally friendly cheap
advertising and free peas for every London Underground worker. How can it
Omri's peas, please
Omri Stephenson, London
Equip all passengers with personal breathing apparatus and flood the tunnels using water from ye mighty Thames. Passengers may need rubber wet suits to prevent electric shock, BUT an extra advantage would be a cheap source of stunned fish.
Rick Hough, UK
Replace those tired old tracks and trains with canals and gondolas. The cool water and slow pace of travel will make it much more pleasant.
Julian Burgess, UK
Each train should be equipped with an additional wagon that contains a large quantity of an extremely cold liquid substance (e.g liquid nitrogen or perhaps salty water) that has been cooled above ground. As the train pulls the wagon through the tunnels, air is forced through "radiators" (really coolers) built into the wagon that cool the air in the tunnels and heat the very cold substance. When the train arrives at the end of the line the cold wagon is switched or re-charged.
Gordon K. Chisholm, Italy
The concept is to maintain conditions in the train similar to those outside, ie not total cooling. But you mechanically ventilate platforms, provide a small amount of cooling in trains to achieve, say, 28C peak. The cooling works on the basis of thermal store, rejecting heat when above ground, and absorbing it below.
Graham Beadle, East Finchley
The main problem is with the trains rather than the platforms. My suggestion is that instead of transferring the heat directly into the tunnels, you have a tank of water for each train. Using the normal heat transfer mechanisms used in fridges, you transfer the heat from the train into the water. At each stop, you pump a bit of water out of each tank and replace it with cold water so that it is still able to absorb heat. You can then use the hot water in the toilets or pump it up to the surface and use it for showers. If this system was not efficient enough, you could use a fluid with a higher specific heat and a heat exchanger at the stops to convert the energy in the cooling fluid into heat in a water system.
Giles's piping hot solution
Giles Hogben, Italy
Partially flood the tunnel such that shallow underground river is created beneath the tube-train.The cool water will cool the tube system. (may be some electrical issues - not insurmountable) Tracks are elevated and allow for up to 18 inches of clearance. 6/9 inches of water would be more than sufficient in the flow area. Water feed pumps turned off in autumn in preparation for winter OR heat the water and heat the tube system when cold.
Paul's secret river
What about drawing air from pipes that run through the River Thames and then into much of the central tube network? This would take 'fresh' London air into the system and cool it too.
James Cozens, UK
A small cavity in the roof space of each cab would contain a network of liquid nitrogen filled pipes, the pipes would be finned to allow the air around them to be cooled, hot air would rise through vents in the ceiling and fall through ducts as cool air to floor level, convection would occur. The nitrogen would be re-filled as required.
Simon's liquid nitrogen cooler
Using cooling colours like deep blues and whites would create the impression of cool. Painting the walls and installing drinking fountains would help. Having certain areas with cool running water flowing down, i.e. a waterfall, would be far cheaper than installing huge fans, etc.
Brett Nicolle, UK
Pairs of shafts set at 45° from each other could be sunk from the street to the tube roof, within these shafts are unidirectional valves controlling the air flow. As a train approaches it pushes air in front of it, when that air reaches a tube that is angled in the direction of travel the air will be pushed up the tube and out through grating at street level. As the train passes the vacuum it creates could be used to pull air down the opposing shaft and into the tube helping to cool it. If needs be the direction of the vales could be computer controlled so that no warm air is returned to the tube by the passing of the train.
Richard's unidirectional valves
My idea has the dual advantages of being both cheap to produce, requiring only water and flavoured syrup, and thoroughly delicious. I'm sure all Tube commuters would agree, this is the way forward. I would therefore like to claim my £100,000.
Harry's lolly idea
Large scale vending machines at key stations selling (at low cost) frozen ice packs to passengers to take with them on their journey. This will give personal cooling, be a source of water in an emergency and take heat from the local environment. At the end of the journey the packs would be returned for re-use.
Peter Maggs, UK
Remove the ends of each carriage and replace with large fans. As the train moves through the tunnels, air flow would cause the fans to spin, forcing cool air through the carriages. Attach a flywheel to each fan and they would continue to spin when the carriages are stationary, keeping the carriages cool.
Cooling the carriages is the key to it all. The challenge is to exchange the heat into packs that can retain it without transferring it to the outside air. You could have a train that keeps the carriage cool and the heat transfers to special packs on the sides of the carriage. When the trains are in tunnels, they retain the heat. but when they move outside, or in areas where ventilation is better, they can expel the heat.
Gene Reynolds, UK
Jo's personal oscillating head fans
I'm sorry what's the big problem?
These people look as cool as cucumbers with their personal oscillating head
Jo Geary, UK
The Tube should have ice panels - like the ones you put in your cool box when you have a picnic. The panels could be removable to be used in the summer months only and placed in carriages and up escalators. Also why not employ 'cool officers' - say, students who are responsible for supplying free cold water to passengers. This significantly reduces body temperature you know!
Nia Jones, UK
Use giant heat sinks. Have a metal (must be good heat conductor) net attached to the roofs in the station and link it to the surface by a metal shaft. At the surface have another mesh that can be air cooled.
Flat heat exchanging fins fitted to the track giving the opposite effect to a condenser boiler. Please make the cheque out to D J Gregson, thank you!!