Welcome to the London Underground, or as any regular commuter will attest; Hell on Earth.
Its not just the constant delays or the crush of people, but during summer months
temperatures can reach upto 40 degrees Celsius.
So why is the tube so hot, and how can we cool it down?
The underground the only spot for comfort when the days are hot… well, at least back
in 1926 when this poster was commissioned.
Today, however, that’s obviously no longer the case, so what went wrong?
London is built on clay, which is an excellent tunnel building material.
Its soft enough to cut easily but also firm enough to support the weight of the buildings above.
It’s also pretty watertight.
However, it is precisely these properties which make it an excellent insulator. Just like a warm blanket during winter.
Because of the insulating properties of clay. About 80% of all the heat
thats ever been produced in the underground
remains trapped inside the walls.
Slowly, train by train, decade by decade, the London underground is heating up.
The first step in cooling down the tube is to make sure this heat doesn't get produced
in the first place.
Surprisingly, the almost 1.5 billion annual passengers actually contribute very little
to overall heat, with the majority being produced by the trains themselves.
A big train, travelling fast, has a lot of kinetic energy. Just like this spinning bike tire.
I'm going to slow it down by using friction from my hand.
This is just like brakes on a train. Although it works pretty well, it also produces a lot of heat.
As you can see in the infrared as the train comes into the station.
This is a wind-up torch to which I've attached a slightly wobbly wheel.
We're going to use it to slow the tire down again.
As it comes to a stop you'll notice that the light glows brighter.
That's because of a small generator inside the torch
which produces electricity as we turn it round.
This is whats known as regenerative braking. If we were to use it on the tube then we could cut back on lots of the heat being produced.
We can also store the electricity to use to get the train moving again.
You might think adding in air-conditioning to the cars might help cool them down, but actually
this could make the problem even worse.
Fridges, air cons, and other coolers work by taking heat from one place and putting
it somewhere else.
If you have a train, that somewhere else is in the tunnel right behind you – heating it up.
When the doors open this warm air rushes back in, while the cool air comes back out.
We need to find a better place to put this heated air. But wheres that?
Well, lets ask the world's greatest consulting detective.
This is the false façade of Leinster Gardens, made famous by BBC’s Sherlock.
On first glance appearance it appears to be completely ordinary, but closer inspection reveals some clues
as to whats really going on.
The doors have no door handles,
there’s no letter box, and the windows are painted on.
A walk along Porchenster Terrace reveals the lie of Leinster Gardens.
This hole opens out into a tunnel, through which runs the Metropolitan Railway.
As London’s oldest underground line, the trains that would have originally used it ran off of coal.
Holes like the one here in Leinster Gardens as well as in various other
locations along the route would have allowed steam and smoke to escape.
Most importantly for us, its also a great way to release excess heat.
You’ve probably noticed that as the train arrives at the station, it becomes really windy.
By making this train only slightly narrower than the tunnels it goes through, the whole
thing acts like a giant syringe.
If you pay attention, there are lots of ways in which air can escape.
It can go up vacant staircases. Out the same way as people. There are vents in the roof and on the platforms.
You'll even find a building or two which is just a giant air-vent.
All of these passageways means that the trains push hot air out and pull cooler air in.
Unfortunately, as we saw at Leinster Gardens, these shafts often take up a lot of space.
To have any real effect, you’d need to rip up so many buildings that you
might as well have an above-ground railway instead.
So far all of these solutions have either focused on cutting back on heat or getting it out.
into the environment as quickly as possible.
However, here at the Bunhill Energy Centre they've got a better idea.
A new heat-exchange takes in thermal energy from the tunnels below and converts it into electricity.
Some of the extra heat can even be used to warm people's homes.
The tube network has lots of empty stations and abandoned lines which aren’t in use
One way to use these is as reservoirs of heated air.
Which will retain their heat because
of the insulating properties of clay.
Then, in winter, this can be used to produce electricity and heat up people’s homes.
When this hot air is used up, we can fill it with cooler air from the winter outside;
releasing it during the summer months to keep the tube cool.
They say that hell will freeze over before you can find a seat during rush hour.
And while we may be waiting some time for either of those to happen,
at least the passengers tomorrow will be travelling to work a little more comfortably.