Talk:London Underground cooling

The beginnings of an interesting article: physicists, air conditioning, tunnelling etc engineers please contribute!

This promises to be a really interesting article and very significant over the next few years with environmentalism, Ken Livingstone's congestion charge, the 2012 Summer Olympics and media focus on London as 2012 approaches. Looking at it from the physics angle, please can you think about/address my comments:

I am reasonably sure the ground temperature in the deep tube is fairly constant summer to winter. Why don't the trains in summer 'cool' down much. Do they carry a lot of heat into the tunnels from when they were on the surface being heated by the sun?

What is the contribution from sun heating before they enter the tunnels?

Can (are) the trains painted in infrared reflective paint to reduce this?

How is the kinetic energy dissipated in regenerative braking stored? Does it go straight back into the power rails (I would think very inefficient) or is it stored perhaps in batteries which could also be used for train lighting perhaps?

The 50 gigawatts per day contribution from passengers confuses me and I think it needs looking at. If he refers to a period of time he should use energy. A power is an energy conversion rate so I would suggest it varies through the day peaking with the maximum number of passengers. Also at about 50 W per passenger, 50 GW needs 1E9 passengers to be using it at the same time, I don't think so.

The passenger heat loads are indeed wrong. The original source is a TfL press release titled "LU briefing on Tube heat and ventilation issues" from May 2005, which states:-

Each year the Tube's one billion passengers emit 56GW of heat each year and is equivalent to 63,925 100w light bulbs burning continuously.

As you say, the dimensions don't stack up but the additional data with the light bulbs gives a clue. The press release should have said 56 GWh each year (GWh (gigawatt-hour) is a unit of energy).

If you run 63,925 hundred-watt bulbs for a year, you use up 3925*100*365*24*3600 = 2.016e14J. One kilowatt-hour is equal to 3.6e6J: divide the first by the second and you get 56e6kWh, equal to 56GWh. On the basis of this, I'm fairly sure that TfL's press officer mistakenly wrote 'GW' instead of 'GWh'.

The external source referenced in the wiki article is The Londoner: Why does the Tube get so hot?, July 2005. Its author garbled the information even more, by changing 'each year' to 'each day' and '56 GW' to '50 GW'. Fortunately, he kept in the bit about running 63,925 hundred-watt bulbs continuously so they must be from the same source.

Annoyingly, I can't find any trace of the LU briefing on "Tube heat and ventilation issues" on TfL's website. It seems to have vanished. I'll alter the page to suit my interpretation, but if there's a flaw in the above reasoning, feel free to re-edit it.

Ecb 21:49, 6 February 2007 (UTC)[reply]

Actually I am not convinced that the human body heat is that significant down there unless you get stuck for some time in a crowded train. I think it is more to do with sun heating and hot air from the surface being sucked in?

Does the piston effect actually cool the trains much if not much air passes the trains? Perhaps there should be a more controlled change of air.

Certainly conventional air conditioners on the trains would just move heat from one place to another and add extra heat as well surely very wasteful.

The new section of the Jubilee line seems much cooler than the old tube lines, how did they achieve that? ChrisAngove 22:26, 22 December 2006 (UTC)[reply]

As far as i understand it regenerative braking can return electric energy into the power rails, but i read somewhere that it didnt really work since it interfered with the signalling system. Most of the energy probably comes from the trains. The traction motors and the brakes use up (and emit) a lot of energy. The tube moves about 1 billion ([million to be precise] which is almost 1E9) passengers per year, so the maths would work if all these people were moved in tunnels. The piston effect moves air, it doesnt seem to cool the trains. It can be used for ventilation Ysignal 18:08, 23 December 2006 (UTC)[reply]

I have tried to update this article by putting on a reference to a lecture given by - Kevin Payne Director of the Transport for London's 'Cooling the Tube' Program on the 11th March 2008 and full notes from people attending that very full lecture in London. It was somewhat demoralising to have the links initially immediately removed by someone who could not have spent more than two seconds looking at them. This article is clearly old and has not been updated for years. So I was only trying to make it up to date with something very relevant. On the one hand you ask people to contribute to the stub, on the other you initially delete their references. It is only because I feel passionate about the Tube that I put the link back and am pleased to say that is has remained. Thank you.