{{Short description|Temperature control on the London Underground}} {{Use dmy dates|date=August 2022}} {{Use British English|date=January 2013}} In summer, temperatures on parts of the London Underground can become very uncomfortable due to its deep and poorly ventilated tube tunnels: temperatures as high as {{cvt|47|C|F}} were reported in the 2006 European heatwave.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/england/london/5191604.stm|title=Baking hot at Baker Street|publisher=BBC News | date=18 July 2006 | accessdate=11 May 2010}}</ref> Posters may be observed on the Underground network advising that passengers carry a bottle of water to help keep cool.<ref>{{cite web|url=https://www.flickr.com/photos/anniemole/166070278/|title=Carry a bottle of water TfL poster}}</ref>
==Source of the heat== {| class=wikitable style="text-align:right; float:right" !Heat source !% |- |align=left|Braking losses||38% |- |align=left|Mechanical losses||22% |- |align=left|Drive losses||16% |- |align=left|Train auxiliaries||13% |- |align=left|Tunnel systems||4% |- |align=left|Station systems and passengers||4% |- |align=left|Train passengers||3% |- |colspan=2 align=left|Source: [http://www.plantengineer.org.uk/article-images/23757%5Ccooling.pdf Rail Engineering] |}
The heat in the tunnels is largely generated by the trains, with a small amount coming from station equipment and passengers. Around 79% is absorbed by the tunnels' walls, 10% is removed by ventilation, and the other 11% remains in the tunnels.<ref name=PE>[http://www.operationsengineer.org.uk/article-images/23757/cooling.pdf Cooling the tube] Rail Engineering, November/December 2007</ref>
Temperatures on the Underground have slowly increased as the clay around the tunnels has warmed up; in the early days of the Underground it was advertised as a place to keep cool on hot days. However, over time the temperature has slowly risen as the heat sink formed by the clay has reached its thermal capacity. When the tunnels were built the clay temperature was around {{cvt|14|C|F}}; this has now risen to {{cvt|19–26|C|F}} and air temperatures in the tunnels now reach as high as {{cvt|30|C|F}}.<ref name=PE/><ref name="Wired">{{cite magazine |last1=Temperton |first1=James |title=Why is London's Central line so hot? Science has the answer |url=https://www.wired.co.uk/article/central-line-temperature-london-weather-heatwave |access-date=1 July 2022 |magazine=Wired UK |date=28 June 2018}}</ref><ref name="Rail Magazine">{{cite news |last1=Stephen |first1=Paul |title=Cooling the Tube |url=https://www.railmagazine.com/infrastructure/stations/cooling-the-tube |access-date=1 July 2022 |work=railmagazine.com |date=3 February 2016 |language=en}}</ref>
==Cooling methods== ===Tunnels=== Heat is extracted from the tunnels using ventilation shafts, with air forced out of the vents by the piston effect (trains pushing air forwards as they pass through the tunnels) or fans.
===Stations=== [[File:Victoria Air Cooling close up.jpg|thumb|Air cooling on trial at Victoria station (Alternative picture)]] Heat pumps were trialled in 1938 and have been proposed again recently to overcome this problem. Following a successful demonstration in 2001 funds were given to the School of Engineering at the London South Bank University to develop a prototype; work began in April 2002. A prize of £100,000 was offered by the Mayor of London during the hot summer of 2003 for a solution to the problem, but the competition ended in 2005 without a winner.<ref name = why>{{cite web|url=http://www.london.gov.uk/londoner/05july/p4b.jsp?nav=news|archiveurl=https://web.archive.org/web/20070930184514/http://www.london.gov.uk/londoner/05july/p4b.jsp?nav=news|archivedate=30 September 2007|title=Why does the Tube get so hot|publisher=The Londoner}}</ref>
A year-long trial of a groundwater cooling system began in June 2006 at London Victoria station. If successful, the trial will be extended to 30 other deep-level stations.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/england/london/5058362.stm|title=Water pump plan to cool the Tube|publisher=BBC News | date=8 June 2006 | accessdate=11 May 2010}}</ref> For this trial Metronet installed London South Bank University's system comprising three fan coil units which use water that has seeped into the tunnels and is pumped from the tunnels to absorb the heat, after which it is discharged in the sewer system. The scheme was one of the winners in the Carbon Trust's 2007 Innovation Awards.<ref>{{cite web|url=http://www.carbontrust.co.uk/News/presscentre/2007/23407_InnovationAwards07.htm|title=Carbon Trust announces finalists for 2007 Innovation Awards}}</ref>
In July 2022 an experimental installation of panels cooled by water was installed on a disused platform at Holborn tube station. If successful, this system could be rolled out to cool the platforms of operational deep-level lines.<ref>{{cite news |title=London Tube cooling system trial for deepest lines begins |url=https://www.bbc.co.uk/news/uk-england-london-62172343 |access-date=22 July 2022 |publisher=BBC News |date=22 July 2022}}</ref><ref>{{cite news |title=TfL Is Experimenting With These Cooling Panels To Make Tube Temperatures Less Ridiculous |url=https://londonist.com/london/transport/tfl-tube-heat-cooling-panels-reduce-temperatures-holborn |access-date=22 July 2022 |work=Londonist |date=22 July 2022 |language=en}}</ref>
===Tube trains=== Newspapers are often discarded onto the existing air vents behind seats, which increases the problem.<ref>{{cite web |url=http://www.iaindale.com/posts/transport-ive-just-cooled-down-the-tube |title=Transport: I’ve Just Cooled Down The Tube! |website=Dale & Co. |first=Gareth |last=Knight |date=14 June 2012 |archive-url=https://web.archive.org/web/20120818050128/http://www.iaindale.com/posts/transport-ive-just-cooled-down-the-tube |archive-date=18 August 2012}}</ref>
Conventional air conditioning was initially ruled out on the deep lines because of the lack of space for equipment on trains and the problems of dispersing the waste heat these would generate. Different systems were proposed to cool Underground trains, including the use of large blocks of ice inside the train. The blocks would have been in refrigeration units, preventing them from melting completely.<ref>{{cite news|url=https://www.timesonline.co.uk/tol/news/uk/article1884626.ece|archiveurl=https://web.archive.org/web/20080705235938/https://www.timesonline.co.uk/tol/news/uk/article1884626.ece | archive-date=5 July 2008 |title=How do you keep a Tube train full of commuters cool? Just add ice|work=The Times| location=London | first=Lewis | last=Smith | date=5 June 2007 | access-date=11 May 2010}}{{unreliable source?|date=March 2013}}</ref>
Air-conditioning will be introduced on the deep lines as part of the New Tube for London, which is planned to replace the existing fleet of the Piccadilly, with options for replacing the Bakerloo, Central and Waterloo & City line fleets.<ref>{{Cite web|title=Improving the Tube – What we're doing – Improving the trains|date=n.d.|url=https://www.tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains|access-date=15 August 2021|website=Transport for London|language=en-GB|url-status=dead|archive-url=https://web.archive.org/web/20210815084031/https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains|archive-date=2021-08-15}}</ref>
===Subsurface trains=== In 2010 new S-stock trains were delivered to replace the A, C and D stock trains on the subsurface Lines (Metropolitan, Circle, Hammersmith & City, and District). These have standard air-conditioning, as the subsurface tunnels are large enough to displace the exhausted hot air.<ref>{{cite web|url=http://www.alwaystouchout.com/project/39|title=Subsurface network (SSL) upgrade|publisher=alwaystouchout.com|access-date=20 October 2006|archive-date=29 October 2006|archive-url=https://web.archive.org/web/20061029232900/http://www.alwaystouchout.com/project/39|url-status=dead}}</ref>
===More efficient braking=== Conventional brakes on trains rely on friction to slow the train down, transforming kinetic energy into heat. Older dynamic brake systems likewise work by converting the kinetic energy into heat via electrical resistors. More modern trains feature regenerative braking systems that can feed the energy from braking back into the power supply, minimising heat generation. This has the additional advantage of reducing the amount of brake dust produced by the trains.
==References== {{Reflist}}
==External links== *[http://www.undergroundcooling.com/ The Underground Cooling Website] *[https://web.archive.org/web/20061205061723/http://cibse.org/pdfs/Cooling.pdf Sustainable Cooling Schemes For The London Underground Railway Network] CIBSE *[https://london-underground.blogspot.com/2008/03/notes-from-cooling-tube-talk.html Notes from Cooling the Tube Lecture 11 March 2008] Kevin Payne Director of the Transport for London's 'Cooling the Tube' Program
Category:London Underground infrastructure