London Underground cooling
Encyclopedia
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 47°C
(116 °F) were reported in the 2006 European heat wave
. Posters may be observed on the Underground network advising that passengers carry a bottle of water to help keep cool.
in the tunnels is generated by the trains (motors and braking systems etc.), station equipment and body heat from the passengers. About 80% of the heat comes from the operation of the trains, 15% from other equipment, and 5% from people—it is calculated that tube passengers account for about 56 gigawatt-hours of heat energy emitted on an average year.
Temperatures underground are slowly increasing as the ground around the tube tunnels warms up. When a new line is built, the temperature of the surrounding ground, and of the air in the tunnels, is about 14°C; however, unless the line has very high capacity ventilation, the air warms up as soon as trains begin to operate, and gradually transfers heat to the ground. Over about thirty years, the background temperature rises by ten or fifteen degrees.
Conventional brake
s on trains rely on friction
to slow the train down. This friction transforms the train's kinetic
energy into heat. More modern trains feature regenerative braking systems that can feed the energy from braking back into the power supply
. This means that the energy derived from braking is used somewhere else to power a train. This way energy is "re-used" and the amount of heat generated by braking is minimized. Another advantage is minimizing the amount of brake dust that is produced by the trains. This dust collects inside the tunnel systems; although it has been shown not to be hazardous to health in the quantities involved, it certainly detracts from the appearance of the tube.
Piston effect
Trains moving through the tight deep-level tunnels push air forward through the tunnels, and draw air down into the tunnels through stations and draught-relief shafts. This is called the piston effect
. This effect can produce a strong wind blowing though the tunnels and stations. The usefulness of the piston effect as a way of drawing air through the system varies from place to place, its key limitation being that it ceases to operate if trains stop moving.
Heat pump
s 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 London's 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.
A year-long trial of a groundwater cooling system began in June 2006 at Victoria station
. If successful the trial will be extended to 30 other deep-level stations. 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.
has been 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 have been proposed to cool Underground trains, most notably the use of massive blocks of ice inside the train. The blocks would be kept in refrigeration units, preventing them from melting completely.
trains will be delivered to replace the current A
, C
and D
stock trains on the subsurface Lines (Metropolitan, Circle, Hammersmith & City, and District). These will have standard air-conditioning, as the subsurface tunnels are large enough to displace the exhausted hot-air.
London Underground
The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...
can become very uncomfortable due to its deep and poorly ventilated tube tunnels: temperatures as high as 47°C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
(116 °F) were reported in the 2006 European heat wave
2006 European heat wave
The 2006 European heat wave was a period of exceptionally hot weather that arrived at the end of June 2006 in certain European countries. The United Kingdom, France, Belgium, Netherlands, Luxembourg, Italy, Poland, the Czech Republic, Hungary, Germany and western part of Russia were most affected....
. Posters may be observed on the Underground network advising that passengers carry a bottle of water to help keep cool.
Source
The heatHeat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
in the tunnels is generated by the trains (motors and braking systems etc.), station equipment and body heat from the passengers. About 80% of the heat comes from the operation of the trains, 15% from other equipment, and 5% from people—it is calculated that tube passengers account for about 56 gigawatt-hours of heat energy emitted on an average year.
Temperatures underground are slowly increasing as the ground around the tube tunnels warms up. When a new line is built, the temperature of the surrounding ground, and of the air in the tunnels, is about 14°C; however, unless the line has very high capacity ventilation, the air warms up as soon as trains begin to operate, and gradually transfers heat to the ground. Over about thirty years, the background temperature rises by ten or fifteen degrees.
Conventional brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
s on trains rely on friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
to slow the train down. This friction transforms the train's kinetic
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
energy into heat. More modern trains feature regenerative braking systems that can feed the energy from braking back into the power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
. This means that the energy derived from braking is used somewhere else to power a train. This way energy is "re-used" and the amount of heat generated by braking is minimized. Another advantage is minimizing the amount of brake dust that is produced by the trains. This dust collects inside the tunnel systems; although it has been shown not to be hazardous to health in the quantities involved, it certainly detracts from the appearance of the tube.
Piston effectPiston effectPiston effect refers to the forced air flow inside a tunnel caused by moving vehicles.-Cause of the Effect:Air in a tunnel is confined by the tunnel walls, hence the movement of air is restricted. In open air, when a vehicle travels along, air is being pushed and can move to any directions except...
Trains moving through the tight deep-level tunnels push air forward through the tunnels, and draw air down into the tunnels through stations and draught-relief shafts. This is called the piston effectPiston effect
Piston effect refers to the forced air flow inside a tunnel caused by moving vehicles.-Cause of the Effect:Air in a tunnel is confined by the tunnel walls, hence the movement of air is restricted. In open air, when a vehicle travels along, air is being pushed and can move to any directions except...
. This effect can produce a strong wind blowing though the tunnels and stations. The usefulness of the piston effect as a way of drawing air through the system varies from place to place, its key limitation being that it ceases to operate if trains stop moving.
Stations
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
s were trialled
Tottenham Court Road chiller
London Transport Board's experimental refrigeration plant was a chiller installed on the London Underground at Tottenham Court Road tube station. The plant was operational between 1938 and 1949....
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 London's London South Bank University
London South Bank University
London South Bank University is a university in south London. With over 25,000 students and 1,700 staff, it is based in the London Borough of Southwark, near the South Bank of the River Thames, from which it takes its name...
to develop a prototype; work began in April 2002. A prize of £
Pound sterling
The pound sterling , commonly called the pound, is the official currency of the United Kingdom, its Crown Dependencies and the British Overseas Territories of South Georgia and the South Sandwich Islands, British Antarctic Territory and Tristan da Cunha. It is subdivided into 100 pence...
100,000 was offered by the Mayor of London
Mayor of London
The Mayor of London is an elected politician who, along with the London Assembly of 25 members, is accountable for the strategic government of Greater London. Conservative Boris Johnson has held the position since 4 May 2008...
during the hot summer of 2003 for a solution to the problem, but the competition ended in 2005 without a winner.
A year-long trial of a groundwater cooling system began in June 2006 at Victoria station
Victoria station (London)
Victoria station, also known as London Victoria, is a central London railway terminus and London Underground complex. It is named after nearby Victoria Street and not Queen Victoria. It is the second busiest railway terminus in London after Waterloo, and includes an air terminal for passengers...
. If successful the trial will be extended to 30 other deep-level stations. For this trial Metronet
Metronet
Metronet Rail was one of two companies in a public-private partnership with London Underground.Metronet was responsible for the maintenance, renewal, and upgrade of the infrastructure on nine London Underground lines from 2003 to 2008. This included track, trains, signals, civil work and stations...
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
Sanitary sewer
A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
. The scheme was one of the winners in the Carbon Trust's 2007 Innovation Awards.
Tube trains
Conventional air conditioningAir conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
has been 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 have been proposed to cool Underground trains, most notably the use of massive blocks of ice inside the train. The blocks would be kept in refrigeration units, preventing them from melting completely.
Subsurface trains
In 2010, new S-stockLondon Underground S Stock
The S Stock is a class of sub-surface train currently being delivered by Bombardier Transportation in Derby to the London Underground to replace 177 existing trains on the Metropolitan, District, Hammersmith & City, and Circle lines, with a new fleet of standardised car design, totalling 191 trains...
trains will be delivered to replace the current A
London Underground A60 Stock
The A Stock is the type of train used on the Metropolitan Line of the London Underground. It was built in two batches by Cravens of Sheffield in the early 1960s. The trains replaced all the previous stock then used on the Metropolitan Line...
, C
London Underground C69 Stock
C Stock is the name given to the trains currently running on London Underground's Circle and Hammersmith & City lines as well as on the District Line between Edgware Road and Wimbledon...
and D
London Underground D78 Stock
The London Underground D Stock is a type of electric multiple unit used on the London Underground District Line . The entire fleet is due to be replaced with S Stock trains in 2015.- History :...
stock trains on the subsurface Lines (Metropolitan, Circle, Hammersmith & City, and District). These will have standard air-conditioning, as the subsurface tunnels are large enough to displace the exhausted hot-air.
External links
- The Underground Cooling Website
- Sustainable Cooling Schemes For The London Underground Railway Network
- Notes from Cooling the Tube Lecture 11 March 2008 - Kevin Payne Director of the Transport for London's 'Cooling the Tube' Program