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Cooling London Underground (The Tube)

When the world's first underground railway system was conceived, the engineers did not anticipate that there would be a problem of heat build-up in the narrow tunnels . This is now a serious problem as air temperatures as high as 47 degrees have been recorded.

The problem is much more severe in the deep tunnels such as the Northern, Central, Picadilly, Jubilee and Victoria lines.

Since 2004 when our website was first created there has been the introduction of the Cooling the Tube Project with already some improvements being evident.

The rapid introduction of measures to cool the air within the deep tunnels of the London Underground is a still high priority. Summertime Travelers and staff of the London Underground Railway System still have to endure extremely unpleasant conditions.

A plan to return the air temperatures to bearable levels has to consider the age of the system and the escalating cost of energy. It has to be implemented responsibly and it has to be pursued over long timescales, and have sufficient numbers of people committed to the task.

A substantial part of the effort has to be committed to education of the decision makers;politicians, directors, managers and the public. Everyone concerned has to be aware of the size of the tasks and also the benefits of a properly engineered solution.

If we approach the 'problem' intelligently then we could simultaneously be cooling the Travellers and providing winter warmth for Londoners.

Engineers, inventors and those with ideas please feel free to contribute. We could even publish a tirade or two if you want to get something off your chest. Even those who have never suffered the merciless heat and crowding of a London Underground carriage in summer are invited to have a say. Silly and 'off the wall' ideas are welcome. 


The problem should be tackled simultaneously on several levels. Our suggestion for these are:-

  • Phase 1 - to focus on cooling the air within the tunnels.

  • Phase 2 - cooling other public areas of the system - in particular the station platforms.

  • Phase 3 - the environmentally responsible utilisation and recycling of existing energy and the heat generated by trains and Travellers and in the process of cooling the tunnels; the use of underground storage of energy, in both forms, i.e. hot and cold. see UTES



The priority is to reduce the temperature of the air and eventually the ground surrounding the tunnels.

Passive systems such as improving the basic ventilation should be pursued before anything else is tried, but it is almost inevitable that some more aggressive solutions using refrigeration plant will be required.

A basic (but in its simplest form a wasteful) system is one where dry, cooled air is introduced in the tunnels themselves, ideally mid-station.  There are often sub-stations and Ventilation Shafts between stations and whenever possible they should be used to install refrigeration plant. The shafts carrying power cables or air vents to be used to route the pipes to the tunnels.



The midpoint between stations is the ideal point to be introducing air from outside the system.

Simply by purging the tunnels with air in winter time will achieve a significant cooling of the ground around the tunnels.



Conventional refrigeration and heat exchanger technology can be used to extract heat from the system.

Located preferentially in the many power sub-stations.  Use to be made of the shafts and tunnels that currently route electrical power to the tracks. Air pressure is to be controlled to prevents leakage of the coolth back up through the shafts. In some locations plant could be installed at lower level and this may be necessary in central locations where there are no sub-stations/vent shafts or where other factors prevail e.g. real estate prices are prohibitively high. The heat exchange process selected for application of coolth can utilise fluid filled flat pipes but where appropriate is to use fan units or both. Brine filled pipes carry risks; potentially corrosion and electricity conduction problems. Helium could possibly be used as a working fluid, as could demineralised water but in both cases bulk could be a problem.  Ice or slush transported by compressed air is a technology that is being developed for South African Gold Mines but the technology may be inappropriate for this application. 

Ingenious suggestions such as using the pumped groundwater to carry the heat to storage are to be utilised wherever possible and are potentially useful in a number of locations. 



Heat removed from the tunnels and stations should be stored in the summertime and made available to use for domestic and industrial heating in Winter. Conversely the large number of unused tunnels and voids could be used to store coolth extracted from winter air, a saving of 60% to 80% of costs is theoretically possible using this method. (Sounds easy ????)

Aquifers, Borehole and Cavern Storage all to be investigated Gravel beds, too are a possibility. The abundance of unused tunnels is an obvious resource to be exploited as heat and coolth stores. Some investigation and testing will be needed to establish the principle.



As mentioned earlier there are opportunities for co-locating the refrigeration plant with power conditioning equipment and in locations previously used for power generation. Again the large number of caverns, unused tunnels and voids can be used. An example is the large unused substation void off the eastbound District Line platform at Embankment station.


ACTION - First steps

  • Establish the extent to which the tunnels are heating up. Install instrumentation to achieve this.
  • Survey to identify existing passive ventilation and how it can be improved upon.
  • Survey to identify which sub-stations and Vent Shafts are suitable for installing refrigeration plant and routes for piping to the tunnels.
  • Identify the areas where cooling is becoming urgent - Monitoring and survey.
  • Design of plant and systems, most components would be conventional but some aspects are likely to require special attention. 



Deep fast lines are to introduced with thermal performance and control of temperatures to be considered early in the the design process . UTES technology is seen by many as a new and untested technology and as such is likely to be passed over in favour of shorter term solutions, however we favour a UTEScentric approach particularly since significant energy savings can be achieved. If Carbon-Neutral status is to be achieved in the next few decades then it seems to be the only way forward.



Heat originating from stations and equipment within the stations should always be prevented from entering the tunnels. an instance of this is Bond Street Station where heat from equipment rooms leaks into the tunnels  (as at 2007)

Air movement management can make a significant difference, particularly during the early stages of the project. Many of the existing ventilation equipment is not fully functional and could be used much better.



Additionally a large number of small to medium scale measures can be taken to mitigate the problem, these however, should not be used as publicity exercises or spin to delay the action to a point in time  beyond the politicians event horizon. 

Suggestions from our readers are welcome see Cooling 3 Webpage for our own and our readers ideas. Silly ideas frequently evolve into solutions, so we are happy to  include ones that more sensible folk would discard. 

A large scale competition was recently organised by the London Transport authorities to come up with ideas for a solution. Our request for ideas unfortunately cannot be accompanied by a large cash prize



London Underground (LUL), uses a significant amount of its energy from renewable resources. Approximately 15% came from green power generation systems (2004).

3.5% of all of the energy used in London, went to power the underground rail system. In total 1.087 TeraWatt Hours were consumed. September 14, 2004


Cooling the Tube does not bring in more revenue consequently there has to be more pressure applied to the political and business gatekeepers to act in the interests of the public and London Underground staff.

      * Underground Thermal Energy Storage - a form of Interseasonal Energy Storage.

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