Cooling London's Underground
As a frequent and longsuffering traveler on the 'Tube' and an Engineer (of sorts) I decided to single handedly solve the problem. I have in this page of the Alkalyn Website produced a combined Design Brief, Discussion Document and
Draft Plan for a Cooling System for London's Underground System.
The suggestions apply to the deep tunnels such as the Northern, Central,
Jubilee and Victoria lines.
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The problem is to be tackled
simultaneously at several levels. My 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 in the process of cooling the tunnels;
the use of underground storage of energy, in both forms, i.e. hot
and cold. see the *UTES section.
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COOL TUNNELS
In a basic system the coolth to be introduced in the tunnels themselves, ideally
mid-station. The first action should be to use passive methods before resorting to using refrigeration systems.
When a shaft exists between stations it could be used to inject fresh air. Large dampers can open when a train has passed and is receding from the mid-point shaft. Air would be sucked in to the tunnel. Much of the heat is generated in the tunnels during the braking and acceleration phases of the journey between stations. The heat is produced in the vicinity of the stations and is to be encouraged to exit from the station entrance.
There are often
sub-stations and Ventilation Shafts between stations and whenever
possible they should be used to introduce the colder air, either using a passive method based on dampers or fans. If a passive method is not possible or feasible then refrigeration plant should be installed. The shafts carrying
power cables or air vents are to be used to route the pipes to the
tunnels.
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THE PLANT
Conventional refrigeration and heat exchanger technology are to be used to
extract heat from the system. These are to be located
preferentially in some of the many power sub-stations. Use has to be made of the shafts and tunnels that
currently route electrical power to the tracks. If required air pressure
is 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 could utilise
fluid filled flat pipes but
where appropriate will 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 bulk could be a problem. Ice
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.
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RECYCLING and THERMAL
STORAGE
(UTES)
Heat removed from the tunnels and stations is to 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. Some testing will be needed to establish the principle.
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PLANT LOCATION
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 are to be used. An example is the large
unused substation void off the eastbound District Line platform at Embankment
station.
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ACTION - First steps
- Establish the extent to which the tunnels are
heating up. Install instrumentation to achieve this.
- Survey to identify which
sub-stations and Vent Shafts are suitable for installing the 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.
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THE FUTURE
Deep fast lines are to introduced with thermal performance and control
an early feature of the design. 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.
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BAD PRACTICE
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
Air
movement management can make a significant difference, particularly
during the early stages of the project.
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ADDITIONAL MEASURES
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 politician's
event horizon.
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Philosophy
When planning future underground systems and sub systems a strategic approach is necessary.
There must be co-existence with other systems.
Environmentally responsible approaches are the only ones to be considered. A Carbon Neutral transportation system is what is being aimed at.
The deep tunnels are becoming Cavern Thermal Stores. Over the years, there has been a steady build-up of heat in the ground surrounding the tunnels. We have suddenly discovered that the London Underground deep tunnels is becoming a massive UTES System. Currently the problem is working against us, however it should be possible to reverse the situation and start taking advantage of the large number of potential storage areas.
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Rationale
The summertime overheating on the Underground Transportation System or "The Tube" as Londoners know it as is not going to go away, we may be lucky and have a temporary reversal in the Global Warming trend but make no mistake the trend is up.
The demand for increased capacity is also trending upwards.
Energy costs will increase, at least for the foreseeable future
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Assumptions
The highest priority is to cool the tunnels, it is tempting to look at the platforms and public areas within the station, however only in exceptional circumstances should the initial effort be applied elsewhere.
It is incumbent upon us to recycle and utilise the thermal energy developed underground.
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Approach
A first step would be to halt the unnecessary generation of heat within the tunnels.
Where heat from stations and equipment rooms is entering the tunnels dump it somewhere else for the time being then work out ways of recycling it.
More efficient trains equipped with regenerative braking. see Griswold.
Improving the existing ventilation systems and other means.
A tried and tested system which is used on the Channel Tunnel is to place pipes on walls (ensuring adequate mounts). If brine is not acceptable then helium is a possible alternative working fluid. Flat tubes are the way to deal with the much smaller diameter tunnel used on the Underground.
UTES technology is an excellent match to the problem of cooling London Underground. Good fortune has provided opportunities in the shape of an abundance of unused tunnels and voids that lend themselves to roles as cavern stores. Simply applying tunnel air-cooling derived from winter temperature air to the deep tunnels and communicating tunnels and caverns will provide stored coolth which can be used to halt and reverse the root cause of the problem and into the bargain create opportunities to store usable energy.
Finally, a significant proportion of the 1.087 Terawatt Hours used in the past year (2004) to power London's underground rail system has become heat energy stored in the ground in the proximity of the deeper tunnels. There is a question about ownership of this vast store of energy. Will it benefit London's residents through cheaper heating, or will it go to large corporations or politicians or combinations of corporations and politicians - or simply go to waste.
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Suggestions and Comments
Suggestions
from my readers are welcome.
One of the main reason that the Underground is so hot is that the trains use
Rheostatic braking, i.e. the trains use the motors to generate electricity which is fed into resistors which dissipate the energy as heat (like an electric heater). Regeneration into the power supply is not very effective as the trains generally accelerate or brake at the same time, using electrical power all together and then generating power together. One solution I read about was using excess (or unusable) generated electrical energy to spin heavy flywheels, which would then be used to generate electricity when the demand returned (i.e. when the trains were accelerating). Whatever happened to this proposal - it seemed very sound to me.
--
Stay cool, Griz -
Stewart Grisman stewart.grisman(at)uk.transport.bombardier.com
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In some instances
large mobile refrigeration plants
vehicle-mounted or in containers. parked at stations or vent shafts - DE - August 2004
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Unused areas of the
Underground can in some instances be used as active heat sinks and others as locations for plant.
Long tunnels (there are many miles of such tunnels available) can have air
directed through them to form "coolth tubes" This is a passive
cooling technique. - DE - August 2004
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At terminals and perhaps at other points in the system trains could charge up with liquid nitrogen or coolant liquid to fill tanks
installed under seating and in other unused 'volumes' in the train.
- DE - August 2004
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Spraying the cars with water
before and after entry to the tunnels is another suggestion. - DE - September 2004
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When the trains are stationary
in the platform alternate open doors could be the target for a directed stream
of cooled air. The doors will change over at successive stations. - DE - September 2004
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Selective coatings would help to
dissipate the heat, There are smart materials available to achieve this (Tabor
et al). - DE - September 2004
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More effective use of the
relative difference of air velocity past the moving vehicle. At present the
opening of windows is the only method in use. I envisage scoops of some
description, although where and how escapes me - someone suggested open carriages? <g> - DE - September 2004
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An interesting
website has had a debate running on the subject. www.halfbakery.com contributors floridamanatee and jonthegeologist have come up with some very
good ideas.
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Some of the concepts in my proposals are unfamiliar to
non-technical people so we hope
that we can be forgiven for using this rather corny way of laying out my
plans. Hopefully it will be useful to decision makes. Comments Please.
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Bronze Plan: Placing refrigeration plant so that heat
from the tunnels is extracted at points between stations
Silver Plan: Using UTS technologies to store energy underground in the form
of coolth. Unused tunnels etc.
Gold Plan: In addition to concept used in the Silver Plan, storing heat acquired in
the summertime to heat living spaces of city dwellers, heating and cooling
offices and industrial premises.
| Plan |
Advantages |
Disadvantages |
Risk |
Comments |
| Bronze |
Immediately effective - Initial cost low |
Energy costs mount up in time --Thermal
Pollution. |
Low |
Do it NOW please |
| Silver |
Energy cost savings of 60% to 80% |
Up front investment required |
Medium |
Medium term feasibility. |
| Gold |
Efficient - Low carbon consumption |
Large educational effort - needs cooperative political atmosphere |
High |
Societal cohesion problem in Britain?? |
Are we likely to see a UTES based
Underground Cooling and Public Heating system in the UK?
One of the causes for pessimism that leads us to believe that a UTES system will not be considered seriously in the near future is that CHP or Combined Heat and Power systems have
poorly received in the UK, this is despite the fact that CHP can achieve a conversion efficiency of around 80%. Unfortunately Britain is poorly equipped to use such systems and as a result most of the energy used to generate electricity is lost to the atmosphere in the form of heat. In the UK attempts have been made to produce such systems but the necessary approvals and
commitments from government have not been given, a CHP system in London has been generating electricity for ten years but not a single calorie of hot water for winter heating has reached the consumers.
It needs champions who can promote ideas like UTES and CHP. Perhaps a celebrity like Bono can get behind it.
They are obviously not as glamorous or important as preventing children dying in sub Saharan Africa but surely preventing conflicts over energy is important. Not to mention the vast amounts of carbon dioxide kept out of the atmosphere and the consequent need for even more energy-hungry air conditioning systems.
Smart and subtle methods of energy conservation such as UTES and CHP are not the kind of ideas that are likely to get the attention of
current Prime Ministers and Presidents, but (hopefully) have an important part to play in the overall energy policy of a wealthy and 'advanced' country such as the UK.
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