TfL is testing a world's first idea to cool the London Underground

TfL is testing a world’s first idea to cool the London Underground

The famous hot parts of the London Underground could become much more pleasant to use if a new way of cooling the tube proves effective, and if the money is found to install it in underground stations.

When tube tunnels were first dug, they were so cold that the fact that the tube offered respite from the scorching sun was a selling point in early advertisements. However, over the past century the cool clay that surrounds the tube tunnels has absorbed so much heat that it can’t absorb any more heat, and with nowhere for the heat to go, the tube trains have become uncomfortably hot to travel in travel.

Transport for London has been searching for a way to remove the heat for decades, and with such a large and varied network there would never have been a one-size-fits-all solution, and now TfL has a new idea to try.

Long-term readers of this website will be familiar with the tube cooling project, and also how cold groundwater from Green Park is used to cool this tube station.

The Green Park trial worked in that it cooled, but it turns out that the large ventilation units fitted above the platforms aren’t ideal for use in a live underground station. The main problem is one that anyone who’s been on a Hidden London tour will recognize – and that’s dirt. The tube tunnels are filled with dust and blown particles, and these clog the fans and ducts used in the cooling units. This means a lot more maintenance than is ideal, and being in a live train tunnel means a lot more work to safely climb up to the fans to clean them when the station is closed.

What was needed was a way to provide plenty of cooling with minimal ventilation.

About 5 years ago, TfL lead engineer Tony Ridley was asked to think about how to solve this problem, and after some brainstorming and computational design, he came up with an idea that was interesting enough to get internal funding for innovation.

What has been created is a curved metal panel unit that can be suspended from the ceiling of a subway station with a series of rectangular aluminum tubes running through them. The large spaces in the rectangular ducts are for pumping air, and the air is cooled by a cold water supply that flows through pipes built into the structure. A key innovation is that running the cold water in parallel to the airflow reduces dirt buildup inside the units.

Although the cooling panel could be fitted with a fan directly above it, as in the test unit, the ideal model would be to place the fans in a closet elsewhere and direct the air into the panels via ducts. The main advantage is that the cooling panel itself is pretty much an inert component, made up of just metal pipes, so there’s virtually no mechanical equipment to maintain overhead. This should and reduce maintenance work at height, maintenance personnel can perform work on fans stored in a closet in a more sensible location.

That’s the theory – but does it work?

Although a small-scale model was built and the theory modeled on computers, it wasn’t until they built a full-scale prototype in their Acton office that they could see if the theory matched. the practice.

And it exceeded expectations.

This was enough to move on to the next step, which is a live installation inside a subway station for testing. And the disused Holborn station platform is where TfL does tests like this.

The cooling panel demonstrator project was 70% funded by the Department for Transport and Innovate UK under the government’s TIES Living Lab scheme. Direct Engineering/INAL, based in Chesterfield, manufactured the cooling panel and OCL, based in Essex, installed it at Holborn station.

Passing through normally locked gates on the long disused Aldwych branch of the Piccadilly line, the empty platform is a little cooler as it’s not in use, but it’s still warm, and at the far end is find the test unit.

And the moment you walk under it, it’s as if you’re walking through a bubble of cold air. It is truly remarkable how the metal unit above our heads which has hardly any moving parts created a sheet of cold air that descends to the platform.

This unit comes with a fan for testing, the fan was turned on full power while I was there and it’s no surprise people tend to linger in the air a bit cold coming out of the device. Although it is not intended to blow cold air out of the unit in public areas, as it is only a test unit, there might be an option to do so if that was necessary. One of the test engineers confessed that he sometimes had to step away while checking the temperature readings in order to warm up a bit because the cooling is so efficient.

Tony said it was exciting to see his computer designs appear like a physically built machine in a subway station, though admitting he was more relieved than excited when it was first turned on and found to work. as expected.

The exhausted heat has to go somewhere, and since this is a test setup, the water cooling unit sits on the same platform in an empty cabinet for monitoring and returns the heat back into the platform. -form.

It’s indirectly useful, as a rule of thumb to know if something is cooling a room is not to stand in front of the fan, as they still feel good, but feel the heat being carried away at the other end. If the heat exchanger is actively removing heat, that is what cools a room or a subway station, and here the heat coming out of the heat exchanger is very noticeable.

So the system works.

But even in theory

They still need a fan to pull air into the unit, and that air will still contain dust, so they want to be sure the ceiling unit won’t get clogged with dirt. The air channels are large enough not to reach, but they must be certain. Also, if they clog, they have to check in practice how easy it is to clean with the TfL equivalent of a long duster.

Fans are still needed to blow air through the cooling panels, but to help reduce fan clogging, they’ve turned to the jet engine for inspiration. To reduce dirt intake, the fans only draw in about one-third of the air needed, and the airflow behind the fan is used to draw in the remaining two-thirds of the air that passes through the cooling panel. Current plans are to test the fans in a live tube tunnel for several months to ensure they cope with the dirty environment.

They also want to refine the design of the unit and determine what end-consumer finishes will make it more attractive in subway stations. It took a week to install that first unit, but lessons from that will be included in future models, and they expect the cooling panel installation to be reduced to a single weekend.

In the long run, unless something totally unexpected proves they aren’t working, these panels could be deployed on the tube array, providing much-needed cooling to insufficiently hot tube rigs.

One of the other niceties of the design is that it’s modular – so several of them can be hung along a platform rather than being in one fixed spot, and they have plenty flexibility in how they route air and cold water through the unit.

They also need to evacuate the heat from the station, and although standard water cooling units do the job and can be mounted on roofs to get rid of the heat, they would ideally prefer greener ways of doing this. This could see, for example, existing cooling systems being repurposed to use these cooling panels instead, and the heat could also be useful to people, such as the Bunhill Energy Grid which uses heat from the Northern Line Tunnel to generate electricity.

There are also opportunities to add new cooling equipment when stations are upgraded to support cooling panels. This is exactly what is happening at Knightsbridge station, which is being upgraded, and TfL has included plenty of cooling pipes in the new on-site building to make it easier to add a cooling unit to the platforms. shapes.

Knightsbridge was not chosen as the first possible live deployment simply because it is being upgraded, but specifically because it is on the Piccadilly line. Many new trains will arrive in a few years, and although the trains use about 20% less energy than existing trains and emit much less heat, there will also be many more trains running on the network. More trains inevitably means more heat, and how to deal with this is a key part of the Piccadilly line modernization project.

Although currently unfunded, TfL ultimately aims to increase the frequency of trains on the Piccadilly line to 33 and then 36 trains per hour. It is at this point that additional cooling at five stations on the Piccadilly line would be needed, according to TfL’s modelling. The five stations would be Knightsbridge, Green Park, Holborn, Leicester Square and Piccadilly Circus. TfL could then identify other places where the panels could provide an advantage.

What’s really good about this essay is that it’s based on an idea from someone inside TfL, who’s had the space to think about the issue and lots of support not just from the upper management, but also engineers in the field who saw an opportunity to try something innovative.

Unfortunately, at the moment there is no money to pay for the extension of the cooling system beyond the current trial.

However, if the trials end as hoped and the money is found, then a journey on the Underground could one day be as cool as it was for our Edwardian ancestors a century ago. Bring a sweater.

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