HN Gopher Feed (2017-06-26) - page 1 of 10
Cooling the tube - Engineering heat out of the Underground
194 points by mzehrerhttps://www.ianvisits.co.uk/blog/2017/06/10/cooling-the-tube-eng...
eecc - 6 hours ago
For one thing I'm surprised they're not using regenerative brakes.
It sure will cost some of the profit but refurbishing the trains
with these will cut somewhat on that 80% of heat
k-mcgrady - 5 hours ago
>> It sure will cost some of the profitAll profits are re-
invested with TFL so I don't think cost (within reason) would be
a major concern.
FatalLogic - 5 hours ago
They are already using regenerative braking extensively,
according to this
lucaspiller - 4 hours ago
> It sure will cost some of the profitTfL isn't a private
organisation, they are a government body. In 2015/16 only half of
their costs were covered by ticket sales and other income
(advertising, sponsorships, etc). The rest comes from government
funding, so taxes.
Brakenshire - 1 hours ago
That's actually mostly not true any more. By next year day to
day costs will be 100% self-funded, only capital investment
will be funded by the state.http://www.mayorwatch.co.uk/govt-
franciscop - 53 minutes ago
The Tokyo (and Japan in general) underground/subway is actually
quite fresh and amazing in the hot summer. How do they do it? It
might be interesting to learn from them and a good question for the
Underground of London Engineers.
amoorthy - 2 hours ago
Interesting article. However I can't recall tube stations being
much warmer than outside temperatures in winter (on non-windy
days). If that's right then how is the heat dissipated better in
winter?I don't live in London so anyone with regular riding
experience please correct me if I'm wrong.
askvictor - 1 hours ago
When I was there it was definitely warmer than outside in winter.
Don't live there either mind you.
an_account - 1 hours ago
I was wondering that too. If they clay is able to cool off and
"reset" in winter then the real story is just that these lines
see more use today.
robotresearcher - 1 hours ago
The tube is warm in winter. It would be nice except you are
typically wearing a winter coat so it's hard to get it just
memracom - 43 minutes ago
Here is an idea that I sent to the Underground in 2006 when they
solicited suggestions from the public.Add cool to the tunnels,
rather than taking heat out.Build liquid air plants above ground, 2
or 3 floors up in the air so that the heat of the pumps is released
above street level and the noise can be kept away from the street.
Feed the liquid air into the tube tunnels through insulated pipes
which takes up far less volume than air vents. Let gravity bring
the liquid air down the pipes. Release the liquid into the tunnels
near platforms where the air pump effect of moving trains caused
lots of air circulation. Also the car doors open on the
platforms.Since you are liquifying the air, not just the oxygen, it
can be safely released anywhere in the tunnels. And if your air
intakes are high up you will actually be improving the air quality
in the tunnels as well, i.e. cleaner air flows in.
yev - 25 minutes ago
For those who also didn't know about liquid air: "Liquid air is
air that has been cooled to very low temperatures (cryogenic
temperatures), so that it has condensed into a pale blue mobile
liquid. To protect it from room temperature, it must be kept in a
vacuum insulated flask." (c) WikiPlan sounds great and very
ziikutv - 3 hours ago
Silly question, is the heat so low that it cannot be used for
something other than releasing above ground?
scotthtaylor - 5 hours ago
Elon Musk could probably come up with an answer to this whilst he
was out walking the dog :)
kator - 5 hours ago
Subways in NYC are not fun in the summer either. I always assumed
it was because when they were designed they didn't consider a
future state where air conditioners on the trains dump their heat
into the tunnel.I tried searching for a similar study for NYC but
all I found was old articles from years back.It doesn't look like
the MTA shares any measurements of temperature in their data feeds:
http://web.mta.info/developers/download.htmlDoes anyone have ideas
on how we could get this sort of data for NYC subways?
ice109 - 26 minutes ago
there is no way that the NYC Subway's AC's dumping heat into the
tunnels contributes in any meaningful way to the temperature
inside the stations - the tunnel system is enormous relative to
the trains. much more it's simply NYC summers are sweltering and
the stations aren't well ventilated at all.
CydeWeys - 23 minutes ago
Did you read the linked article? The heat of the London
Underground tube tunnels is directly caused by heat released by
trains (though primarily from brakes and friction, not AC), and
has nothing to do with season. It's swelteringly hot down
there in winter.I don't see why it'd be any different for NYC,
where I live.
tomohawk - 21 minutes ago
I wonder if using a different means of regenerative breaking would
work, such as hydraulic
more of the power would be preserved, leading to less heat.
mixedmath - 2 hours ago
I wonder, how long would they need to shut down the tube before
BillinghamJ - 50 minutes ago
Years, possibly even decades. The problem is that the clay just
doesn?t really release the heat - it?s very good at retaining it.
iamflimflam1 - 7 hours ago
More information available from the article's source:
pasbesoin - 6 hours ago
This is a much better and more thorough read.
OJFord - 3 hours ago
This is the much better article for this audience. The submitted
article is an expansion of tweets summarising this one.
hengheng - 4 hours ago
These are the first trains that I hear of with no regenerative
mschuster91 - 2 hours ago
The first generation of Munich subway trains (manufactured from
1967-1983) uses resistor banks for braking, so the energy from
braking goes right into heat.Only the later generation B and
the new C generation can move brake energy back into the grid.
mrec - 4 hours ago
> indeed, the use of regenerative braking now converts about
half the heat loss back into electricity. However, that can
only work where trains are accelerating and braking at the same
time, on the same electricity sub-station loop.Besides that,
Tube tracks often rise slightly at stations, so that trains get
a small gravity assist to both stopping and starting off again.
(Unfortunately it also means that hot air from the tunnels
tends to collect there, but you can't win 'em all.)
flai - 4 hours ago
That is a pretty cool way to implement regenerative breaking
that I honestly never thought of (even though the tram in my
hometown feeds energy in the grid when driving downwards)
crote - 4 hours ago
Correct me if i'm wrong, but it seems that regenerative braking
is a bit troublesome because it is a third rail direct current
system: a "regular" AC system can simply feed power back
through the transformers to the power grid, but this is not
possible here, so power must be consumed by another train fed
by the same rectifier.
mhb - 2 hours ago
You're not wrong: However, that [regeneraative braking] can
only work where trains are accelerating and braking at the
same time, on the same electricity sub-station loop.
hydrogen18 - 4 hours ago
It would be much more difficult to feed power back into an AC
grid from a regenerative brake. With a DC grid, no
synchronization is needed.
F_r_k - 3 hours ago
That's not true.1) modern railway is fully IGBT powered. In
this case it is trivial to inject current.2) with DC
current you need a substation capable of converting AC to
DC (easy: bridge rectifier) but also DC to AC (to given
tolerances) which is much more cumbersome.
Jyaif - 4 hours ago
The Montreal subway system has a very clever way of somewhat saving
energy (and emitting less heat): the section of the track at the
station stop is higher than the rest of the track. This means that
the train's kinetic energy is converted to/from potential energy
whenever the train arrives/leaves the station stops.
ant6n - 1 hours ago
I feel like in the long term, this may become a liability
compared to regenerative braking and level tracks.For example the
Montreal metro currently only allows a train to leave a station
when the platform of the next one is free, limiting the frequency
of this very crowded system. With modern signaling, trains can
creep up to the ones before them and reduce the time between them
down to 40 seconds - but it's more difficult with all those
slopes around.It's also making extending platform lengths or
moving/adding stations nearly impossible.
cnorthwood - 4 hours ago
The Tube does similar, with uphill approaches to stations and
agumonkey - 4 hours ago
I was wondering if this was used, especially for cars.
f_allwein - 6 hours ago
Related: tube map showing temperatures
kevin_thibedeau - 2 hours ago
So two lines just barely break 30C for a couple months in the
year. Not exactly a crisis.
estel - 2 hours ago
I believe those are temperatures in the actual tunnels, a
passenger's experience in a crowded tube car will be quite a
bb611 - 1 hours ago
Underground cars don't have AC/heat? At least in the US those
are ubiquitous on subways
poooogles - 1 hours ago
The deep level lines don't no. Only the sub surface cut and
cover style lines.
matthewmacleod - 1 hours ago
The deep level London tube lines would be difficult to fit
AC units to given the small size and tight tolerances.Newer
units on the subsurface lines do have AC fitted.
poooogles - 1 hours ago
In the cars it gets hotter , the humidity is what makes it
Roritharr - 6 hours ago
What is so "experimental" about the air coolers in the picture?
They look like normal A/Cs
pjc50 - 6 hours ago
The tube did not have powered A/C until fairly recently - it was
built with ambient air ventilation only.
avianlyric - 6 hours ago
And that A/C is only on cut and cover lines (circle etc) not
deep level trains.On deep level trains there is no good place
for the trains to dump the heat.
stan_rogers - 6 hours ago
It's not so much that the coolers are experimental, but what
they're doing with them is an experiment.
Symbiote - 6 hours ago
Normal air conditioners produce a lot of heat, which is usually
ventilated outside. That's more difficult to achieve deep
underground.According to Wikipedia, it's a groundwater based
ricw - 2 hours ago
I never got why the heat in the tube was not being used as a heat
source. You could extract the heat and supply it to surrounding
buildings at a cost, thereby cooling the tube. The tech is readily
available. It would be a win win situation. Plus it'd be be very
CydeWeys - 19 minutes ago
The problem is that the heat isn't a point source, it's diffused
across hundreds of kilometers of tunnel. The amount of
infrastructure you'd have to build to extract it at scale would
simply cost way too much. It's cheaper for any reasonable
timeframe to simply continue burning natural gas at the surface
for heat than to invest all of this into infrastructure at a very
adekok - 2 hours ago
If they don't have room available to get cool air/water down to
the tube, they don't have room available to get hot air/water up,
Tharkun - 2 hours ago
How much heat are we talking about? I'm guessing it wouldn't be
enough to use for district heating, the way some industrial waste
heat is converted to hot water for homes?
manmal - 1 hours ago
The original source  has a graphic at the bottom where it says
about 300m kWh per year currently, so about 34MW on average if I
f_allwein - 6 hours ago
> offered a prize of ?100,000 to anyone who could come up with
fresh ideasToo late now, but I wonder if they considered district
cooling, where e.g. cold water from rivers is used as an
alternative to air conditioning. Seems to be used successfully in
my hometown of Munich:
avianlyric - 6 hours ago
They have used water cooling from rivers in some stations (I
can't find the source, but I think it was a previous ianvisits
post).Unfortunately only a couple of stations have an appropriate
water supply, and enough free vertical shaft space to fit the
twic - 2 hours ago
There are some details on that in the Ian Visits article linked
to in another comment.There was also this, from 1938, although
i don't know where they got the water:https://en.wikipedia.org/
inetknght - 8 minutes ago
The article even mentions it!> Elsewhere, they?ve been using
cool ground water to cool some of the stations. An experiment
at Victoria station was the first, as water from the River
Tyburn was used to cool the air in the station. This was only
an experiment, but at Green Park, a permanent version was
installed in 2012.
bb611 - 1 hours ago
From the article in the top comment :> Elsewhere, they?ve been
using cool ground water to cool some of the stations. An
experiment at Victoria station was the first, as water from the
River Tyburn was used to cool the air in the station. This was
only an experiment, but at Green Park, a permanent version was
installed in 2012.
tonfa - 6 hours ago
> Nobody could think of anything TfL wasn?t already trying, and
the prize went unclaimed.I'd assume they did, especially if it's
something that's done elsewhere.
avar - 4 hours ago
I don't understand why lack of space above ground is a hindrance to
building new ventilation shafts. Surely these aren't going to be
wider than a sidewalk, and in central London the distance between
any two roads on a block is rarely more than 50-100 meters.You'd
end up with lots of ventilation grates on the sidewalks on the
surface, but that seems like an easy and space efficient solution.
eponeponepon - 4 hours ago
A substantial part of the problem is the sheer age of central
London; people have been digging beneath it and piling more
buildings on top of it for nearly 2000 years, so given any
particular spot in the Tube network, there's every chance that if
you try and drill upward from it, you'll hit part of the sewer
system, a buried river, someone's wine cellar, something top-
secret belonging to the state, a lost graveyard, a plague-pit...
l5870uoo9y - 4 hours ago
Is the temperature still rising or have it plateaued?
rwmj - 2 hours ago
And how long is it "stored" in the ground? If they closed the
tube for a week (I know) would the earth return to 14C?
TheOtherHobbes - 1 hours ago
No. I doubt anything less than a decade would make much of a
difference.It's taken a century or so to raise the temperature
in the tunnels by around ten degrees C. That already includes
the cooling effect of cold air being pushed into the tunnels
for most of the year, balanced by the relatively small number
of days a year when the air temp in London is more than
14C.Without that cooling heat has nowhere much to go. It will
radiate out into the air, which will make its way up and out
rather slowly. And it will diffuse into the clay/soil around
the tunnels, even more slowly.A fully passive cooling-off
period would take years - at least.The problem isn't impossible
to solve. All kinds of active cooling solutions are
possible.The problem is that it's impossible to solve
affordably. You effectively have to build a heat exchanger the
size of central London, which is never going to be cheap.
raverbashing - 6 hours ago
How much would it cost to add regenerative braking to the cars?And
instead of ventilation shafts you would probably need active heat
pjc50 - 6 hours ago
Regenerative braking is already widespread, as mentioned in the
article. Unfortunately some of the stock is very old.
zkms - 6 hours ago
tube... there already is regenerative braking on some cars, the
issue is that regenerative braking can't happen if there's no
train on the same section of DC bus that can accept the power.
There needs to be some sort of inverter to sink the higher DC
voltage and send it back into the grid.
Shivetya - 5 hours ago
why not incorporate storage in the car and discharge it when
launching from a stop. I am sure there has to be a little
onboard storage but it appears they need more if they cannot
discharge it. Isn't this ideal for ultra capacitors?it really
reads like the cars must be changed to fix the problem as they
are the heat source. so unless an economical means can be found
to store/discharge it between stations their only solution is
to cool the tube itself.So isolate the passenger area from the
tube area at all stations and force cool air from points where
you have easy access to cooling. the air flow would of course
move in the direction of trains. can that work?
Symbiote - 4 hours ago
Adding stuff to trains ("cars"?) increases the weight, which
means more energy is needed to move the thing. It also takes
up space, which is very limited.Some storage system near a
station (where there is more ventilation) could make sense,
but probably costs more than the system mentioned in the
IanVisits blog to return power to the city (i.e. convert the
DC the trains use back to AC for the city).I don't think the
isolation idea would work. Where does the air for people on
trains to breath come from?
robryk - 4 hours ago
Or you can just convert that energy into heat, but do that on
the surface. Have large resistor banks on the surface that you
connect to the DC grid when the voltage is too high.
raverbashing - 4 hours ago
That would be acceptable 100 years ago. Not today
robryk - 3 hours ago
Why is moving the place one dumps heat from below ground to
above ground not acceptable?
raverbashing - 1 hours ago
Because you can use it for something else other than
heating, like, putting it back into the grid, storing
(either battery, flywheel or supercapacitor).
jrockway - 2 hours ago
Why? Stopping the trains wastes energy regardless of
whether you dump the extra power into the wheels with
friction brakes or into a resistor bank. Dynamic brakes on
diesel trains already sink the power into resistors.
hydrogen18 - 3 hours ago
That would work, but a large flywheel would also be a good
solution. You could spin up the flywheel to store energy and
if it reaches maximum speed then use the resistors. You'd
also need to detect load on the grid and then run the
flywheel system in reverse to assist vehicles that are
late2part - 54 minutes ago
"run the flywheel system in reverse to assist vehicles that
are moving"Just to be clear, you wouldn't actually run the
flywheel in the opposite direction.. You'd take energy out
of the flywheel versus putting it in?
CydeWeys - 22 minutes ago
CydeWeys - 21 minutes ago
How about just batteries, or heck, large capacitor banks?
How much energy is recovered from a single train braking
MiguelHudnandez - 2 hours ago
If you can run wires all the way to the surface, you can sink
the power into the grid or traditional batteries.
zkms - 1 hours ago
You can do that, but you can also use it to power
accelerating trains that live on every other track section /
DC bus -- by inverting it back into AC and dumping that onto
the AC grid that's used to supply your rectifiers.
toyg - 6 hours ago
>The future of the cooling the tube project will be judged not so
much by how they cool the hot tunnels, but by how they stop tunnels
becoming hot in the first place.That's a very good metaphor for our