"The average temperatures on the Victoria line have risen by almost seven degrees since 2013 – nearly a *30%* increase.
Conversely, the increase in the average annual temperatures across all Underground lines from 2013 to 2024 was merely *seven percent*, placing Victoria’s temperature rise vastly above that."
Using percentages to talk about changes in non-Kelvin temperatures is crazy.
28 degrees Celsius is not 30% warmer than 21 degrees Celsius. This same stat rendered in Fahrenheit would say 70 degrees -> 82 degrees, or 17%. In kelvin it would be 294 -> 301, or 2.3%
Or we could invent a new measure indexed to Celsius but offset by 20 degrees, and declare a 1 -> 8 change, a whopping 700%.
You see the opposite effect with reporting on the DJIA, where a 500 point move is treated like a big event even though it's is not nearly as significant today as it was 30 years ago. They ignore the more relevant percentage change in favor of the more sensational representation.
That's not statistics as much as sensationalism. Every morning on WSJ at about 7am you'll see a 'live' update about how the markets and futures are in a 'selloff' or 'surging' even if the percentages are like 0.3% in either direction.
Even Kelvin is the wrong model. What we need is temperature, humidity and air speed to interfere anything meaningful. ISO 7730 is even more precise. Any meaningful discussion should use the models from there.
Yeah. It's obviously incorrect in the sense celsius has no meaning as an absolute temperature scale and so its not 30% more anything, but in terms of colloquial meaning the average Brit probably does see it as ~30% further along an indoor temperature scale from "someone put the heating on please" to "crikey, it's sweltering in here"
Feynman was complaining about this error appearing in textbooks back in the sixties[0].
The trouble (of course) is that Celsius properly is not a proper unit, but a "scale", or a "unit of difference" (equal to kelvin), or even torsor[1].
The trouble with the kelvin here is that if you see the 7 kelvin increase as a proportion of the 295K starting temperature the you only get a 2% increase. Nobody is going to buy your newspaper if you're putting up weak numbers like that.
To make matters worse, not all ranges and percentages on that scale are equal, whether they're the same in absolute or relative terms. Humans have a narrow relevant "operational" temperature band. Even 20 degrees between 10-30C feel like nothing compared to the 5 degrees between 37-42C.
Humidity in London is also awful as the temperature gets closer to freezing. I found the damp cold in London to be common over the year and truly horrid (a reason to never live there).
At home (Christchurch, NZ) we often get dry cold which can be pleasant: however when we do get the occasional vile damp cold I personally call it "London cold" because it made so much impression upon me in my 20s.
Your upper band of 30C is making this Englishman sweat just thinking about it. Which I think proves your point about narrow operational temperature even further.
You’re right in principle but that’s probably the worst example you could have given. So bad an example that I think it could easily be argued to disprove your point.
For us people not living in Arabia or South Texas the difference between 37 and 42 Celsius is indeed quite important. 37 feels pretty hot, but yet livable, while 42 (and even 40 for me) means that nothing non-urgent should bring me out of the house.
Indeed. At 3C in London, the humidity seeps into every pore and settles into your bones. Riding a bike at 3C, unless you're wearing a balaclava and a ski mask, is an exercise in pure pain, as the wetness sublimating off your face has approximately the same effect on your facial nerves as being flayed.
Ok the other hand, -2C in London is crisp and invigorating and entirely preferable in every possible way.
Where I live, the current daily temperature is between 33 in the morning and hits forty something mid day, so I have very recent experience with those 5 degrees, and I completely disagree with your assessment.
Difference between 10 and 30 degrees C feels, way, way bigger than 37 to 42.
One goes from straight up cold to quite hot, while the other just goes from very hot to even more very hot.
I bet you’re casually discounting the fact that you spend most of that time with 40+C temps in an air conditioned space.
At 42 degrees your body can’t cool down and this causes a lot of deaths or even the “casual” fainting described in the article due to hyperthermia. This goes way beyond your subjective feeling.
I think the whole thread is to show the Celsius scale in particular but temperature degrees have different impacts in different places in general, but especially in the range supporting human life. One degree can mean nothing or be the difference between being alive or dead, depending on where that degree is on the scale and maybe other compounding factors like humidity.
Talking about relative temperature differences without anchoring to an absolute reference is meaningless. Using percentages is even worse.
I'm with you: very hot to more very hot. I think the real issue in the fainting story is that he/she had to take their coat off. 42 is just not life threatening if one knows when to take one's coat off (and drink water).
There are few or no human scale situations where percentages of absolute temperature are meaningful, absolute zero is too far away and we live in a too narrow range of temperatures. Unless you're in a scientific context just don't use percentages on absolute temperature, only on rates.
People who complain about Fahrenheit vs. Celsius are correct to the degree (sorry) that the Celsius degree unit of difference is the standard in a lot of engineering calculations. But Celsius as a temperature scale is no more logical than Fahrenheit, which is arguably more practical for day to day use--and Kelvin is more likely required for a lot of engineering and chemical calculations anyway.
> But Celsius as a temperature scale is no more logical than Fahrenheit
Celsius is more logical:
(1) the endpoints of Celsius are boiling/melting point of water (at standard atmospheric pressure). The lower endpoint of Fahrenheit is the lowest temperature Fahrenheit could achieve using a mixture of water, ice and ammonium chloride-using the freezing point of pure water is more logical than using the freezing point of an ammonium chloride solution-water is fundamental to all known life, ammonium chloride solutions don’t have the same significance (and why ammonium chloride instead of sodium chloride or potassium chloride? of the salts readily available to Fahrenheit, the ammonium chloride solution had the lowest freezing point)
(2) Fahrenheit initially put 90 degrees between his two “endpoints” (ammonium chloride solution freezing point and human body temperature), then he increased it to 96. Celsius having 100 degrees between its endpoints is more logical than 90 or 96
(3) while for both Celsius and Fahrenheit, there is error in the definition of their endpoints (the nominal values are different from the real values, because our ability to measure these things accurately was less developed when each scale was originally devised, and some unintentional error crept in)-the magnitude of that error is smaller for Celsius than for Fahrenheit
(4) nowadays, all temperature units are officially defined in terms of Kelvin - and Celsius has a simpler relation to Kelvin than Fahrenheit (purely additive versus requiring both addition and multiplication)
(5) Celsius is the global standard for everyday (non-scientific) applications, not Fahrenheit, and it is more logical to use the global standard than a rarely used alternative whose advantages are highly debatable at best
> which is arguably more practical for day to day use
No, it is not. Americans say this only because they're used to it. The common arguments are that is that it is more precise, and 'you see temperatures from zero to one hundred degrees Fahrenheit throughout the year'.
Firstly, the problem with Fahrenheit is that its realisation is inaccurate by modern standards—which is why every single non-SI unit is now just an exact multiple of a corresponding SI unit with the same dimensions; the mediaeval and early modern definitions having been entirely forgotten. A bowl of salted ice and his own armpit? Truly an 18th-century invention.
Next, the extra precision that a difference of one degree Fahrenheit gives you is frankly useless. Within a single room one can experience a difference of over five degrees Celsius or more, depending on what's in the room—a radiator or air conditioner running, or the gas stove in a kitchen, or a high-end PC. Forget rooms. On the human body itself there can be a two to three degree Celsius difference between the extremities and the thorax/torso/head. Any field that requires extreme precision will naturally end up using SI units, so kelvin (or some related scientific unit). (Excluding the absolutely crazy bunch of American machinists who like using thousandths and ten-thousandths of an inch—at this point the joke writes itself).
As for climates, there are places that see very little difference in temperature, and definitely not the 'nice 0 – 100' range that Americans claim. Even in the US there are places like southern Louisiana and Florida that have borderline tropical climates, and don't really go below ~15 °C or above 35 °C.
All of this is not really logical either, and all end up being a manifestation of familiarity.
I'm not generally a Fahrenheit defender, but I think it's silly to deny the user-friendliness of having more integer values in the day-to-day temperature range, without going too far out of the two-digit measurement range. It lets you have a little more precision without being much effort to do casual math on. Milli-kelvin are far too small, a single kelvin is too big a perceptual range, and decimals are too annoying when we just want to talk about the weather.
I’m legitimately surprised by this idea - surely people in countries that use Fahrenheit don’t go around saying things like “Oh I thought it was going to be 54 degrees but it’s actually 55, so much different!”
I’ve grown up with Celsius and never felt the need to use decimals in day to day weather discussion… Many air conditioners let you go up by half a degree C and that’s more than enough precision, more than I’ve ever felt was necessary in everyday conversation.
1 degree F is right on the borderline of detectability, and in my opinion that's just right. FWIW I do make single degree changes to the AC reasonably often and notice the difference. That might be due in part to convection nonsense in my house, but that's arguably another argument in favor of that level of precision being useful in practice. I can believe centigrade-and-a-half works fine too, but that doesn't itself undermine the idea that F is kind of handy, with that tiny bit less bother.
Again, not saying F is great, just that that one minor advantage is in fact real.
Oddly the same system that's enamoured with measurements like "sixty-fourths of an inch" can't countenance the sort of witchcraft entailed in "half a degree Celsius"
Eighth of an inch is about the limit of precision in most circumstances.
Countries that use Imperial for day to day use still do tend to use metric for a lot of purposes including many engineering tasks. (Imperial is terrible for certain types of engineering calculations--especially involving pounds and lets not get into slugs--but it's fine for cooking even if I tend to use grams for weight on my scale when baking.)
"Imperial countries" are actually pretty hybrid for the most part to greater or lesser degrees. UK is more SI than the US but they still commonly use a lot of Imperial units including some "odd" stuff like stones.
I presume if you think eighths of an inch is good enough then you mostly work with large objects. Luckily outside of USA, Liberia, and Myanmar inch-based scales are rare nowadays, but I still come across specifications in small fractions of inches for such things as manufacturing tolerances, drill bits, coating thickness, cable diameters.
Informal measurement of humans and beer is a nice quirk of the UK system, but in my experience it's not commonplace to use imperial units for anything where accuracy is important (except maybe jewellers, and arguably road speeds/distances).
So why do those air conditioners go up and down by half a degree C rather than a full degree if people don't care about precision? Never seen an F degree thermostat do stuff in half degrees.
It literally doesn’t matter at all what’s 0 and 100 though. Honestly if you’re familiar with one system, the scale feels intuitive to you, and if you’re familiar with the other then the other one does.
Like people tell me that the US customary system is “more human scale and intuitive” but I literally cannot picture, say, 15 inches or ten feet - it just means nothing to me unless I mentally convert to centimetres or meters.
So much of these arguments boil down to “I grew up with this system so I can intuitively use it, so it must be superior”
> I grew up with this system so I can intuitively use it, so it must be superior
This is essentially every American argument for USC or Imperial units. In fact, there are actually legitimate reasons why some legacy units are superior—for instance the duodecimal or sexagesimal systems which have many more factors than the decimal. But every other argument is a variation of 'it's better because I know it better'.
0°C tells you the very practical information that it's freezing outside and that you must be careful, or you can expect snow. For F° you have to know the value by heart.
Zero is just as arbitrary as 32 but ever so slightly easier to remember. Anyone for whom that slight difference in remembering is actually a real impediment likely has other issues that require them to be under the care of others so it ceases to be relevant to them. At the other end, 100 vs 212 is of no practical use for anyone. Outside of the laboratory and manufacturing, people just boil water without thinking about the number associated with it. And in those settings, many other variables are tracked so the difference is of near zero consequence.
In case any of you are distilling your own moonshine, please be aware that at 350 kelvins (77 Celsius) you're likely to be getting methanol[0]. You should have the antivenom (ethyl alcohol, like vodka) on hand just in case.
Home distilling is great fun, and sometimes it's even legal, but please have an accurate thermometer and try not to poison yourself and others unless absolutely necessary.
(These temperate levels are also humidity and altitide/pressure dependent, if your still is in the high Appalachies then just listen to your heart.)
Amen to that. I wasn't trying to encourage anyone to try their hand on distilling without learning more about it.
Only highlighting that one can "humanly relate" to Kelvin-based temperatures. If one so wishes. And that "reference points" there needn't be any more "arbitrary" than for °F/°C.
> 0° C: It's cold outside but not really that cold.
> These things are the case for humans
Who says so?
0 °C is very cold by many people's standards. About half the human population lives within the tropics. In fact I'd like to see Americans walk around in the UK wearing just a T-shirt and bermudas when it's barely above freezing, and insist 'it's not really that cold, it's only 32 °F'.
Maybe this is the perspective of someone who has spent a lot of time in the northern US, but it's cold but really not that cold. I might even run outside briefly in bare feet in the snow. But, yes, get to 0 degrees F and you're in bitter cold territory although, of course it gets colder in the northern Midwest/mountains/etc. And my contractor has been in shorts and a T in 40s-ish weather this week.
The point is that F degrees seems a pretty human scale that doesn't usually need a lot of decimals or minus signs for routine purposes. That it doesn't correspond to a couple of water transitions at standard pressure/temperature is sort of irrelevant. Of course, I and many other people are perfectly happy with using Celsius/Kelvin degrees for various purposes.
When winter is coming, if it's 3 deg C outside, I typically don't need to worry about ice. If it's -3 deg C outside, I need to worry about ice.
When winter is waning, if it's been icy and it's -3 deg C outside, I typically don't need to worry about water on top of the ice. If it's 3 deg C outside, I typically do need to worry about water on top of the ice making it super slippery.
Again, it's not about where you live. 0°F is approximately the temperature at which the risk of frostbite becomes significant. 100°F is approximately the temperature at which the risk of heat-related illnesses becomes significant. Temperatures in between are far less hazardous to humans, even if the numbers near the edges are starting to get uncomfortable.
It would definitely be crazy in Fahrenheit, but in centigrade I think it makes some sort of intuitive (if not scientific) sense. (Together with the sea-level assumption we always make in casual temperature discussion anyway.)
Maybe because I was brought up with centigrade it makes more sense to me. The centigrade number is how far you are from water freezing. If it goes up 100% then you are twice as far away. I'm not aware that doubling the fahrenheit number has a similar easy to understand meaning?
> The centigrade number is how far you are from water freezing
The Fahrenheit scale is how far your are from your own body temperature. It was designed that 100 is the temperature of a human. (Adjusted later to 98.6 due to inaccuracies.)
0 was designed to be as cold as you can get with ice and salt (also ended up being slightly inaccurate).
> Maybe because I was brought up with centigrade it makes more sense to me.
Yup. People brought up on Fahrenheit think it is superior. For temperature neither argument is objectively better. (In contrast to imperial distance measurement with non-powers of 10 and factions, where there are good arguments against it, with temperature both scales are ultimately arbitrary.)
> For temperature neither argument is objectively better.
I think Celsius is objectively better in that:
(1) its endpoints–freezing and boiling point of water–are more natural / less arbitrary / more fundamental than Fahrenheit's–coldest temperature you can reach with salt and ice to average human body temperature. Water is a fundamental substance to all known life; the freezing point of pure water is much more fundamental than the freezing point of a water + NaCl mixture (actually apparently Fahrenheit used ammonium chloride not sodium chloride, which is arguably even more arbitrary than sodium chloride would be). If you imagine some extraterrestrial civilisation independently invents a temperature scale, they'd be more likely to come up with something close to Celsius than something close to Fahrenheit
(2) while both scales contain some error in that the nominal value of their endpoints differs from the real value, the error is greater for Fahrenheit
(3) According to Wikipedia, Fahrenheit didn't have 100 degrees between his two endpoints, he originally had 90 then increased it to 96 – given base 10 is the standard number base used by humans, 100 divisions is less arbitrary than 90 or 96
(4) nowadays, all other temperature scales are officially defined in terms of Kelvin – and Celsius has a simpler relationship to Kelvin than Fahrenheit does (for Celsius it is purely an additive offset, for Fahrenheit it involves both addition and multiplication)
(5) conforming to the global standard is objectively better than sticking with an alternative which lacks clearcut advantges
They're natural, sure, but not really natural in a way that directly affects the most common everyday use case for temperature: the weather.
Fahrenheit's 0-100 is for now approximately the range of "normal" weather for the continental US, which is a useful if accidental property for Fahrenheit as a weather temperature system. Celsius's use of water's boiling point as a value for 100 is a nice property from an aesthetic perspective but means that it doesn't use the full 100 degrees when representing any earth-based climate.
> (2) ... (3)
Both of these aren't really advantages if you treat the scales as arbitrary, which in either case you are for most real-world uses of either scale. Water's boiling point at sea level is totally irrelevant when you're measuring the temperature of the outdoor air, a human body, or a steak.
> (4)
Only matters if you're actually doing work that needs to translate to and from Kelvin, which most people will never do in their entire lives.
> (5)
Standardizing would be helpful for sure, but it's not obvious that it would be worth the headache of making the switch given that the only real advantage to Celsius for most use cases is the mere fact that it's a standard.
> Fahrenheit's 0-100 is for now approximately the range of "normal" weather for the continental US, which is a useful if accidental property for Fahrenheit as a weather temperature system.
Only if you live in the continental US - and even the continental US has parts where that generalisation doesn’t hold true. From a global perspective, there’s nothing special weather-wise about 0 Fahrenheit or 100 Fahrenheit-where I live, it has literally never been that cold (our record daily minimum is positive even in Celsius), while days of 38 Celsius or above are infrequent but far from exceptional. As a global standard, Fahrenheit has no meteorological advantage over Celsius - and indeed, Celsius is the global standard for meteorology, used by >95% of the planet
> Standardizing would be helpful for sure, but it's not obvious that it would be worth the headache of making the switch given that the only real advantage to Celsius for most use cases is the mere fact that it's a standard.
You are ignoring all the costs incurred by immigrants and international travellers having to learn to juggle two different systems in their heads, the obstacle it poses to international communication (e.g. “40 degree day” means radically different things in American vs Australian English), products having to support both units and then having configuration settings to change them, people being inconvenienced when they can’t work out how to change the units setting, publications forced to include both units to ensure all readers understand, etc. Those costs are ongoing and cumulative over time, whereas the cost of switching is a once-off which most of the world has already paid
Fahrenheit is about half the size of increments without decimals or fractions which, having grown up with it ,seems useful. Yeah, I kinda want to know about 32 degrees but that doesn't seem a huge cognitive load. Knowing sub-zero is fricking cold is a decent benchmark as is knowing that >100 degrees is fricking hot. Yeah, 212 degrees for boiling is a bit weird but don't really need that much and that's only at standard pressure anyway.
The slope of the scales has no bearing on whether percentages are meaningful here. The problem with both systems when it comes to percentages is that neither system has 0 set to a natural 0. This leads to an entirely arbitrary point on the scale where decreases in the unit will approach a 100% difference and then suddenly start decreasing again.
If anything Fahrenheit should be less insane because at least the artificial 0 is likely to stay much further away in the data they're quantifying so the percentages stay reasonable.
The slope of the Fahrenheit scale matches that of the Rankine scale.
I would still say that the in the Rankine scale percentage increases make sense, and Fahrenheit changes to not.
The thing that matters isn't the slope, but the zero point; "X% farther from absolute zero" is a useful measurement, "X% farther from an arbitrary zero point" is not. Especially when negative or zero temperatures are involved.
In both it makes a sort of intuitive sense. 7% of the way from freezing to boiling is a meaningful way to visualise temperature; 7% of the way from ice melting in a bath of salt to slightly above Mrs Fahrenheit's armpit temperature is also meaningful, although perhaps a little idiosyncratic.
Edit: this comment was deeply stupid for obvious reasons and I regret trying to interact with other people when I should be asleep.
The issue is a percentage of a Celsius value is not that. For example, an increase from 1°C to 2°C is a "100% increase", but is only 1 percentage point from freezing to boiling.
You could say things like that with anything in percentages? 100% increase in your pension from 100k to 200k is only 10% (increase, to 20% total) of your target 1M, or whatever.
100k to 200k is a 100% increase in absolute, but a 10 percentage point increase to your target of 1M. The difference between the example you give and the one in the article is that 0 in the case of your pension meaningfully refers to its emptiness, but in the case of Celsius, it has no "emptiness" interpretation.
The equivalent would be saying that going from 600k to 700k was a 100% increase... compared to 500k.
It's not completely meaningless, to be fair. Saying 10°C to 20°C is a 100% increase has the meaning of "it's twice as far from freezing", which isn't totally meaningless (kind of like saying Everest is twice as high as Mont Blanc, which really means "its summit is twice as far from sea level").
Yes? I didn't see any link in comment I replied to between 100% and 100deg besides it happening to be the same number - I already changed that to 1M, changing it to 50k no different either.
If the argument was saying there's something special about 100% being 100 quantity then.. no? I don't really know where to go from there, what I said still holds with a 100k target, but I'm not going to be able to give 'another' example where the 100 quantity is meaningful because it isn't for degrees either. It's the freezing point at 0 that makes it work better for centigrade than Fahrenheit, imo.
And they manage to make it even more crazy by also comparing it to average external temperatures.
==
The Victoria Line average temperature in August last year was 60% higher in temperature than the average external temperature that month, measured at 19.5 degrees.
==
Certainly for January it must have been hundreds of percent higher.
And what would the numbers be for e.g., the Moscow metro in winter months where the average outside temperature is negative?
Yikes. I posted this, and I missed that, something I realised soon into my first year physics degree lab. I learnt more than just dipping calculators in liquid nitrogen for fun.
Maybe the right thing to do is to measure from ideal room temperature? From zero doesn't make any sense but setting an anchor temperature makes sense.
This is done when people rate the efficiency of home heating: SCOP is a function of the heat pump's ability to hit a particular temperature, for instance.
I'd guess the baseline temperature on the tube should be 21C maximum. Percentages don't make sense here, but 7C over the target temperature (for instance) is pretty bad in those terms. I'd be surprised if TfL hadn't set that somewhere.
Also worthy of note is that it sounds like the tube is a prime source of heat for a district heating system. Win win, perhaps.
I don’t know if I’m worried about it. While the measurement makes little scientific sense it makes intuitive sense, and, importantly, the intuitive implications are the scientific implications.
It’s a huge increase, if not for the reasons they describe.
Is it? I think it puts the Victoria rise in perspective to the other lines quite effectively.
Everyone knows where the zero is in Celsius using countries anyway and days in the negative are so rare in the UK you can discount them (plus they are none inside the tube).
Looking at the temperature chart and the significant drop in 2020 during the pandemic, the source is certainly the trains and people themselves. (fewer trains moving, less heat added back then). At this point I expect the infrastructure is heat soaked and will need a prolonged period of cooling to bring temps down. i.e. don't expect instant results.
Moving more air through the tunnels, adding A/C systems - both have a problem of needing room up on the surface for blowers and compressors, something that is hard to do in modern London. Tough problem.
I wonder if they can carry hundreds of opened barrels of ice on open-bed trains through the tunnels at night, go slowly and let them melt to water (but kept in the buckets, because you don't want to flood the tunnels)...
I would expect them to already have some kind of drainage system, so if the line has some connection to some line that goes outside, just pulling cargo trains full of ice down there and dumping them might work.
That said, a typical shitty single-hose monoblock air conditioner has 9000-12000 BTU/h of rated cooling capacity. 12000 BTU/h is also known as "one ton". Sometimes, stupid units can be helpful, because "one ton" of cooling is what you get if you dump one ton of ice (short ton, of course) per day in the place. So you'd need a lot of ice, many tons per station, to make a significant difference.
Either way, since this is such an obvious idea, and they had a competition to solicit solutions, I'm sure this was evaluated and discarded - although it would be interesting to read the official analysis of the idea and learn why it wouldn't work.
Some parts of the London underground use passive energy recovery by locating stations nearer to the surface than most of the tunnel between them. Trains start by rolling downhill and when they approach a station, uphill.
The trains in London can be up to 50 years old at this point. Where the technology was available during the building of the trains, you can generally expect regenerative breaking. But it’s far from universally available unfortunately.
> If the line is unreceptive, braking energy is dissipated in on-board resistors
How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week?
Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels?
> Regenerated braking energy is transmitted to the London Underground high voltage distribution network
If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need.
(Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)
> Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels?
It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons.
1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid.
2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely.
3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions.
As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
Even with isolated segments, the measurements performed with Southern found 10% of regenerative power was turned into heat as the line voltage was already at max threshold from other trains; if that holds true today, then there’s still opportunity to consider optimizations for ensuring that 10% is weighted towards aboveground rather than below.
How exactly are you going to “weight” that 10%? Each segment is independent, you can’t “weight” the voltages, because that would require the ability to move power between track segments, which you can’t do, because then they wouldn’t be track segments anymore.
Additionally you’re making the assumption that line voltages are stable and constant, and can be tweaked as needed. They’re not, they’re some of the most noisy, electrically unpleasant power systems in the world, with voltage bouncing up and down as trains accelerate and decelerate, consuming up to a MW each under peak load.
Power distribution companies hate providing power to train systems because you need so much infrastructure to handle the noise and prevent the train line from seriously degrading the local power grid. The substation that connect train lines to the power grid are constantly having their switchgear trip in and out as the huge spikes in demand cause the equipment to momentary disconnect to protect downstream equipment.
So creating headroom for extra regenerative breaking isn’t a simple thing to do. When each train can instantly consume as much power as 10 households all maxing out their power supply, electrical systems stop behaving anything like “normal”.
These are all valid concerns. My goal was to highlight an opportunity for improvement that does not require capital equipment purchases. As you note, analysis may not reveal any opportunity for improving the regenerative controls. Given their inability to address the problem today, I expected they’d rather investigate a low-odds opportunity than disregard it. I was incorrect; I will raise my minimum-likelihood thresholds at HN in the future. ‘Simple’ was meant only in relation only to all other identified options, that each require non-zero capital expenditure and thus invoke the complexities of capital expenditure. It was not my intent to diminish the intricacies or difficulties of rail electrical engineering with my imprecise use of that adjective and I apologize for the disrespect inflicted.
The space on tube carriages is used for ... passengers. Unlike long-distance trains (where the locomotive is a rather sizeable unit of its own and has pretty much an electric substation of its own in it), the parts of a tube train reserved for driver, engines, electrical distribution are comparatively tiny.
How many watts of extra energy would be required to accelerate each kilogram of batteries on the train? Would the additional thermal load introduced by battery charge and discharge effects counteract or worsen the desired cooling outcome?
It may be better to install such batteries somewhere on each track circuit as fixed stations, that can vent their charging and dispersal heat away from passenger tubes, rather than mobile — assuming that onboard emergency power needs are already met.
> How many watts of extra energy would be required to accelerate each kilogram of batteries on the train?
That's not really the problem; the problem is there is _no space_. Ever been on a London Underground train? You certainly wouldn't want the interior getting _smaller_.
I'm sure they'd consider the worst-case scenario, and at present that's probably some serious arcing within a motor causing a fire. Cutting the track power (easily done by the driver) then makes that a fire that can be handled with water and/or foam.
Smoke from large batteries would be very hazardous.
To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids.
I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes.
If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques!
Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
Where there’s space, this has already been done. Unfortunately for many lines there simply isn’t space.
Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible.
TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.
The problem isn't so much space, iirc. It's that the blowers make a lot of noise and upset the residents, so they can't be run at full speed all the time.
The trains probably push a lot of air around. Wonder whether closing off sections with doors would help to push air out at one point and pull it in at others.
Possibly, but the pressure difference would pop people's ears, moreso than they do already. I'm sure the piston-like effect of moving trains is considered too to help move air around. Question is whether that's enough air movement to offset the heat generated by the trains, after all (and this is secondary school level understanding of thermodynamics), the energy needed to move the train is the train weight itself, plus track friction, plus air resistance. That is, in my head, it costs more energy to move the train than the amount of air that is moved around, so it in itself wouldn't be enough.
> Historically, the Underground infrastructure offered a respite from warm weather, indicated in Austin Cooper’s ‘It is cooler below’ poster, issued in 1924 by the Underground group to promote a more comfortable experience of travel during warm weather.
A century of burrowing commuter-worms unfortunately managed to bake all the beautiful wet clay that kept the tunnels tolerable when the sun was shining about.
It seems straightforward to me that it would be enough to rehydrate the ground. Just need (approximately),
400km of track * 25m average depth * 3m tunnel width * 20% moisture content of wet clay
= 6 billion litres of water
Sounds like a lot but it's only about 1/300th of the yearly flow of the Thames.
I don’t think the hydration of the clay is the important element here. Rather I suspect it’s simple just the sheer mass of clay, wet or otherwise, that’s involved.
There’s a reason why ground source heat pumps work so well. It’s because the ground is such a fantastically huge heat sink/source that in most scenarios we consider it capable of sinking or sourcing a practically unlimited amount of heat.
Unfortunately one of the scenarios where this breaks down, is when you stick a bunch of tunnels in the ground, then pump a crap ton of energy into those tunnels years round, and expect the ground to sink all the heat away. Turns out, if you do that, the ground itself starts heating up, and given that clay is a reasonable good insulator, it’s like wrapping all those tunnels in wool jumpers.
I would point out as well that all these tunnels are “deep level” tunnels running at an average depth of 24 meters and getting as low as 67 meters. The heat of the sun on the ground surface will have approximately zero impact on the tunnel temperatures. 24 meters of clay is a lot of insulation to work with.
My original comment was meant to be tounge-in-cheek, but I would like to add the advantage of wet clay is really in its thermal conductivity[0] which is roughly two to four times higher than dry clay. It will also have higher thermal capacity, so that high frequency fluctuations (like day/night) will be smoothed out.
(I don't think my comment implied that the sunshine makes it hot in the tunnel, only that when it's hot above ground it's nice to be cool below, like in the poster. And I did include a figure of 25m for average depth, I've spent enough time on their endless stairs to know that the TfL delved to greedily and too deep. This spiral staircase has 320 steps, I shudder.)
I think you are right. The graph at the bottom of the article shows that temperatures dropped around 2020 (presumably less traffic due to the pandemic).
So the ground can take up more heat, but it can't do it quickly enough.
<man walks into sauna room> Ooh, it's a bit hot in here! I better throw some water on these rocks to cool them down.
Joking aside, I actually don't know how dry it is in the underground, and therefore whether adding water for evaporative cooling would work. I would have assumed it was quite humid, but maybe not?
It would be if they tried cooling it with water, for sure; evaporative cooling would only work if there's enough airflow, else they'd just get 100% humidity so it would be both hot and humid.
It seems implausible to me that the clay is dehydrated. The Victoria line was only built in the 60s and has a waterproof lining. (It's also built with asbestos cement, unfortunately, which is no doubt a problem when they need to cut it for whatever reason)
The cement can negatively effect the water retenction of the clay, as does of course the temperature. The water needn't seep into the tunnel, just be moved away from it to adjacted areas.
As I see it, it is just a marketing problem with easy solutions.
There is psychology and reverse psychology. You could fool people into embracing the heat by redecorating the stations and trains to make it a 'journey to hell, via the centre of the earth'. The stops south of the river could be marketed as Dante's inferno and hellish.
Or you could go the other way, to make it kitch Hawaiian themed, so people expect the heat and to embrace it as a mini-holiday.
Or, the stations could be redecorated as if it were a trip to the Antarctic, so people see images of penguins braving the ice, with murals from the Shackleton days, to imagine they are cold.
In places like Moscow the underground train stations give the impression that people are in splendid palaces, this works pretty well. As I see it, TfL just need to up their decor game, problem solved.
In fairness, TfL ran a public competition to source cooling ideas some years ago, so the people whose day job is to explore all the possibilities clearly felt like they were out of ideas.
Unfortunately, hydrating clay is extremely hard to do. Clay is what you use as a water-tight material in dams, artificial lakes, waste dumps and stuff like that, because water doesn't really pass through it.
It was just a bit of a shower thought to be honest, but it looks like there are cleverer and more responsible people who've considered similar schemes.
Isn't heat free energy in a place like London? I know very little about metro systems so please correct me if this is insane: wouldn't the people living above the tubes be happy to get a heat exchanger (passive) or heat pump (active, but takes more of the heat) that prewarms their hot water supply? People still take warm showers and boil tea and rice/pasta in summer, and in winter the purpose should be obvious. If the water comes in at 30 instead of 10 degrees C, you need to add only a few degrees for showers and floor heating
A problem is the clay surrounding the tunnels insulates them - it traps heat because heat flows through it very slowly. So you drill down and put a heat exchanger pipe down there, you pump heat from 3cm of clay around the pipe and now no heat flows through the clay to your pipe even though there’s a lot of heat still down there.
Your pipe becomes a tiny worm of cold pipe in a big lump of hot clay and you’ve done very little to cool the underground or warm your water. That is, if heat moved easily through the stuff then the problem of heat buildup would be easy to solve but in that case heat wouldn't build up so there wouldn't be a problem; and vice-versa.
Yes but the only places we care about extracting heat are the tunnels, so you'd just run pipes through the tunnels themselves to extract heat. I think the bigger issue is the amount of energy needed to get the water down there and back up just means it doesn't make much sense on its own.
The catch here is the cost of the buildings you'd need to destroy in order to build the surface portion of the windcatcher. The deep underground lines run under heavily populated areas of London.
To build enough windcatchers to move the needle on tunnel temps, you'd need to buy many plots in one of the most expensive cities in the world.
Your are correct in principal, though implimenting your idea, now, is essentialy impossible as installing the plumbing after the fact might cost more than just starting over with a whole new line, and would in fact make things much worse durring the many years it takes to find out if the
added systems even work.
Given that there is only clay under London, it is by far better to start over and build a whole new line, and/or go all in on a mega high tech ,high pressure refrigeration systems for the human occupancy areas, and hope that there are no break downs in the "hot zones"
orrible mess
Heat is to energy as feces to food. It's not quite valueless by mass or by volume, but close enough that for most purposes the major issue is rejection.
Nice analogy, in hindsight only it’s in the name: waste heat. It takes the tiniest bit of impolite thoughts to make that lovely connection, thanks for that morning coffee bit of trivia.
Well, it's the human condition, once a day more or less whenever healthy. That's not only unpleasant, though! Also part of that condition is being a member of a species with the wit to invent soap.
>wouldn't the people living above the tubes be happy to get a heat exchanger (passive) or heat pump (active, but takes more of the heat) that prewarms their hot water supply
Ground source heat pumps are expensive to build, even more so in a dense area like London. So even if everything you said is true, I suspect the juice isn't worth the squeeze.
In this case, though, the excess heat is a major burden, so there is room to negotiate with a district thermal provider that pays that provider to absorb and redistribute the heat, as long as it's less than the cost to pump it out to the environment.
I'm not saying it's easy (it will likely be a bespoke solution). Given the organizations, I expect the difficulty to be as much business (setting the prices) and political (defending the prices set) as technical.
There is at least one on this line (north of Kings Cross) and one on the Northern line (north of Moorgate). It's for district heating or electricity generation.
The entire issue is that the earth surrounding the tubes is acting as a giant buffer. Enough heat has been dumped into it over the years that it has permanently warmed up. Draw heat from it during the winter to warm up homes, and it'll be able to absorb more heat from the tunnel air during the summer.
And because it's permanently warmed up, the long term consequence is the line becomes a health hazard and has to be closed for increasingly long periods.
When wet bulb > body temp people start getting heat stroke, which leads to fainting and potentially death - a bad look for a public transport system.
The likely remedy is to install gigantic refrigeration units in the ventilation shafts and pump in cold air. This will be hugely expensive to build and run.
But the alternative is a tube line that can't be used. So there may not be much choice.
It won't be zero so spreading it across enough people might already solve it. If that still leads to insufficient demand during the hottest weeks, idk, it's energy, surely there's something useful you can do? Store it for next week, pre-heat water for the nearest steam engine (e.g. gas power plants are steam engines running on methane, so if they have to heat the water by fewer degrees.. The problem will be finding a steam engine close to the heat source), supply it to an industrial process that needs temperatures above ambient (egg breeding for vaccine production? Idk), create electricity from the temperature differential between this system and the Thames water using the Peltier effect
I've surely got a too naïve view of economics but if the goal were to not waste resources then there will be things you can do before dumping it into the hot summer air
Indeed, the Department for Transport was renamed in 1997, and TfL followed suit in 2000.
There is a minor fandom controversy over the Ministry of Magic in the Wizarding World and whether the "Ministry for Magic" and "Minister for Magic" are valid alternate terms, but I have only identified one instance where JK Rowling wrote it this way, and it was outside the novels. Canonically, Harry turned 17 in 1997, so I suppose Tony Blair's reforms wouldn't apply post-Voldemort. However, Platform 9¾ is now "properly labelled" in the Muggles' King's Cross Station.
Travellers should also mind the gap between "TfL" and "TLF Travel Alerts", a defunct account which was part of Weird Twitter, and somewhere I hope I can dig up an archive, because the daily alerts were comic genius in 140 characters or less.
The arrival of Paddington Bear from Darkest Peru may be partly explained by the heating of the Tube stations. He surely would be right at home in a dark, humid and warm environment. My mother encouraged me to read about Paddington Bear, and in 2008 I was privileged to have a layover in Westminster, where I passed through Paddington Station and totally missed out on visiting the Paddington Bear statue therein. But I was able to purchase a refrigerator magnet bearing the "MIND THE GAP" official logo, which I presented to her in gratitude.
Of a special tube train with blocks of ice. You’d need to have various pits dug in, and pumps to drain the water. Yes water and power electronics is “fraught”.
I just like the idea of trains trundling along, blocks of ice being carted out and gradually melting.
Another idea is to move mechs-bots via Underground in a post-apocalyptic scenario, but that’s not so relevant here.
Make tram cars that sit on giant plates that straddle giant cuboids of ice, and rail beds that are like luge lanes, pulled along by overhead ropes. Have the water in the lanes flow at the ends into waterwheels that help drive the ropes as a primitive form of energy recovery, all driven by a power-take-off from a giant coal power steam engine on the surface that also serves to power a massive reverse-rankine cycle refrigerator that makes the ice blocks and slides them down into the tunnels - the gravity also helping pull the ropes that drive the trams. Of course, the massive coal plants are going to accelerate global warming, so you're gonna need to build more of these ice-cooled underground transit systems and even water chilled underground housing for people as the surface temperatures rise and rise....
And now you've got this wild 19th century Jules Verne-esque icepunk world in thermal runaway all built up for a hell of a novel-to-be.
But then they'd spend more energy (and more braking) hauling that ice around; would the amount of heat absorbed be more than the one ice train would generate?
There's probably more efficient materials to use, big lumps of supercooled metal. Someone else mentioned liquid air, that could just be evaporated in the tunnels and stations.
Of course, generating liquid air costs a lot of energy too. I'm sure the problem is easily solved if you assume infinite and free energy.
> The Senior Press Officer added that with many stations in close succession, the Victoria and Central lines experience frequent acceleration and braking, contributing to heat buildup within the tunnels.
I'm sure that this is probably one of those stupid suggestions that shows a lack of understanding of the problem, but could skipping stations help help this? Something like the following gets you 1/3rd less braking energy released into the tunnels:
Taking a look at the peak time schedules they have trains coming every 2 minutes, so this seems like it would be reasonable for most people to have to sometimes wait 6 minutes for the right train, but generally not more than 4.
Probably not, because the limiting factor on train throughput is remaining a safe braking distance behind the train in front. If the train in front of you has stopped at station D then you need to stop in station C even if you don't open the doors.
(You could get around that by running the trains further apart, but that would be a critical loss of capacity).
Right but the Victoria line puts a lot of effort into keeping station stop time to a minimum for the sake of capacity (it's the most intensive metro line in London, at 36-37tph, and one of the most intensive in the world). One way or another you have to space the trains out more to do skip-stopping.
With frequent trains and close stop spacing you've plausibly got a situation where each train is entering and leaving each station at about the same time? So skip-stop might not save much acceleration/braking.
I mean sure, less trains would help alleviate the problem (to simplify your proposal), but they still need to move all those people every day. Hence the 2020 reduction in heat increase, less people = less trains = less heat buildup.
> tunnel ventilation installations, chiller systems pumping chilled air into mid-tunnel shafts and regenerative braking to reduce heat generated by trains breaking
The hoops TfL jumps through just to not extend AC to the rolling stock in more lines are baffling. At least we finally got some AC in the new Piccadilly rolling stock.
I think AC net adds heat to the system, we just don't usually care because the hot end is outside. Here the hot end of an ac unit on the rolling stock would be in the same clay-insulated tube and not escape, so I think it would be a problem? They have to get the heat out of the underground and up to the surface somehow.
You can redesign the signalling systems etc to work at even 40C, plenty of countries do it. You can't redesign humans to feel comfortable inside a stuffy carriage at 35C.
Sure, but that means the stations will also have 40C air. Can the humans handle that? And it's going to be 42C the next year, 44C the year after, and so on...
What do you do if some incident halts full trains (possibly depowering them but for things like emergency lighting) near the midpoints of longer sections of 40 degC deep tunnels?
You can survive a few hours at that temperature, so not an immediate catastrophe. You should be still able (though not comfortable) to walk to the next emergency exit or station.
One key question is that with the construction of the Elizabeth line, and this being a known issue how was that designed and built differently to solve this problem, assuming it has fixed it.
Update:
There’s not a huge amount, but with careful search term tweaking I did find this on the Elizabeth line thermal loads:
I dont quite understand what’s stopping them from just buying hundreds of chillers, putting them on the surface close to each station, and running chilled water loops down. Other than cost of course.
They're running trains. Trains use a lot of electricity, and they turn almost all of it into heat. You'd have to have as much chilling capacity as the current electricity demand of the entire tube line, which is quite a lot.
However, if the buildings above were to sink ground source heat pump loops into the warmed ground to heat the buildings in winter, this would basically be what you just suggested, and would be a win-win situation.
Huh? Modern modular air cooled chillers go up to 800 tons each and can remove multiple MW of heat load continuously pretty much 24/7.
500 of them could remove 1.4 GW of heat.
Of course there are many ways to improve efficiency, but even assuming the worst case it’s still technically feasible to remove many times more heat than the line generates.
And where is the energy to power all of them coming from?
GP is saying that you can approximate the energy going into the system by looking at the electricity consumption of the trains, as all then energy is eventually going to end up as heat.
A heat pump can have a CoP topping out at 5. So 1 unit of energy needed to move 5 units heat out. That means a “net zero” cooling system would consume a minimum of 20% as much energy as the trains themselves. Realistically it’s probably closer to a CoP of 3.5, so 28% more energy. For something like the underground that gonna be a 5-10% increase in there operational costs at a minimum. Where does the funding for all that come from? And that before we even look at the capital costs of heat pumps and various ancillary equipment needed to run them.
As a point of reference TfL underground trains have an average power consumption of 140MW continuous. Now only about 45% of the underground is actually underground, but that’s still 63MW in just the underground parts. At an optimistic CoP of 5, that means 12.6MW of additional energy needed to cool the tunnels using your approach.
Wholesale electricity prices in the UK are something like 7p per kWh. So over a year that’s an additional £17m of electricity, just for cooling.
That's £17M of electricity, not including all the equipment, staff, installation costs etc.
To put this in perspective, Sadiq Khan already runs the system at a massive loss. They just about cover their operating costs at the momemt, and rely entirely on grants from the rest of the country to do upgrades of any kind. So cooling efforts have to be very cost efficient. Also the UK grid is very supply constrained. New nukes are being built but there have been the expected massive cost overruns and problems, so any large new energy demands in the UK just aren't happening anytime soon. It's actually been deindustrializing due to very high electricity costs.
Yes doing things at scale does cost lots of money. That often why doing the “obvious” is the wrong approach. When you’re operating at that kind of scale, small savings are still substantial, and scale often makes more innovative, less obvious solutions a better pick. Especially given the cost of exploring those options is so cheap compared to total cost of the project.
Also the underground is funded pretty much entirely by fares paid. Past UK governments have cut any tax payer subsidies for TfL to zero for day-to-day operational costs, and there’s zero indication that’s going to change any time soon.
I’m pointing out how shallow and unhelpful your comment is. I provided an analysis as to why a seemingly obvious solution has serious problems, you made an unhelpful comment that seems to suggest that commenting on the cost of a project means I’m confused about the political acceptability of a project, rather than the fact I’m trying to demonstrate why the obvious solution might have some problems. Which has nothing to political acceptability, but is simply a comment on the poor value-for-money that specific solution represents.
This problem is also an illustration of the potential of geological thermal energy storage.
The thermal time constant of a lump of matter scales as the square of its linear dimensions (for a given geometry). This can easily reach many years for large enough chunks of underground stuff. This is why geothermal energy works at all; the heat energy flowing up from the deep earth is stored for many thousands of years at reachable depths and can be mined. And, if one has excess energy, it could be reinjected underground as heat and later recovered.
I live in a country where summers are warm and winters are cold. One idea I've thought about is why we don't just have massive water tanks under our houses.
Energy can be dumped in during the summer for cooling, and taken out during winter for heating.
It would be more efficient that ground source geothermal as it's a closed loop system, so heat won't leak away.
My house needs around 2500kWh per year, so you'd need a tank of around 100,000 litres. That is 8x8x1.5 metres - basically a small basement. To get that energy out youd need to heat it to 60c in the summer, and it would cool to 30c in the winter. You could even do that with passive water flow, no heat pumps needed.
Or, you could flow heat transfer fluid through buried pipes and let the soil or rock around the pipes retain the heat. This is the idea behind geothermal heat pumps. The obstruction to doing this is cost.
Is there a reason why they can't drill a couple bowling ball sized holes at strategic intervals and put some high speed extraction fans in?
Stations entrances are open to outside so if you create enough negative pressure the hottest parts in the tunnels it'll pull in air. Do that long enough and presumably ambient & clay cools?
Presumably engineers dismissed this already, but why?
They have added ventilation to the tunnels, it's mentioned in the article. It's more than just a couple bowling sized holes, but apparently still not enough
Unfortunately, hydrating clay is extremely hard to do. Clay is what you use as a water-tight material in dams, artificial lakes, waste dumps and stuff like that, because water doesn't really pass through it.
I think people might object to TfL drilling a bowling ball sized tunnel in the middle of their house/garden/park/road/driveway/swimming pool/historic monument.
Remember the deep level network is some 23m down, and runs under buildings. At lot of it doesn’t follow roads, or have any kind of conveniently clear space on the surface above it.
Yep ... know people who commute on the Victoria and it doesn't sound fun. I've had to get it when my usual commute on the Northern line was impossible (only once, thankfully) and it was horrendous.
Why not look at it like a nuclear power plant and build a similar solution? You can reject gigawatts of power with one wet cooling tower.
If pumping water up and down that distance is infeasible, then make the primary coolant loop use a phase change refrigerant. Much easier to pump long vertical distances. Condensed fluid would flow down with gravity, evaporated gas would flow up.
> Temperatures hiked as high as 31.1[C] degrees in August 2024 [...]
So, I can imagine that this is a long-term problem, but it seems odd that the panic is setting in already, when some platforms in the NYC subway regularly exceed 40C / 104F every summer? This article seems in a similar genre to the breathless advice to remain inside in Britain when the outside temperature might get above 27C / 81F, otherwise known as a not-particularly-warm spring day in much of the US in most years.
> This article seems in a similar genre to the breathless advice to remain inside in Britain when the outside temperature might get above 27C / 81F, otherwise known as a not-particularly-warm spring day in much of the US in most years.
It’s really not breathless, because high temperatures and how to handle them is completely absent from the cultural baggage. I don’t live in the UK, but in a place which similarly does not have much in the way of high temperatures historically and low AC penetration, and during heat spikes I see a significant fraction of my neighbours with windows wide open at 4PM.
Habituation is also a significant factor. The UK does not get a smooth transition into higher normals, it gets heatwaves.
I live in the UK and a lot is down to the tabloid newspapers trying to get some sales with 'Horror Heatwave!' type headlines when it's 27C. Brits go on holiday to Spain, we are familiar with heat.
Statistically we know that humans who live somewhere that you'll just die in the regular environment due to climate behave very differently from humans who live in a temperate climate like the UK when the actual temperature warrants the same behaviour. If you live in Nunavut or the Iran / Pakistan border you already knew that you can just die from temperature extremes and so you need to ensure you stay at a survivable temperature, in Wales it's quite unexpected.
As a result you actually get many more deaths from extremes in countries where the usual climate is temperate like Britain, even when the actual temperatures aren't as extreme as in countries where that would be more common.
I'm only in London occasionally but I can confirm that some lines are unbearably hot, in the summer I have no idea how people commute in that heat every day. And I'm originally from a much hotter country than the UK.
Surely that says more about how NYC than it does about London?
If I had to suffer overcrowded trains with standing room only, people’s armpits in my face and all, at 40C temperatures everyday in the summer, then I wouldn’t be laughing at London for trying to avoid the same fate. I’d be complaining that my own city isn’t taking their problems seriously enough.
What if trains brought their heat with them instead of leaving it in the tunnels? I'm thinking some kind of large seal like thing in front of and behind trains that keeps the train surrounded by the same air. Stations serve as a spot to dump hot air and blow in cooler air. I guess the problem is it would take a lot of energy to push all that air around. Also the trains would be hotter.
That... Is a hilarious and good point. You could seal the stations like they do on the Elizabeth line but it's still a stupid idea. I just got back from London actually and am still incredibly jet lagged, for which I blame my suggestion
Oh, don't apologize. I cackled at the thought - what a commute! And for a way to cool off after being baked in the tube like a jacket potato, I can hardly think what'd work better.
Maybe something less extreme like a skirt that sits around the wheels and track and traps the hot air off the brakes. The regenerative braking mentioned in the article makes this easier as you can dispute the heat anywhere in the train you like, for instance some large dedicated heat sink car instead of the air in the tunnel
The Victoria line trains only stop briefly at the stations and are underground the entire time. For other lines TfL has air conditioning systems that capture heat during the underground sections and then dump it in the open-air parts, but that won't work for the Victoria line.
So if I have this right, TfL is constructing a giant thermal mass, and therefore is banking heat energy. If we (for example) piped cold water through this, we'd get warm water. So in winter, this could reduce heating bills substantially for people connected to such a system.
Actually it is. My house has radiant underfloor heating built into the concrete slab, and the water runs through at 30c. Keeps it a toasty 24c when it's -20c outside.
London had both water, and air pressure delivery systems embedded in the street scape to manage cranes at the docks, machinery and for letter delivery.
Heating and cooling benefits from remarkably small differences in temp. Thats how heat pumps work. And, lifting the input temp by only 5-10 degrees C can make a huge difference to the energy required to get to the next level.
It takes about 200Kj to heat 1L of water from 10C to 60C and 125Kj to heat it from 30C to 60C -A 37.5% saving in energy inputs. You better believe a corporate would seek a 1/3 reduction in energy input costs.
(my sarcasm meter is broken sorry if I ruined a joke)
Well, "had." That's just my point: how many trillions of pounds of attempting to navigate subsurface London will need to be amortized atop that 1/3 reduction in energy transport costs? Input is well and good, but if you don't think of where all that energy is going, you end up self-vitrifying the Victoria Line bore. And if the infrastructure of my own barely three-hundred-year-old city is too complex for a fiber provider to navigate in hopes of billing the $250/month we'd gladly pay at first - even a duopoly being preferable - then it's hard to imagine a successful modernization or installation of high-volume, low-temperature water transport infrastructure beneath London. Especially since with a small difference in working temperature, I believe you may need to construct a very large heat exchanger to get anything like continuous or even timely operation.
The line passes below some of the most valuable real estate in the world. Much of it commercial premises.
The line is itself a giant distribution system and is pretty much designed to retrofit pipes into.
The commercial premises would merely have to tap into something which is within a few tens of metres of their basements, and in some cases they very probably have access hatches already.
You are heating your working fluid to a temperature equal to what's ambient within the heat exchanger, which takes the longest possible time of any heating this exchanger can perform. (Think it over.)
For the exchanger to operate continuously - that is, to sustain outflow at final temperature equal to inflow at initial - this means you need a lot of piping, because however many CFM of water at 10° (or whatever) come in, you need to supply exactly that many CFM at 30° out.
All that piping takes volume, which has to be excavated out of the clay in which has been sunk the heat we're striving to remove. There's no moving that without some heat exchanger, after all. So we're still stuck expressing time basically as volume, which is perhaps the worst possible misfortune when working underground. (Caissons can be built and pumped dry, where earth must be dug.)
Perhaps you're thinking of a cooling jacket lining the tunnel bore. This would make sense but will only operate at a net energy cost, because to sustain livability you're going to need to exchange heat outside the system and supply, effectively, refrigerant. From plants all over town...
I suppose it's odd to use cubic feet per minute and degrees Celsius at once. I polled Gemini three times and received three unique answers varying only in relatively insignificant digits, so feel confident expressing the conversion factor thus: one cubic foot per minute is about half a liter per second.
Hopefully they would, sarcasm aside, but there seem to have been plenty of places than run cooling and heating against each other, my mind boggled in hearing that.
In the longer run, give up the old deep tube lines. They could be gradually replaced by Elizabeth Line-style tracks (larger capacity, fewer stops, good air conditioning).
Doesn't Elizabeth run even deeper than the current ones, though? Certainly seemed so in the elevators of the Whitechapel station. And it's not like you could replace the current lines without building the new one first and I bet there isn't too much empty space between the surface and the existing lines.
Yes. As somebody who has used dozens of metro systems around the world, it is literally the only one that is not ~room temperature. In the summer, it is so uncomfortable on the tube that I almost always take a taxi, even if a taxi is materially slower.
Why is the London underground so warm? Where is the heat coming from? Most underground locations are cooler in hot places in my experience. Is it just people?
Interesting. My question was one others had asked - so much so that the answer has it's own Wikipedia page with a table!
It looks as if regenerative breaking on the trains would fix the problem.
"The average temperatures on the Victoria line have risen by almost seven degrees since 2013 – nearly a *30%* increase.
Conversely, the increase in the average annual temperatures across all Underground lines from 2013 to 2024 was merely *seven percent*, placing Victoria’s temperature rise vastly above that."
Using percentages to talk about changes in non-Kelvin temperatures is crazy.
Yep. That 30% is a bad use of statistics.
28 degrees Celsius is not 30% warmer than 21 degrees Celsius. This same stat rendered in Fahrenheit would say 70 degrees -> 82 degrees, or 17%. In kelvin it would be 294 -> 301, or 2.3%
Or we could invent a new measure indexed to Celsius but offset by 20 degrees, and declare a 1 -> 8 change, a whopping 700%.
You see the opposite effect with reporting on the DJIA, where a 500 point move is treated like a big event even though it's is not nearly as significant today as it was 30 years ago. They ignore the more relevant percentage change in favor of the more sensational representation.
That's not statistics as much as sensationalism. Every morning on WSJ at about 7am you'll see a 'live' update about how the markets and futures are in a 'selloff' or 'surging' even if the percentages are like 0.3% in either direction.
Even Kelvin is the wrong model. What we need is temperature, humidity and air speed to interfere anything meaningful. ISO 7730 is even more precise. Any meaningful discussion should use the models from there.
But 28C or 82F is swelteringly hot in Britain so it kinda makes sense even it's incorrect.
Yeah. It's obviously incorrect in the sense celsius has no meaning as an absolute temperature scale and so its not 30% more anything, but in terms of colloquial meaning the average Brit probably does see it as ~30% further along an indoor temperature scale from "someone put the heating on please" to "crikey, it's sweltering in here"
This is not okay. If it makes sense for you, your sense for percentages is wrong.
Feynman was complaining about this error appearing in textbooks back in the sixties[0].
The trouble (of course) is that Celsius properly is not a proper unit, but a "scale", or a "unit of difference" (equal to kelvin), or even torsor[1].
The trouble with the kelvin here is that if you see the 7 kelvin increase as a proportion of the 295K starting temperature the you only get a 2% increase. Nobody is going to buy your newspaper if you're putting up weak numbers like that.
[0] https://mathematicalcrap.com/2024/03/05/the-feynman-story/ [1] https://math.ucr.edu/home/baez/torsors.html
To make matters worse, not all ranges and percentages on that scale are equal, whether they're the same in absolute or relative terms. Humans have a narrow relevant "operational" temperature band. Even 20 degrees between 10-30C feel like nothing compared to the 5 degrees between 37-42C.
Not to mention that wet bulb temperature, measuring the effect of humidity, is actually the most important measure in those temperature ranges.
Humidity in London is also awful as the temperature gets closer to freezing. I found the damp cold in London to be common over the year and truly horrid (a reason to never live there).
At home (Christchurch, NZ) we often get dry cold which can be pleasant: however when we do get the occasional vile damp cold I personally call it "London cold" because it made so much impression upon me in my 20s.
Humidity in summer is just as bad. At 30 degrees C London feels stifling hot because of the humidity
‘London cold’ can be found a bit north, in Auckland.
The only upside is that your lips don’t split in winter.
Your upper band of 30C is making this Englishman sweat just thinking about it. Which I think proves your point about narrow operational temperature even further.
You’re right in principle but that’s probably the worst example you could have given. So bad an example that I think it could easily be argued to disprove your point.
For us people not living in Arabia or South Texas the difference between 37 and 42 Celsius is indeed quite important. 37 feels pretty hot, but yet livable, while 42 (and even 40 for me) means that nothing non-urgent should bring me out of the house.
And, inversely, the five degree drop from, say, 3C to -2C represents means water can and will freeze, which is another massive change in livability.
Indeed. At 3C in London, the humidity seeps into every pore and settles into your bones. Riding a bike at 3C, unless you're wearing a balaclava and a ski mask, is an exercise in pure pain, as the wetness sublimating off your face has approximately the same effect on your facial nerves as being flayed.
Ok the other hand, -2C in London is crisp and invigorating and entirely preferable in every possible way.
I moved countries just so I can experience 20C weather instead of 30C weather. It is very noticeable haha
Where I live, the current daily temperature is between 33 in the morning and hits forty something mid day, so I have very recent experience with those 5 degrees, and I completely disagree with your assessment.
Difference between 10 and 30 degrees C feels, way, way bigger than 37 to 42.
One goes from straight up cold to quite hot, while the other just goes from very hot to even more very hot.
I bet you’re casually discounting the fact that you spend most of that time with 40+C temps in an air conditioned space.
At 42 degrees your body can’t cool down and this causes a lot of deaths or even the “casual” fainting described in the article due to hyperthermia. This goes way beyond your subjective feeling.
You right in the sense that I rarely spend more than 10 minutes in either 37 nor 42 degrees at a time.
I thought this thread was discussing the subjective feelings of temperature.
I think the whole thread is to show the Celsius scale in particular but temperature degrees have different impacts in different places in general, but especially in the range supporting human life. One degree can mean nothing or be the difference between being alive or dead, depending on where that degree is on the scale and maybe other compounding factors like humidity.
Talking about relative temperature differences without anchoring to an absolute reference is meaningless. Using percentages is even worse.
I'm with you: very hot to more very hot. I think the real issue in the fainting story is that he/she had to take their coat off. 42 is just not life threatening if one knows when to take one's coat off (and drink water).
42C is eventually life threatening naked if the humidity is high enough, especially if you’re in the sun.
It just takes a long time for your body temperature to increase, thus you have a while to find a cooler spot.
Then just don't use percentages, and rely on people realizing that a 7 degree difference is big!
There are few or no human scale situations where percentages of absolute temperature are meaningful, absolute zero is too far away and we live in a too narrow range of temperatures. Unless you're in a scientific context just don't use percentages on absolute temperature, only on rates.
People who complain about Fahrenheit vs. Celsius are correct to the degree (sorry) that the Celsius degree unit of difference is the standard in a lot of engineering calculations. But Celsius as a temperature scale is no more logical than Fahrenheit, which is arguably more practical for day to day use--and Kelvin is more likely required for a lot of engineering and chemical calculations anyway.
> But Celsius as a temperature scale is no more logical than Fahrenheit
Celsius is more logical:
(1) the endpoints of Celsius are boiling/melting point of water (at standard atmospheric pressure). The lower endpoint of Fahrenheit is the lowest temperature Fahrenheit could achieve using a mixture of water, ice and ammonium chloride-using the freezing point of pure water is more logical than using the freezing point of an ammonium chloride solution-water is fundamental to all known life, ammonium chloride solutions don’t have the same significance (and why ammonium chloride instead of sodium chloride or potassium chloride? of the salts readily available to Fahrenheit, the ammonium chloride solution had the lowest freezing point)
(2) Fahrenheit initially put 90 degrees between his two “endpoints” (ammonium chloride solution freezing point and human body temperature), then he increased it to 96. Celsius having 100 degrees between its endpoints is more logical than 90 or 96
(3) while for both Celsius and Fahrenheit, there is error in the definition of their endpoints (the nominal values are different from the real values, because our ability to measure these things accurately was less developed when each scale was originally devised, and some unintentional error crept in)-the magnitude of that error is smaller for Celsius than for Fahrenheit
(4) nowadays, all temperature units are officially defined in terms of Kelvin - and Celsius has a simpler relation to Kelvin than Fahrenheit (purely additive versus requiring both addition and multiplication)
(5) Celsius is the global standard for everyday (non-scientific) applications, not Fahrenheit, and it is more logical to use the global standard than a rarely used alternative whose advantages are highly debatable at best
> which is arguably more practical for day to day use
No, it is not. Americans say this only because they're used to it. The common arguments are that is that it is more precise, and 'you see temperatures from zero to one hundred degrees Fahrenheit throughout the year'.
Firstly, the problem with Fahrenheit is that its realisation is inaccurate by modern standards—which is why every single non-SI unit is now just an exact multiple of a corresponding SI unit with the same dimensions; the mediaeval and early modern definitions having been entirely forgotten. A bowl of salted ice and his own armpit? Truly an 18th-century invention.
Next, the extra precision that a difference of one degree Fahrenheit gives you is frankly useless. Within a single room one can experience a difference of over five degrees Celsius or more, depending on what's in the room—a radiator or air conditioner running, or the gas stove in a kitchen, or a high-end PC. Forget rooms. On the human body itself there can be a two to three degree Celsius difference between the extremities and the thorax/torso/head. Any field that requires extreme precision will naturally end up using SI units, so kelvin (or some related scientific unit). (Excluding the absolutely crazy bunch of American machinists who like using thousandths and ten-thousandths of an inch—at this point the joke writes itself).
As for climates, there are places that see very little difference in temperature, and definitely not the 'nice 0 – 100' range that Americans claim. Even in the US there are places like southern Louisiana and Florida that have borderline tropical climates, and don't really go below ~15 °C or above 35 °C.
All of this is not really logical either, and all end up being a manifestation of familiarity.
I'm not generally a Fahrenheit defender, but I think it's silly to deny the user-friendliness of having more integer values in the day-to-day temperature range, without going too far out of the two-digit measurement range. It lets you have a little more precision without being much effort to do casual math on. Milli-kelvin are far too small, a single kelvin is too big a perceptual range, and decimals are too annoying when we just want to talk about the weather.
I’m legitimately surprised by this idea - surely people in countries that use Fahrenheit don’t go around saying things like “Oh I thought it was going to be 54 degrees but it’s actually 55, so much different!”
I’ve grown up with Celsius and never felt the need to use decimals in day to day weather discussion… Many air conditioners let you go up by half a degree C and that’s more than enough precision, more than I’ve ever felt was necessary in everyday conversation.
1 degree F is right on the borderline of detectability, and in my opinion that's just right. FWIW I do make single degree changes to the AC reasonably often and notice the difference. That might be due in part to convection nonsense in my house, but that's arguably another argument in favor of that level of precision being useful in practice. I can believe centigrade-and-a-half works fine too, but that doesn't itself undermine the idea that F is kind of handy, with that tiny bit less bother.
Again, not saying F is great, just that that one minor advantage is in fact real.
Oddly the same system that's enamoured with measurements like "sixty-fourths of an inch" can't countenance the sort of witchcraft entailed in "half a degree Celsius"
Eighth of an inch is about the limit of precision in most circumstances.
Countries that use Imperial for day to day use still do tend to use metric for a lot of purposes including many engineering tasks. (Imperial is terrible for certain types of engineering calculations--especially involving pounds and lets not get into slugs--but it's fine for cooking even if I tend to use grams for weight on my scale when baking.)
"Imperial countries" are actually pretty hybrid for the most part to greater or lesser degrees. UK is more SI than the US but they still commonly use a lot of Imperial units including some "odd" stuff like stones.
I presume if you think eighths of an inch is good enough then you mostly work with large objects. Luckily outside of USA, Liberia, and Myanmar inch-based scales are rare nowadays, but I still come across specifications in small fractions of inches for such things as manufacturing tolerances, drill bits, coating thickness, cable diameters.
Informal measurement of humans and beer is a nice quirk of the UK system, but in my experience it's not commonplace to use imperial units for anything where accuracy is important (except maybe jewellers, and arguably road speeds/distances).
See also, the monstrosity that is AWG: https://en.wikipedia.org/wiki/American_wire_gauge
No one here is defending inches. In particular I don't think anyone is "enamored" with 64ths. We all agree they're a pain.
On the edges, absolutely. 66F is comfortable working temperature for me. 65F is too cold and I will start to shiver.
So why do those air conditioners go up and down by half a degree C rather than a full degree if people don't care about precision? Never seen an F degree thermostat do stuff in half degrees.
> As for climates, there are places that see very little difference in temperature, and definitely not the 'nice 0 – 100' range that Americans claim.
That's not really the point.
0° F: It's cold outside. 100° F: It's hot outside.
0° C: It's cold outside but not really that cold. 100° C: Dead.
0 K: Dead. 100 K: Dead.
These things are the case for humans regardless of whether you live in a place that actually gets cold or hot outside.
It literally doesn’t matter at all what’s 0 and 100 though. Honestly if you’re familiar with one system, the scale feels intuitive to you, and if you’re familiar with the other then the other one does.
Like people tell me that the US customary system is “more human scale and intuitive” but I literally cannot picture, say, 15 inches or ten feet - it just means nothing to me unless I mentally convert to centimetres or meters.
So much of these arguments boil down to “I grew up with this system so I can intuitively use it, so it must be superior”
> I grew up with this system so I can intuitively use it, so it must be superior
This is essentially every American argument for USC or Imperial units. In fact, there are actually legitimate reasons why some legacy units are superior—for instance the duodecimal or sexagesimal systems which have many more factors than the decimal. But every other argument is a variation of 'it's better because I know it better'.
0°C tells you the very practical information that it's freezing outside and that you must be careful, or you can expect snow. For F° you have to know the value by heart.
Zero is just as arbitrary as 32 but ever so slightly easier to remember. Anyone for whom that slight difference in remembering is actually a real impediment likely has other issues that require them to be under the care of others so it ceases to be relevant to them. At the other end, 100 vs 212 is of no practical use for anyone. Outside of the laboratory and manufacturing, people just boil water without thinking about the number associated with it. And in those settings, many other variables are tracked so the difference is of near zero consequence.
Please sir/madam, if you can, spare a thought for us lost souls who spend most of their finite lives in the laboratory and/or manufacturing.
So to put it short: if I know what I'm talking about I'll use K, and if I have no idea it doesn't matter anyway.
Even that isn’t quite true because you can get ice on the road or the sidewalk when air at 2m is ~3C.
250K: quite cold.
300K: beach weather.
350K: you're distilling your own moonshine right ?
(worksforme)
In case any of you are distilling your own moonshine, please be aware that at 350 kelvins (77 Celsius) you're likely to be getting methanol[0]. You should have the antivenom (ethyl alcohol, like vodka) on hand just in case.
Home distilling is great fun, and sometimes it's even legal, but please have an accurate thermometer and try not to poison yourself and others unless absolutely necessary.
(These temperate levels are also humidity and altitide/pressure dependent, if your still is in the high Appalachies then just listen to your heart.)
[0] https://diydistilling.com/distillation-temperatures/
Amen to that. I wasn't trying to encourage anyone to try their hand on distilling without learning more about it.
Only highlighting that one can "humanly relate" to Kelvin-based temperatures. If one so wishes. And that "reference points" there needn't be any more "arbitrary" than for °F/°C.
> 0° C: It's cold outside but not really that cold.
> These things are the case for humans
Who says so?
0 °C is very cold by many people's standards. About half the human population lives within the tropics. In fact I'd like to see Americans walk around in the UK wearing just a T-shirt and bermudas when it's barely above freezing, and insist 'it's not really that cold, it's only 32 °F'.
Maybe this is the perspective of someone who has spent a lot of time in the northern US, but it's cold but really not that cold. I might even run outside briefly in bare feet in the snow. But, yes, get to 0 degrees F and you're in bitter cold territory although, of course it gets colder in the northern Midwest/mountains/etc. And my contractor has been in shorts and a T in 40s-ish weather this week.
The point is that F degrees seems a pretty human scale that doesn't usually need a lot of decimals or minus signs for routine purposes. That it doesn't correspond to a couple of water transitions at standard pressure/temperature is sort of irrelevant. Of course, I and many other people are perfectly happy with using Celsius/Kelvin degrees for various purposes.
The minus sign is quite practical though.
When winter is coming, if it's 3 deg C outside, I typically don't need to worry about ice. If it's -3 deg C outside, I need to worry about ice.
When winter is waning, if it's been icy and it's -3 deg C outside, I typically don't need to worry about water on top of the ice. If it's 3 deg C outside, I typically do need to worry about water on top of the ice making it super slippery.
Again, it's not about where you live. 0°F is approximately the temperature at which the risk of frostbite becomes significant. 100°F is approximately the temperature at which the risk of heat-related illnesses becomes significant. Temperatures in between are far less hazardous to humans, even if the numbers near the edges are starting to get uncomfortable.
It would definitely be crazy in Fahrenheit, but in centigrade I think it makes some sort of intuitive (if not scientific) sense. (Together with the sea-level assumption we always make in casual temperature discussion anyway.)
It makes just as much intuitive sense in Fahrenheit as it does in centigrade.
Maybe because I was brought up with centigrade it makes more sense to me. The centigrade number is how far you are from water freezing. If it goes up 100% then you are twice as far away. I'm not aware that doubling the fahrenheit number has a similar easy to understand meaning?
> The centigrade number is how far you are from water freezing
The Fahrenheit scale is how far your are from your own body temperature. It was designed that 100 is the temperature of a human. (Adjusted later to 98.6 due to inaccuracies.)
0 was designed to be as cold as you can get with ice and salt (also ended up being slightly inaccurate).
> Maybe because I was brought up with centigrade it makes more sense to me.
Yup. People brought up on Fahrenheit think it is superior. For temperature neither argument is objectively better. (In contrast to imperial distance measurement with non-powers of 10 and factions, where there are good arguments against it, with temperature both scales are ultimately arbitrary.)
> For temperature neither argument is objectively better.
I think Celsius is objectively better in that:
(1) its endpoints–freezing and boiling point of water–are more natural / less arbitrary / more fundamental than Fahrenheit's–coldest temperature you can reach with salt and ice to average human body temperature. Water is a fundamental substance to all known life; the freezing point of pure water is much more fundamental than the freezing point of a water + NaCl mixture (actually apparently Fahrenheit used ammonium chloride not sodium chloride, which is arguably even more arbitrary than sodium chloride would be). If you imagine some extraterrestrial civilisation independently invents a temperature scale, they'd be more likely to come up with something close to Celsius than something close to Fahrenheit
(2) while both scales contain some error in that the nominal value of their endpoints differs from the real value, the error is greater for Fahrenheit
(3) According to Wikipedia, Fahrenheit didn't have 100 degrees between his two endpoints, he originally had 90 then increased it to 96 – given base 10 is the standard number base used by humans, 100 divisions is less arbitrary than 90 or 96
(4) nowadays, all other temperature scales are officially defined in terms of Kelvin – and Celsius has a simpler relationship to Kelvin than Fahrenheit does (for Celsius it is purely an additive offset, for Fahrenheit it involves both addition and multiplication)
(5) conforming to the global standard is objectively better than sticking with an alternative which lacks clearcut advantges
> (1)
They're natural, sure, but not really natural in a way that directly affects the most common everyday use case for temperature: the weather.
Fahrenheit's 0-100 is for now approximately the range of "normal" weather for the continental US, which is a useful if accidental property for Fahrenheit as a weather temperature system. Celsius's use of water's boiling point as a value for 100 is a nice property from an aesthetic perspective but means that it doesn't use the full 100 degrees when representing any earth-based climate.
> (2) ... (3)
Both of these aren't really advantages if you treat the scales as arbitrary, which in either case you are for most real-world uses of either scale. Water's boiling point at sea level is totally irrelevant when you're measuring the temperature of the outdoor air, a human body, or a steak.
> (4)
Only matters if you're actually doing work that needs to translate to and from Kelvin, which most people will never do in their entire lives.
> (5)
Standardizing would be helpful for sure, but it's not obvious that it would be worth the headache of making the switch given that the only real advantage to Celsius for most use cases is the mere fact that it's a standard.
> Fahrenheit's 0-100 is for now approximately the range of "normal" weather for the continental US, which is a useful if accidental property for Fahrenheit as a weather temperature system.
Only if you live in the continental US - and even the continental US has parts where that generalisation doesn’t hold true. From a global perspective, there’s nothing special weather-wise about 0 Fahrenheit or 100 Fahrenheit-where I live, it has literally never been that cold (our record daily minimum is positive even in Celsius), while days of 38 Celsius or above are infrequent but far from exceptional. As a global standard, Fahrenheit has no meteorological advantage over Celsius - and indeed, Celsius is the global standard for meteorology, used by >95% of the planet
> Standardizing would be helpful for sure, but it's not obvious that it would be worth the headache of making the switch given that the only real advantage to Celsius for most use cases is the mere fact that it's a standard.
You are ignoring all the costs incurred by immigrants and international travellers having to learn to juggle two different systems in their heads, the obstacle it poses to international communication (e.g. “40 degree day” means radically different things in American vs Australian English), products having to support both units and then having configuration settings to change them, people being inconvenienced when they can’t work out how to change the units setting, publications forced to include both units to ensure all readers understand, etc. Those costs are ongoing and cumulative over time, whereas the cost of switching is a once-off which most of the world has already paid
Fahrenheit is about half the size of increments without decimals or fractions which, having grown up with it ,seems useful. Yeah, I kinda want to know about 32 degrees but that doesn't seem a huge cognitive load. Knowing sub-zero is fricking cold is a decent benchmark as is knowing that >100 degrees is fricking hot. Yeah, 212 degrees for boiling is a bit weird but don't really need that much and that's only at standard pressure anyway.
Reading this quote made me finally realize why the name centigrade exists. It’s a gradient scale of 100.
Reading this comment about the previous quote made me finally realize why the name centigrade exists.
Why? The slope of the Fahrenheit scale is different to the Celsius and Kelvin scales, but the slope of the latter two does match.
The slope of the scales has no bearing on whether percentages are meaningful here. The problem with both systems when it comes to percentages is that neither system has 0 set to a natural 0. This leads to an entirely arbitrary point on the scale where decreases in the unit will approach a 100% difference and then suddenly start decreasing again.
If anything Fahrenheit should be less insane because at least the artificial 0 is likely to stay much further away in the data they're quantifying so the percentages stay reasonable.
Ah right, okay, that makes sense.
The slope of the Fahrenheit scale matches that of the Rankine scale.
I would still say that the in the Rankine scale percentage increases make sense, and Fahrenheit changes to not.
The thing that matters isn't the slope, but the zero point; "X% farther from absolute zero" is a useful measurement, "X% farther from an arbitrary zero point" is not. Especially when negative or zero temperatures are involved.
Ok. Then please explain what % does the temperature rise when going from 0 Celsius to 5 Celsius!
Or -1 to 1 Celsius, for that matter.
Obviously it's -200%, which means that going from -1C to 1C is a drastic decrease in warmness!
Early measurements were done by individuals and they were idiosyncratic to the process of discovery/calibration.
Kelvin is refined measurements used to relate to a wider scale of temperatures. Celsius is a metric human scale subset of Kelvin.
In both it makes a sort of intuitive sense. 7% of the way from freezing to boiling is a meaningful way to visualise temperature; 7% of the way from ice melting in a bath of salt to slightly above Mrs Fahrenheit's armpit temperature is also meaningful, although perhaps a little idiosyncratic.
Edit: this comment was deeply stupid for obvious reasons and I regret trying to interact with other people when I should be asleep.
The issue is a percentage of a Celsius value is not that. For example, an increase from 1°C to 2°C is a "100% increase", but is only 1 percentage point from freezing to boiling.
You could say things like that with anything in percentages? 100% increase in your pension from 100k to 200k is only 10% (increase, to 20% total) of your target 1M, or whatever.
100k to 200k is a 100% increase in absolute, but a 10 percentage point increase to your target of 1M. The difference between the example you give and the one in the article is that 0 in the case of your pension meaningfully refers to its emptiness, but in the case of Celsius, it has no "emptiness" interpretation.
The equivalent would be saying that going from 600k to 700k was a 100% increase... compared to 500k.
It's not completely meaningless, to be fair. Saying 10°C to 20°C is a 100% increase has the meaning of "it's twice as far from freezing", which isn't totally meaningless (kind of like saying Everest is twice as high as Mont Blanc, which really means "its summit is twice as far from sea level").
But in your example, the 10% has nothing at all to do with the increase of 100%.
If your ”whatever” target instead was 50k, is the argument that going from 100k to 200k would be 400%?
Yes? I didn't see any link in comment I replied to between 100% and 100deg besides it happening to be the same number - I already changed that to 1M, changing it to 50k no different either.
If the argument was saying there's something special about 100% being 100 quantity then.. no? I don't really know where to go from there, what I said still holds with a 100k target, but I'm not going to be able to give 'another' example where the 100 quantity is meaningful because it isn't for degrees either. It's the freezing point at 0 that makes it work better for centigrade than Fahrenheit, imo.
And they manage to make it even more crazy by also comparing it to average external temperatures.
== The Victoria Line average temperature in August last year was 60% higher in temperature than the average external temperature that month, measured at 19.5 degrees. ==
Certainly for January it must have been hundreds of percent higher.
And what would the numbers be for e.g., the Moscow metro in winter months where the average outside temperature is negative?
Yikes. I posted this, and I missed that, something I realised soon into my first year physics degree lab. I learnt more than just dipping calculators in liquid nitrogen for fun.
I apologise.
Maybe the right thing to do is to measure from ideal room temperature? From zero doesn't make any sense but setting an anchor temperature makes sense.
This is done when people rate the efficiency of home heating: SCOP is a function of the heat pump's ability to hit a particular temperature, for instance.
I'd guess the baseline temperature on the tube should be 21C maximum. Percentages don't make sense here, but 7C over the target temperature (for instance) is pretty bad in those terms. I'd be surprised if TfL hadn't set that somewhere.
Also worthy of note is that it sounds like the tube is a prime source of heat for a district heating system. Win win, perhaps.
And only in specific contexts with Kelvin.
If you go from freezing water to boiling, it's only 37% hotter!
I don’t know if I’m worried about it. While the measurement makes little scientific sense it makes intuitive sense, and, importantly, the intuitive implications are the scientific implications.
It’s a huge increase, if not for the reasons they describe.
So how many decibels louder is it now?
Is it? I think it puts the Victoria rise in perspective to the other lines quite effectively.
Everyone knows where the zero is in Celsius using countries anyway and days in the negative are so rare in the UK you can discount them (plus they are none inside the tube).
I came here to say this. It rankled me no end. Good to see that this is the top comment because we’re a scientifically literate crowd.
I logged in just to give this an upvote :-)
Looking at the temperature chart and the significant drop in 2020 during the pandemic, the source is certainly the trains and people themselves. (fewer trains moving, less heat added back then). At this point I expect the infrastructure is heat soaked and will need a prolonged period of cooling to bring temps down. i.e. don't expect instant results.
Moving more air through the tunnels, adding A/C systems - both have a problem of needing room up on the surface for blowers and compressors, something that is hard to do in modern London. Tough problem.
I wonder if they can carry hundreds of opened barrels of ice on open-bed trains through the tunnels at night, go slowly and let them melt to water (but kept in the buckets, because you don't want to flood the tunnels)...
I would expect them to already have some kind of drainage system, so if the line has some connection to some line that goes outside, just pulling cargo trains full of ice down there and dumping them might work.
That said, a typical shitty single-hose monoblock air conditioner has 9000-12000 BTU/h of rated cooling capacity. 12000 BTU/h is also known as "one ton". Sometimes, stupid units can be helpful, because "one ton" of cooling is what you get if you dump one ton of ice (short ton, of course) per day in the place. So you'd need a lot of ice, many tons per station, to make a significant difference.
Either way, since this is such an obvious idea, and they had a competition to solicit solutions, I'm sure this was evaluated and discarded - although it would be interesting to read the official analysis of the idea and learn why it wouldn't work.
Ice blocks were trialed in the past. https://en.wikipedia.org/wiki/London_Underground_cooling#cit...
They could flood the tunnels with an appropriate amount of liquefied air.
This. Brake friction pumps heat into the ground at a higher rate than it could dissipate away.
Aren't they using regenerative braking?
Some parts of the London underground use passive energy recovery by locating stations nearer to the surface than most of the tunnel between them. Trains start by rolling downhill and when they approach a station, uphill.
The trains in London can be up to 50 years old at this point. Where the technology was available during the building of the trains, you can generally expect regenerative breaking. But it’s far from universally available unfortunately.
Yes.
https://tfl.gov.uk/corporate/transparency/freedom-of-informa...
> If the line is unreceptive, braking energy is dissipated in on-board resistors
How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week?
Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels?
> Regenerated braking energy is transmitted to the London Underground high voltage distribution network
If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need.
(Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)
> Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels?
It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons.
1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid.
2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely.
3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions.
As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
Even with isolated segments, the measurements performed with Southern found 10% of regenerative power was turned into heat as the line voltage was already at max threshold from other trains; if that holds true today, then there’s still opportunity to consider optimizations for ensuring that 10% is weighted towards aboveground rather than below.
https://railknowledgebank.com/Presto/content/GetDoc.axd?ctID...
Also:
> A super capacitor is being used in a substation by Docklands Light Rail in London, UK
So at least they were considering what to do about this fifteen years ago. I wonder if they've made progress?
How exactly are you going to “weight” that 10%? Each segment is independent, you can’t “weight” the voltages, because that would require the ability to move power between track segments, which you can’t do, because then they wouldn’t be track segments anymore.
Additionally you’re making the assumption that line voltages are stable and constant, and can be tweaked as needed. They’re not, they’re some of the most noisy, electrically unpleasant power systems in the world, with voltage bouncing up and down as trains accelerate and decelerate, consuming up to a MW each under peak load.
Power distribution companies hate providing power to train systems because you need so much infrastructure to handle the noise and prevent the train line from seriously degrading the local power grid. The substation that connect train lines to the power grid are constantly having their switchgear trip in and out as the huge spikes in demand cause the equipment to momentary disconnect to protect downstream equipment.
So creating headroom for extra regenerative breaking isn’t a simple thing to do. When each train can instantly consume as much power as 10 households all maxing out their power supply, electrical systems stop behaving anything like “normal”.
These are all valid concerns. My goal was to highlight an opportunity for improvement that does not require capital equipment purchases. As you note, analysis may not reveal any opportunity for improving the regenerative controls. Given their inability to address the problem today, I expected they’d rather investigate a low-odds opportunity than disregard it. I was incorrect; I will raise my minimum-likelihood thresholds at HN in the future. ‘Simple’ was meant only in relation only to all other identified options, that each require non-zero capital expenditure and thus invoke the complexities of capital expenditure. It was not my intent to diminish the intricacies or difficulties of rail electrical engineering with my imprecise use of that adjective and I apologize for the disrespect inflicted.
Why don't they use batteries to buffer between consumption / regen and the upstream power?
The space on tube carriages is used for ... passengers. Unlike long-distance trains (where the locomotive is a rather sizeable unit of its own and has pretty much an electric substation of its own in it), the parts of a tube train reserved for driver, engines, electrical distribution are comparatively tiny.
see https://tfl.gov.uk/corporate/transparency/freedom-of-informa...
Seems not trivial to just put extra batteries and the circuitry for regen breaking charging in.
How many watts of extra energy would be required to accelerate each kilogram of batteries on the train? Would the additional thermal load introduced by battery charge and discharge effects counteract or worsen the desired cooling outcome?
It may be better to install such batteries somewhere on each track circuit as fixed stations, that can vent their charging and dispersal heat away from passenger tubes, rather than mobile — assuming that onboard emergency power needs are already met.
> How many watts of extra energy would be required to accelerate each kilogram of batteries on the train?
That's not really the problem; the problem is there is _no space_. Ever been on a London Underground train? You certainly wouldn't want the interior getting _smaller_.
It's also a fire hazard.
I'm sure they'd consider the worst-case scenario, and at present that's probably some serious arcing within a motor causing a fire. Cutting the track power (easily done by the driver) then makes that a fire that can be handled with water and/or foam.
Smoke from large batteries would be very hazardous.
To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids.
I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes.
If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques!
Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
Believe regenerative breaking is used to supplement Oxford Circus’ electricity supply
Big fans to pull surface air down into the tubes when the tubes are warmer than surface ambient ? Cool the tunnels, warm the surface.
Where there’s space, this has already been done. Unfortunately for many lines there simply isn’t space.
Just about every abandoned station, elevator shaft, and maintenance tunnel on the network is already fitted out with huge fans where possible.
TfL also runs a semi-continuous works project that looks a custom and novel one-off cooling solutions that can be retrofitted into whatever space is left. Including complicated hydronic systems that pump around huge quantities of water where the infrastructure allows for it.
The problem isn't so much space, iirc. It's that the blowers make a lot of noise and upset the residents, so they can't be run at full speed all the time.
The trains probably push a lot of air around. Wonder whether closing off sections with doors would help to push air out at one point and pull it in at others.
Possibly, but the pressure difference would pop people's ears, moreso than they do already. I'm sure the piston-like effect of moving trains is considered too to help move air around. Question is whether that's enough air movement to offset the heat generated by the trains, after all (and this is secondary school level understanding of thermodynamics), the energy needed to move the train is the train weight itself, plus track friction, plus air resistance. That is, in my head, it costs more energy to move the train than the amount of air that is moved around, so it in itself wouldn't be enough.
There are quite a few of these on the Victoria line, one next to my friend's house and it is really really noisy!
> Historically, the Underground infrastructure offered a respite from warm weather, indicated in Austin Cooper’s ‘It is cooler below’ poster, issued in 1924 by the Underground group to promote a more comfortable experience of travel during warm weather.
A century of burrowing commuter-worms unfortunately managed to bake all the beautiful wet clay that kept the tunnels tolerable when the sun was shining about.
It seems straightforward to me that it would be enough to rehydrate the ground. Just need (approximately),
Sounds like a lot but it's only about 1/300th of the yearly flow of the Thames.I don’t think the hydration of the clay is the important element here. Rather I suspect it’s simple just the sheer mass of clay, wet or otherwise, that’s involved.
There’s a reason why ground source heat pumps work so well. It’s because the ground is such a fantastically huge heat sink/source that in most scenarios we consider it capable of sinking or sourcing a practically unlimited amount of heat.
Unfortunately one of the scenarios where this breaks down, is when you stick a bunch of tunnels in the ground, then pump a crap ton of energy into those tunnels years round, and expect the ground to sink all the heat away. Turns out, if you do that, the ground itself starts heating up, and given that clay is a reasonable good insulator, it’s like wrapping all those tunnels in wool jumpers.
I would point out as well that all these tunnels are “deep level” tunnels running at an average depth of 24 meters and getting as low as 67 meters. The heat of the sun on the ground surface will have approximately zero impact on the tunnel temperatures. 24 meters of clay is a lot of insulation to work with.
My original comment was meant to be tounge-in-cheek, but I would like to add the advantage of wet clay is really in its thermal conductivity[0] which is roughly two to four times higher than dry clay. It will also have higher thermal capacity, so that high frequency fluctuations (like day/night) will be smoothed out.
[0] https://www.mdpi.com/2571-8789/8/2/47
(I don't think my comment implied that the sunshine makes it hot in the tunnel, only that when it's hot above ground it's nice to be cool below, like in the poster. And I did include a figure of 25m for average depth, I've spent enough time on their endless stairs to know that the TfL delved to greedily and too deep. This spiral staircase has 320 steps, I shudder.)
I think you are right. The graph at the bottom of the article shows that temperatures dropped around 2020 (presumably less traffic due to the pandemic).
So the ground can take up more heat, but it can't do it quickly enough.
<man walks into sauna room> Ooh, it's a bit hot in here! I better throw some water on these rocks to cool them down.
Joking aside, I actually don't know how dry it is in the underground, and therefore whether adding water for evaporative cooling would work. I would have assumed it was quite humid, but maybe not?
It would be if they tried cooling it with water, for sure; evaporative cooling would only work if there's enough airflow, else they'd just get 100% humidity so it would be both hot and humid.
It seems implausible to me that the clay is dehydrated. The Victoria line was only built in the 60s and has a waterproof lining. (It's also built with asbestos cement, unfortunately, which is no doubt a problem when they need to cut it for whatever reason)
The cement can negatively effect the water retenction of the clay, as does of course the temperature. The water needn't seep into the tunnel, just be moved away from it to adjacted areas.
There's a nice article here which goes into more detail: https://www.ianvisits.co.uk/articles/cooling-the-london-unde...
At a couple of stations a river passes by and that is used to cool the station.
I think Oxford Circus is one.
> Austin Cooper’s ‘It is cooler below’ poster
As I see it, it is just a marketing problem with easy solutions.
There is psychology and reverse psychology. You could fool people into embracing the heat by redecorating the stations and trains to make it a 'journey to hell, via the centre of the earth'. The stops south of the river could be marketed as Dante's inferno and hellish.
Or you could go the other way, to make it kitch Hawaiian themed, so people expect the heat and to embrace it as a mini-holiday.
Or, the stations could be redecorated as if it were a trip to the Antarctic, so people see images of penguins braving the ice, with murals from the Shackleton days, to imagine they are cold.
In places like Moscow the underground train stations give the impression that people are in splendid palaces, this works pretty well. As I see it, TfL just need to up their decor game, problem solved.
I hate that I think Theres a lot to this
Have you thought of suggesting this to TfL? There has to be something here.
Yes, people whose day job is to explore all possible options have surely missed this extremely obvious idea.
In fairness, TfL ran a public competition to source cooling ideas some years ago, so the people whose day job is to explore all the possibilities clearly felt like they were out of ideas.
Alright smart arse.
Unfortunately, hydrating clay is extremely hard to do. Clay is what you use as a water-tight material in dams, artificial lakes, waste dumps and stuff like that, because water doesn't really pass through it.
It was just a bit of a shower thought to be honest, but it looks like there are cleverer and more responsible people who've considered similar schemes.
As I posted in a cousin comment, I found this nice blog post examining some of the more serious ideas, including water-cooling: https://www.ianvisits.co.uk/articles/cooling-the-london-unde...
Isn't heat free energy in a place like London? I know very little about metro systems so please correct me if this is insane: wouldn't the people living above the tubes be happy to get a heat exchanger (passive) or heat pump (active, but takes more of the heat) that prewarms their hot water supply? People still take warm showers and boil tea and rice/pasta in summer, and in winter the purpose should be obvious. If the water comes in at 30 instead of 10 degrees C, you need to add only a few degrees for showers and floor heating
A problem is the clay surrounding the tunnels insulates them - it traps heat because heat flows through it very slowly. So you drill down and put a heat exchanger pipe down there, you pump heat from 3cm of clay around the pipe and now no heat flows through the clay to your pipe even though there’s a lot of heat still down there.
Your pipe becomes a tiny worm of cold pipe in a big lump of hot clay and you’ve done very little to cool the underground or warm your water. That is, if heat moved easily through the stuff then the problem of heat buildup would be easy to solve but in that case heat wouldn't build up so there wouldn't be a problem; and vice-versa.
Yes but the only places we care about extracting heat are the tunnels, so you'd just run pipes through the tunnels themselves to extract heat. I think the bigger issue is the amount of energy needed to get the water down there and back up just means it doesn't make much sense on its own.
You could use this kind of technology to extract the heat: https://enerdrape.com/en/solution/
From their FAQ:
> WILL THIS GEOTHERMAL PANEL SYSTEM COOL MY UNDERGROUND SPACE?
> No, the Enerdrape system primarily draws its energy from the ground. This does not affect the comfort of people using the underground space.
Have you seen how small the clearances involved are? The trains are very close to the walls of the tunnels.
Definitely an unfortunate domain name they've got there.
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The problem isn’t so much finding uses for the heat, it’s getting the heat out of the tunnels to begin with.
These are some of the deepest tunnels going under some of the most built up parts of the UK.
I wonder if an extremely tall subterranean windcatcher [0] with its bottom at the top of a tunnel could passively cool the tunnel.
[0] https://en.wikipedia.org/wiki/Windcatcher
The catch here is the cost of the buildings you'd need to destroy in order to build the surface portion of the windcatcher. The deep underground lines run under heavily populated areas of London.
To build enough windcatchers to move the needle on tunnel temps, you'd need to buy many plots in one of the most expensive cities in the world.
These basically already exist around the network. But that simply isn’t even close to moving enough energy to make a difference.
Your are correct in principal, though implimenting your idea, now, is essentialy impossible as installing the plumbing after the fact might cost more than just starting over with a whole new line, and would in fact make things much worse durring the many years it takes to find out if the added systems even work. Given that there is only clay under London, it is by far better to start over and build a whole new line, and/or go all in on a mega high tech ,high pressure refrigeration systems for the human occupancy areas, and hope that there are no break downs in the "hot zones" orrible mess
Heat is to energy as feces to food. It's not quite valueless by mass or by volume, but close enough that for most purposes the major issue is rejection.
Nice analogy, in hindsight only it’s in the name: waste heat. It takes the tiniest bit of impolite thoughts to make that lovely connection, thanks for that morning coffee bit of trivia.
Well, it's the human condition, once a day more or less whenever healthy. That's not only unpleasant, though! Also part of that condition is being a member of a species with the wit to invent soap.
>wouldn't the people living above the tubes be happy to get a heat exchanger (passive) or heat pump (active, but takes more of the heat) that prewarms their hot water supply
Ground source heat pumps are expensive to build, even more so in a dense area like London. So even if everything you said is true, I suspect the juice isn't worth the squeeze.
I think you are correct.
In this case, though, the excess heat is a major burden, so there is room to negotiate with a district thermal provider that pays that provider to absorb and redistribute the heat, as long as it's less than the cost to pump it out to the environment.
I'm not saying it's easy (it will likely be a bespoke solution). Given the organizations, I expect the difficulty to be as much business (setting the prices) and political (defending the prices set) as technical.
There is at least one on this line (north of Kings Cross) and one on the Northern line (north of Moorgate). It's for district heating or electricity generation.
You need a temperature gradient to turn heat into energy, and the smaller the gradient, the less efficient your heat engine will be.
What do you do in the summer when the homes don’t want the heat?
That doesn't have to be a problem in practice.
The entire issue is that the earth surrounding the tubes is acting as a giant buffer. Enough heat has been dumped into it over the years that it has permanently warmed up. Draw heat from it during the winter to warm up homes, and it'll be able to absorb more heat from the tunnel air during the summer.
And because it's permanently warmed up, the long term consequence is the line becomes a health hazard and has to be closed for increasingly long periods.
When wet bulb > body temp people start getting heat stroke, which leads to fainting and potentially death - a bad look for a public transport system.
The likely remedy is to install gigantic refrigeration units in the ventilation shafts and pump in cold air. This will be hugely expensive to build and run.
But the alternative is a tube line that can't be used. So there may not be much choice.
It won't be zero so spreading it across enough people might already solve it. If that still leads to insufficient demand during the hottest weeks, idk, it's energy, surely there's something useful you can do? Store it for next week, pre-heat water for the nearest steam engine (e.g. gas power plants are steam engines running on methane, so if they have to heat the water by fewer degrees.. The problem will be finding a steam engine close to the heat source), supply it to an industrial process that needs temperatures above ambient (egg breeding for vaccine production? Idk), create electricity from the temperature differential between this system and the Thames water using the Peltier effect
I've surely got a too naïve view of economics but if the goal were to not waste resources then there will be things you can do before dumping it into the hot summer air
People still take hot showers and use hot water
In case you also couldn’t guess the “f” in TfL, it’s Transport for London.
https://tfl.gov.uk/
https://en.wikipedia.org/wiki/Transport_for_London
You can blame Blair, I think, for the fashion of putting “for” into the names of administrative organisations.
Indeed, the Department for Transport was renamed in 1997, and TfL followed suit in 2000.
There is a minor fandom controversy over the Ministry of Magic in the Wizarding World and whether the "Ministry for Magic" and "Minister for Magic" are valid alternate terms, but I have only identified one instance where JK Rowling wrote it this way, and it was outside the novels. Canonically, Harry turned 17 in 1997, so I suppose Tony Blair's reforms wouldn't apply post-Voldemort. However, Platform 9¾ is now "properly labelled" in the Muggles' King's Cross Station.
https://commons.wikimedia.org/wiki/File:Cmglee_London_Kings_...
Travellers should also mind the gap between "TfL" and "TLF Travel Alerts", a defunct account which was part of Weird Twitter, and somewhere I hope I can dig up an archive, because the daily alerts were comic genius in 140 characters or less.
https://commons.wikimedia.org/wiki/File:Paddington_Bear_Stat...
The arrival of Paddington Bear from Darkest Peru may be partly explained by the heating of the Tube stations. He surely would be right at home in a dark, humid and warm environment. My mother encouraged me to read about Paddington Bear, and in 2008 I was privileged to have a layover in Westminster, where I passed through Paddington Station and totally missed out on visiting the Paddington Bear statue therein. But I was able to purchase a refrigerator magnet bearing the "MIND THE GAP" official logo, which I presented to her in gratitude.
In case you missed the 4 places it's made explicit in the graphs, or 'London' in the URL.
I had an idea, perhaps a weird fantasy.
Of a special tube train with blocks of ice. You’d need to have various pits dug in, and pumps to drain the water. Yes water and power electronics is “fraught”.
I just like the idea of trains trundling along, blocks of ice being carted out and gradually melting.
Another idea is to move mechs-bots via Underground in a post-apocalyptic scenario, but that’s not so relevant here.
This was actually tried: https://www.theguardian.com/uk/2007/jun/05/transport.world
Make tram cars that sit on giant plates that straddle giant cuboids of ice, and rail beds that are like luge lanes, pulled along by overhead ropes. Have the water in the lanes flow at the ends into waterwheels that help drive the ropes as a primitive form of energy recovery, all driven by a power-take-off from a giant coal power steam engine on the surface that also serves to power a massive reverse-rankine cycle refrigerator that makes the ice blocks and slides them down into the tunnels - the gravity also helping pull the ropes that drive the trams. Of course, the massive coal plants are going to accelerate global warming, so you're gonna need to build more of these ice-cooled underground transit systems and even water chilled underground housing for people as the surface temperatures rise and rise....
And now you've got this wild 19th century Jules Verne-esque icepunk world in thermal runaway all built up for a hell of a novel-to-be.
But then they'd spend more energy (and more braking) hauling that ice around; would the amount of heat absorbed be more than the one ice train would generate?
There's probably more efficient materials to use, big lumps of supercooled metal. Someone else mentioned liquid air, that could just be evaporated in the tunnels and stations.
Of course, generating liquid air costs a lot of energy too. I'm sure the problem is easily solved if you assume infinite and free energy.
This would also increase the humidity to swamp-like levels.
Not if it was kept separate a metal box with fins could absorb the heat without leaking any humidity.
Besides at that temperature, more water can be absorbed in the air, so not just latent heat of melting, but heat absorbed in evaporation too.
Of course that would have to be wafted out, and not pumped were it just water.
Various fungi would love it.
> The Senior Press Officer added that with many stations in close succession, the Victoria and Central lines experience frequent acceleration and braking, contributing to heat buildup within the tunnels.
I'm sure that this is probably one of those stupid suggestions that shows a lack of understanding of the problem, but could skipping stations help help this? Something like the following gets you 1/3rd less braking energy released into the tunnels:
Taking a look at the peak time schedules they have trains coming every 2 minutes, so this seems like it would be reasonable for most people to have to sometimes wait 6 minutes for the right train, but generally not more than 4.Probably not, because the limiting factor on train throughput is remaining a safe braking distance behind the train in front. If the train in front of you has stopped at station D then you need to stop in station C even if you don't open the doors.
(You could get around that by running the trains further apart, but that would be a critical loss of capacity).
There are some metro lines which use this skip-stop system, the distance between trains is created by staying longer in the station.
https://en.wikipedia.org/wiki/Skip-stop
Right but the Victoria line puts a lot of effort into keeping station stop time to a minimum for the sake of capacity (it's the most intensive metro line in London, at 36-37tph, and one of the most intensive in the world). One way or another you have to space the trains out more to do skip-stopping.
With frequent trains and close stop spacing you've plausibly got a situation where each train is entering and leaving each station at about the same time? So skip-stop might not save much acceleration/braking.
I mean sure, less trains would help alleviate the problem (to simplify your proposal), but they still need to move all those people every day. Hence the 2020 reduction in heat increase, less people = less trains = less heat buildup.
> tunnel ventilation installations, chiller systems pumping chilled air into mid-tunnel shafts and regenerative braking to reduce heat generated by trains breaking
The hoops TfL jumps through just to not extend AC to the rolling stock in more lines are baffling. At least we finally got some AC in the new Piccadilly rolling stock.
I think AC net adds heat to the system, we just don't usually care because the hot end is outside. Here the hot end of an ac unit on the rolling stock would be in the same clay-insulated tube and not escape, so I think it would be a problem? They have to get the heat out of the underground and up to the surface somehow.
AC will only make the problem worse in the long term. Picadilly got AC because it has above-ground sections.
You can redesign the signalling systems etc to work at even 40C, plenty of countries do it. You can't redesign humans to feel comfortable inside a stuffy carriage at 35C.
Sure, but that means the stations will also have 40C air. Can the humans handle that? And it's going to be 42C the next year, 44C the year after, and so on...
Platform screen doors can isolate tunnel temperatures from platform temperatures.
That doesn't help the people maintaining the tunnels and everything inside them.
What do you do if some incident halts full trains (possibly depowering them but for things like emergency lighting) near the midpoints of longer sections of 40 degC deep tunnels?
You can survive a few hours at that temperature, so not an immediate catastrophe. You should be still able (though not comfortable) to walk to the next emergency exit or station.
how many times has this scenario happened in last 20 years?
This is exactly the kind of thinking that lead to https://en.wikipedia.org/wiki/King%27s_Cross_fire
In safety engineering you do have to think about low-probability events.
One key question is that with the construction of the Elizabeth line, and this being a known issue how was that designed and built differently to solve this problem, assuming it has fixed it.
Update:
There’s not a huge amount, but with careful search term tweaking I did find this on the Elizabeth line thermal loads:
https://learninglegacy.crossrail.co.uk/documents/the-design-...
I had the same idea as proposed in this paper: dump tunnel heat into nearby buildings. Win-win! However:
> This paper for a possible energy segment installation was written during the design phase but the proposal was not implemented.
Bleah.
This is a generational buildup of heat, being tackled seasonally.
TfL must run its cooling operations in the winter as well as the summer.
It’s about net energy difference over the whole year.
Finding cold air in the winter will also be substantially cheaper
I dont quite understand what’s stopping them from just buying hundreds of chillers, putting them on the surface close to each station, and running chilled water loops down. Other than cost of course.
They're running trains. Trains use a lot of electricity, and they turn almost all of it into heat. You'd have to have as much chilling capacity as the current electricity demand of the entire tube line, which is quite a lot.
However, if the buildings above were to sink ground source heat pump loops into the warmed ground to heat the buildings in winter, this would basically be what you just suggested, and would be a win-win situation.
Huh? Modern modular air cooled chillers go up to 800 tons each and can remove multiple MW of heat load continuously pretty much 24/7.
500 of them could remove 1.4 GW of heat.
Of course there are many ways to improve efficiency, but even assuming the worst case it’s still technically feasible to remove many times more heat than the line generates.
And where is the energy to power all of them coming from?
GP is saying that you can approximate the energy going into the system by looking at the electricity consumption of the trains, as all then energy is eventually going to end up as heat.
A heat pump can have a CoP topping out at 5. So 1 unit of energy needed to move 5 units heat out. That means a “net zero” cooling system would consume a minimum of 20% as much energy as the trains themselves. Realistically it’s probably closer to a CoP of 3.5, so 28% more energy. For something like the underground that gonna be a 5-10% increase in there operational costs at a minimum. Where does the funding for all that come from? And that before we even look at the capital costs of heat pumps and various ancillary equipment needed to run them.
As a point of reference TfL underground trains have an average power consumption of 140MW continuous. Now only about 45% of the underground is actually underground, but that’s still 63MW in just the underground parts. At an optimistic CoP of 5, that means 12.6MW of additional energy needed to cool the tunnels using your approach.
Wholesale electricity prices in the UK are something like 7p per kWh. So over a year that’s an additional £17m of electricity, just for cooling.
£17 million doesn't sound that unreasonable for climate control for a system as large as London's
That's £17M of electricity, not including all the equipment, staff, installation costs etc.
To put this in perspective, Sadiq Khan already runs the system at a massive loss. They just about cover their operating costs at the momemt, and rely entirely on grants from the rest of the country to do upgrades of any kind. So cooling efforts have to be very cost efficient. Also the UK grid is very supply constrained. New nukes are being built but there have been the expected massive cost overruns and problems, so any large new energy demands in the UK just aren't happening anytime soon. It's actually been deindustrializing due to very high electricity costs.
TfL spends close to 100% of its income on operating costs. It does not get any other money.
Doing things on a large scale cost money… often more than what taxpayers are willing to bear, are you genuinely confused about that?
Yes doing things at scale does cost lots of money. That often why doing the “obvious” is the wrong approach. When you’re operating at that kind of scale, small savings are still substantial, and scale often makes more innovative, less obvious solutions a better pick. Especially given the cost of exploring those options is so cheap compared to total cost of the project.
Also the underground is funded pretty much entirely by fares paid. Past UK governments have cut any tax payer subsidies for TfL to zero for day-to-day operational costs, and there’s zero indication that’s going to change any time soon.
How is that relevant to my comment?
I didn’t claim all technically possible solutions would be politically acceptable.
I’m pointing out how shallow and unhelpful your comment is. I provided an analysis as to why a seemingly obvious solution has serious problems, you made an unhelpful comment that seems to suggest that commenting on the cost of a project means I’m confused about the political acceptability of a project, rather than the fact I’m trying to demonstrate why the obvious solution might have some problems. Which has nothing to political acceptability, but is simply a comment on the poor value-for-money that specific solution represents.
Are you even replying to the actual comment?
This problem is also an illustration of the potential of geological thermal energy storage.
The thermal time constant of a lump of matter scales as the square of its linear dimensions (for a given geometry). This can easily reach many years for large enough chunks of underground stuff. This is why geothermal energy works at all; the heat energy flowing up from the deep earth is stored for many thousands of years at reachable depths and can be mined. And, if one has excess energy, it could be reinjected underground as heat and later recovered.
I live in a country where summers are warm and winters are cold. One idea I've thought about is why we don't just have massive water tanks under our houses.
Energy can be dumped in during the summer for cooling, and taken out during winter for heating.
It would be more efficient that ground source geothermal as it's a closed loop system, so heat won't leak away.
My house needs around 2500kWh per year, so you'd need a tank of around 100,000 litres. That is 8x8x1.5 metres - basically a small basement. To get that energy out youd need to heat it to 60c in the summer, and it would cool to 30c in the winter. You could even do that with passive water flow, no heat pumps needed.
Or, you could flow heat transfer fluid through buried pipes and let the soil or rock around the pipes retain the heat. This is the idea behind geothermal heat pumps. The obstruction to doing this is cost.
Is there a reason why they can't drill a couple bowling ball sized holes at strategic intervals and put some high speed extraction fans in?
Stations entrances are open to outside so if you create enough negative pressure the hottest parts in the tunnels it'll pull in air. Do that long enough and presumably ambient & clay cools?
Presumably engineers dismissed this already, but why?
They have added ventilation to the tunnels, it's mentioned in the article. It's more than just a couple bowling sized holes, but apparently still not enough
Unfortunately, hydrating clay is extremely hard to do. Clay is what you use as a water-tight material in dams, artificial lakes, waste dumps and stuff like that, because water doesn't really pass through it.
I think you replied to the wrong comment?
Yes, sorry.
I think people might object to TfL drilling a bowling ball sized tunnel in the middle of their house/garden/park/road/driveway/swimming pool/historic monument.
Remember the deep level network is some 23m down, and runs under buildings. At lot of it doesn’t follow roads, or have any kind of conveniently clear space on the surface above it.
You need large extractor fans and they make a lot of noise that bothers the residents.
At what point does it become illegally warm?
I thought 30°C was the limit for office work in the UK.
I recall when there was a terrorist bombing for the Stratford Olympics that emergency service people had to work in a tunnel at 60°C.
I avoided the deep tube for several years after that.
> I recall when there was a terrorist bombing for the Stratford Olympics
Was there? I don't recall the event, and can't find references on google.
Sorry, I meant there was a terrorist bombing for the announcement of the Olympics at Stratford. I left the word ‘for’ do a lot.
I had assumed that it was infamous enough not to require much more detail, has it really been that long ago that people didn’t know about it.
https://www.btp.police.uk/police-forces/british-transport-po...
It seems I had muddled the name, I meant to say the tunnel by Russell Square tube station.
Coming up to years ago in a few months…
https://www.bbc.com/news/uk-33253598.amp
> Coming up to years ago in a few months…
20 years
I've never heard 7/7 associated with the olympics before.
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Yep ... know people who commute on the Victoria and it doesn't sound fun. I've had to get it when my usual commute on the Northern line was impossible (only once, thankfully) and it was horrendous.
And the Northern line is no picnic either.
Why not look at it like a nuclear power plant and build a similar solution? You can reject gigawatts of power with one wet cooling tower.
If pumping water up and down that distance is infeasible, then make the primary coolant loop use a phase change refrigerant. Much easier to pump long vertical distances. Condensed fluid would flow down with gravity, evaporated gas would flow up.
Probably because the temperature gradient isn't enough for it to be worth it
> Temperatures hiked as high as 31.1[C] degrees in August 2024 [...]
So, I can imagine that this is a long-term problem, but it seems odd that the panic is setting in already, when some platforms in the NYC subway regularly exceed 40C / 104F every summer? This article seems in a similar genre to the breathless advice to remain inside in Britain when the outside temperature might get above 27C / 81F, otherwise known as a not-particularly-warm spring day in much of the US in most years.
> This article seems in a similar genre to the breathless advice to remain inside in Britain when the outside temperature might get above 27C / 81F, otherwise known as a not-particularly-warm spring day in much of the US in most years.
It’s really not breathless, because high temperatures and how to handle them is completely absent from the cultural baggage. I don’t live in the UK, but in a place which similarly does not have much in the way of high temperatures historically and low AC penetration, and during heat spikes I see a significant fraction of my neighbours with windows wide open at 4PM.
Habituation is also a significant factor. The UK does not get a smooth transition into higher normals, it gets heatwaves.
I live in the UK and a lot is down to the tabloid newspapers trying to get some sales with 'Horror Heatwave!' type headlines when it's 27C. Brits go on holiday to Spain, we are familiar with heat.
Statistically we know that humans who live somewhere that you'll just die in the regular environment due to climate behave very differently from humans who live in a temperate climate like the UK when the actual temperature warrants the same behaviour. If you live in Nunavut or the Iran / Pakistan border you already knew that you can just die from temperature extremes and so you need to ensure you stay at a survivable temperature, in Wales it's quite unexpected.
As a result you actually get many more deaths from extremes in countries where the usual climate is temperate like Britain, even when the actual temperatures aren't as extreme as in countries where that would be more common.
I'm only in London occasionally but I can confirm that some lines are unbearably hot, in the summer I have no idea how people commute in that heat every day. And I'm originally from a much hotter country than the UK.
I commute on the northern line 3 times a week ... it's not fun, but it's bearable ... just.
The trick is, if the window at the end of the carriage isn't open, make a beeline and open it, as the air moving past does help keep you cooler.
Surely that says more about how NYC than it does about London?
If I had to suffer overcrowded trains with standing room only, people’s armpits in my face and all, at 40C temperatures everyday in the summer, then I wouldn’t be laughing at London for trying to avoid the same fate. I’d be complaining that my own city isn’t taking their problems seriously enough.
NYC Subway trains have AC. They feel like refrigerators in the summer. Platforms get hot but can be avoided if you time carefully.
London Tube trains largely do not have AC, so heat in the tunnels is a big problem.
Yeah I’m familiar with the tube.
If NYC Subway has AC then it’s silly for the GP to compare the London Underground to the Subway.
What if trains brought their heat with them instead of leaving it in the tunnels? I'm thinking some kind of large seal like thing in front of and behind trains that keeps the train surrounded by the same air. Stations serve as a spot to dump hot air and blow in cooler air. I guess the problem is it would take a lot of energy to push all that air around. Also the trains would be hotter.
Also you'd blow everyone off the platform, up the escalator, and a hundred feet in the air at each station stop.
At that point you don't need trains. Just don your Zorb ball, choose the appropriate shaft, and dive into the air stream.
That... Is a hilarious and good point. You could seal the stations like they do on the Elizabeth line but it's still a stupid idea. I just got back from London actually and am still incredibly jet lagged, for which I blame my suggestion
Oh, don't apologize. I cackled at the thought - what a commute! And for a way to cool off after being baked in the tube like a jacket potato, I can hardly think what'd work better.
Maybe something less extreme like a skirt that sits around the wheels and track and traps the hot air off the brakes. The regenerative braking mentioned in the article makes this easier as you can dispute the heat anywhere in the train you like, for instance some large dedicated heat sink car instead of the air in the tunnel
The Victoria line trains only stop briefly at the stations and are underground the entire time. For other lines TfL has air conditioning systems that capture heat during the underground sections and then dump it in the open-air parts, but that won't work for the Victoria line.
So if I have this right, TfL is constructing a giant thermal mass, and therefore is banking heat energy. If we (for example) piped cold water through this, we'd get warm water. So in winter, this could reduce heating bills substantially for people connected to such a system.
Is TfL not monetising this thermal mass? Why not?
30 degree water isn’t warm enough for direct residential heating but with a geothermal system it’d be great.
Actually it is. My house has radiant underfloor heating built into the concrete slab, and the water runs through at 30c. Keeps it a toasty 24c when it's -20c outside.
However heating 30C water to the desired temperature is cheaper than heating 10C water
Steam heat at 30°? In London? Can't imagine...
London had both water, and air pressure delivery systems embedded in the street scape to manage cranes at the docks, machinery and for letter delivery.
Heating and cooling benefits from remarkably small differences in temp. Thats how heat pumps work. And, lifting the input temp by only 5-10 degrees C can make a huge difference to the energy required to get to the next level.
It takes about 200Kj to heat 1L of water from 10C to 60C and 125Kj to heat it from 30C to 60C -A 37.5% saving in energy inputs. You better believe a corporate would seek a 1/3 reduction in energy input costs.
(my sarcasm meter is broken sorry if I ruined a joke)
Well, "had." That's just my point: how many trillions of pounds of attempting to navigate subsurface London will need to be amortized atop that 1/3 reduction in energy transport costs? Input is well and good, but if you don't think of where all that energy is going, you end up self-vitrifying the Victoria Line bore. And if the infrastructure of my own barely three-hundred-year-old city is too complex for a fiber provider to navigate in hopes of billing the $250/month we'd gladly pay at first - even a duopoly being preferable - then it's hard to imagine a successful modernization or installation of high-volume, low-temperature water transport infrastructure beneath London. Especially since with a small difference in working temperature, I believe you may need to construct a very large heat exchanger to get anything like continuous or even timely operation.
The line passes below some of the most valuable real estate in the world. Much of it commercial premises.
The line is itself a giant distribution system and is pretty much designed to retrofit pipes into.
The commercial premises would merely have to tap into something which is within a few tens of metres of their basements, and in some cases they very probably have access hatches already.
Right, but it's that "something" I'm discussing.
You are heating your working fluid to a temperature equal to what's ambient within the heat exchanger, which takes the longest possible time of any heating this exchanger can perform. (Think it over.)
For the exchanger to operate continuously - that is, to sustain outflow at final temperature equal to inflow at initial - this means you need a lot of piping, because however many CFM of water at 10° (or whatever) come in, you need to supply exactly that many CFM at 30° out.
All that piping takes volume, which has to be excavated out of the clay in which has been sunk the heat we're striving to remove. There's no moving that without some heat exchanger, after all. So we're still stuck expressing time basically as volume, which is perhaps the worst possible misfortune when working underground. (Caissons can be built and pumped dry, where earth must be dug.)
Perhaps you're thinking of a cooling jacket lining the tunnel bore. This would make sense but will only operate at a net energy cost, because to sustain livability you're going to need to exchange heat outside the system and supply, effectively, refrigerant. From plants all over town...
I suppose it's odd to use cubic feet per minute and degrees Celsius at once. I polled Gemini three times and received three unique answers varying only in relatively insignificant digits, so feel confident expressing the conversion factor thus: one cubic foot per minute is about half a liter per second.
Hopefully they would, sarcasm aside, but there seem to have been plenty of places than run cooling and heating against each other, my mind boggled in hearing that.
Using the London subway is an adventure.
https://www.bbc.com/news/articles/cy9xxlky2pno (2024)
> Phone signal goes live on 25% of underground Tube
In the longer run, give up the old deep tube lines. They could be gradually replaced by Elizabeth Line-style tracks (larger capacity, fewer stops, good air conditioning).
Doesn't Elizabeth run even deeper than the current ones, though? Certainly seemed so in the elevators of the Whitechapel station. And it's not like you could replace the current lines without building the new one first and I bet there isn't too much empty space between the surface and the existing lines.
Am I the only person who thinks 31C is not actually that warm for August on the only line that is entirely underground?
Yes. As somebody who has used dozens of metro systems around the world, it is literally the only one that is not ~room temperature. In the summer, it is so uncomfortable on the tube that I almost always take a taxi, even if a taxi is materially slower.
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Losing the battle or not even trying to fight? It's
Why is the London underground so warm? Where is the heat coming from? Most underground locations are cooler in hot places in my experience. Is it just people?
https://en.wikipedia.org/wiki/London_Underground_cooling
Interesting. My question was one others had asked - so much so that the answer has it's own Wikipedia page with a table! It looks as if regenerative breaking on the trains would fix the problem.
You could read the linked article ;-)
It's one of the oldest metro (retrofit cooling), it's deep, high usage, it's surrounded by isolating clay, dense city.