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Comment by vallode | Hacker News Reader

If I understand correctly, it is not about "not emitting heat", they reduced the natural output of heat of the trains and gave the excess allowance to the new AC system.

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I wonder, are we now at equilibrium with the surrounding earth so the heat of the trains is now actually vented outside, or is the clay still absorbing heat?

If it's the latter than this merely kicks the can down the road and ambient temperatures will keep rising.

The article is not quite explicit about that, but it does say "cooler running trains could help to cool the tunnels, but it would take decades to notice the difference, or they can use that temperature gap between the new and old trains to put air conditioning inside the carriages today... If a future plan to run even more trains through the tunnels goes ahead, that will require increased cooling in the stations, which, funding permitting, is being developed at the moment."

The implication seems to be that an equilibrium (or something very close to it) has been reached for the current traffic volume (and putting aside climate change, presumably.)

The earth is naturally at equilibrium with the average air temperature outside. (when you get really deep the earth's core makes a difference, but at these depths we can ignore that). However when you add heat like the tube does, the earth is enough insulation that it can be decades before it reaches equilibrium again. For purposes of this discussion clay should be seen only for the R-value. (absorbing heat is a very useful property of clay for other purposes, but in this discussion that is not relevant)

According to https://en.wikipedia.org/wiki/New_Tube_for_London, "energy consumption 20 per cent lower than existing trains due to regenerative brakes, LED lighting and lighter construction"

...and apparently they managed the "lighter construction" mostly by reducing the number of bogies? According to https://en.wikipedia.org/wiki/London_Underground_1973_Stock, current Piccadilly line trains have two 3-car units, which means 2x3x2 = 12 bogies. If you look at the video, the new train seems to be just one unit with 5 "actual" cars (with bogies) and 4 bogie-less segments suspended in between, which means just 10 bogies. Also, the new trains are 7 meters longer than the old ones.

As an American that has been to Europe several times, I would say "not emitting heat" is an accurate description of AC in western Europe in general. I'll never forget driving with a friend in Germany when it was about 85 degrees outside and they set the AC to 78 with low fan speed. I'm not trying to throw shade, I just wish I could be happy with that amount of cooling. I would have turned it down to 68 and blasted the fans (when I'm sweating, I want my AC to feel like I just entered a walk-in fridge loaded with box fans). I suppose it explains why Americans have such a huge energy footprint.

I'm an American, and I typically don't use the AC in a car unless it's above about 90 degrees, I just open the windows.

Is there a reason why? If it's fuel efficiency the AC is far more efficient than the drag open windows adds. Fresh (ish given you're on a road) air I kind of get but at anything other than city speeds the noise gets unpleasant fast for me.

Yeah I just prefer fresh air (even knowing that newer cars with in-cabin air filters probably have cleaner air than outside). If I'm sitting in city traffic and not moving much, I do use the AC more.

That's fair. I grew up in the midwest where it gets pretty humid in the summers. Even when it's in the 70's, driving with your window open doesn't help with feeling gross and sticky.

If I travel from Northern Europe to hot places, the first thing I have to do in the hotel room is turn the temperature up about 5-10°C.

If it's 30°C outside, 25°C is a reasonable room temperature. I don't want a shocking transition when I go in and out.

Last year I visited a place with almost 40°C outdoor temperatures, and I set the car AC to 28-30°C.

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