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I'm guessing not. Earth's heat is way lower down. Think of a cave: always cold. I think what's going on is they're taking the heat out and storing it more effic

by JohnL4 5y ago

I'm guessing not. Earth's heat is way lower down. Think of a cave: always cold. I think what's going on is they're taking the heat out and storing it more efficiently than just dumping it down the ground, where (1) it would leak away, representing energy loss, and (2) as it leaks away, the air would lose pressure. (It would leak away b/c it's harder to insulate an entire mine, basically.) So, they pull it out ahead of time and put it back in when they decompress the air (which I think would add pressure back in due to heating a gas and maybe reduce problems caused by super-chilling other plant hardware? Anyway, seems fitting to add back what you took out if you're shooting for a closed system.)

JohnL4 5y ago
"Looked the temp gradients up, after 50ft, temp of the earth is 50F, and raises one degree F every 60ft." (So, at 300 feet, 54 degrees; at 500, 57.5 degrees.) (http://www.welshcoalmines.co.uk/forum/read.php?14,46717,46718#msg-46718 http://www.welshcoalmines.co.uk/forum/read.php?14,46717,4671...) "...but other parts of the mine was very cold you made sure you had plenty to ware it depended where you worked" (https://www.quora.com/Are-coal-mines-cold/answer/Keith-Scott-84 https://www.quora.com/Are-coal-mines-cold/answer/Keith-Scott...) "Underground mines maintain a constant temperature, around 55 degrees Fahrenheit." (https://www.quora.com/Are-coal-mines-cold/answer/Tom-Inghram https://www.quora.com/Are-coal-mines-cold/answer/Tom-Inghram) «The temperature on average is in the 50s, but you still sweat an enormous amount when you start laboring.“ - Alan Bates, working in the coal mines of Letcher County, Kentucky.» (https://www.quora.com/Whats-it-like-working-in-a-coal-mine/answer/Amit-Kumar-1878 https://www.quora.com/Whats-it-like-working-in-a-coal-mine/a...) Yes, a 4000m gold mine is hot. I doubt that's where they're storing their compressed air.
- JohnL4 5y ago
  And finally: https://startcaving.com/info/caves-are-cold-find-out-how-cold-and-why https://startcaving.com/info/caves-are-cold-find-out-how-col...
Raidion 5y ago
This isn't correct. Deep mines are notoriously hot, because you're digging towards magma. Google says temps increase by 3° C for every 100m.
- emptysongglass 5y ago
  Naive question but couldn't our forerunners who otherwise succumbed to cold in harsher climates have exploited this fact to dig subterranean villages and towns? What's the element I'm missing as to why they didn't?
  - cortesoft 5y ago
    That it is really hard to dig down 100m without modern digging equipment.
  - sulZ 5y ago
    Digging 100m down is difficult and dangerous
  - PixelOfDeath 5y ago
    Ever tried to dig down a few 100m in your garden?
    - mikewave 5y ago
      More like, ever tried to dig down more than a foot or two? Unless you have really soft ground, even a good steel spade and shovel aren't any guarantee of success. Powered augers are often needed to make holes for fence posts, etc.
    - m4rtink 5y ago
      Try 390m, by hand: https://en.m.wikipedia.org/wiki/Woodingdean_Water_Well https://en.m.wikipedia.org/wiki/Woodingdean_Water_Well
  - WiseWeasel 5y ago
    Difficulty of digging with the tools they had, inability to stabilize the structure to prevent cave-ins, lack of pumps to remove accumulating water, insufficient ventilation and filtration technology/unable to deal with poison gases, inability to light their environment without contributing to the poor air quality, difficulty accessing resources like food and clean water, lack of desire to live in a damp, dusty hole.
OneLeggedCat 5y ago
> Earth's heat is way lower down Very incorrect.
benreesman 5y ago
This comment is an example of why I’ve become skeptical of the downvote button. It sounds like people read it, knew better, and politely pointed out that it was incorrect. Everyone who might have shared the same misapprehension learned something and the parent wasn’t being an asshole. Doesn’t that add to the discussion?
- nkurz 5y ago
  Yes, when considered along with the corrective responses, it adds to the discussion. This is why it shouldn't be flagged and removed. On the other hand, it's factually wrong and would be misleading if people were to trust the claims uncritically, which I think justifies a downvote. Keeping it visible but lower on the page and showing it in gray seems like a pretty good compromise. Can you suggest a better way of giving more prominence to correct information? Or do you think that's not the right priority for the site?
- ndm000 5y ago
  Side question - do you need to reach a certain level of membership with HN to see the downvote button? I may be missing something, but seems that's only allowed for certain individuals.
  - nkurz 5y ago
    Yes, there's a minimum number of points required to downvote. I think it's currently 500. Here's an unofficial FAQ that give more information about the thresholds: https://github.com/minimaxir/hacker-news-undocumented/blob/master/README.md https://github.com/minimaxir/hacker-news-undocumented/blob/m...
- nautilius 5y ago
  Didn't downvote, but I am not a big fan of simply making stuff up on the fly as response. I've met my share of people who rather go this route than put in a 5sec Google search or simply admit they don't know something, and I try to avoid them.

by JohnL4 5y ago

JohnL4 5y ago

"Looked the temp gradients up, after 50ft, temp of the earth is 50F, and raises one degree F every 60ft." (So, at 300 feet, 54 degrees; at 500, 57.5 degrees.) (http://www.welshcoalmines.co.uk/forum/read.php?14,46717,46718#msg-46718 http://www.welshcoalmines.co.uk/forum/read.php?14,46717,4671...) "...but other parts of the mine was very cold you made sure you had plenty to ware it depended where you worked" (https://www.quora.com/Are-coal-mines-cold/answer/Keith-Scott-84 https://www.quora.com/Are-coal-mines-cold/answer/Keith-Scott...) "Underground mines maintain a constant temperature, around 55 degrees Fahrenheit." (https://www.quora.com/Are-coal-mines-cold/answer/Tom-Inghram https://www.quora.com/Are-coal-mines-cold/answer/Tom-Inghram) «The temperature on average is in the 50s, but you still sweat an enormous amount when you start laboring.“ - Alan Bates, working in the coal mines of Letcher County, Kentucky.» (https://www.quora.com/Whats-it-like-working-in-a-coal-mine/answer/Amit-Kumar-1878 https://www.quora.com/Whats-it-like-working-in-a-coal-mine/a...) Yes, a 4000m gold mine is hot. I doubt that's where they're storing their compressed air.

JohnL4 5y ago
And finally: https://startcaving.com/info/caves-are-cold-find-out-how-cold-and-why https://startcaving.com/info/caves-are-cold-find-out-how-col...

Raidion 5y ago

This isn't correct. Deep mines are notoriously hot, because you're digging towards magma. Google says temps increase by 3° C for every 100m.

emptysongglass 5y ago
Naive question but couldn't our forerunners who otherwise succumbed to cold in harsher climates have exploited this fact to dig subterranean villages and towns? What's the element I'm missing as to why they didn't?
- cortesoft 5y ago
  That it is really hard to dig down 100m without modern digging equipment.
- sulZ 5y ago
  Digging 100m down is difficult and dangerous
- PixelOfDeath 5y ago
  Ever tried to dig down a few 100m in your garden?
  - mikewave 5y ago
    More like, ever tried to dig down more than a foot or two? Unless you have really soft ground, even a good steel spade and shovel aren't any guarantee of success. Powered augers are often needed to make holes for fence posts, etc.
  - m4rtink 5y ago
    Try 390m, by hand: https://en.m.wikipedia.org/wiki/Woodingdean_Water_Well https://en.m.wikipedia.org/wiki/Woodingdean_Water_Well
- WiseWeasel 5y ago
  Difficulty of digging with the tools they had, inability to stabilize the structure to prevent cave-ins, lack of pumps to remove accumulating water, insufficient ventilation and filtration technology/unable to deal with poison gases, inability to light their environment without contributing to the poor air quality, difficulty accessing resources like food and clean water, lack of desire to live in a damp, dusty hole.

OneLeggedCat 5y ago

> Earth's heat is way lower down Very incorrect.

benreesman 5y ago

This comment is an example of why I’ve become skeptical of the downvote button. It sounds like people read it, knew better, and politely pointed out that it was incorrect. Everyone who might have shared the same misapprehension learned something and the parent wasn’t being an asshole. Doesn’t that add to the discussion?

nkurz 5y ago
Yes, when considered along with the corrective responses, it adds to the discussion. This is why it shouldn't be flagged and removed. On the other hand, it's factually wrong and would be misleading if people were to trust the claims uncritically, which I think justifies a downvote. Keeping it visible but lower on the page and showing it in gray seems like a pretty good compromise. Can you suggest a better way of giving more prominence to correct information? Or do you think that's not the right priority for the site?
ndm000 5y ago
Side question - do you need to reach a certain level of membership with HN to see the downvote button? I may be missing something, but seems that's only allowed for certain individuals.
- nkurz 5y ago
  Yes, there's a minimum number of points required to downvote. I think it's currently 500. Here's an unofficial FAQ that give more information about the thresholds: https://github.com/minimaxir/hacker-news-undocumented/blob/master/README.md https://github.com/minimaxir/hacker-news-undocumented/blob/m...
nautilius 5y ago
Didn't downvote, but I am not a big fan of simply making stuff up on the fly as response. I've met my share of people who rather go this route than put in a 5sec Google search or simply admit they don't know something, and I try to avoid them.