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I'm writing a story where there is a large mining outpost built on a moon. This mining outpost is one large building holding around a thousand people, with an extensive system of passages and mines under the complex. I would imagine there would need to be ventilation shafts to supply air to the miners (this moon/planet does have a breathable atmosphere). I would like for the purpose of the story to have shafts connecting the passages directly to the walls of the compound, instead of simply ventilation holes on the surface of the moon.

Is it logical to use mine shafts to control temperature. And if so, would the air likely be hot, providing heat, or cold, cooling the residents?

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  • $\begingroup$ Welcome to World Building Stack Exchange PjRock! I strongly recommend you to visit our tour. And if you need help please visit our help center. Good luck with your question! $\endgroup$ – Ender Look Jun 17 '18 at 2:10
  • $\begingroup$ Does the mining expose or release hazardous gasses that need to be vented away from the habitat? Conversely, is there life on the moon that needs to be kept out of the air supply? Is the moon's atmosphere healthy to breathe without processing? $\endgroup$ – user535733 Jun 17 '18 at 2:47
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I once lived in Idaho's Silver Valley, wherein are many, many mines.

  • Shallow mines (like caves) are cool, not cold. Because they are only cool, the power needed to pump something (e.g., water) into the area to vent heat to cool the surface would likely exceed power needed to cool by actual refrigerant. In other words, it's not a cost-effective solution, whether it works or not.

  • The deep mines (say, over 500 ft deep), on the other hand, are HOT. The deeper you go, the hotter it gets (not from magma, but from pressure). The mine companies must spend a considerable amount of money cooling the mines so miners can work.

Therefore, you can't effectively cool a building or settlement on a hot surface, but you could easily warm a building or settlement on a cold surface. Consider this simple plan for a deep mine (source, "working face" is the bottom of the mine):

enter image description here

Note the upper left-hand area where the excess heat collected from cooling the mine areas is utilized in various ways.

HOWEVER

You can't simply do this with an air exchange. Remember the pressures involved. Yes, heat rises, but nowhere near fast enough for many reasons, one of which is increasing air pressure as you descend into the mine. Like the Earth's atmosphere, the air is warm at the bottom where it's thick and can hold lots of heat, and cold at the top where it's thin and can't hold as much heat. Therefore, from the perspective of realism, you can only heat your colony through the process of removing heat from the mine as real mines do today.

ONE MORE THING

No mining company in its right mind would leave the mine shaft exposed to human habitation. In other words, it wouldn't be enclosed for any reason. Let me introduce you to the idea of an "air blast."

Air blasts occur for a variety of reasons, but one of the worst is that a big chunk of rock face at the bottom of the mine shifts. It needn't shift by much. Sometimes only tens of feet, but you need to understand the astronomical inertia involved along with deep-mine air and rock pressures. A massive amount of energy is released and it's following the path of least resistance: the air channel to the surface. The result is an air blast.

Air blasts kill miners. I could hear the air blasts from deep mines (2,500+ feet) on the surface 30 miles away. An air blast would obliterate anything enclosing the mine head. They represent, quite literally, the world's biggest cannons.1

So, no living near or enclosing the mine head. Nope. Nosireebob. Anyone with mining experience (or related to a miner) who reads your book would instantly recognize that as unrealistic.


1No, you couldn't actually fire a round via an air blast. The weight of a munition round large enough to fit in the mine shaft would be too heavy for even an air blast to push. Frightening as they are, they can't be used as ranged weapons — just in case you were wondering. Physics be a harsh taskmaster, yessiree.

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    $\begingroup$ Love the air blasts! Always delighted to learn something i didn't know. Since this moon has a breathable atmosphere this means it's the future. Improvements in heat transfer, for example, thermal superconductors could make the concept more feasible. But beware air blasts, so the habitat wouldn't be open to the mines. No wonder mining is so dangerous. Plus one. $\endgroup$ – a4android Jun 17 '18 at 7:21
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    $\begingroup$ Keep in mind the heat won't increase as fast with depth on a non-geologically active moon. $\endgroup$ – John Jun 17 '18 at 18:09
  • $\begingroup$ @John, that's a curious statement as mine heat is 99% pressure. If the mass were substantially lower then I'd agree (less pressure), but geologic activity (aka, magma and the friction caused by slippage or shaking)... I don't have a geology background, but it seems less relevant. Do you know of an article somewhere? I'd love to read more about it. $\endgroup$ – JBH Jun 17 '18 at 18:13
  • $\begingroup$ Re cooling with shallow mines, you're wrong about it not being effective. See e.g. ground-source heat pump. Re living near mine heads, I give you Virginia City as a counter-example: en.wikipedia.org/wiki/Virginia_City,_Nevada $\endgroup$ – jamesqf Jun 17 '18 at 18:13
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    $\begingroup$ @JBH on earth somewhere between 45-75% of the heat is due to the radioactive heat from the core, nature.com/articles/ngeo1205 without knowing the moon gravity it is hard to say which would be dominate at the mines depth but it would not get as hot as fast with depth $\endgroup$ – John Jun 17 '18 at 18:21
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passive cooling using underground tunnels has been practiced for hundreds of years, Derinkuyu in turkey is famous for it as are several persian cities. By combining windtowers and subterranean wet tunnels (qanat) they can cool buildings by tens of degrees. The design exploits low pressure created by wind induced suction to draw in air cooled by the evaporative cooling on the qanat.

Using deeper tunnels you can heat a building use geothermal heat as manassehkatz mentioned.

enter image description here

enter image description here

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    $\begingroup$ See also Zimbabwe's Eastgate Center $\endgroup$ – Draco18s Jun 17 '18 at 15:50
  • $\begingroup$ Sorry, your upper picture will never work. The cold air is heavier and will go down. If it were as on this picture, it would go backward. Really, these towers went up - up to 10 storeys in Yemen, and the air in upper storeys became HOT, and created the negative pressure. That "wind" explains nothing - for it creates the same negative pressure in both holes. $\endgroup$ – Gangnus Jun 17 '18 at 22:50
  • $\begingroup$ @Gangnus: It's not clear what you're talking about. The tower DOES go up in the picture. Air is drawn up by the Coandă effect, according to Wikipedia, and also by heated air rising in the tower (stack effect), and the system is designed so that the replacement air for the draft up the tower will be cooler than ambient. $\endgroup$ – Nick Matteo Jun 18 '18 at 1:12
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    $\begingroup$ @Gangnus arguing they won't work does not make a lot of sense when they exist and function, what you say would be true IF there was no wind but there basically always i. It exploits brnoulli's principle to generate a pressure differential. $\endgroup$ – John Jun 18 '18 at 13:44
  • $\begingroup$ @John 1. The fact that natural climatization of Arabs and Persians worked does not prove that this picture is correct. 2. The scheme of the air circulation is drawn by some contemporary author. Obviously, physically illiterate. 3. I had given the concrete physical arguments. Answer them or if you can't, wait for somebody who can to support your thoughts. $\endgroup$ – Gangnus Jun 21 '18 at 22:10
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Geothermal Heat Pump - Heating & Cooling

A Geothermal Heat Pump can work well on Earth for both heating and cooling. If you have a moon/planet where the temperature below ground is fairly constant (like Earth) but has dramatic swings above ground due to issues with the atmosphere, length of day or other factors, then a geothermal heat pump is an ideal solution. Natural air convection through the mine shafts would not be enough to do the job. Even pumped air (blowers) would not get the job done, unless you moved it an unsafe speeds. But if you dig mine shafts for other purposes and install a pumped liquid system, then you can easily transfer heat to the surface when you need it and away from the surface when you don't. You would need large heat exchangers installed in the mines and small ones in each living area. All the necessary technology exists - and is in use - today on Earth.

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    $\begingroup$ Air-based systems are conceptually simple, but the specific heat of air is pretty small, which means that for a given system you need to pump a lot of it around to transfer a given amount of heat. My impression is that systems using water or refrigerants such as Freon, ammonia, or isobutane are a lot more common here on Earth. (And hey, you could use Freon on the moon—no ozone layer to worry about there...) $\endgroup$ – Michael Seifert Jun 17 '18 at 12:27
  • $\begingroup$ @MichaelSeifert I'll adjust a little to emphasize liquid vs. air. But I wouldn't assume Freon is not an issue - if there is a breathable atmosphere then there may an ozone layer. $\endgroup$ – manassehkatz-Reinstate Monica Jun 17 '18 at 14:49
  • $\begingroup$ Good point. I missed the "breathable atmosphere" part in the question and thought we were talking about Earth's satellite. $\endgroup$ – Michael Seifert Jun 17 '18 at 15:40
  • $\begingroup$ This is a ground-source heat pump, not geothermal, which would be taking advantage of a hot spring or other geothermal resource. $\endgroup$ – jamesqf Jun 17 '18 at 18:15
  • $\begingroup$ @jamesqf True, but I called it a Geothermal Heat Pump based on the Wikipedia article - which also mentions ground source heat pump as an alternate name. $\endgroup$ – manassehkatz-Reinstate Monica Jun 17 '18 at 18:20
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The temperature of relatively shallow mines (and things like subway tunnels) are (close to) constant throughout the day and the year -- it's the average temperature on the surface (not the average high temperature, just the average 24/7/365 temperature).

But if you duct air out to provide warmth or coolness, you're going to change that -- either by cooling or warming the air so it loses it's effectiveness. So yes, this can work, to provide either warming or cooling (but not both) but not on a large scale like whole blocks of office buildings.

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