zlacker

> But geothermal cooling would be great on the moon too. Run a pipe 2 meters under the lunar surface and it is -21C.

Isn't the moon geologically dead though - no water or geological movements?

I worry this would just result in the ground absorbing the waste heat and eventually becoming too warm to effectively cool anything. Especially because the ground itself would eventually still be limited by the rate of radiative cooling into space, right?

>>solid_+(OP)
You have to worry about changing the ground temperature even on earth FYI. When designing district heating/cooling systems with borehole fields, one of the things that you check for is to make sure that you don’t inject too much heat (or extract too much) seasonally - ideally it’s roughly balanced so any drift year over year is small.

Obviously things like the diffusivity (so conductivity, mass, density etc) of the ground matter a lot, as does the rate of heat exchange at the surface for it to reject (or absorb) heat to the environment.

>>szvsw+K
Right, I'm roughly aware that's a concern on Earth too which is why I was wondering. How's the thermal conductivity of the moon?

>>solid_+o1
Looked up some papers, and seemingly super low compared to what I would have initially guessed - probably because it’s porous/fluffy/sharp dust with lots of small voids/less compacted I’m guessing. Like, orders of magnitude less than the ground on earth. Not my area of expertise though and was just cursorily skimming papers for values. Specific heat cap and density seem like what you would expect for any rocky materials.

>>solid_+o1
Geothermal heat transfer is greatly affected by the moisture of the soil, which on the moon would be pretty low as you can imagine.

>>solid_+o1
No one ever drilled the Moon to any useful extent. All we know is that it's mostly dusty on top.

>>szvsw+H4
Might need to pour a bunch of water on the soil to increase the thermanl conductivity and make sure to never heat it above freezing?

>>solid_+(OP)
Geological activity is usually a problem for geothermal cooling. Conductivity of lunar subsurface is your main problem. Generally what makes geothermal really effective is the monstrous thermal mass of solid and liquid material compared to air as well as it's much higher conductivity. While that is true on Earth, on the Moon things are very different.

The problem isn't so much geological activity or lack thereof, as the nature of lunar regolith. Lunar regolith has a conductivity of 0.004W/mK. That is lower than aerogel! So unless the subsurface has a much higher conductivity, using subsurface cooling would be doomed.

Edit: Lunar Regolith is only the first 4-5 meters of the lunar surface.

>>justin+TG
Water would boil on the moon, any ice would sublimate. You would be better off just compacting the regolith.