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I've read that on Mars you lose 30% of your heat through convection and 70% through black body radiation. (The much lower amount from convection due to the tenous atmosphere vs. Earth.) http://www.sciencemag.org/news/2014/06/no-wind-chill-mars

If so could the heat be used in greenhouses attached to the base? It seems wasteful to not use it elsewhere. The greenhouses would have a higher pressure than the atmosphere which should also increase convection from the radiators of the habitat.

One final question, what pressure would be high enough on Mars that you would not need to heat or cool? I understand Mars is too low in pressure, as is obviously the ISS or the moon, and Earth pressure is too much so that you quickly become cold due to convection. 30,000 feet also appears to have too much pressure and cause excessive cooling due to convection. The paper below appears to be a study of altitude, pressure and convection rates in avionic equipment but the data is not easily extracted.

https://dspace.mit.edu/bitstream/handle/1721.1/39011/20404614-MIT.pdf

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    $\begingroup$ Excellent question. I've also been wondering if a Mars colony would be "exothermic" or "endothermic". My suspicion is that colonies would be heavily insulated to help manage the day/night temperature fluctuations and would need to discard low grade heat produced by humans and life support machinery. But presumably it would also be possible to make lightly insulated buildings that utilize waste heat from a nuclear reactor to stay warm especially at night. $\endgroup$ – Blake Walsh Oct 5 '17 at 7:24
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Yes, it would.

The base, for sustenance, would require a lot of electric power, which would dissipate as heat upon use.

Greenhouses, to produce useful, edible plants, room-efficient plants would require extra lighting, and quite a bit of it. Natural light levels on Mars are sufficient to grow some ferns or other plants accustomed to deep shade. You might get some berries. You wouldn't get nearly enough to feed the crew. You need actual, efficient cultivars - legumes, potatoes, maybe grains - plants that provide abundant, highly nutritious crop. And their light requirements are so high you'll need a lot of growth lights - which will produce a lot of excess heat.

The greenhouses are hardly mass- and volume-efficient where it comes to production of oxygen. Scrubbing excess CO2 and production of oxygen through MOXIE would produce another couple kilowatts per human.

Add heat from all the electronic equipment, heat from losses on charging/discharging batteries (to last the night), human body heat, machinery for purifying water and so on - you'll quickly find the heat budget of the base goes way above expenditure - especially if the base is at least partially covered by soil to protect it from cosmic radiation, which severely limits radiative dissipation.

How much heat dissipation capacity the base would need is still subject to study - we don't have complete plans, we don't know all the variables, but we know already radiators will be a must.

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  • $\begingroup$ Interesting, is there anything useful the heat can used for? Melting ice, heating up rocks for processing, heating up a large low pressure greenhouse with lichen and other none food plants for slow oxygen/soil production, something! $\endgroup$ – Brooks Nelson Dec 10 '17 at 15:56
  • $\begingroup$ @BrooksNelson: basic problem: a lot of heat, but not too high temperature gradient; you can't remove the heat from the greenhouses only after the plans boil! This is not very useful. I'm sure it would be usable to keep outdoor infrastructure heated to provide optimal operational conditions (e.g. keep grease of bearings soft, prevent thermal stresses between day and night) but I don't have any solid data on this. $\endgroup$ – SF. Dec 10 '17 at 17:51
  • $\begingroup$ do you have any numbers for any of this? $\endgroup$ – Mohammad Athar Dec 11 '17 at 14:23
  • $\begingroup$ @MohammadAthar: Somewhere... separate calculations for MOXIE and for growth lights. The first should be easy to do yourself, extrapolating current MOXIE power requirements and output to human oxygen requirements. For the latter, search calculations why Mark Watney in "The Martian" wouldn't be able to keep his potato plant running. $\endgroup$ – SF. Dec 12 '17 at 18:04
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    $\begingroup$ Just have to mention how wrong it is to describe sunlight at Mars as "deep shade", using any sensible lux scale the brightness on Mars would be between "indirect sunlight" and "full sun", it's actually hard to identify plants that most definitely wont get enough sunlight on Mars, plants grown in the open on Earth are typically far more limited by temperature and water than getting enough sunlight, if you've ever seen the outstanding plant growth in very cloudy/rainy climates you'll know what I mean. "deep shade" would accurately describe the illumination level out at Jupiter or even Saturn. $\endgroup$ – Blake Walsh Jul 15 '18 at 23:42
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Would it not be possible to use semiconductor sandwiches using the Seebeck-Peltier (thermoelectric) effect to derive heat from the excess heat? Pump the warmed air into a holding container (or use an air conditioner to cool the air, which unit then expels much hotter air out its exhaust) to collect and concentrate the heat, which could then be used for various commercial and industrial processes--clothes washing, cooking, waste treatment, kilning, preheating of blast furnaces, etc. All that is needed for a thermoelectric effect is a temperature difference, and if the gradient is not strong, then the efficiency will be low, but it will still produce a nonzero amount of electricity, which can be used to supplement or replace the output of the main generator or reactor, allowing it to be run less often or for reduced duration, thus lowering the total heat output. Eventually, the system (including human consumers of ambient heat in water and air) would reach an energy-heat economic equilibrium, even if it never reaches a classical "thermal equilibrium."

The most likely use to which the colony will put the "excess" heat is in expansion of the colony by pre-conditioning as-yet-empty lavatubes, heating the perimeter and the pressurized CO2 they have pumped into it. Add in some drip irrigation, sunlamps (once these reach sufficient output density, you can redirect the heat), and soil/hydroponic vats, and add seedlings. Come back in a month to bleed off the excess oxygen, rinse and repeat.

I daresay that a colony determined to enact both self-sufficiency and expansion will always find a use for excess heat, to the extent that Mars may even have to import heat from Earth (/humor/).

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  • $\begingroup$ The idea of "harvesting" your waste heat using thermoelectrics is flawed and generally unworkable. Your grow lights' waste heat will turn your greenhouse into an oven. If you try to harvest the waste heat at the light, the hot side is the lamp, cold side is your greenhouse, and as you generate power you pass heat to the "cold side" until it's the same temperature as your grow lamp and your plants are cooked. You need to pipe the heat to a convector/radiator outside with an 80° "hot side" cooling loop if that's your greenhouse temp. You can harvest power there but your radiator size doubles +. $\endgroup$ – Kengineer Jan 17 '18 at 19:51

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