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The heat wave that my area is going through got me looking longingly at the ice in my freezer. I understand that leaving the freezer door open does not help cool the house, but it got me thinking...

Take a world that has an exceptionally long day/night cycle (or exceptionally long and severe seasons). As normal during the "day" times the planet gets inhospitably hot, and during the "night" times it gets to deathly cold temperatures. For some reason there is some unobtainium ore or similar on the planet that makes colonizing a decent (or at least profitable) idea. Lets say that either you cannot bury the colony in the ground to protect from the temperatures, or that it confers no benefit for some reason.

Using that world, I thought of a cycle where during the cold spells the colony would manufacture large amounts of ice and store them in large vaults and use the heat generated by the process to warm the colony. In the warm months the colony would then use the ice to help keep things cooled off.

Using all of this:

  • Would this even be possible?
  • How much ice would have to be converted in both seasons?
  • Is this a practical solution in this case, or would traditional HVAC still be better?
  • How long would each season have to be in order for this to even work?
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You are simply using the heat capacity of water as a heat sink. This totally works, but nobody does it (that I know of) for the very simple reason that you can use any naturally occurring body of water or large mass of dirt as a heat sink to get the same result. The specific technology is called "Seasonal thermal energy storage". Looking at the article it seems somebody has been studying building artificial "heat banks".

There is also a more general category of "renewable heat" that you might find interesting.

Really only even questionable thing about your idea is that it seems to suggest storing manufactured ice. If you can't use the ground and there is no natural body of water, you would essentially be building an artificial lake. As long is it is deep enough (and you have access to mining equipment and possibly redundant mine shafts) its bottom will be at +4 centigrade even after you pump lots of heat in or out.

It just needs to be large enough to have the heat capacity you need. Which obviously depends on the climate and the size of the settlement. That is not really an issue, since such systems have the nice property of being able to be built incrementally. A reservoir that holds 10% of the heat you need is still useful.

Compared to HVAC the big differentiator is the high initial cost. So fundamentally it comes down to economics (availability of funds) and how long you expect the settlement to be in use. For short term use HVAC is cheaper, for permanent settlements with funds available seasonal heat storage can pay itself back.

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  • $\begingroup$ Interesting...so there would be little advantage to using ice over a lake in the settlement for heat storage? $\endgroup$ – Emerson Jul 6 '15 at 2:35
  • $\begingroup$ @Emerson I would say that it depends a bit: seeing as your extreme climate planet-wise seems to lead to an absence of atmosphere. If that's the case, ice is really preferable to water bodies. Otherwise it depends on the system you use. Having a constant temperature on one side is an advantage for thermal exchanger, so you need a large lake, or a lot of ice. $\endgroup$ – clem steredenn Jul 6 '15 at 7:10
  • $\begingroup$ @Emerson That depends, as JDlugosz mentions in his answer there are cases there the higher energy density from the phase change or dealing with solid instead of liquid is useful. So while there is little advantage in general that I can see, you can make up something if you wish. Note though that either way you have to deal with both liquid and solid phases and you will lose some water to evaporation and leakage, so you really need to think of the entire water cycle of the settlement. $\endgroup$ – Ville Niemi Jul 6 '15 at 22:50
  • $\begingroup$ @Emerson Although you also need to think of the energy system as a whole, there might be an excess of waste heat available from refining and other processes related to mining and similarly dumping excess heat into the mines might be trivial. So there might be no economic sense in storing thermal energy at all. $\endgroup$ – Ville Niemi Jul 6 '15 at 22:50
  • $\begingroup$ Some great thoughts to think about, thank you! $\endgroup$ – Emerson Jul 7 '15 at 2:27
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That is in fact done. I recall a building system where the refrigerator makes ice when power is cheapest and workin-space A/C is not needed. In the hot part of the day, chilled watter circulates through pipes in the walls without any need to run the compressor while it's expensive to do so.

Water itself has an awsome heat capacity. The phase-change involves another large jump of energy: as much as changing the water by 80° C. That is more than the energy between summe and freezing temperature, so it makes sense to bank it that way.

Ice does not convect and actually insulates itself (how igloos work) and ice bouses show that it can be stored all summer with no technology.

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