2
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Assume you have a reasonably well thermally insulated box of air which you want to keep warm. It has at least one heat source, and it has at least one heat sink. One of the options available to you is to attach a second volume to the first, on the bottom of it, hoping to rely on the idea that the coldest air will collect in the lower volume that you do not care about.

Example:

+---------------+
|Volume 1       |  <-- at least one each of heat sink/source in here
|        S      |
+------------+  |
         ^   |  |
heat     |   |V2|  <-- Volume 2 added hoping to keep Volume 1 warmer
source(S)|   |  |
             +--+

How do we figure out what affect adding the second volume will have on the temperature of the first, upper volume?

For context, this question was actually raised initially from the topic of winter camping in cold areas. Someone had heard of advise to dig a hole straight down through the snow in the bottom of your igloo to give cold air a lower place to go that won't bother you, keeping the rest of the igloo slightly warmer. We are skeptical, but we are hoping to approach this logically instead of just dismissing the idea. We want to figure out how to estimate the effect that such a hole would really have.

So the heat source is human bodies resting on the floor of the upper volume, and the heat loss is due to various things including draft from door and ventilation holes and from loss through insulation (not very significant I don't think, as the snow actually insulates surprisingly well).

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  • $\begingroup$ I think the title of this does not make it clear at a glance. If anyone can suggest a better title that makes the question clear, especially since I don't know the thermodynamics lingo, I'd appreciate it. Similar goes for the body too I suppose; if I've misused any terms or need to make similar adjustments, I'm open to that. $\endgroup$
    – Aaron
    Jun 26, 2018 at 22:18
  • $\begingroup$ I've heard of the idea that the portal to the outside would be placed below the heated level and below the outside level. There it would function as a "cold trap", so that heated air didn't flow out the exit and leave. But that's because the exit is necessary to have in the first place. Not that the hole is dug to give cold air somewhere to go. $\endgroup$
    – BowlOfRed
    Jun 26, 2018 at 22:24
  • $\begingroup$ @BowlOfRed Yes, I agree completely, and that was what I thought the person was talking about at first, but then I realized that they had heard of digging a separate hole to collect cold air at a lower elevation. I think that the benefit would not even be noticeable, quite negligible, but I don't want to dismiss it in case I'm wrong. $\endgroup$
    – Aaron
    Jun 26, 2018 at 22:32
  • $\begingroup$ And I would just go test it, except that this would not be an easy thing to test. $\endgroup$
    – Aaron
    Jun 26, 2018 at 22:33
  • $\begingroup$ Where do you presume the heat sink and source are placed in the room? $\endgroup$
    – Deep
    Jun 28, 2018 at 10:36

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