Theoretical temperature question

[Jack91]

Hi all,
Been wondering something lately and can't work it out.

If you had a shipping container in the middle of a paddock, and it had a split system in it. Say it's 40 degrees c outside and with the aircon going it's 20 degrees c inside the container and you opened the doors and timed how long it took to equalise to the 40 degrees outside. Then did the experiment again with it being 0 degrees outside and heated to 20 degrees inside and opened the doors, would it take more or less or the same amount of time to equalise to outside temperature? Excluding factors like shade inside the container and time of day etc, and why?

[Citroënbender]

Humidity and breeze may affect the result, too.

Thermal conductivity of the corten will remain constant, and the opening size/position won’t change. I reckon time to equalise should be fairly similar in theory; all external factors like wind, breeze, surrounding objects being unchanged.

All that said and done, red car at fault.

[Jack91]

Everyone I've asked says the heating would escape the container faster than the heat entering it. Perhaps it would be better to imagine 40 outside 20 inside, then 20 outside 40 inside, for an even comparison. It doesn't have to be a container even, even just a plastic bag, or somehow temporary concealed pocket of air.

[94_ef]

I'm with the general consensus.

The heat will want to rise. So it will flow out the top. There is essentially no restriction to convection.

The cold air will want to spread sideways. Air resistance will work against it.

However if the container was suspended in the air and not on the ground then it might be a different story. Basically just think pressure applied to surface area. The warm air will all be pushing up. The cold air on the ground spreading sideways will have a larger area and therefor less pressure to move air out of the way.

[MattSAU2XR8]

Sounds like you are thinking of making a container residence?

I think for the situations described the result would be largely similar whether its heat gain or heat loss, if the doors were wide open, certainly less than 5 mins to equalise either way

Although the interior walls and other fittings would take longer to warm up or cool down providing a sort of buffer or 'heat sink' if you closed the doors again the container would probably swing back several degrees toward the desired 20 as the walls took up or shed some heat.

If you were using a container for a home then I'd suggest:
- If it will be in a hot climate then paint it gloss white, at least on the north side since the heat load from direct sunlight can be up to 1000 watts per metre squared, way more than the aircon will be able to remove
- And line and insulate it
- And ideally install a simple frame with some steel roofing perhaps a foot above the container to prevent direct sunlight hitting it, or water pooling on the top
- And get some stumps or blocks poured so its up off the ground a bit, won't help with heating or cooling but will stop it rusting away and dirt blowing in and give drainage for shower and toilet and so on

The other thing that could be worth looking at, on the off change that its available, would be an old refrigerated container or truck body - much more suited to a dwelling...

[b0son]

Originally Posted by Jack91

would it take more or less or the same amount of time to equalise to outside temperature?

Airflow depends on what, if any, pressure differential there is between inside/outside, as this governs in which direction the air will flow, and how fast.

If they start at the same temperature/pressure, and then you seal the container to run the aircon, upon opening, air would flow from 40deg (out) to 20deg (in, lower pressure), and 20deg(in, higher pressure) to 0deg (out).

BUT... for air flowing in, the rate of flow slows as the pressure rises because you are moving air into a confined space. OTOH, for air flowing out, it is effectively an open space, the air outside never rises in pressure relative to the room, so in theory should flow at a constant rate until equilibrium.