Condensation within unoccupied space

[rmk625]

Can someone please help- I get confused with dew point temperature especially at the extremes and odd situations. For example, if you've got a room, say more of an electrical enclosure type building (90"H x 36"W x 96"D), not normally occupied, metal construction and no insulation, small heaters are put in and I'm trying to determine if a couple of 250W heaters would be sufficient to prevent condensation. But without any latent heat generating stuff inside (e.g., people or tea kettles), is there ever really a likelihood of condensation on the interior walls even with no heat?

I've done some quick hand calcs (and can move onto the official load calcs via software if necessary) and come up with a U-value of 1.3 Btu/hr-ft2-deg F (no real help from metal walls that are uninsulated of course), which gives a delta T of about 7 deg F if I had 500 W heaters and 28 Deg F if I assume 2000 W (which of course tells me if I'm -10 deg F outside, the inside surface temp would be 18 Deg F for example), but that's where I get lost. What am I calculating anyway? It's not like I'm trying to maintain a temperature for human occupancy and what is the RH inside necessary to determine a dew point temp?

Please help: I know there is something fundamental I am missing or have forgotten.

Thanks.

 

[MintJulep]

Is there some form of ventilation in the enclosure? A fan, or even just some grilles or louvers?

If so then air from the outside will be inside too.

If the surface temperature of your walls is colder than the dew point of that air then you will have condensation.

So the trick is, what is the dew point of outside air, after it's been warmed up a little bit. The answer is "it depends".

Just assume that at some point there will be condensation and design accordingly.