Hi Dave,
The evaporation and air movement probably do help keep the temp down, but that is offset in my case by the heat from the lights, even though they are separated from the growing area by plexiglass. The temperature range seems to have more to do with proximity to the lights as well - it's probably about 5 degrees difference between the top and bottom of the case, though that varies a bit with the opening and closing of the doors. The warmth of the lights seems to add some heat to the top of the case, even though the plex is there.
When I built my first case I tried to make a kind of evaporative cooling system, using cloth on one side of the case that hung down in the water at the bottom and exhaust fans at the other end to draw the water through the case, but that didn't work. I'm still convinced, however, that something like that could be done, though it probably wouldn't work here since the humidity is usually high here and evaporate cooling works best in a dry environment.
If I built another I'd make it higher by at least a foot, since you can always raise the plants up, but you can't lower them any further than the bottom of the case.
Looking back over this, I should have mentioned that this is in a basement which helps keep the temp down and in cooler weather I also control the temp by opening a window (or closing it), but the temperature of the room is pretty much the temperature of the case.
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