DIY cooling system for terrarium/orchidarium/vivarium?

You may be able to go down to 80-82F with a swamp cooler; notice that lowest temp decreases with increasing humidity. If you need lower temperature, you will need some active cooling. I use an aquarium chiller that flows cold water over a rock face, and a fan blows the terrarium air over it. Cools as well the air and also adds humidity. Aquarium chillers are quite expensive (particularly new). Some people use the chiller form an old fridge for DYI projects.
I once tried a peltier cooled cold finger, but that is by far too low in power (for my 90 gal tank). That may work for up to about 5 gals.

 

If the cooler relies on evaporation, it may actually be less-effective in a closed volume.

 

No, that's pretty much what it'll have to do. Dry outside air evaporates and cools the air going into the chamber. Will it be enough cooling? I can't say, but my gut tells me that the needed volume of air might make it too windy in the tank.

 

I think if you added ducting to a pad and fan humidifier and ran said ducting into your grow space, that would basically work a decent cooler. I definitely remember my old humidifier dropping the room it was in a few degrees. Also What sort of light are you using? I had been using T5s on my tank and it was running a bit hot(well not problematic now but would be in the summer) and switched in LED retrofit bulbs into the fixture, and that dropped my tank by like 10 degrees.

 

Do you have anywhere cooler (like a basement) you could move it too? That would help. Also my light were separated by a few inches (when I had the flurosecent bulbs, now the light directly on the glass) and a piece of glass but I still got a decent temp drop just going to all LEDs

 

What do you mean by cooling blanket?

 

I have seen pictures of people using an aquarium chiller and running lines of cold water through their tanks to cool them so its been done. I'd run the lines on the interior of the terrarium if at all possible, to be most efficient. If you run it on the outside, you're also cooling the room its in.

 

I built myself a peltier cooler for my cold orchid box.
I managed to cool it by about 5deg celsius under the room temperature.