Cooling a very small space

I also grow many intermediate or I-W growers in a 30g terrarium indoors and haven't had much trouble with that temp range or maybe a bit higher in the summer. With that being said, you could use two glass panes for the top with a gap for outside air exchange and add a cool mist humidifier. The dryer outside air combined with the humidifier seems to create an evaporative cooling effect and keep it a little cooler in the tank.

 

A few things. First, 70°F daytime temps are already on the cooler side of intermediate; I wouldn't worry about cooling during the day. Second, if you can figure out how to set it up, I'd recommend a Peltier/thermo-electric cooler. Sadly, I have no clue where to start with them, so I can't offer any pointers. Third, In my mini-fridge, I use the ZooMed hygrotherm to control the daytime and nighttime temps; it's got a nifty feature where the nighttime temperature drop is regulated by a photocell, which is handy, especially if your light's on a timer.

Lastly, what all have you got in there right now?

 

Jon has a thread somewhere on here where he used a peltier cooler set up to cool a larger tank, but I'd imagine the same concept could be applied to your situation.

There was also Chris's cool 10g tank where he dissected a dorm fridge and used the cooling parts to truly create a cold tank (down into the 40s, I think). Those threads might have been lost in the ownership changeover, though.

I'm sure you could find a wine chiller that will fit in that space. I've seen some at Lowes much smaller than 10g with adjustable temp settings. I have a thread on here explaining how I set up my cool tank using a fridge, but you could rig up the thermostat in the same way. I used the same one that Zack mentioned.

You may also want to search on CP forums. It seems there's been more effort/research put into providing conditions for highland Neps and Heliamphora in non-ideal climates than there has been with orchids, though, the information is still applicable to orchids.

Zach from Josh's Frogs posted a thread on the dart frog forum about a cooled tank for highland lamasi that contained a good bit of information and ideas regarding cooling tanks for cloud forest species. PM me if you don't know the site I'm referring to. I wasn't sure if I could mention it here, but I recognize your username from "over there".

 

No problem! In Zach's lamasi thread over there, there's a link to one of the CP forums. If you search "cool tank" or something related and only include results for that site through Google, you'll find many different methods to create highland Nep tanks.