So my fermentation fridge died and left me in the lurch. I decided that I wanted to be able to ferment more than a 10 gallon batch and would need to find space to fit multiple fermenters. Luckily I have a closet in my garage very close to where I do all of my brewing. It is under a set of stairs so it shrinks the deeper you get into the closet. Also, the back of the closet backs up to the crawl space under the foundation of the house. Seems like it would make a nice fermentation closet/cellar.
I cleared it out and started gathering supplies. The closet was already finished off with drywall and I didn't really want to rip that out. So, I bought some reflectrix insulation and stapeled it up to the ceiling and along the walls. The floor is concrete so I put down some foam insulation and covered it with mdf board. I picked up a portable air conditioning unit from Costco and ran the vent hose through the back of the closet and vented it out under the house. I will eventually run an electrical outlet from under the house to the back of the closet as well. Currently for power I am running an extension cord from the garage into the closet to the air conditioning unit.
I've had the closet up and running for a couple of weeks now and even in 100* heat I can keep the room at 64* fairly easily. Unfortunately the ac unit only goes down to 64*, so I'll have to either hot wire it or find a cheap wine cellar unit to get the temp down farther. Luckily, I brew almost exclusively ales, so that temp works out fine for now.
The closet is big enough for me to put 2 15 gallon mini brew fermenters (I only have one now) plus a ton of cornies. I currently have one 15 gallon fermenter, 14 cornies, and 2 ale pails in the closet.
Finally a picture of the almost final result. Sorry for the size of the picture.