This article is taken form a thread on www.homebrewtalk.com by John Beere http://www.homebrewtalk.com/showthread.php?t=11440
So I've started my latest project - a walk-in cooler. It will be roughly 5' X 5' X 7' and will be located in our utility closet / laundry room in the garage and take up slightly more than half of the room. I am going to insulate the walls with R30 insulation (the heaviest I can find) and then 2 layers of this insulated foam board I found at Lowes which is 2" thick and listed as R15. I've picked out a frigidare 12k BTU window AC combined with a Ranco controller to cool it. My goal is to keep the entire cooler between 35 and 37 degrees year round.
I am also considering creating a fermentation cooler that is external to the cooler but is fed cold air on demand from a hole in the side of the cooler. It will have its own temperature controller which will power two fans (one push, one pull) and baffles to exchange cold air as necessary to maintain whatever my target fermentation temperature is.
I will update this post as I make progress but it will be a little slow going as I am pretty busy with work right now. I also plan on detailing the entire process on my website www.johnbeere.com when I get it setup as there is very limited information on this type project on the net - but from the info I've found (mainly on this forum), I am confident in the results.
I made some progress today... bought 5 rolls of Reflectix 24" wide foil insulation at Lowes and got it installed on the two brick walls. I was able to put it between the brick and the joists due the to way the room was originally constructed. They recommend airspace of at least 1/2"... I don't think I ended up with that much overall but there is some airspace due to the crap mortaring on the inside of the wall. I'm going to end up pushing it closer to the wall when I lay the insulation as that R30 stuff is thick stuff... still better than nothing right? I also used expanding foam and duct tape to begin closing all the gaps... gotta go get more tape tomorrow.
Update on the AC: I test wired a new Ranco controller into the AC this evening. This was the step I was most worried about and, now that its done, I can't believe how easy it was... I was able to completely bypass the built-in controls on the first try. I will officially re-wire it tomorrow. The diagram at http://franklinbrew.org/members/sj/walkin.html is correct, even for my brand new AC.