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.