A note, years on. I don't have this shed anymore, and I haven't run that walk-in in a long time. I've left the original tour below exactly as I wrote it, because the idea behind it has aged well. A window air conditioner paired with a good controller is still about the cheapest walk-in cooler a homebrewer can build, and these photos show you what that actually looks like.
The one thing I would add today is about the controller. Mine was sized to the air conditioner it switched, and that is the part people tend to skip. A walk-in's compressor pulls real current (far more than the fermentation fridge most of the inexpensive plug-in controllers are built for), and a number of those cheaper units are rated well below what a window air conditioner draws. Whatever controller you use, check its amp rating against your air conditioner's running amps and leave yourself some headroom. Get that part right and the rest is mostly insulation and patience.
I described this cheap walk-in cooler on the MoreBeer forum and on The Brewing Network show, and some people asked for photos. Here's the tour.
This is the brew shed. It used to just be the garden shed. Now it holds all my junk, plus the walk-in cooler.With the door open, you can see some of the brewing gear on the shelving unit.I use 30-gallon trash cans for storing base grain. Each is lined with thick trash bags, and I keep the grain in its original sack. I've never had a rodent or a single bug of any kind in my grain. There's one bin for English Pale Ale malt (usually Crisp Maris Otter), one for Pilsner (usually Durst), and one for Munich (also Durst). One wall of the walk-in is on the left side of this picture.Specialty grains: only a portion of them. I keep them in jars that screw closed airtight, each holding just over 5 lbs. I've got every grain here that MoreBeer and the local stores carry. No sense in not having the right tool on hand.The cooling unit for the walk-in: just a 12,000 BTU Daewoo wall A/C unit I bought at Fry's on winter clearance for about $100, hooked to a Ranco controller from morebeer.com (it can handle ~13 amps; the A/C draws a max of 11). An A/C guy down the street swore it wouldn't last a week at 37°F. About four years later it still worked perfectly. (At about 5+ years the compressor finally died, right when the Zymurgy article on walk-in coolers was being printed. Worth it? For me, yes. I replaced it with a 6,000 BTU unit, my only winter option; it now holds steady around 40°F.) A few questions people have asked: the inside is about 4.5′ × 5.5′ × 7′ (~175 cubic feet). Keeping it below 40°F is no problem even in our 110°F summers. Even on 110°F days it runs maybe 30 minutes total once or twice a day, costing about $2–$3 a month averaged across the year. Insulation: 4″ of urethane board (two 2″ boards) over insulated 2×4 stud walls, about $200 worth when I did it. Regular Styrofoam board costs about a tenth as much but insulates less. (The dollar amounts in this caption are 2007 prices.)Some of the case boxes of beer. I can fit about 30 cases on each side. The slips of paper are inventory sheets telling me what's in each box, so I can find the right beer for a competition or just to enjoy.On the other side, about 10 kegs, stacked two high and two deep. To build the walk-in, I insulated the stud cavities with roll insulation, then added two layers of 2″ urethane to make a giant box. The insulation was the most expensive part; cheaper Styrofoam works but won't be as temperature-stable.
