This brewing closet is based upon the Son of Fermentation Chiller design by Ken Schwartz. This design uses a cold air well and a fan to pump the cold air over the fermenting beer. 7 milk jugs full of frozen water keep the air in the bottom cold. Since warm air rises and cold air sinks, the fermenter is only subjected to cooling air when the fan is on.
Where my design differs is the use of a closet from Wal-Mart, an inexpensive house thermostat, and an dual sensor digital thermometer from Radio Shack . I chose the closet as I had already confiscated it and been storing my beer ingredients for a couple months and it was sturdy. The total cost of modifications to this normal closet to make it a fermentation closet amounted to about $50.The brewing closet was lined with 3 layers. The shelf to hold the fermenting beer was additionaly supported by 4 1x3 legs placed around the edges of the shelf. These legs are hidden by the foam insulation lining the cabinet. I used construction adhesive to glue the insulation to the cabinent and to the previous layers of insulation. of 3/4 inch thick white styrofoam insulation.
After the foam, I added the cooling controls which included a cheap house thermostat (with a cooling switch), a 3 inch squirrel cage computer fan, and a 9 volt 200 milliamp DC power supply. The power runs directly through the mercury in the thermostat, through the fan, and out throught the other power supply line. With the thermostat set, any temperature greater than the setpoint causes the mercury bulb to tilt and make contact allowing the current to flow and start the fan. The fan extracts air from the bottom of the cold air chamber and pushes it up into the fermentation chamber. The air exits the fermentation chamber through a vent in the top back right corner and flows down into the cold air chamber over the frozen milk jugs where it is cooled again.
The digital thermometer with external sensor was used to monitor the internal temperatures without opening the brew closet up. As you can see I can get the temps down easily within fermentation range. A test was a full carboy of water and the closet was able to cool 6 gal of water from 74F to 55F in a day starting with 7 one gallon milk containers of 15F ice. After that day, I still had ice in the jugs and the thermostat was kicking the fan off. I'm not sure how low of a temperature I could have gotten by switching the fan to constant on.
