Originally Posted by Mattbastard
I could see that mini fridge cooling the space occupied by ONE carboy, but four is a bit of a stretch. If you upgraded to a larger mini fridge, then maybe.
Why don't you just cut the side off a fridge and put it right in the chamber with the carboys?
One thing i found when putting mine together was that most of the mini fridges I looked at, ranging from 1.5 cuf to 6.5cuf had the exact same compressor ratings. With that knowledge, you can find the formulas on line to determine the BTU usage you would need to keep an area of X cubic feet at Y temperature difference from ambient with Z insulation rating. Its a bit of a chore, but worth it when you figure out what kind of compressor is needed to keep your area cool.
As for the project, it may be easier to scrap the fridge you have (see the link above or in my sig) instead of trying to pipe in cold air from above. My main concern is not so much the fridge keeping up with all those fermentors, but the ability to pipe enough cool air from that small space, through those pipes to keep an area that large at a reasonable temperature. It could be possible, but you would need a pretty decent blower and a fairly good diameter pipe to move enough air to accomplish your goal.