I've used a submerged fermentor in a 25gal keg tub. Then I use an old copper submersible chiller wrapped around the fermentor. That is plumbed to a cooler with an in and out powered by a pond water pump. The pump is electronically controlled by a thermostat whichcycles the ice.water through the keg tub around the fermentor and back to the ice slurry sump which is the cooler. It will cycle until the temp drops enough and is actually fairly efficient. I wouldn't necessarily advise this method as a first attempt. I had to whip something up fast and I had all this craps laying around already. Its some kind of rigged unjacketed cooling system I guess. Ice was free at work which helped out a bunch.
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