I've been drawing up designs for a system to control fermentation temperature. My current plan involves a blanket with flexible tubing stitched back and forth over one side, so I can wrap the blanket around the fermenter and velcro it tight. The hosing would run through some copper windings which are thermally bonded to one side of a peltier unit (for those unaware, peltier units work to rapidly and dramatically cool one side while heating the other, depending on which way the voltage is applied). I'll use a microcontroller and a thermistor to sense the temperature of the wort, decide whether it needs to be heated or cooled and flip the voltage of the peltier as needed, then activate a pump to circulate the fluid (most likely just water).
My thoughts are that the blanket will help insulate the fermenter, and although it will likely not be the quickest way to change the temperature, it should theoretically be capable of keeping the beer within the set range. My concerns are that the tubing might not cool/heat the fermenter as well as I hope, that I'd have trouble getting the peltier to chill/heat the water as much as is needed without pumping very slowly, or that it'll be too loud.
Any thoughts? Anyone else tried something similar?