corny keg, copper coil soldered to outside. these all have plastic quick disconnects and miraculously don't leak.
the rabbit controller drives two pumps. one goes through the 'cold' side of the peltier (if it's in cooling mode. for heating it simply reverses the current through the peltier and cooling goes in reverse) then through the corny coil and back to reservoir. the 'hot' side goes from the other side of the peltier to a car radiator (very rusty inside hence brown water) which has a PC fan blowing on it to dissipate the heat.
the whole thing is temporarily (which has become long-term temporary with a million other projects including moving/house construction) mounted on a very rickety wooden frame. the rabbit has a wireless IP address, so you connect via phone or laptop and it runs a simple program that lets you input set point and tolerance, monitors the beer temp and temp on both sides of peltier, auto shuts off at a high temp, stuff like that. if the keg is insulated well it works very well, i can do lagers at 10 degrees in ambient temps of high teens to maybe 20, but i couldn't do a lager in 30 for instance. but i can hold ales easily around 20 in most conditions, very precisely.
in this pic i actually shut it off and am using a heat belt and stc-1000 to raise and hold at higher than ambient temp to get the yeast (fuller's/wyeast 1968) to finish off and diacetyl rest. it's less noisy than running pumps and fan. but you can see the whole thing, it's small and fits in the corner of my old apartment stairwell
there's a mistake on the screen- the second setting is tolerance not set point!
first trial, before neoprene jacket and realizing i needed to use blowoff tubes
