I have been playing around with the idea of cooling my carboy by creating an ice water jacket. I would use fleece or an old sweatshirt to make a jacket for the carboy and sew in a long length of vinyl tubing run back and forth to contact the carboy. Then, cold water would be pumped through the tube as needed to cool the carboy.
The simplest version could use a thermostat to control a pump, with the pump forcing ice water from my 10 gallon igloo MLT through the jacket. The thermostat would have to have the temperature sensor extended to tape it to the carboy and would probably have to drive a relay or FET switch to handle the current for the water pump (I have a 12 volt liquid pump).
If the basic idea works there are many ways to get fancy such as better insulation, or other sources of cool liquid, or adding a heating feature. What I like about the basic idea however is that it is not very expensive and requires virtually no extra space to store it when not in use.
Will this work? Has this been tried before?