To cool my beer during fermentation, I made something simple. It's similar
to a wort chiller. But this completely wraps around the outside of the
carboy. attached to the top end of the coil is an upside down frozen 2 liter
of water. The ice melts and ice cold water drips down through the coil and
into a bucket at the other end. Thus keeping the glass cold and chilling the
beer. Install an insulating jacket over the carboy and coils. Rotating 2
liters need to be changed every 2-3 days depending on ambient temps.
Actually, I just made a mock up of this, but will try this on a real batch
when my basement gets too hot. Seems like a good idea, but we'll have to see
what the actual readings show...