Before acquiring my modified under-counter freezer I used an automated swamp cooler. I would place the carboy in a large bucket of water with a towel wrapped around it. Your typical swamp cooler, but to regulate evaporation I controlled a fan blowing over the towel with a solid state relay and PID controller. I used a 24" stainless thermocouple probe to measure the fermentation temperature directly. It worked well but you are limited on the cooling capacity.
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