We have brewed indoors for about 7 years and tried several different ventilation approaches. Our current and favorite is a cone made of stainless sheet metal that connects directly to 6 inch duct pipe and vents or the wall via a vortex vent fan. The cone hood is about 2 inches bigger in...
You are right, it's not going to be use zero electricity, but having a minifridge running to the max to cool a large space is much less efficient than 1 small pump. The freezer stays completely intact & is still in use for storing food & hops (so I'm writing that off in the electricity dept)...
Our current fermentation chamber uses a minfridge & we have to keep a drip tray in the fridge section for the condensate (it fills about 1/4 gallon every few weeks). Maybe the smallest AC unit you can find & build your chamber plenty big...?
The best way to set this up is to cool the liquid directly not the air around it. Look at how the pros do it (water jackets). The temp swing can be dramatic if you are trying to adjust 5 or 10 or even 15 gallons of liquid by cooling the air (to drop the liquid a couple degrees means it will...