If you're building a large ferment chamber the A/C is the way to go. I've been running an AC to cool my 15 gal conical for the last few years. I just have a box with 1" EPS foam insulating it. It's not well constructed, nor well sealed, but it will get the chamber down below 10F regardless of ambient conditions. The coil does freeze up when it's humid and I try to do anything below ale temps, but that can be managed with good sealing and control scheme. I've just been too lazy to bother with those things.