draft beer is stored in a walk in cooler. I try to keep that box at about 33 degrees. The colder the better. The it goes out to the taps in 1 big insulated line, that usually has a "chilled" loop in the middle of the tube bundle. The chilled loop is a supply and return to a glycol bath, that is chilled with a small condensing unit. I am not exactly for sure on what the manufactures set these up at, I just know by doing it, but, the glycol temp, you want to see about 26 to 28 degrees. Your after a 7 to 10 degree TD so that your beer/loop will maintain that temperature it left the walk in as.
If your loop goes through an uninsulated/unconditioned false ceiling your gonna have to lower your glycol temp in the middle of the heavy heat.
You can indeed go to low, and freeze your beer. So be carefull.
Perlick, out of Milwaukee, WI are the experts in this kind of stuff, and there website is not that great, but if you call their tech support, they can tell you specifically what to look for and what your benchmarks will be.
Incidently. How I got some knowledge on these is. If your a refrigeration man in WI, you will eventually come into contct with a beer draft chiller system. It's inevitable.