has anyone used the idea of immersion chilling to help control fermenter temps?

Just thinking out loud and there might be a ton of reasons NOT to do this but has anyone ever tried controlling fermentation temperature from the INSIDE of the vessel instead of the outside? even something as simple as a SS tube carefully folded over on itself and inserted into the fermenter. Then hooked up to hoses and a pump to a container of liquid (ice water?) nearby and the pump connected to the temp controller. if the temp gets too hot, cold water cycles through the wort.

Is this a bad idea? If the coolant is too cold, would it stall or kill the yeast?

Again, just thinking out loud. My batch from Saturday is in a 1/2 barrel Sanke, in a styrofoam box that I made in the garage hooked up to the temp controller with only a means to heat it. Well, it was WARM in NJ today and that didn't help keep fermentation temps where I'd like them so I'm thinking of ways that don't take up too much space (eventually I'll take apart on old fridge for a cooling mechanism) and are more controlled that just putting some ice nearby.

Thanks!

Yes, they've thought of it. I've seen 15 gal unitanks that have SS coils built for the inside of them that keep the fermentation going at a regulated temp.

I think electric brewing setups use something like this, right?