I have built a cold room for my BBT which are not insulated. The room is well insulated. It is cooled with a air blaster in the ceiling. 5 BBT * 20 hl, the room is about 50 m3, the blaster has a max effect of 4 kW. To keep the temperature in the tanks at -1 deg.Celsius, the room temp. is about 1-2 degrees cooler.
In Sweden we call it "water locks" (the water that makes the drain not smell). My "water locks" are placed about 50 cm under the insulated concrete floor so they don´t freeze.
I cool down the beer from the fermenters with a heat exchanger, with a max effect of 15 kW, (cooling down from 8 to 0 deg C), otherwise it takes too long time to cool down in the cold room.
As far as I can see after a couple of months in production it works well. The only thing is not to get rinsing water left in hoses and in the CIP tubings (Then you have to borrow your kids hair dryer)