Okay I am a fridge guy and dont do any build automation but if you want cheap, reliable and easy, could you not just use a Belimo damper motor and a floating point controler, or a 2-10vdc,0-10vdc, 2-20mA space temp controler?
Very cheap, Very tough and low tech.
Just a thought, but I might be WAY off. What do I know about Chilled water? Not much I could freeze it for you