But if you don't have the extra air flow , you won't get the benefit of adding 12,000 btu. You may just circulate colder water until a freeze-stat shuts it down. You can't just pipe cold water around a loop for cooling, there are cooling coils in that loop with a fan/blower. Their just not technically evaporators, that happens in the heat exchanger in a chiller system, usually tube in tube but can be plate type. Are you going to use this system for heating also ? 5 ton chillers usually draw ~35 amps and are on 8 gauge wire (40 amp), I was just saying going to 6 ton you may need 6 gauge wire. Who ever recommended take your total heat load and install two compressor/ chiller units and 2 loops in case one fails. It's also possible to have just one cold water loop cooled by 2 chiller units.