You learn something new every day...I just did.
eamarquardt said a one ton unit can freeze one ton 32 degree water into ice in a day. I didn't know that.
madjack says he thought a one ton unit was 12,000 BTUs. I didn't know that.
So, 2000 pounds of water divided by 24 hours times 144 BTUs per pound = 12,000 BTUs.
2000/24*144=12000
Hey, math works again. So, yes, MJ is correct on the 12,000 BTU number. Or we all just got real lucky with numbers we pulled out of our butt.
As for cascading systems, I intend to pick up one of these for my 3 ton home AC unit.
http://www.mistcooling.com/acprecool.html
It pre-cools the air before it goes into the AC condenser to make it more efficient.
We could do all this math again with dry ice at 246 BTUs/pound to sublimate and you would use about 45% less in weight but it will cost you a lot more and can kill you if done wrong.