Oh, from the Great Lakes area!
You should investigate evaporative coolers or wet walls or wet pads. Basically you run water through a large pad at one end of the greenhouse. A series of fans blow this "water cooled air" from one end of the greenhouse to another.
Pipes recirculate the water up and then down the wall.
I have seen them take 100+ greenhouses and get them close to 80 degrees.
