Last year we added a misting system which is basically just a misting system that people use on or around the deck or patio, to keep you cool on super hot days. You could buy them easily online this is just one example of the many that are out there.
We basically just tied them to the greenhouse frame using zip ties and than put it on a timer on the spigot coming into the greenhouse. This really reduces the temperature in the greenhouse on hot days. I always have the two fans running (avoiding the direct mist) to eliminate excess humidity and to keep the air circulating – very important.