The purpose of the fans is to move air over the water to help evaporation. A tank works like a big evaporative cooler. Increasing air flow increases evaporation, and thus increase the amount of cooling for the tank. You're not really cooling the bulb or the air, you are simply increasing evaporation.

The hardest time I have with cooling is when the windows are open in the fall and spring and its a little humid. That's because the air is already saturated with water and have less capability to absorb evaporation. Extremely dry air like we have in the winter increases evaporation. Of course air conditioned air is dryer than what's outside.

Gary