If you have a fan you can have it blowing on the wet towels that you wrapped around your fermenters. This will give you about 10˚F of evaporative cooling. The key is to keep the towels moist at all times. I do this by placing my fermenter in a container with some water in it, and have ends of the towels sitting in the water. The water will wick up into the towel, keeping it wet.