I'm located in Houston, Texas and I would like to move my rat breeding to my garage. I would like to build a rat rack, but I need an effective system to keep my rats cool.

Temps in the garage are high 70's to 80's at night and probably high 80's to low 90's during the day, but I'm not 100% sure on the day temps.

I have a large fan which I can use, but that won't be enough to keep them cool. I really don't want to buy a Window AC unit. Does anyone have any effective methods that they use?