The authors of "The Best of Growing Edge, Volume 1" say that the standard way to control a grow room's temperature is to use a vent fan with adequate cubic-feet-per-minute capacity. That means that to cool your grow room, you need a way to vent out the heat while also making way for cool air to go inside. The best way to do so is to remember that heat rises and cold air stays low to the ground. With that in mind, use exhaust blowers to create a venting system for your grow room that takes advantage of these facts.
Install one exhaust blower on the inside of your grow room. Mount your indoor exhaust fan up high where heat concentrates. Set it up to blow the hot air out of the room.
Mount one exhaust fan on the outside of your grow room. Install the outdoor exhaust blower down low where the cool air stays. Set this exhaust blower to pull air into your grow room.
Connect the blowers to a thermostat. This step will automate the cooling process for you by triggering the exhaust fans to go to work whenever your grow room reaches a certain temperature.