In summer, it takes energy to dehumidify and chill the air inside your home. You're talking about using a vent to blow conditioned air from inside your home to outside your home. Every cubic foot of air you push out of that vent is replaced by a cubic foot of outside air leaking in from the environment.
Unless you have a second vent to bring in external air to your case, isolating it from your interior air entirely, you will be burning energy in the form of lost, conditioned air. Depending on how much best you're producing and how much air you're moving, you migh use less power with the vent closed than with swapping interior and exterior air.
If I were considering this, I'd consider water cooling. Two little pipes going through the wall instead of a large vent.