Easy and cheap way to increase ventilation

I built my coop this past fall, but since then, have decided I probably need more ventilation for Louisiana's stupid hot summers.
Looked at adding vents or more windows with hardware cloth. I like the idea of being able open and close in the winter, or during bad weather. Came up with these 7"x 12" foundations vents at Lowes for $6. Very easy to open and close.