For someone with a greenhouse, you haven't done you homework. Without proper vetilation, it's a rott house... I'd first decide the general direction the wind blows in the summer. Here, it's from the south. I'd put one inflow fan fairly low on the south side (to get the coolest breeze, and high exhaust fan on the North side. Place pea gravel on the floor, & water down with cool water to decrease temp. An auto timer that kicks in at aboutt 88 degrees would be nice. The plants has to have a breeze on them, also. An ocolationg fan is a must, also. Black mesh over the top allows enough sunlite, but helps the temp problem.