The trick is to have effective ventilation, good aerodynamic designs when temperatures are high and wind is 1 mph. While gutter vents are more popular and less expensive to install, they aren't as effective in this model as ridge vents, he says. Side vents should open windward. Growers can modify existing structures to enhance ventilation. Opening the sides of poly greenhouses can provide good cross ventilation, he says.
Air comes in through the side or first roof vent in a scoop toward the wind.
The vents downwind suck the air out of the greenhouse. If all vents are downwind, little happens unless you have a lot of air coming in some other way. Natural ventilation starts by opening the windward side and then determining the outlet, which could be the other side of the greenhouse. You're not given much of a choice. In most cases, mechanical is the most dependable.