using both roof vents and fans/shutters for ventilation
I've seen this topic discussed here, but not quite this way.
Fans are great for cooling, but can put too much cold air in the GH too quickly if it's 24 degrees outside...conversely, roof vents don't really do the trick if it's even moderately warm outside.
Can a GH be designed in such a way, that it can be ventilated by roof vents, but, in an automated fashion, if temps still get too hot, a fan and shutter system also kicks on?
Almost a "two-stage" thing. Roof vent opens at 67, fans at 82 or whatever...
In winter, I'd envision that the roof vents would suffice on most days unless you're keeping the GH very cool (like 50s or cooler). In summer, the fans only (plus shade cloth or whatever else).
It's the spring/fall time where it might get dicey. I've heard that if you have an open vent on the roof *and* a fan running on the sidewall, you can end up basically creating an "air loop" (I can't think of what else you'd call that) between the two, meaning air moves between the vent and fan but doesn't circulate - leaving the air in the rest of the GH unventilated - meaning no temperature regulation either.
Is there a way to design this so that you could have a fan kick on and shutters open only if temps still get too high with the roof vent, but to ensure the above "air loop" situation doesn't happen?
Or would you have to do this manually - watching the forecast and, on warmer days, just keeping the vent closed and using the fan only, and vice versa on cold days?
Or is there a thermostat that would open the vent at XX temp, and CLOSE it again at the same temp at which the fan kicks on so they're not operating together?