I have some numbers on the needs of any vent system and for my system specifically.
For a passive ventilation system, the vents need to be 20% of the size of the square footage of the growing space. so a 200 sq ft space would need 40 sq ft of ventilation (eg. wide open windows or doors).
Because we are in transition, we will be starting seeds for Riverpark Farm in my personal hoophouse. The hoophouse measures 10' X 20' with a 90” Diameter hoop. The space is big enough to do the work I need, but isn't a perfect seed-starting location. I don't have any electricity on-site where I could power exhaust fans or circulation fans, which are crucial to successful seed-starting in transitional weather. Additionally, as the hoophouse will largely be unattended while I'm at work during the day, the system must be automated.