There are so many different factors that go into the greenhouse climate, but in general, these are some seasonal changes to consider.

Ventilation systems should be able to make one full air change per minute during the summer based on fan volume (cubic feet, length x width x approximate height of greenhouse). Shading over the outside greenhouse covering and reflective indoor shades improve efficiency and can reduce the use of fans to cool the greenhouse in the summer.

Ventilation is not usually run in the winter for temperature control but can help control humidity. Most greenhouses that operate in the winter will need to run heaters which can result in condensation and high humidity due to the large difference in indoor and outdoor temperatures. Winter ventilation requires three air changes per hour (one every 20 minutes). You may benefit from "burping you greenhouse" in the winter.

Intermediate ventilation volume to summer and winter is ideal in fall and spring. Temperature and humidity have high variability during these seasons and is best controlled with a controller system.