Fluid/Air Dynamics question

[RandallPink]

We are trying to make an inflator for the double roof on a greenhouse using 4" pvc and a vane on the back to keep it pointed into the wind. There is a lot of disagreement on whether a funnel on the intake end will make it work any better than just the 4" pipe facing into the wind.

[russ_watters]

Theoretically, a funnel shouldn't help because pressure is pressure and you can't multiply it, but in reality the system isn't closed and you'll need airflow through it to keep the greenhouse inflated. I think it may be a losing battle, though.