There must be so much humidity here that dust is not an issue. My coops are not that dirty. I cleaned them out about 5 weeks ago and put down fresh shavings.
I have tried the fans in both directions, blowing out and blowing in. I have thermometers in both rooms and watch what makes the difference.
This works for me.
This the brooder room window and fan. The window is on the north side. I have insulation on the ceiling, north and south walls to help keep out cold and heat. The east and west walls have coops on them so that helps.
The only other opening is the door on the south side. I like to blow the air in from the shaded north side. It drops the temps down about 10 degrees from the outside.
My Silkie/Cochin shed is shaded so that helps. Here is the fan in the east window.
And from the outside at about noon.
It blows through the shed nicely, lowering the temps again by about 10 degrees. I run it on high during the day and medium at night. Otherwise the Silkies get blown off the roost.
It helps that the south and west sides have trees and plenty of shade.
And that the north side has a big screen/hardware cloth door.
And it helps that I had windows put on all 3 walls and the big open door. This is the window and pop door on the south side.
You just have to work with what you have and see how best to make it work. I have read from a very smart person here on BYC
that ventilation is best for the chickens and have tried to do my best to allow for it, even in the winter with snow on the ground.
Also this shed has insulated walls and ceiling. I hope to put in new big vents I recently purchased, too, on the ends up near the roof inside. It has small ones but I would like to put in these much larger ones.