Is there a way to keep condensation down in the GH?

My friend has a nice sized GH that is double lined but it resembles a rain forest in there! The sides are begining to get mouldy and they have seen some mold on a few plants too, this can not be a good thing. Is there a good way to prevent so much moisture from forming?? My only suggestion was to leave the door open as much as possible for ventilation when weather permits. Now that we are going in to winter, this may not be an option. You can be standing still and suddenly be pelted with 'raindrops'.

How is the circulation? I have a small fan hanging from the top rafter that runs 24/7.

If your friend can put a small fan on each end and opposite corners (left rear/right front) of their GH it will keep the air moving in a circular motion and cut down on a lot of the condensation.

I have an outdoor ceiling fan in my greenhouse for air circulation. In winter, it helps to blow the warm air downward.

Thanks I will pass this on to her.