tachigi

I myself have a double walled polycarbonate greenhouse. However, my neighbor a orchid grower of some repute has a double walled poly greenhouse. After reading your post I took a stroll down to his place and looked at his covering setup.

As far as venting goes. He on either side of the greenhouse has two spots that he has reinforced with polypatch and polyethelyne tape and made a very small (and I do mean small) incision as a relief. I put my hand over it and could just make out the slightest air movement coming from it. It should be noted that the relief was on the inside of the greenhouse.

As far as pulling outside air. He doesn't, he pulls inside air as he claims it helps with the insulating effect and aids ever so slightly in air movement.

It should be noted that his greenhouse's appear to be about half the size of yours. Which I would think would make a difference in your approach. Common sense would tell me with a surface area as large as yours that you would get some relief from the blower as there is probably some natural leakage in a surface area as big as yours.

__________________
Tom

Shady Side Bonsai
Bonsai Vault
4MAAT