In order to do what I think you're saying wouldn't it get awfully cold inside the building if its subzero with a stiff wind?

I'm assuming you're opening the down wind curtain enough to get enough pressure in the barn to push air out the door?   

This is also dependent on the wind not blowing directly at the door, which is where it is nearly all the time when the truck is backed up and catching the wind.

I might have to try it but I'm not extremely optimistic it will help much.

I've got a cousin that put reversing switches on all of his tunnel fans so that they blow air the opposite way while he is loading.  If I had a tunnel building I would definitely look into doing that.