I also have 2 large industrial fans that we use in summer at either end of the barn to push air. They are awesome....before that we used to give each horse there own fan on their stall as you described. But I found it always a pain in the ass to set up and take down, so when we purchased to 2 larger fans I thought to myself why didn't I do that sooner!
This past summer I still set up a box fan for our Mare w foal as our summer was so hot, and w foals not being able to regulate their temperature felt this was necessary to ensure they were both getting adequate air movement.
The large fans we have at either end of the barn are on all day, and depending on temperature at night shut off when we do our barn check. If temp doesn't go down adequately we leave them on.