Howdy,
I wanted to increase ventilation in my office without the risk of rain damaging any electronics as my server and printer are right beside the window. My solution was to print a few ventilation panels that simply slot in together.

I started off with just two and kept my blind down, then I decided I'd like to fill the window for max ventilation and no risk. Seems to work exceptionally well, I've had it bucketing down and no rain has made it in at all.

My window is 1200mm tall and the gap for the vents (the track the window slides in) is approx. 1160mm.

This definitely isn't going to useful for everyone, but if you're like me and happen to have the same size window and want more ventilation, it might be the answer!

Just print a Top + Bottom + as many middles as you need. I needed 6 middle panels for 1200mm window.

I used 0.28 layer height, 10% infill, 80mm/s and I printed with support (it should only generate support for the wedge slots).

Update:
I decided I wanted to put one of my systems in a grow tent and then be able to pump the heat out.

I've added:
Louvre_Mid_200mm_duct.stl
150 duct to 200 duct.stl

It's two parts which use the pins to align and then just glue together. Prints very easily.

I printed both with supports. Was a decent waste of filament but didn't want the job to fail towards the end of such a large print.