They screw plastic bottles to a piece of cardboard and hang it in the window. The air flows...

I've always been a fan of "field expedients". The best I ever came up with was using dog tag chains to replace typewriter chains that rusted away in the dense humidity of Vietnam. Mine was primitive compared to this. I wonder who thought of it...

[BTW: I added "Field Expedients" as a new topic. I'd love to hear of others]