Sounds simple yet effective. I never thought of the furnace filter over the window (great idea to keep the bugs out). By turbine type of fan I assume you mean what we call a "squirrel cage" around here. It is basically an old fan off of a furnace. Your idea basically sounds similar to what I was thinking with the addition of the furnace filter. Also did you build a frame for the plastic or just let it hang down from the ceiling? Thanks for sharing.