Ok Fuddy,I'll try and help you with your fan blade question and let the other hands help you decide between whole house fan or a 10 ton refrigerated air unit for your barn? :laughing: Ever picture look's like blade is in different positions but your sketch #1 and pic where air flow direction is marked with Sharpie are correct,,,if,,,rotation is cw looking at end of shaft. I bring up rotation because (A) you say it look's like blade has been moved up and down shaft. That make's me think someone was trying to find the sweet spot while blade was mounted backwards.(B) the fan might have been free because it didn't move enough air due to improper blade orientation. I've replaced hundreds of ac condenser motors where that square nut on your hub was between blades and motor. Ditto for allen setscrews. If I had $50 for every blade a "PRO" installed backwards,I could afford a big hat and new truck. You need long tee-handle allen wrench or square nut socket with ratchet and extension in order to get in there. While you check that out,I'll jump into the debate over correct location of whole house fan.
Few if any direct drive fans can do what it take's to circulate air in average size homes. The problem is that slow moveing large blades are far superior to smaller fast moving. RPMs are similar to a ceiling fan. A good set up is belt drive,step pulley mounted in gable. There's a formula based on sq ft living area to determine fan size. 36-42-48-52 inch are common sizes. After
installed,speed(cfm)is tweeked using step pulley. Mechanically operated movable shutters are centrally located in ceiling (occasionally two sets for unusual room arrangement). Shutter blades are often insulated and require motor drive to open when fan run's. Right about here is where most people are satisfied but for large homes with several occupants and commercial applications,other options are available. The shutters,cfms and auxillary incomeing outside air openings can be modulated for optimum performance. Some insight on why gable mount offer's advantage. As others point out,evacuating hot attic air is an improvement even if living area isn't. If the fan pressurizes attic space,leaks can occur between attic and living area resulting in dust pushed into living area. Gable mount always results in negative pressure in attic. How much negative pressure? That's where auxillary incomeing outdoor air inlets come into play. With the right bells and whistles,fan can evacuate attic and replace it with outside air from aux soffit inlets while refrigerated air is running.