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Is this fan suitable for outdoor usage. Under an open patio with roof shelter

The product is not IP 44. 
Rated to IP44, the fan is designed to withstand direct water spray.
So it can rain on the fan, it will not impact on its operation. 
Here your case is different, the product is covered, so you don't have to fear water splashes. 
You can therefore install this product, especially as the blades are made of composite materials, and are not affected by humidity.