@JimmyT - Putting a fan under the house is an interesting idea. I am certainly no expert, but at least in my experience, the crawlspace under a house stays at a fairly cool temperature during the summer. I'm sure a fan could make it a little colder, but it probably wouldn't be enough to have a huge effect.
I am curious, though, about how loud one of these fans would be. I have see similar fans in barns and warehouses, and they are quite loud. Are there fans made especially for houses that are quieter than their industrial counterparts?