woudln't Your floor would get cold from the cold attic air, cooling the air above it, and forcing your furnace to run more often?
Once you cyled the air completly once, the radiant heating from the earth would take a while to warm the air under the house again, more likely it would be the heat escaping thru the floor that would be warming the air under the house, so I think the net benifit would be little to none, ...