It's pretty dry here in the 4 corners region of New Mexico, as well as most of the southwest US. Swamp coolers are the norm, but not very economical or efficient. Water is our most precious commodity. Besides installing a backup refrigerated air unit, is there some sort of dual purpose unit? Swamp for dry times and a/c for humis times? Do they make a/c units that will fit in the same roof mount locations. We have ceiling vented ducts. Can a roof mount a/c unit make use of this type of duct work.