solving the HVAC location puzzle
Hi, first post here. I'm building a new home near Augusta, Georgia and getting bids back from builders now. I want to build a common sense, resilient, energy efficient house: tight envelope, HVAC in conditioned space, spend money on the shell, but keep it simple and easy maintenance. Green building and building science haven't caught on in my town. Air handlers and ductwork are almost always in hot attics or vented crawlspaces.
I could only find one builder who has done a conditioned crawlspace. He proposes insulating the crawl walls with 2 inches of rigid foam and closed cell sprayfoam around piers and band joists. The house walls are 2x4 with blown fiberglass and 1/2 inch of insulated R3 sheathing (DOW SIS) instead of OSB. The attic floor would have closed cell R15 first, then blown cellulose up to R50. He puts active returns in every room. The main house would have a 14 seer heat pump (electric resistance heat for backup) and the inlaw suite would have a ductless minisplit.
A second builder wants to use 5.5 inches of open cell sprayfoam on the roofline rafters and gable ends to enclose a huge attic space covering the main house and inlaw suite, as well as open cell in the walls. But he's proposing putting in a single ZONED 15 Seer heat pump in the crawlspace which would have vents, but have one layer of rigid foam on the walls covering those vents, to have the option of putting a dehumidifier down there someday. The zoned supply duct to the inlaw suite would have to pass under an unconditioned Portico. He's a "rule of thumb" guy who says 600 sq ft/ton, and is proposing a 3.5 to 4 ton system for 2400 sq ft total. 3 returns total: in master bedroom, great room, and inlaw suite.
I was hoping for about 1000 sq ft/ton, and to spend my money on either the crawlspace or the attic, but not both.
So, how would you rank these options for locating the air handler and ductwork as far as economics and efficiency?
unvented, sprayfoamed attic?
vented attic with radiant barrier?
air handler in a conditioned mech room, ductwork in a crawlspace?