Mini-split options for cooling a small home?
Building a small home (700 sq ft) in Phoenix AZ (Zone 2) where cooling is paramount and heating is practically an after thought. I’m aiming for R20+ walls and R40+ attic. Few windows but big glass doors everywhere. Patios and overhangs everywhere, too, so tons of shade.
House has one main area incl. kitchen and living room + one bedroom + a bathroom.
I did a quick ersatz Manual J on loadcalc.net and came up with a maximum cooling load of just under 12,000 Btu for the whole house (worst case scenarios with my assumptions). Mini splits look to be the best fit for such a small space and (relatively) small load. But how?
Option 1: One 12,000 Btu (maybe one notch bigger) head unit in the main living space.
From a pure square footage and load perspective, this seems like it would work. But I’m concerned about the temperature in the two rooms with doors — the bedroom and bathroom. I’ve seen references to the bedroom being 5 degrees off the main temp overnight… but those are invariably referring to heating modes. I can find very little concrete info on how a single head would work in a closed-door bedroom when extensive cooling is at play.
Option 2: Dual zone; one unit in the main living space and one in the bedroom
Is this actually an option? I’m not sure they even make a unit small enough to service one small (12×12) bedroom? Adds a bit to the cost, if it is possible.
Option 3: Ducted mini-split with low static ducts
Ducted air handler in the attic with a “pair of pants” duct coming off splitting into the main area and bedroom (and maybe even bathroom). Maybe the return is also split into the various rooms. This would almost surely work to keep a super consistent temperature. But… it’s not as efficient as a head unit; costs more; and would almost surely require having a conditioned attic since all installation examples suggest that the unit and ducts can’t be buried in insulation. An R40+ conditioned attic would be notably more expensive than a vented attic with just a lot of blown in cellulose.
Am I missing anything obvious? What are y’all thoughts on these options, with specific focus on cooling?