Detached Garage with Loft: Mini Split with dual zone or single zone with registers?

[das_V8]

For reference my build thread: Suburban Hobby Garage

Planning HVAC for my detached garage. Central Ohio location, well insulated new construction. First floor is 28' x 30' x 12.5' with dual 10' x 9' insulated doors. Open staircase to storage loft above 30' x 14' x 7.5'.

I ran Man-J calcs and have the following:
1st floor: 3k cool / 16k heat (840sq ft)
2nd floor: 1.5k cool / 3k heat (420 sq ft)

Looking at Mini Split systems, either a Mitsu 20k 18SEER 6+15 dual zone, or a ACiQ 27k 24.6SEER 6+18 dual zone. The Mitsu might be a bit undersized but I have a big delta in sizes between the 2 zones. Not sure on the quality of the ACiQ, have not seen negative reviews but also still a newer system. Much cheaper than the Mitsubishi though which seems suspect but does offer a 12/7yr warranty.

Which had me thinking, what if I put a bigger, single head on the first floor and used register transfers between 1st and 2nd floor? I'll also have the open staircase. For winter heating, this is probably fine, but will I be fighting massive humidity issues in the loft in the summer?

 

[Andx0r]

ACiQ is a brand that sells rebadged Carrier and ICP products direct-to-consumer. Just like Carrier-branded splits, the ACiQ mini-splits are made by Midea in China, an outfit that produces probably about 1/3 of all mini splits on the planet and a lot of OEM parts. Mitsu is the Cadillac...still made in Japan, the last manufacturer still building them there besides Fujitsu, so that's the premium you're paying. All the others are in China now.

Find out what your installer thinks the parts availability is going to be like.

As for your plan - it's a bad idea. Don't do it. Stick with two heads.

 

[pcmeiners]

Best to have two single zone units, single zones units are cheaper to run, less of an emergency if one goes down. A SEER of 18 is low for efficiency. Read warranty information carefully, most warranties are not worth much if you are required to have service calls by a professional, if you plan on DIY, do not expect a part replace in a short time. Carefully shop, prices vary tremendously . You should search this sub forum for information, spend a few hours reading posts....purchasing mistakes can cost you.

For an idea of your BTU needs, I have a 30x36, single level, average insulation, 2 roll up door, 2 windows. Have a high efficiency 12k Fujitsu minisplit, more than enough from -7 to 102 F.