Is this the place for a multisplit?
I’m deciding on a minisplit for a new build and having never done a specification before, I’d like to check my theory against the intuition of an experienced designer. Several articles on this site suggest that multiple, single-head mini splits operate more efficiently in practice than a multisplit. However, my project seems to me to be a good candidate for a single minisplit with two heads for the two zones in the project, because the zones have roughly equivalent heating loads. So my question boils down to this: are multiple, single-head minisplits always the best solution, or is this a case where a two-head multisplit really does make sense?
Building Information:
600sqft apartment with 200sqft loft (Zone A) above 600sqft conditioned garage / woodshop (Zone B), separated by R30 floor
Climate Zone 6b
~8000 Heating Degree Days
Design Temperature 7*F
Peak Heating Load for Zone A: 7,000 btu/hr
Peak Heating Load for Zone B: 6,000 btu/hr
I intend to keep Zone B at a lower temperature most of the time, perhaps 50*F.
Option 1: Two separate, single-head minisplits, likely sized at 9,000 btu/hr, one for each zone.
Option 2: A single 18 kbtu/hr condenser driving two 9,000 btu/hr heads, one for each zone.
My second question is if the pre-charged “DIY” units are worth consideration against established companies like Mitsubishi. On one hand, it’s hard to trust a brand titled “Mr. Cool”. On the other hand, the installed cost would be significantly lower since HVAC labor is extremely expensive in my area. And perhaps the pre-charged linesets and quick-connect fittings actually lead to a more reliable installation?
Any expert perspective on these two questions would be much appreciated!
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Replies
Multi split is almost never the right answer. About the only time it is worth it is if you are tight on outdoor space.
Besides the lower efficiency, one issue with them is they are always sending refrigerant to indoor units when heating. The problem with your setup is that since you won't be heating the garage most of the time (or barely heating it), that head would still get refrigerant even when off, this will make the COP of heating upstairs much lower most of the time.
As for DIY, except for the ducted units, I don't think any of them are hyper heat. You want something with decent capacity near you design temp for this application. I've had good luck with Midea units, better value than most out there.
An oversized multi split is a certain recipe for unhappiness.
No, you are not an exception I don’t think the lower cost of the multi splits are worth it, you lose controllability efficacy and redundancy.
Check the instruction many miny systems will not let one set the temp below 55°.
Understand there are only a few big assembly lines that make all the mini systems to the spec for that order and then the different labels get applied, so the quality is pretty much the same.
I installed a DIY MRCOOL it worked great the only real down side is what to do with the excess tubing. Move the unit or coil it up behind it.
Walta