Multizone minispalit for old small home – does it make sense?
I haven’t had any actual calculations done and so I realize it may be difficult to answer. But in general, would a 4 zone mini split system make sense in a old (1946) small (1100sft) home in a pretty cold climate (western NY) that has humid summers due to lake effect? Currently only have central heat; central AC would likely not cool upstairs effectively at all given the old ductwork.
One zone would be for downstairs and three for the bedrooms upstairs. Each bedroom is rented separately and mostly kept closed, thus my want for individual zones. One bedroom is 280sq ft, one 200, and one 120sq ft. The fourth zone would cover downstairs that is very open and around 550sq ft. Attic insulation is sufficient, but walls are probably down to nothing. New double glazed windows.
Is there even a unit small enough to not over-size such a setup? Do multiple zones even make sense for such a situation? My main concern is with cooling during humid summers months, but the added benefit of zone heating would be nice. Perhaps there’s a more efficient way (besides individual window ACs) to cool the home that would make more sense than a multi zone mini split? Thank you so much for all of your expertise!
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When it comes to minisplits and humid areas, the concerns are condensate lines — basically need to have them plumbed out of the building, meaning external wall installations only — and cleaning. With humidity, it's more likely to build up mildew, and need more frequent cleaning.
My family has a few in Puerto Rico and instead of multizone, they've just gone with independent, isolated systems. A tiny wall unit and coordinating outdoor compressor/condenser. Sure, it's not as high-tech as a VRF system with copper lines running in place of your ducts, but it gets the job done.
I think window units would fit better. A multi-split which fits 4 indoor units will be extremely oversized for both heating and cooling. You could do 4 separate minisplits too.
By the far the lowest cost option is a set of PTHP units for each bedroom. This gives each room full climate control and very simple install.
Midea has also started selling in the US an inverter based window heat pump unit. These are significantly quieter and more efficient than any standard window unit or PTHP but only heat down to 40F.
https://www.midea.com/us/air-conditioners/window-air-conditioners/12000-btu-wndow-air-conditioner-maw12hv1cwt
Normally I would recommend against a multi split for this application but in terms of what you are specifically looking for which is independent climate control of four zones without any shared ducting for noise, it can be made to work. It won't be the most efficient setup and it won't be cheap but will be the cleanest.
The key to making it work is selecting the right combination. The smallest 4 zone unit will be way oversized no matter what you do and efficinecy will be bad when only heating the main floor.
What I would go for a pair of 2 zone units, one set for the main floor plus the most used bedroom and another for the other two bedrooms. Since the main floor unit will be doing the bulk of the heat, it is the only one that needs to be a hyper heat unit. You can save some cost by getting a non-hyper-heat for the rest. A good option would be
-hyper heat two zone Dainkin MXL:
https://ashp.neep.org/#!/product/33586/7/25000///0
-non-hyper heat two zone Daikin MXS:
https://ashp.neep.org/#!/product/33587/7/25000///0
These have much better turndown than most multi splits, still oversized but you'll get less cycling.
The two zone Samsung units specs also look pretty good:
https://ashp.neep.org/#!/product/53983/7/25000///0
https://ashp.neep.org/#!/product/53986/7/25000///0
Thank you all!
@akostoth - what is the difference between a pthp and a ptac unit (which they also sell)?
I wonder about permanent mounted through the wall units - a la hotel room style. Wonder what the smallest of these that is available if I was to put one into the smallest bedroom.
PTHP is the heat pump version, lot of times also referred to as a heat pump PTAC. The smallest is usually 6000BTU, which is still pretty large for a bedroom.
The one issue with a PTHP is most (all?) use older compressor technology which can be pretty loud. Less of an issue if mounted into masonry wall but that 60Hz/120Hz vibration can carry through wood frame walls making impossible to sleep in there. I've had this issue in bunkie using a window shaker mounted into a 2x4 wall, the whole place sang when the AC was running, ended up having to replacing the AC with a Midea U shape inverter unit.