Mitsubishi hyperheat multi-splits and modulation
I’m thinking about having an MXZ-4C36NAHZ installed. The indoor units would be one (1) MVZ-A18AA7 ducted air handler and and two (2) MSZ-FH09NA wall units.
The 4C36NAHZ submittals say it can modulate down to 6,000 btu cooling and 7,200 btu heating.
I cannot find the minimum operating capacity of the MVZ-A18AA7, but the similar PVA-A18AA7 can modulate down to 7,000 btu cooling. The MSZ-FH09NA units can modulate down to 1,600 btu cooling.
I had previously assumed that, as long as the sum total of the indoor units operating capacities equaled or exceeded the minimum 6,000 of the outdoor compressor, that the indoor units could modulate freely. For example, I assumed that, if the air handler were turned on and operating at 7,000 btu, that each wall unit would have the capability of operating at its minimum 1,600 btu, and the total load on the compressor would be 7,000 + 1,600 + 1,600.
However, I recently read a post from Dana Dorsett, who seems to be an expert, that the Mitsubishi MXZ compressors do not modulate. The post is here: https://www.greenbuildingadvisor.com/community/forum/general-questions/105304/mitsubishi-pvapuz-central-heat-pump-or-mini-split.
Dana wrote: “MXZ compressors are not full-on VRF systems. They will support a number of different heads/cassette capacities, but as I understand it even those heads/cassettes that can modulate when married to a dedicated compressor do NOT modulate when on an MXZ compressor. That means the heads have to be reasonably sized to their room/zone loads to hit the efficiency numbers, and provide reasonable comfort.”
Is this accurate? If that is true, then rather than being able to operating at 7,000 + 1,600 + 1,600, my three indoor units would have to operating at 18,000 + 9,000 + 9,000??
Please tell me this is not correct. I was very excited about the possibility of 7,000 + 1,600 + 1,600 operating capacities but am far less excited if the MXZ cannot modulate.
Also, I don’t see how it is possible that it does not modulate. If the minimum cooling capacity is 6,000 btu, as the submittal claims, and it requires a minimum of two indoor units to be connected to it, Mitsubishi’s smallest indoor unit is 6,000 btu rated cooling capacity. If there is no modulation, then the lowest capacity the MXZ would ever operating at is 6,000 x 2 = 12,000. If that were the case, what is the point of a submittal stating 6,000 btu minimum operating capacity?
So surely the MXZ series can modulate in the 7,000 + 1,600 + 1,600 fashion described above?
I’m hoping somebody can tell me that I mis-read Dana Dorsett’s post quoted above, and that the MXZ series does indeed fully modulate within the ranges stated on the submittals!
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