# Min capacity on multi-split Mitsubishi units

| Posted in Mechanicals on

I’m trying to understand the minimum capacity/turn down of Mitsubishi’s multi-split units. However, I’m confused by what appears to be a difference between the min capacity shown on the submittal vs. the min capacity shown on the data sheet.

For example, I see on the submittal for the MXZ-SM36NAMHZ (link 1 below), that the minimum capacity for heating at 47 degrees is 22,500 BTU/H. However, in the data sheet (link 2 below, page 72), the “Min” column shows about 12,000 BTU/H for that outdoor temperature.

Why is there such a stark difference between these two minimum capacities? I’m trying to understand if the unit can actually turn down to roughly 12k or only 22.5k BTU/H at 47 degrees.

Thanks in advance for the help!

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### Replies

1. | | #1

I'm not able to add a lot of insight to this (though eager to learn), but on the neep.org website this unit is listed as min. 22,500 @ 47 F. All MXZ-SM36NAMHZ ducted, ductless, and mixed ducts were the same @ 22,500. I checked out similar sized multi's from other manufacturers and found some with much lower min. @ 47 F. FYI - the links you provided wouldn't open, for me anyway

1. | | #2

Thanks, good idea to check the neep site!

Re links: it’s annoying that the full link isn’t clickable, but you can copy and paste the text of the link, and that will work. I’ve also attached PDFs of the content from those links as a backup option.

2. | | #3

1. | | #4

really great info

2. | | #5

Fantastic detail! Thank you for sharing!

It sounds like these units are good in terms of staying on the set point and dehumidifying but that the problem is energy efficiency in low-load situations. If using them under low load—say 6k BTUs load because of mild weather—they'd still have to produce the minimum of 22,500 BTUs in order to deliver only ~6k BTUs. That would mean a lot of wasted energy.

So what I'm wondering now is how much energy do they use in order to produce that minimum capacity. If looking at the part-load capacity chart on the 1st attachment above, the minimum deliverable capacity at 47 degrees (70 degrees indoor) is ~12k BTUs at 572 watts. Does that mean it'll really use only 572 watts to produce the 22,500 BTUs but delivery only the ~12k BTUs?

1. | | #6

Actually, if you search this forum, you will find that dehumidification and maintaining precise setpoints are significant challenges for these multi-split style units, and that many owners have complaints about exactly those two things.

2. Expert Member
| | #7

When in doubt check out the data book here:

Looks like the min is 12k and uses 570W which is not too bad.

If you want decent efficiency, what you have to watch with these is a only a small zone calling for heat, that is when there is a lot of refrigerant bypass happening and terrible COP.

Generally, if you stick to larger zones that are above the min output, you should be mostly OK.

There are also SM specific indoor units that have a built in EEV that don't require a branch box. These might run better but refrigerant bypass could still be an issue at low load.

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