Pairing cold climate outdoor heat pump with compact ducted air handler
Hi all,
I am looking for a compact ducted air handler to serve two small bedrooms in my house. According to the Manual J heat load calculation, they have a combined heating load of 8,015 Btuh. A 9k compact ducted air handler appears to be well sized, for example, the Mitsubishi SEZ-KD09NA. The bedrooms are adjacent, and the air handler would be in attic, with short, uncomplicated runs to the two rooms.
However, I am having difficultly finding a corresponding outdoor unit that will provide good performance in my climate. The NEEP database pairs the air handler mentioned above with the 9k SUZ-KA09NAH outdoor unit. But this unit is not well suited to the cold climate in which I live. It would require significant supplemental heat and would be in low-load cycling for temperatures as low as 33 F (according to the NEEP advanced sizing for heating calculator).
For ductless heat pumps that I am considering for other spaces in my house with similar loads, the 9k Mitsubishi MUZ-FS09NAH outdoor unit gets very good results. This is a cold climate heat pump and has a balance point close to my winter design temperature (-3 F). It also has a good turn down ratio and would perform well in the shoulder season.
So my question is whether it is possible to pair a compact ducted air handler such as the 9k Mitsubishi SEZ-KD09NA with a 9k cold climate outdoor unit such as the Mitsubishi MUZ-FS09NAH.
Thanks, and all best,
Michael
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Replies
I think you want the SEZ-KD09NA4R1.TH.
https://www.mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10007%5CM_SUBMITTAL_SEZ-KD09NA4R1_SUZ-KA09NAHZ_en_M1.pdf
Thanks, this looks like the right pairing for my cold climate, since the SUZ-KA09NAHZ has H2i Hyper Heat technology. However, looking at the spec sheet, the SUZ-KA09NAHZ has a minimum capacity at 47 F of 8,100 Btuh, which is a very poor turn-down ratio. For comparison, the 9k ductless unit I mentioned has a minimum capacity of 1,600 Btuh at 47 F.
I am afraid that this unit would have very poor efficiency under low-load conditions. I might even see better performance with two 6k ductless 1:1 units in these bedrooms.
It is curious that the Mitsubishi ductless 9k units perform so much better in low-load conditions than their 9k ducted units.
Interesting…I didn’t even bother to look at the minimum output, I assumed it would be reasonable.
Mitsubishi doesn’t list another cold climate outdoor unit compatable with the SEZ.
If you want better cold climate performance and turndown, I would look at Fujitsu or Carrier (Midea).
Thanks for these suggestions.
The Fujitsu model that is best sized for my design conditions is a 9k ADUH09LUAS1 - AOUH09LUAS1, but its minimum capacity is 3,100 Btuh, which would mean that it would enter low-load cycling at temperatures around 33 F and higher (according to the NEEP calculation).
The 9k Carrier 38MARBQ09AA3 - 40MBDQ09--3 looks more promising, with a capacity balance point of -2 F (close to my design temp of -3 F), and a minimum capacity threshold of 46 F. However, the spec sheet does not include data below 5 F, which makes me wonder whether it is suitable for very cold climates. The balance point in the NEEP calculation is extrapolated from performance at 5 F, not based on measured performance at lower temperatures, as in the Mitsubishi and Fujitsu heat pumps.
Any other ideas?
Extended performance data for the Carrier unit. Check out pages 11 and 20. I don’t know of another cold climate ducted mini split that gives better turndown.
https://www.shareddocs.com/hvac/docs/1009/Public/00/38MARB-01PD.pdf
If you go with the Carrier, I would go with the 12k, their performance is very similar. Probably the same equipment but with software limiting the output of the 9k unit. Not sure, but they seem very close in performance.
If you need or want cold weather performance you should look for a unit with vapor injection compressor.
Every brand has its own trademarked name for this technology.
Mit = Hyper heat. Fujitsu = XLTH and a dozen more.
Note the Carrier and Fujitsu models you linked to are not vapor injected.
Walta
Hi Walta,
The Mitsubishi unit I linked is a hyper heat unit, but has poor turndown. Last I checked Fujitsu does not sell a 1:1 XLTH slim duct unit. I don’t know if the Carrier unit has vapor injection, but it does have a base pan heater and has a measured capacity down to -22 F.
I have used this for a small ADU before. No issues supplying the complete heating load for a two bedroom place.
https://ashp.neep.org/#!/product/166782/7/25000/95/7500/0///0
They also have a 9k version but the cold weather performance really drops on it.
The Carrier branded version would work just as well.
The nice part about the Midea/Carrier unit is that it can be mounted vertically. Instead of sticking it in the attic, you can mount it in the back of a closet with supply short runs to each bedroom. This avoids all the issues with attic mounted units (freezing drains, sweating unit/ducts, leaky ducts and low efficiency) and simplifies your maintaince down the road.
Even if you can't get the ducts from the closet directly to the rooms and you have to run them up into the attic, you are still way further ahead than an attic mounted unit.
Odd that mitsubishi would have a low output that is 90 percent of its nameplate rating.
perhaps mistakes somewhere?