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Fujitsu 09LZAH1 vs 12LZAH1 heating performance

Aedi | Posted in Mechanicals on

Hi all,

I’ve bought a new house recently, and am looking to install a minisplit.

The short story is: Raised ranch, in Windsor County, VT. previous owner had Efficiency Vermont come through and do extra air sealing and insulation, so it’s in very good shape energy wise.

The basement is finished, but we are only interested in the first floor. My manual J calculation put the first floor heating load at 15.5k BTUh at the 99% outdoor temp (1F), with conservative assumptions. More reasonable assumptions (detailed further below, for those curious) cut it closer to 12k-13k.

I’ve decided to go with Fujitsu (again, more details later for those interested). So our model options are 09LZAH1, 12LZAH1, 15LZAH1. Guy quoted only $250 less for 09LZAH1 vs the 15LZAH1. He was trying to sell me on the 15LZAH1. I was leaning toward 12LZAH1, figuring that with such a small cost difference I might as well meet the full load. But the contractor pointed out that the 09LZAH1 and the 12LZAH1 have basically identical heating performance. I looked it up, and it seems he is right. Fujitsu advertises their 09LZAH1 as consistently exceeding the nominal heating loads. Specifically, the  09LZAH1 allegedly is capable of ~14k BTUh at -5F and ~11k BTUh at it’s -15F limit — almost identical in performance to the 12LZAH1.

Is the difference between the two units just cooling performance? It seems very strange to me that the units would be so similar, so I was hoping someone might have some firsthand experience with them that could attest to Fujitsu’s figures, or provide a technical explanation as to why that is the case. As it stands now, I’m leaning toward 09LZAH1.


Extra details, for those interested:

The conservative assumptions I mentioned before were as follows:
-The basement garage would be at exterior temp (has R10 foam/air sealing isolating it from house)
-The south facing, partially insulated sun room would be at exterior temp.

More reasonable assumptions of those deltas shaves off ~2-3k BTUh, but unfortunately I don’t have any good real-life data to go off of.

Additionally, there is no need for me to meet the full load with the minisplit; there is electric baseboard in every room, and a propane space heater in the basement and in the living room. None will be going out of commission, so there will be plenty of capacity available in unusually cold weather.

As for why fujitsu was chosen:

Initially I had two contractors come through — one for Fujitsu, one for Mitsubishi. The Mitsubishi guy performed a manual J at a design temperature of -13F, the limit of the unit. I considered that pretty shady, and had him rerun it at 5F. He got 12k BTUh then — but for just the main living area (he didn’t measure the bedrooms at all). When I did the calculation, I got 8-9k for the same space. He would not share his calculations (or even the unit he was going to spec!) so I decided him not to be trustworthy.

Fuijitsu guy didn’t do a calculation and didn’t know what a manual J was (!), and said there was no point in doing a calculation. But his “rule of thumb” was more accurate than the guy who ran the numbers. Still oversized, of course, but at least I didn’t feel like I was being manipulated. Still, not ideal.

If anyone has additional contractor suggestions, I am open to them.

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Replies

  1. kyle_r | | #1

    There actually is a small difference, check out the extended performance tables in the technical manual here: https://www.johnstonesupply.com/product-view?pID=B62-627

    Don’t quote me, but I believe I read that the equipment is the same, but software in the 9k dials back the capacity. I’m sure it’s cheaper from a manufacturing standpoint then having two different units to produce.

    I would go with the 15k, given the cost difference. Same minimum output and if you use it for cooling you will have a better shot of controlling the humidity given it’s greater moisture removal capacity.

    1. Aedi | | #2

      Thanks for sharing that technical manual, those extended performance tables are really useful for understanding the differences in performance between the machines. Other sections in that manual does support the conjecture that they are the same unit, though I am a little surprised that performance was throttled so little, relatively speaking.

      I was eyeing that significantly higher moisture removal figure for the 15k. Since the minimum output is the same, does that mean that efficiency should be roughly equal to that of the smaller units at equal outputs?

      If so, then the only real disadvantage would be the slightly higher noise levels. Since it is in the living room/home theater, it would be more noticeable than usual, but 26 db is still pretty quiet (our projector is 24 db).

  2. kyle_r | | #3

    In general the less hard a heat pump has to work, the higher the COP. For illustration purposes, if a units max heat output at 5F is 15 k btu/hr at a COP of 2, at 5F and a load of 10k BTU/hr it’s COP might be 2.5. Obviously this varies greatly by unit and conditions, but in general the COP improves when not pushed to maximum output.

    The reason right sized equipment is pushed so hard is to avoid cycling. With your heat load, someone trying to install a 2 ton or 3 ton unit with a minimum output of say 12k BTU/hr which causes the equipment to start and stop with comfort problems.

    When you are talking about a 9, 12, or 15 with the same minimum output and the cost is very close, I would go with the bigger unit.

    The 26 db you mention is in quiet mode. This is a very low fan speed. I would not count on your unit operating there in the winter, to get the full output it will need to be able to run all the way to high fan speed ( 43 db for the 9 and 12, 45 db for the 15). Here the larger unit helps as well. Given the same let’s say 15k BTU/hr demand the 9k may have to run at high speed (43 db) while the 15k can run at medium speed (40 db). Again illustration purposes only.

    1. Aedi | | #4

      Thanks, that is very helpful! I am happy to hear that there would not be any other performance concerns when there is no short cycling.

      I was mostly considering the quiet mode since I figured that would be the mode used when volume was an issue (e.g. when watching a movie). I had not considered that the larger output would potentially allow lower fan speeds overall though, partially counteracting higher volume. It seems pretty unlikely the extra couple decibels would ever be an issue.

      With prices being basically equal, It definitely seem the 15k unit is the way to go then. Thanks for your help!

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