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Most mini split manufacturers will use the exact same condensers between two similiar sized models like the 9/12k and 18/24. Their outputs are then software/hardware controlled. The service manuals are usually identical as well. My 12k Midea service manual covers the 9k model as well. The compressor and all the specs are identical.
My guess is the 15k unit is just a derated 18k unit that gets better efficiency at low speed.
Yea I can confirm this to some degree. If you look at part manuals for Mitsubishi indoor wall units you’ll see that almost all parts, including the heat exchanger coils, for 9k and 12k units are the same. The same goes for the 15k and 18k models. The only part number that differs is a circuit board.
> 12k Heating COP at 47F: 5.34
> 15k Heating COP at 47F: 6.06
Yes, despite the demonization of over-sizing, it can perform better.
>more important indicator of a mini-split’s average heating season efficiency and energy use
A lot of decisions are being made with bad data. For example, a study in Vermont measured an actual HSPF of 7.96 on a unit rated at 13.3.
Manufacturers could be required to publish a model of the performance using various conditions as inputs. This would allow more accurate calculation of actual efficiency. IMO, this would result in considerable energy savings at minimal cost. Might also clarify that many heat pumps are being produced with excessively high SHR. This requires a dehumidifier, which kills system efficiency.
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