Context: I am not a fridgy, I work with electronics. I would love to answer my question by tearing open a dozen different aircon units, but I’m sorely lacking in that department.

Question: Are there some optional components or fancier materials that are simply too expensive to use in the lower end aircons; but are used in the higher efficiency expensive units? The range of COP/EER I see advertised is wild, from 2 to 6 or so.

I already vaguely understand that these things help efficiency:

• Bigger indoor & outdoor coils with more metal in them (working fluids get returned hotter/colder gives better carnot efficiency)
• Operating compressor at its optimal power level (I believe they have an efficiency vs power curve with a single peak, so it’s better to use a bigger compressor if you need more power output)
• Inverter control instead of on/off control (most situations, but technically some use cases will have them on par)
• Choice of refrigerant (but that seems to be controlled in my market, I have not seen many options)

Is there anything else they change? Or is that most of the difference?