Quote Originally Posted by Blueboy View Post
You could be using the same energy for all three , if the COP was the same on each unit .

If you hypothetical room is fixed load then possible the most efficient is the unit at max not using the inverter at all. However in the real world that does work as the load will be bigger or smaller at certain times than you have calculated. It also depends what ambient you calculate at. Say you assumed ambient of 28c and its 30 outside where you located the system now your smallest unit is too small on that day or in winter its 5 C and you still need cooling now it's too big - for this reason I would select the middle unit allowing for more and less is by far the best way to go . Energy is a good yard stick but not at the sacrifice of cooling on the worst day of the year .
That makes sense, thank you! I wish the manufacturers provided an efficiency curve for their units like power supply manufacturers do. So presuming the minimum capacity of both units is roughly the same, there would not be any disadvantage to oversizing the unit besides initial cost?

Also, what effect would overloading and undersizing the unit have on its longevity? I remember hearing somewhere that since inverter AC units are variable speed, it isn't great for their longevity to be running at maximum capacity all day every day, similar to driving a car at full throttle all day every day- It's made to handle it, but longevity will likely be adversely affected. Is there any truth to that? Thanks in advance!