The operating power will of course be higher for 12k btu fcus.
But you need to consider that a 12k fcu will cool the room faster than a 9k (assuming the compressor is sufficient). That also means the 12k will work at the rated power, for a shorter duration than a 9k will. The 12k will go into idle earlier than the 9k.
So overall how does the average electricity consumption plays out? I have no concrete answer. My personal gut feeling is the 12k will consume more electricity, but no more than 10% over its 9k counterpart.
25% is too much. Considering the bulk of the energy consumption comes from heat rejection, whose rate becomes (close to) 0 once the room has reached set temperature.
10% is a generous buffer I believe. I attribute it to the extra energy consumed by the slightly larger blower motor in the larger fancoil. That's about the only difference.
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