Electric Fans

Regards.
In Electronic-control it makes little difference, while in old series-Inductance-control Hi speed is more efficient.

But efficiency for an individual is low power comsumption at needed job-done.

Actually it is not the count of efficiciency but
at low speeds you remain a little wet & feel cool.
At Hi speeds U R almost dry and feel warm. If you develope the habit you will feel the difference

At higher speed the more counter electro motive force that needs less net power.

The Back-EMF is more only off-load. As the fan-motor faces air friction at Hi-speed more current is drawn & counter-EMF drops.

It depends on what effect you are after. If you want to feel cooler, high speed for higher air velocity will improve evaporative cooling on the body. If you want to de-stratify warm air off the ceiling, low speed to just barely bring the ceiling air to floor level is adequate.

Several people have put a toe in, but I'm going to take the plunge: define "efficiency." In this case, electrical efficiency, by itself, is irrelevant. What you want is to feel comfortable, and the lowest speed that achieves the result is the most efficient because a fan takes less power at low speeds - whether or not it is actually more or less efficient at low speeds.

Assume there are two fans 'A' and 'B', both running at same speed,and both are overhead at same height.Since both fans are running at same speed,power consumption of both should be equal. [i] Assume a person 'X' feels comfortable (feel cool) under fan 'A', but does not feel comfortable / cool under fan 'B',though both fans are at same level / height and running at same speed. Does it mean Fan 'A' is more ""Efficient"" than 'B'?? [ii] Also, under same conditions {i.e. both fans are at same level / height and running at same speed},assume another person 'Y' feels comfortable (feel cool) under fan 'B', but does not feel comfortable / cool under fan 'A',though both fans are at same level / height and running at same speed. Does it mean Fan 'B' is more ""Efficient"" than 'A'?? Can anyone clarify this?

The question is lacking at least two factors needed for an informed answer. (a)Where is fan? And 'hanging from the ceiling' isn't what I mean. What kind and what size is the room it's in. (b) How large is the fan? i.e.: diameter and configuration of the blades would be nice. And if these things are to hard to come by just remember that it doesn't matter how fast of slow the fan is running, if the supply (volume) of air not greater then the fans ability to move (cfm) then going faster will always be LESS efficient.