This article describes how the power consumption of a ceiling fan changes with a change in the speed through a fan regulator.
The conventional fan regulator has different resistances for regulating the output voltage. The output voltage is governed by selecting the resistance value on the fan regulator. The total input power is equal to the power consumed by the fan plus the heat loss in the resistance-type fan regulator.
As per fan affinity law, the air pressure that the fan delivers is proportional to the square of the speed, and the power consumed is proportional to the cubic of the speed.
So, when the fan’s speed is made to decrease, the power demanded by the fan gets reduced as per the fan affinity law stated above. However, the power loss will take place in the fan regulator.
The fan- when the regulator is at position 5- will consume more power as compared to the power consumption of the fan when the regulator position is at 2. The air delivery at regulator position 5 will be more than at position 2. Thus, the lower the regulator tap position, the higher the power saving.
How to save the lost power in the resistance regulator?
The power loss in the resistance regulator can be eradicated if the electronic fan regulator is used.
The voltage is regulated by controlling the SCR firing angle. Thus, the speed of the fan increases/decreases linearly. The resistance regulator has five fixed speed options and has discrete set points.
Can I use a 120 watt fan regulator for a 72 watt rating fan?
The rating of rheostatic type fan regulator must be selected as per the fan rating. The resistance values change with change in the rating of ceiling fan. If you use 120 watt fan regulator with 70 watt fan, it will work but fan speed with regulator taps may be different than what you expected.