Can we reduce power consumption by running fans at slow speeds?

Yes, we can save power with the electronic regulators but not with the old regulators based on rheostat. Speed of a fan, as we know, is controlled with the help of a regulator.

 The old regulators are based on rheostats which have 5 or 6 steps corresponding to different speeds. They consume a fixed power all the time. If we select the highest speed all the power is fed to the fan’s motor. If a lower speed is selected, electric power proportional to selected level is fed to the motor and the remaining power tapped from the mains is wasted as heat in the rheostat. That’s why when we run the fan at slow speeds for a long time the regulator becomes hot.

The new electronic regulator now available in the market, are based on a semiconductor device called triac. (Triac is a trademark of the General Electric Company.) It is an electronic switch designed for power control and phase control. According to the encyclopedia, using triac, power output can be continuously varied from about 5 per cent to 95 per cent of the maximum power without any loss. Depending on the speed selected, the electronic regulator draws, from the mains, only the required power. So it is prudent to use the new electronic regulator and save power.