HowTo: How to Understand Fan Power Increasing With Speed and Energy Saving

  1. Significantly more Power is required from an Inverter Drive and its fan motor to increase the speed of a fan.  This is because Power required follows the ‘Cube’ of speed. 
    The reasons are as follows: -
    1)    Air velocity follows the fan speed in a nearly linear relationship, (The First Fan Law).
    2)    Pressure follows the Square of Air Velocity, meaning double the speed will increase the pressure by four times, (The Second Fan Law).
    3)    Power required therefore follows the Cube of speed, meaning double the speed will increase the power by eight times, (The Third Fan Law).
    The same laws apply when reducing fan speed providing significant energy savings.  Examples are: -
    a)    Building Ventilation or Machine Extraction may be reduced to suit operational needs and/or climatic conditions.
    b)    Cooling Tower fans are speed controlled by Inverter Drives to maintain the cooling water outlet temperature.  This is a simple application for a suitable self-learning temperature controller arranged to control the Inverter drive speed setpoint.  This application will also reduce the amount of cooling water required for the tower.
    c)    Reducing fan speed can significantly reduce fan noise.  This may be a requirement for industrial processes working at night in residential areas.