Many fixed-speed motor load applications that are supplied direct from AC line power can save energy when they are operated at variable-speed, by means of VFD. Such energy cost savings are especially pronounced in variable-torque centrifugal fan and pump applications, where the loads' torque and power vary with the square and cube, respectively, of the speed. This change gives a large power reduction compared to fixed-speed operation for a relatively small reduction in speed. For example, at 63% speed a motor load consumes only 25% of its full speed power. This is in accordance with affinity laws that define the relationship between various centrifugal load variables
When a centrifugal fan or pump is used with mechanical flow control, converting the
application to an adjustable speed AC drive can reduce energy costs by 10 to 60 percent if
the fan or pump is designed to operate between 40 to 80 percent of full speed. This usually
provides a return on investment which is in the 6 to 24 months . These savings are
derived from 2 components:
1. The Laws of Affinity, which shows an operating range that produces the most flow or pressure per horsepower
2. The removal of any mechanical flow device that limits the flow of a fan or pump while the motor turns the application at a fixed speed
affinity laws: The affinity laws can determine the system performance for centrifugal devices, including theoretical load requirements and potential energy savings
1. Flow or volume varies linearly with speed. If speed decreases by 50%, flow decreases by 50%.
2. Pressure or head varies as a square of the speed. If speed decreases by 50%, the pressure decreases to 25% .
3. Power or energy consumption varies as a cube of the speed. If speed decreases by 50%, power consumption decreases to 12.5% .
The potential of energy savings is available as the flow requirement is reduced
APPLICATION AREA :
• HOTEL KITCHEN EXCHAUST AND FRESH AIR FAN
• BANQUET HAAL
• ID AND FD FAN
• WATER PUMP
• AND OTHERS