Learn VSD advantages and misconceptions.
12/26/2018
How much will pump efficiency be affected with the addition of a variable speed drive? It is a misconception that adding a variable speed drive (VSD) to a pump will increase its efficiency. When considering the wire-to-water efficiency of the pump, motor and VSD, each component that is added lowers the wire-to-water efficiency at a respective flow rate because each component has losses associated with it. Image 1 illustrates this concept showing the pump efficiency being the greatest, then the wire-to-water efficiency decreasing at the respective flow rate when the motor and VSD are added to the extended pump product.
![Pump efficiency and wire-to-water efficiency of pump, motor and VSD](/sites/default/files/1218/Wire-to-Water-Efficiency-Curve-PDF.jpg)
![Essential power for variable speed control and wasted power](/sites/default/files/1218/Figure-4.05-both.jpg)