Power characteristics of variable frequency speed control-based water pumps in open cooling water systems

Abstract

The operational power characteristics of variable frequency speed control-based water pumps in an open cooling water system were studied experimentally. It was found through this research that before and after frequency conversion, the ratio of the power of a particular frequency to the power of the rated frequency of the water pump system shows a third-power relationship. A data fitting method was used to obtain the equation for the power and frequency ratio of the system under the overall operating conditions. The experiment shows that the system height difference has no effect on the basic form of the characteristic equation. Finally, when unified consideration is given to the pump, motor and frequency converter, the calculated power of the water pump system is very close to the actual value.This power characteristic equation contributes to calculations relating to the water pump operational speed regulation in an open cooling water system. Practical application: Variable frequency speed-regulating systems for pumps are applied in open loop water systems, such as those supplying cooling towers. However, the standard cube law which is used to determine the power of the water pump system is inappropriate and exaggerates the potential energy-saving. This study determined a new energy model for the water pump system that can more accurately calculate the total power of the variable frequency controlled water pump when used in open loop systems.