Modeling the Efficiency and Power Characteristics of a Pump Group

This note proposes models for efficiency and mechanical input power of a group of parallel identical pumps which can be fixed or variable speed. Two approaches are considered. In the first approach, the power characteristic is evaluated from hydraulic and efficiency curves. In the second approach, the mechanical power is approximated directly by a cubic polynomial and scaled by pump speed and number of pumps. In both cases, the obtained power curves are well suited for use in simulation and optimization software; however, if the power data points are available, the second approach can lead to a more accurate representation. The effects of the electric motor efficiency characteristic on the performance of the entire pump plant are also discussed. The developed theory is illustrated by a practical case study. For completeness, the studies are performed using two types of fitted pump hydraulic curves, one quadratic and one described by a power law.