Optimizing Pump Selection for Energy Efficiency Across Multiple Operating Conditions Using True Weighted Efficiency (TWE)

Energy efficiency is emphasized more actively across the pump industry. Legislation in the European Union and in the United States utilize new energy efficiency ranking metrics, but neither of these methods are conveniently applied to customer specified load conditions. True Weighted Efficiency, or TWE, is introduced as a general-purpose, universal pump efficiency metric for pumps operating under multiple operating conditions. The TWE is derived accurately from first principles, using generalized load profiles that include control curves, multiple discrete operating points based on those control curves, and the time of operation at each operating point. A pump selection/optimization program is used to numerically demonstrate the TWE method. Various examples are presented, contrasting candidate pumps based on three different optimization strategies. The study reveals that the pump with the best design point efficiency may not be the best choice from a TWE or an evaluated cost perspective. This method is applicable to rotodynamic or positive displacement pumps operating at fixed or variable speed, on/off operation, throttle control, or by-pass control. and other turbomachinery as well. The TWE methodology, when combined with a pump selection/optimization program, will help practitioners design systems that reduce energy consumption for new or reconfigured pump applications.