Energy efficiency is emphasized worldwide for motor-driven fluid-handling equipment including pumps, fans, blowers, and compressors. Energy production and consumption comes with financial and environmental costs, making energy savings an important aspect of the life cycle cost evaluation of the pump or compression system. True-Weighted Efficiency, or TWE, is a general purpose method to provide a single efficiency metric applicable to a machine operating under multiple operating conditions.
The TWE method is derived from the first principles, based on useful fluid energy output compared to the energy input into the system. Generalized load profiles are used that include one or more control curves, multiple discrete operating points based on those control curves, and the time of operation at each operating point. This method is applicable to pumps, compressors, blowers, and fans operating at fixed or variable speeds, on/off operation, throttle control, or by-pass control.
As background, the chapter includes a brief survey of legislation known as the Ecodesign requirements for water pumps, and more recently, the United States Department of Energy (DOE) legislation affecting the commercial sale of specific types of pumps or fans sold in the United States.
In order to promote widespread use and understanding of TWE for commercial applications, this chapter provides a general outline of the theoretical method. The fundamental principles and governing equations are introduced along with a simplified TWE equation based on a specified load profile and weighting factors. Two case studies are provided illustrating the use of the TWE method for a pumping system and a turbocompressor. The studies reveal that the machine with the best design point efficiency is not always the best choice from a TWE and energy consumption perspective. The goal of the chapter is to promote broad understanding and use of this method to reduce energy consumption for pump and compressor applications (Chapter 55).
