Development of Formula for Computing Power Input of Variable-speed Centrifugal Pumps

Abstract

Abstract

Variable-speed control of centrifugal pumps is an effective energy conservation method. This method requires substantial investment, which must be justified by energy saving. A popular method for energy saving estimation is the use of the well-known affinity laws, which imply that power input varies with the cube of the flow rate. However, this straightforward application of the affinity laws may lead to an overestimation of energy saving if a pump must deliver a fluid against not only the frictional resistance in the piping system but also static head or differential pressure. Nevertheless, many practicing engineers still rely on the affinity laws due to the lack of alternative formula. This paper shows that a formula that provides better estimation of energy saving of a variable-speed centrifugal pump may be derived provided that sufficient details of pump and system characteristics are known.

Keywords : Energy Conservation; Energy Efficiency; Affinity Laws