engleski

The Efficiency of Small Variable Speed Pumping Systems

Pumping water supply systems, especially closed water supply systems are usually characterized by a variation of flow and pressure. Since pump efficiency is a function of flow, for varying demand values a pump can run fairly inefficiently. To deal with this inefficiency the usual way is to change the performance of a pump by applying the pump speed control. For varying system requirements variable frequency drives recently became most common method used to control the motor speed. The equations relating pump performance parameters of flow, head and power to the motor speed are known as the affinity laws. However, affinity laws assume that the efficiency practically does not change with the speed. For most pumps the affinity laws can be used to predict the performance of a pump but only to a certain level, usually not less than 40 to 50 percent of full speed. At lower speeds affinity laws may yield false predictions. The aim of this paper is to verify how well the theoretical aspects work for a small variable speed pump regarding efficiency.

Affinity laws; pump efficiency; pump speed control; VFD efficiency

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