Operating characteristics of the variable frequency speed-regulating system for a single pump in a closed system

Abstract

This study experimentally investigated the operating characteristics of the variable frequency speed-regulating system of a water pump in a closed system. The test data for the variable frequency water pump under various conditions were obtained by changing the water pump frequency and the opening setting of a regulator valve in the system. This study revealed that the total power ratio of the water pump system before and after the frequency adjustment did not exhibit cubic correlations with its rotational speed ratio as defined by the affinity law, especially in areas other than the high-efficiency area of pump operation. The equations that express the correlations between the frequency ratio and the total power ratio under the full range of operating conditions were obtained in this study by using the data fitting method. The test confirmed that the fitted characteristic equations had a higher precision and a wider scope of applicability than the existing equations when the water pump, motor, and variable frequency drive were considered as a whole. Practical application: The variable frequency speed-regulating system of a water pump was used in cooling, cooled and heating systems. However, the water pump power was calculated by the standard cube law, and its energy-saving potential was exaggerated. This study revealed a new energy model of a water pump system that can more accurately calculate the total power of the variable frequency water pump in practical engineering.