Example analysis on variable frequency drive operation of circulating pumps

With a project example, simplifies the method of calculating general energy consumption of the pump in cooling season according to the weight of different typical operating mode durations. Analyses the energy saving potential of variable frequency drive (VFD) operation of the circulating pumps with different number of pumps in parallel under different control methods. Based on the similitude law of pumps, presents the method for determining the pump efficiency under different working conditions with variable speed, i.e. an equivalent efficiency curve method. The results show that for the common pump control methods, the third power relation between the pump rotate speed (water volume) ratio and the shaft power ratio is not true; for the water system with three pumps in parallel, pump rating working point efficiency can be used instead of typical operating point efficiency in order to simplify calculation; applying VFD devices to an air conditioning water system is sure in better economic effects, which is closely related to the type of buildings.