Evaluation methods for comparing energy savings due to variable speed pumping in wastewater applications

Abstract: The Master Thesis work has been carried out at Xylem HQ, Sundbyberg, Sweden in collaboration with Linköping University, Department of Management and Engineering. The work was to evaluate in different ways energy savings in wastewater pumping stations and conclude what is the discrepancy between them, emphasizing on the theoretical model and measured data. Two pump stations were chosen to be modeled by mathematical calculations based on theoretical pump and system curves. Based on the same inputs, a commercial tool was used to calculate energy savings. Moreover, theoretical curves and variable speed drives were combined into an own developed testing platform in LabView, as an alternative evaluation solution. Finally, measured data was collected and used in a specific energy algorithm, designed to have as inputs water level and energy. In term of method accuracy, initial assumptions are wrong. For a given frequency, the results show similar values for all four evaluation methods. Also, variable speed is confirmed as a good control philosophy for less energy use than direct online.