Pilscikovs D. Energy efficiency analysis for optimization of variable speed pump operation: Ph.D. thesis in engineering science, Riga, RTU, 2014. The paper contains 4 chapters, 115 pp., 25 tables and 74 pictures. References in the paper – overall number are 126. About 10% of the total electrical energy produced in the world has been consumed by centrifugal pumps and close to 60% of that can be saved up. Depending on the type of hydraulic system and centrifugal pump application, it is possible to define a number of criteria to be taken into account during the optimization activities of variable speed pump operation. The objective of the thesis is to develop the criteria of the energy efficiency analysis for further optimization of operation of variable speed centrifugal pumps in public water supply and district heating systems. The main tasks of the research are: - To study aspects of operation and design of variable speed centrifugal pumps. - To determine statistically and experimentally check the energy efficiency improvement potential of variable speed pump operation, if the proportional pressure control mode is applied instead of the constant (differential) pressure control mode. - To calculate statistically the reduction potential of water leakage in network, if the proportional pressure control is applied instead of the constant (dif.) pressure control. - To determine statistically and experimentally check the efficiency change of variable speed pumps according the duty point deviation from pump nominal head. - To define statistically and experimentally check pump efficiency at the best efficiency point of inline single-stage and multi-stage centrifugal pumps as well as end-suction single-stage centrifugal pumps according to flow and head values. Developed criteria of the energy efficiency analysis can be used for water supply and heating systems as: - Recommendations for designers selecting centrifugal pump technology for calculated duty points. - Initial assessment planning the energy efficiency improvement activities: pump audit, reconstruction of pumping system, reduction of water leakage. - Educational tool for technical schools studying centrifugal pumps’ and/or the overall system energy efficiency issues. The research results regarding the promotion thesis have been reported in 7 scientific conferences, and they are represented in 10 international publications.