Evaluation of variable speed pumps in pressurized water distribution systems

Abstract

In pressurized water distribution systems, a constant speed pump is often used because of its simplicity. However, constant speed pumps are not easily able to deal with changing demands in water flows. When the demand for the discharge differs from the design discharge, the required demand (discharge and head) could be met by changing the pump speed without making any special changes in the system. Using an electronic drive circuit, the electrical frequency can be changed, and the rotation speed of the pump motor can thus be modified. In this study, the application of variable speed pumps in pressurized irrigation systems is investigated. Two pumping station scenarios including a fixed speed pump and a variable speed pump are considered. The selected pump station includes a real sprinkler irrigation system near Tabriz city, Iran, with 3 lateral pipes and 600 m length of main pipe. The diameter of the main pipes is 8 and 6 inches. The results show that using a variable speed pump increases the average pump efficiency by 18.7%. In addition, the variable speed pump system reduces the electrical consumption 57.6% compared to a fixed speed pump. Therefore, the use of variable speed pumps in pressurized systems is recommended. Step-by-step calculations for a sprinkler irrigation system design are the contribution of this study. This information helps engineers who are not familiar with commutation process.