Using Additional Time Slots for Improving Pump Control Optimization Based on Trigger Levels

This paper presents a new methodology for optimizing the operation of pumps supplying water from a low source to an elevated tank in water distribution systems (WDSs). It is based on the use of the on/off trigger level technique for each pump present in the pumping station. The novelty of the methodology consists of the addition of time slots for the optimization of the trigger levels. These slots are created at the end of each energy tariff period, to drive the tank level to the highest and lowest points at the beginning and at the end of the peak, respectively. As a result, pumps are led to work more and less during low and high tariff periods, respectively, yielding reductions in energy costs. In the applications, the methodology was introduced within a multi-objective optimization framework, searching for solutions in the trade-off between daily average energy cost and daily average number of pump switches, representative of the stressing conditions for the system. The methodology was applied to case studies with single and multiple pumps, using realistic demand patterns, and was compared with other trigger levels-based methodologies in the scientific literature. The results proved its benefits, in yielding solutions with reduced number of pump switches for prefixed values of energy cost. This is more evident when the operation of three pumps must be optimized. In an explicative example with three operating pumps, for an energy cost around 6000 Euro/day, the newly proposed methodology leads to a number of pump switches between 17% and 33% lower than the results obtained with the methods considered for comparison.