Energy recovery in gravity adduction pipelines of a water supply system (WSS) for urban areas using Pumps-as-Turbines (PaTs)

Abstract

Energy recovery solutions reduce considerably the carbon footprint of Water Supply Systems (WSSs), which accounts for a large share of the energy demand in urban areas. The evaluation of the potential saving requires the availability of water flow rate and net head values in WSSs pipelines; however, this task is not always achievable since flow meters are costly and not installed in all the pipelines. In this paper, a novel methodology to predict the yearly average flow rate in gravity adduction pipelines is presented and validated using measured data coming from a WSS in Italy. A methodology already developed by some of the authors of this work was used to select Pump-as-Turbines (PaTs) and evaluate their Best Efficiency Point (BEP) to maximize the energy recovery. Two different installation layouts were investigated, namely one PaT and two PaTs in parallel, to be installed in the selected branches. The first one showed the best economic profitability, leading to a saving of 1325 €/year and a PayBack Period (PBP) of 11 years. The branch with the highest energy recovery potential led to a saving of 4915 €/year and a PBP of 6 years. Energy Efficiency Certificates (ECCs) were considered, highlighting their pivotal role to lower PBPs.