Pressure Regulation in a Water Distribution Network Using Pumps as Turbines at Variable Speed for Energy Recovery

Pumps that function as turbines (PATs) are considered an economical solution to control pressure in water distribution networks (WDNs) in place of pressure control valves (PCVs). Their use requires a precise operational understanding of various hydraulic conditions in a WDN. Otherwise, the efficiency of the machine is reduced by the off-design operation, making it impossible to regulate the pressure and recovering little energy. This study presents a methodology that details the pressure regulation in a municipal network by controlling the PAT speed. The WDN sectorization steps are described using EPANET 2.0 software. The selection and off-design operation of the pump are presented with several models from the literature. The machines are simulated at constant and variable speeds to replace the valves. The economic advantages are also estimated. At constant speeds, operation as a PCV occurs only in the flow close to the best efficiency point (BEP), impairing the supply in the network. At variable speeds, the PAT maintains the best efficiencies (0.62 to 0.64) and power (3.44 kW) when flows are high and speeds are low (2,400 at 11 am and 3,000 rpm at 6 pm). Thus, the pump outlet pressure and network throughput are maintained according to the values required by the PCVs. With all the pumps in operation, the system can recover 270,192.19 kWh/year. The estimated payback period is 27 months, the net present value (NPV) is US$ 64,476.18, and the internal rate of return (IRR) is 63% for the analyzed PAT.