A Comparison of Energy Recovery by PATs against Direct Variable Speed Pumping in Water Distribution Networks

Abstract

Water systems are usually considered low efficiency systems, due to the large amount of energy that is lost by water leakage and dissipated by pressure reducing valves to control the leakage itself. In water distribution networks, water is often pumped from the source to an elevated tank or reservoir and then supplied to the users. A large energy recovery can be realized by the installation of energy production devices (EPDs) to exploit the excess of pressure that would be dissipated by regulation valves. The feasibility of such a sustainable strategy depends on the potential of energy savings and the amount of energy embedded in water streams, assessed by means of efficiency measures. Alternatively, energy savings can be pursued if the water is directly pumped to the network, bypassing the elevated reservoir. This study focuses on the comparison of two solutions to supply a real network, assessed as a case study. The first solution consists of water pumping to a reservoir, located upstream of the network; the excess of energy is saved by the employment of a pump as turbine (PAT). The second scenario is characterized by a smaller pressure head since a direct variable speed pumping is performed, bypassing the reservoir. The comparison has been carried out in terms of required energy, assessed by means of a new energy index and two literature efficiency indices. Furthermore, differing design conditions have been analyzed by varying the pumping head of both the scenarios, corresponding to different distances and elevation of the water source.

Energy Transfer from the Freshwater to the Wastewater Network Using a PAT-Equipped Turbopump

“…According to the topography of the village, the direction of the wastewater flow produced by the inhabitants of the village has been predicted and a hypothetical drainage network has been overlaid on to the drinking water network, as shown in Figure 5. In Figure 3b, the daily trend of the head drop in the valve is given for the flow rate distribution of Figure 3a, as obtained in [17]. According to Figure 3, the daily average values of the discharge (Q F ) and head loss within the PAT system (∆H PAT ) are 4.35 L/s and 13 m, respectively.…”

“…In Figure 3b, the daily trend of the head drop in the valve is given for the flow rate distribution of Figure 3a, as obtained in [17]. According to Figure 3, the daily average values of the discharge ( ) and head loss within the PAT system ( ) are 4.35 L/s and 13 m, respectively.…”

“…Figure 2. Hydraulic network of the study area (modified from [17]). Figure 2, the network is provided with an upstream valve located along the pipe connecting nodes 8 and 10, to perform a pressure control strategy within the network.…”

“…According to the topography of the village, the direction of the wastewater flow produced by the inhabitants of the village has been predicted and a hypothetical drainage network has been overlaid on to the drinking water network, as shown in Figure 5. In previous research [17], the design of a hydropower plant, replacing the pressure reducing valve in the branch between nodes 8 and 10 ( Figure 2), has been performed, and the hydraulic behavior of the network has been simulated using Epanet [36]. In particular, the plant has been provided with a PAT configured using hydraulic regulation [37] including a series-parallel hydraulic circuit ( Figure 4).…”

“…In particular, a recent study [15] showed that an optimal pump scheduling in a drainage system can ensure an average value of recovered energy up to 32%. It has recently been shown [17] that supplying a reservoir located upstream of a water network and dissipating the excess energy using a hydropower turbine is likely to be preferred over pumping directly to the network, depending on the characteristics of the hydraulic system. Among these energy-saving strategies, the replacement of pressure reducing valves (PRVs) with energy production devices (EPDs) represents one of the most advantageous strategies, which ensures both energy recovery [18] and leakage reduction [19][20][21][22].…”