Giuseppe Del Giudice

Energy Production in Water Distribution Networks: A PAT Design Strategy

Pump operating as turbine (PAT) is an effective source of reducing the equipment cost in small hydropower plants. However, the manufacturers provide poor information on the PAT performance thus representing a limit for its wider diffusion. Additional implementation difficulties arise under variable operating conditions, characteristic of water distribution networks (WDNs). WDNs allow to obtain widespread and globally significant amount of produced energy by exploiting the head drop due to the network pressure control strategy for leak reductions. Thus a design procedure is proposed that couples a parallel hydraulic circuit with an overall plant efficiency criteria for the market pump selection within a WDN. The proposed design method allows to identify the performance curves of the PAT that maximizes the produced energy for an assigned flow and pressure-head distribution pattern. Finally, computational fluid dynamics (CFD) is shown as a suitable alternative for performance curve assessment covering the limited number of experimental data.

PAT Design Strategy for Energy Recovery in Water Distribution Networks by Electrical Regulation

In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and economic convenience are still required. In water distribution networks, an additional design problem comes out from the necessity of ensuring a required head drop under variable operating conditions, i.e., head and discharge variations. Both a hydraulic regulation (HR)—via a series-parallel hydraulic circuit- and an electrical regulation (ER)—via inverter- are feasible solutions. A design procedure for the selection of a production device in a series-parallel hydraulic circuit has been recently proposed. The procedure, named VOS (Variable Operating Strategy), is based on the overall plant efficiency criteria and is applied to a water distribution network where a PAT (pump as a turbine) is used in order to produce energy. In the present paper the VOS design procedure has been extended to the electrical regulation and a comparison between HR and ER efficiency and flexibility within a water distribution network is shown: HR was found more flexible than ER and more efficient. Finally a preliminary economic study has been carried out in order to show the viability of both systems, and a shorter payback period of the electromechanical equipment was found for HR mode.

Combined Effects of Parallel and Series Detention Basins for Flood Peak Reduction

A simple analytical method is proposed that allows a preliminary evaluation of the overall efficiency of a detention basin system for flood risk reduction in a specific target section. Solutions are provided both for parallel and series systems, under some simplifying assumptions concerning the linearity of detention basin, river network and watershed responses. Further, for the series configuration a regressive model is proposed for the computation of the overall efficiency, because of the complexity of analytical solution. A case study is also presented, where the overall efficiency of a system of nine detention basins is computed by means of both the analytical and the regressive model. Results are discussed to assess the different influence of detention basins in parallel or in a series system.

Preliminary Estimate of Detention Basin Efficiency at Watershed Scale

Urban encroachment in natural floodplain areas and infrastructures interfering with watercourses have caused higher flood risks in lowland areas. In this context, detention basins have become a fundamental instrument for stormwater and environmental management at watershed scale. Numerical methods of flood routing are generally coupled with optimization algorithms to investigate the factors that affect the overall efficiency of detention basins in controlling the peak flows throughout a watershed. To overcome the procedure effort due to numerical integration, a simple innovative approach, based on the linear system theory applied to the solution of hydrologic flood routing, is proposed for a preliminary estimate of overall efficiency. First a numerical analysis is performed to ensure that the schematization of the detention basin as a linear system leads to technically acceptable approximation. Then, a simple analytical equation is provided that allows a preliminary estimate of detention basin efficiency in downstream river reaches. Sensitivity analysis of the above equation provides information about the factors that most contribute to the downstream flow reduction variability. Finally, the proposed methodology, adequately extended to a parallel system of stormwater detention basins within a watershed, can be easily integrated in optimization algorithms.

Vortex dropshaft retrofitting: case of Naples city (Italy)

This work describes the main hydraulic features of vortex dropshafts along with some examples of their mis-designs and consequent malfunction. Laboratory experiments were conducted to test the hydraulic performance of subcritical vortex intakes using supercritical approach flow design basis. The purposes of these drop structures are to: (i) convey the storm runoff towards the sea through the existing sewer system located at lower elevations and (ii) by-pass insufficient sewers. The proper operation of these structures is crucial to prevent flooding and to guarantee the urban safety. This issue is particularly relevant for the sewer system of Naples (Italy), which is strongly constrained by its hilly landscape. Several drop structures were realized to connect the modern urban drainage system to the early sewer mains located at the sea level. This work intends to highlight practical issues to enhance the existing vortex dropshafts, with possible applications to other cases similar to the Neapolitan context.

Design of a Scroll Vortex Inlet for Supercritical Approach Flow

Vortex drop shafts are used in urban drainage systems to connect two sewers located at considerably different elevations. After their introduction in 1947, these were studied with particular reference to subcritical approach flow. Vortex shafts for supercritical approach flow can also be used, but the intake structure may have relatively high cost due to the complex geometry. The present study includes experimental results of a specific investigation on the changes to be made in the supercritical approach channel if a subcritical vortex intake is used. The experimental investigation analyzes the effect of a hydraulic jump on the performance of vortex intake structure to define appropriate technical solutions, essentially consisting in a negative step to be located along the supercritical approach channel. Design criteria are finally presented for the evaluation of the step height and its distance from the vortex intake structure.

Vortex Drop Shaft for Supercritical Flow

Vortex drop shafts are used in urban drainage systems to connect two sewers located at considerably different elevations by means of a vertical conduit. The vortex drop shaft was first designed by Drioli (1947). It was then studied by other authors with reference to subcritical approach flow. Vortex shafts specifically conceived for supercritical flow can also used, but at very high costs due to the specially features required for the intake structure. The present study shows the experimental results of a specific investigation into the changes to be made in the approach channel for supercritical flow, when a subcritical vortex intake is used. The proposals concern the definition of the height of the step to be located in the approach channel, and the length of the lower-bottomed section in the approach channel, while maximizing the hydraulic efficiency of the system. Proper step height will cause the hydraulic jump to conveniently occur downstream of the step, whereas a regular subcritical flow in the intake structure of vortex shaft will result from lowering the bottom of the approach channel for the appropriate length.

A Mixed Strategy Based on Self-Organizing Map for Water Demand Pattern Profiling of Large-Size Smart Water Grid Data

In the present paper a procedure is introduced to detect water consumption patterns within water distribution systems. The analysis is based on hourly consumption data referred to single-household flow meters, connected to the Smart Water Network of Soccavo (Naples, Italy). The procedure is structured in two consecutive phases, namely clustering and classification. Clustering is performed on a selection of standardized monthly time series, randomly chosen within the database; different clustering models are tested, basing on K-means, dendrogram and Self-Organizing Map, and the most performant is identified comparing a selection of Clustering Validity Indices. Supervised classification is performed on the remaining time series to associate unlabeled patterns to the previously defined clusters. Final results show that the proposed procedure is able to detect annual patterns describing significant customers behaviors, along with patterns related to instrumental errors and to abnormal consumptions.

Novel Diversion Structure for Supercritical Flow

AbstractIn urban drainage systems, it is usually necessary to split the storm water discharge among different sewer branches because of limited flow capacity of either hydraulic structures or sewer lines. For this purpose, sewer sideweirs and leaping weirs are generally used as diversion overflow structures. For supercritical approach flow, the former is not recommended because of the occurrence of hydraulic jumps, whereas the latter requires an outlet located below the approach flow sewer bottom. To overcome these constraints, a novel compact hydraulic structure is proposed. It consists of a frontal rectangular intake, representing the diversion sewer inlet, located in the approach flow sewer and parallel to its bottom. A 6.67:1 scale model was tested over a range of hydraulic and geometrical parameters to determine its head-discharge relationship, developing a dimensionless equation relating the diversion discharge to the geometrical properties of the intake under supercritical flow conditions. The limi...

Vortex shaft outlet

Vortex drop shafts are widely used in practice to connect sewer mains characterized by large elevation difference. These structures conventionally include three key elements: intake structure, vertical shaft and outlet structure, also named dissipation chamber. The latter has not received much attention as compared to the first two parts, and only few experimental investigations are currently available from the literature (Viparelli, 1950; Kellenberger, 1988). Actually some rules of thumb are available as design criteria (ATV, 1998; Hager, 1999), but no systematic hydraulic investigation is available so far. The aim of the present study is to present preliminary results of an experimental campaign conducted at the Department of Hydraulic and Environmental Engineering, University of Naples, Italy. The physical model of a vortex drop shaft allowed the Authors to investigate the main hydraulic features of the dissipation chamber, in order to characterize the performance of various types of outlet structures.