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.

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.

Water distribution networks face several problems related to leakages, where the pressure control strategy is a common practice for water loss management. Small-scale hydropower schemes, where pumps as turbines replace pressure reducing valves, can be considered an interesting technical solution, which ensures both economic convenience and system flexibility. Due to the water networks’ variable operating conditions, a new methodology to model the effectiveness of pumps as turbines was developed based on the efficiency and the mechanical reliability of the hydropower device and the flexibility of the plant. System effectiveness is proposed as the objective function in the optimization procedure and applied to a real system, enabling one to emphasize that the hydraulic regulation mode of the plant is better than the electric regulation mode for American Petroleum Industry (API) manufacturing standards of pumps.

Pressure reducing valves are frequently used within water distribution networks to reduce pressure values. The use of a pump working as a turbine (PAT) to recover the dissipated energy is generally considered the most cost-effective solution, but PATs are not provided with any regulation device. Thus, in presence of variable hydraulic conditions, a regulation system has to be inserted in the power plant to obtain the requested backpressure value. A comparison among the feasible regulation systems for PAT reg- ulation is discussed and the optimal solution is found by means of the power plant effectiveness, combining system capability, flexibility and reliability

A new approach is proposed for calibrating hydraulic network models. This procedure uses a nonlinear optimization algorithm along with a standard, off-the-shelf, network solver. Pipe roughness is adjusted until simulation results agree with the values observed in the field. To achieve realistic calibrated roughness values, the objective is to minimize the sum of the squares of the differences between the calibrated and initial pipe roughness estimates, under a set of constraints determined from a sensitivity matrix. The algorithm is applied to a sample network, and the resulting calibrated network is tested under different loading conditions.