• Energy Research

Pressure control is one of the main techniques to control leakages in Water Distribution Networks (WDNs) and to prevent pipe damage, improving the delivery standards of a water supply systems. Pressure reducing stations (PRSs) equipped by either pressure reducing valves or motor driven regulating valves are commonly used to dissipate excess hydraulic head in WDNs. An integrated new technical solution with economic and system flexibility benefits is presented which replaces PRSs with pumps used as turbines (PATs). Optimal PAT performance is obtained by a Variable Operating Strategy (VOS), recently developed for the design of small hydropower plants on the basis of valve time operation, and net return determined by both energy production and savings through minimizing leakage. The literature values of both leakages costs and energy tariffs are used to develop a buisness plan model and evaluate the economic benefit of small hydropower plants equipped with PATs. The study shows that the hydropower installation produces interesting economic benefits, even in presence of small available power, that could encourage the leakage reduction even if water savings are not economically relevant, with consequent environmental benefits.

Pressure control is one of the main techniques to control leakages in Water Distribution Networks (WDNs) and to prevent pipe damage, improving the delivery standards of a water supply systems. Pressure reducing stations (PRSs) equipped by either pressure reducing valves or motor driven regulating valves are commonly used to dissipate excess hydraulic head in WDNs. An integrated new technical solution with economic and system flexibility benefits is presented which replaces PRSs with pumps used as turbines (PATs). Optimal PAT performance is obtained by a Variable Operating Strategy (VOS), recently developed for the design of small hydropower plants on the basis of valve time operation, and net return determined by both energy production and savings through minimizing leakage. The literature values of both leakages costs and energy tariffs are used to develop a buisness plan model and evaluate the economic benefit of small hydropower plants equipped with PATs. The study shows that the hydropower installation produces interesting economic benefits, even in presence of small available power, that could encourage the leakage reduction even if water savings are not economically relevant, with consequent environmental benefits.

AbstractThe use of pump operating as turbine (PAT) instead of traditional turbines is an effective source of reducing the equipment cost in small hydropower plants. However, the lack of information on the PATs performances represents a limit for their wider diffusion. Furthermore, while for the design of traditional hydropower plants the knowledge of the best efficiency point of the turbomachine is sufficient, additional difficulties arise under variable operating conditions for the exploitation of hydraulic power within water distribution networks: a procedure for the design of the optimal machine operating under variable hydraulic conditions, named variable operating strategy (VOS), has been recently developed, and for its implementation a full set of characteristic curves of several different PATs rotating at different speeds is needed. In order to face the hydraulic variability, variable operating strategy considers either a hydraulic or an electric regulation. The hydraulic regulation system consists in a series-parallel circuit with a PAT and two regulating valves, while for the electric regulation the PAT generator is connected to an inverter which modifies the rotational speed of the machine. If the performances curves of a single PAT are known, all the information needed for the applica- tion of VOS can be obtained by the application of the affinity law of turbomachines, wich allows to extent the given information to a complete set of similiar machines. This paper focuses on the study of the affinity law for the evaluation of the behaviour of a single machine under variable speed. A large database of experimental curves of several PATs operating at different speeds is available and the experimental data are compared with the results of the application of the affinity law herein.

AbstractThe use of pump operating as turbine (PAT) instead of traditional turbines is an effective source of reducing the equipment cost in small hydropower plants. However, the lack of information on the PATs performances represents a limit for their wider diffusion. Furthermore, while for the design of traditional hydropower plants the knowledge of the best efficiency point of the turbomachine is sufficient, additional difficulties arise under variable operating conditions for the exploitation of hydraulic power within water distribution networks: a procedure for the design of the optimal machine operating under variable hydraulic conditions, named variable operating strategy (VOS), has been recently developed, and for its implementation a full set of characteristic curves of several different PATs rotating at different speeds is needed. In order to face the hydraulic variability, variable operating strategy considers either a hydraulic or an electric regulation. The hydraulic regulation system consists in a series-parallel circuit with a PAT and two regulating valves, while for the electric regulation the PAT generator is connected to an inverter which modifies the rotational speed of the machine. If the performances curves of a single PAT are known, all the information needed for the applica- tion of VOS can be obtained by the application of the affinity law of turbomachines, wich allows to extent the given information to a complete set of similiar machines. This paper focuses on the study of the affinity law for the evaluation of the behaviour of a single machine under variable speed. A large database of experimental curves of several PATs operating at different speeds is available and the experimental data are compared with the results of the application of the affinity law herein.

With reference to a classical wet tank equipped with a wastewater submersible pump, in this research, an advanced numerical model has been used in order to obtain the optimal pump scheduling of on/off operation and variable pump speed. Then, in order to evaluate the time decay of pump performances, the mechanical wear has been artificially simulated and the performance curves have been experimentally obtained for different rotational speeds. Finally, the benefits, as well as the feasibility, of pump scheduling have been evaluated for differing operating conditions. According to the results, the optimal pump scheduling achieves large energy savings up to 43%, for soft mechanical wear. If the mechanical wear is considered, the energy savings are large as well, between 35.60% and 26.70%, for medium and hard mechanical wear, respectively. On the other hand, the limitation of such a strategy has been highlighted: the feasibility of pump scheduling is limited by the elevation of the downstream tank. According to the results, energy savings can be achieved until the elevation of the downstream tank is 67% of the pressure head at the best efficiency point, whereas such percentage decreases to 50% for hard mechanical wear. Finally, the results show that plant efficiency is strongly affected by the mechanical wear: an accurate maintenance of the pumping system is therefore recommended in order to attenuate the time decay of pump performances.

With reference to a classical wet tank equipped with a wastewater submersible pump, in this research, an advanced numerical model has been used in order to obtain the optimal pump scheduling of on/off operation and variable pump speed. Then, in order to evaluate the time decay of pump performances, the mechanical wear has been artificially simulated and the performance curves have been experimentally obtained for different rotational speeds. Finally, the benefits, as well as the feasibility, of pump scheduling have been evaluated for differing operating conditions. According to the results, the optimal pump scheduling achieves large energy savings up to 43%, for soft mechanical wear. If the mechanical wear is considered, the energy savings are large as well, between 35.60% and 26.70%, for medium and hard mechanical wear, respectively. On the other hand, the limitation of such a strategy has been highlighted: the feasibility of pump scheduling is limited by the elevation of the downstream tank. According to the results, energy savings can be achieved until the elevation of the downstream tank is 67% of the pressure head at the best efficiency point, whereas such percentage decreases to 50% for hard mechanical wear. Finally, the results show that plant efficiency is strongly affected by the mechanical wear: an accurate maintenance of the pumping system is therefore recommended in order to attenuate the time decay of pump performances.