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.
Highlights
Since the industrial revolution, population growth has been responsible for a significant increase in energy consumption
The authors did not consider any energy recovery in the indirect pumping scheme, where a hydropower production plant, which converts the dissipation of the valves into energy, could increase the energy efficiency of the whole water system
In the direct pumping scenario, the required daily energy is equal to 61 kWh/day, while the indirect pumping daily energy is equal to 89 kWh/day and 6 kWh/day can be recovered by the pump as turbine (PAT)
Summary
Population growth has been responsible for a significant increase in energy consumption. Sustainable growth can be achieved by the development of several strategies aimed to guarantee hydraulic and energy efficiency, such as: pressure management for reduction of water losses due to leakage [7,8,9]; pipe repair, improvement, or replacement to reduce the problem of water leakage and to save the embedded energy [10,11,12,13]; and energy recovery using microturbines [2]. Energy recovery is of considerable importance in pressurized systems: the priority of such a strategy is not just the production of energy [14,15], and the increase of sustainability and efficiency of water exploitation [2]. The authors did not consider any energy recovery in the indirect pumping scheme, where a hydropower production plant, which converts the dissipation of the valves into energy, could increase the energy efficiency of the whole water system. The efficiency of the two different technical solutions under variable values of pumping head, head losses, and head ratios between indirect and direct pumping have been investigated with the aid of a new energy index and two literature efficiency indices [34,35]
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