Abstract
Pressure Reducing Valves (PRV) have been widely used as a device to control pressure at nodes in water distribution networks and thus reduce leakages. However, an energy dissipation takes place during PRV operation. Thus, micro-hydropower turbines and, more precisely, Pump As Turbines (PAT) could be used as both leakage control and energy generating devices, thus contributing to a more sustainable water supply network. Studies providing clear guidelines for the determination of the most cost-effective device (PRV or PAT) analysing a wide database and considering all the costs involved, the water saving and the eventual power generation, have not been carried out to date. A model to determine the most cost-effective device has been developed, taking into account the Net Present Value (NPV). The model has been applied to two case studies: A database with 156 PRVs sites located in the UK; and a rural water supply network in Ireland with three PRVs. The application of the model showed that although the investment cost associated to the PRV installation is lower in the majority of cases, the NPV over the lifespan of the PAT is higher than the NPV associated with the PRV operation. Furthermore, the ratio between the NPV and the water saved over the lifespan of the PAT/PRV also offered higher values (from 6% to 29%) for the PAT installation, making PATs a more cost-effective and more sustainable means of pressure control in water distribution networks. Finally, the development of less expensive turbines and/or PATs adapted to work under different flow-head conditions will tip the balance toward the installation of these devices even further.
Highlights
World water use has risen considerably in recent decades and this growing tendency is likely to continue due to the expected population growth in the coming years [1]
The application of the model showed that the investment cost associated to the Pressure Reducing Valves (PRV) installation is lower in the majority of cases, the Net Present Value (NPV) over the lifespan of the Pump As Turbines (PAT) is higher than the NPV associated with the PRV operation
CSt t=1 (1 + r)t where TC (€) is the total installation cost, t is an index related to year, L is the lifespan of the device considered, PRV or PAT
Summary
World water use has risen considerably in recent decades and this growing tendency is likely to continue due to the expected population growth in the coming years [1]. Large cities are increasingly concentrating a higher number of people, leading to water scarcity conditions in many urban areas [2]. One quarter of the largest cities in the world were recently estimated to be water stressed [3]. In Europe, and in its southern regions, a 24% decrease in renewable water resources has been detected during the period 1960–2010 [4]. World energy consumption is expected to increase by 28% in 2040 with respect to 2015 [5]. The sustainable use of water and energy resources is currently one of the main concerns worldwide
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