Assessing the Impact of Network Layout on Energy Efficiency, Water Losses and Water Quality in water supply ABSTRACT

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1 Assessing the Impact of Network Layout on Energy Efficiency, Water Losses and Water Quality in water supply Aisha Mamade 1, Laura Monteiro 2, Nuno Maricato 3, Zélia Alves 4, Dália Loureiro 5, Dídia Covas 6 1,2,6 CERIS, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal 3,4 Serviços Municipalizados de Castelo Branco, Castelo Branco, Portugal 1,5 National Laboratory for Civil Engineering, Lisbon, Portugal 1 aisha.mamade@tecnico.ulisboa.pt ABSTRACT Reducing water losses and improving energy efficiency are major concerns for water utilities due to the associated costs, the inefficient use of water, the impact on water quality and the indirect emission of greenhouse gases (GHG). The aim of this paper is to diagnose, define and compare alternative solutions that go beyond the traditional approaches to improve energy efficiency in water supply systems. The case study consists of a rural water distribution system, with an ageing infrastructure, high water losses and huge energy inefficiencies. Analyzed solutions are: status-quo; improving pump efficiency and changing network layout. These solutions are compared using keyperformance indicators (KPI) on water losses, energy efficiency and water quality. A long-term cost-benefit analysis of each alternative is also carried out. Results show that improving pump efficiency (traditional approach) is not always the best response to meet water loss targets. Instead, changing the network layout has proven to be an effective solution to cut energy costs and reduce real water losses. Keywords: Energy Efficiency, Water Losses, Water Quality, Water Distribution Systems 1 Introduction Climate change, uncertainties associated with water supply and growing energy costs are some of the current challenges faced by the water utilities. Solutions that take benefit from the water-energy nexus in water supply systems are needed to face these challenges. To find these solutions, water losses and energy inefficiencies should be addressed in a common and integrated framework. This means assessing the impact of water losses in energy and vice-versa. Water-energy losses management plans that diagnose systems performance and identify improvement solutions [1] are therefore necessary. These plans should not disregard other utility goals, such as the continuous supply of safe water and the systems long-term reliability and resilience. However, integrated studies on the impact of water-energy losses improvement measures in concurrent goals are scarce [2]. Pressure management is a common option for leakage reduction, [3] while pump scheduling has been widely implemented for reducing energy costs [4]. Infrastructure rehabilitation, operational and layout changes (despite not frequently documented) can also be important water-energy losses improvement measures, often forgotten. Operational and layout changes that modify water pathways and retention times in the systems are likely to affect water quality, namely chlorine residual concentrations. Few studies have focused on the effect of these changes on drinking water quality. The main objective of this paper is to diagnose, define and compare alternative solutions that go beyond the traditional approaches to improve energy efficiency in water supply systems. The casestudy is a rural village in Castelo Branco, Portugal that supplies water to 256 clients through a

2 7.8 km of distribution pipes. This case-study was initially analysed in the scope of iperdas, a oneyear Portuguese collaborative project to improve water and energy losses in water supply systems [5], and has been further analysed in the scope of the current paper. 2 Methodology The methodology for water-energy losses assessment is a four-step procedure. The first step is the Water-energy loss diagnosis and consists of three main stages: (i) defining an assessment system with objectives, criteria and key-performance indicators (KPI); (ii) assessing annual water and energy balances and (iii) calculating water-energy loss KPI. An assessment system was developed by the water utility in the scope of iperdas project and has been complemented with additional KPI related to energy efficiency and water quality. For the water balance, the IWA standard has been adopted [6]. For the energy balance, the balance proposed by [7] was calculated. Water balances aim at assessing the volumes of water consumption (e.g., authorized, unauthorized, billed, unbilled) and water losses (real and apparent). Similarly, energy balances aim at assessing the energy associated with water consumption and water losses. This includes calculating components such as natural input energy (e.g., potential energy from storage tanks), shaft input energy (e.g., electric energy from pumps), minimum required energy to supply water to consumers, surplus energy (e.g., water delivered with excessive pressure) and dissipated energy due to continuous (e.g., pipe friction) and singular headlosses (e.g., valve headlosses, pump inefficiencies). Two approaches have been defined to carry out energy balances: top-down and bottom-up [8]. The top-down approach requires minimum data (no hydraulic model is needed) and provides an effective diagnosis of energy inefficiencies in WSS. The bottom-up approach allows for the calculation of all energy balance components, but it is more data-demanding and most utilities do not have their networks modelled. Both approaches have been followed in the current paper. Water balances are annually requested by ERSAR, the Portuguese Water and Waste Regulator, so the utility had the experience of collecting the data and providing the results for each component. The calculation of energy balances was not so obvious and the utility was reluctant to do the calculations since their system is 99% gravity-fed. The assessment of energy efficiency in gravityfed systems is relevant, despite having no costs associated with energy consumption for two main reasons: (i) It is highly probable to have energy consumption (associated with water treatment and transport) that might be reduced at the systems upstream. For instance, if water losses are reduced through the reduction of energy associated with water losses, less energy needs to be treated and transported and (ii) the assessment of surplus energy helps evaluating excessive pressures in the system and may even indicate opportunities for water loss reduction. For water quality assessment, water age was computed using the hydraulic model developed on EPANET [9]. This diagnosis has primarily been carried out for the global system and, then, for subsystems, to identify the most critical areas. This paper focuses on a specific sub-system identified as critical. Following the diagnosis, the second step is the Definition of alternative solutions for improving the system s performance. Typical solutions to improve energy efficiency are equipment-driven and include: pump-scheduling and improving pump equipment efficiency, e.g., through the replacement of pumps or the installation of variable-speed drives [10]. The utility made an effort to go beyond the traditional solutions and think of system-driven solutions that are built on the diagnosis of the system as a whole. These are analysed herein. The third step is the Comparison of alternative solutions. Alternatives have been compared using the same KPI as in the diagnosis, complemented by a cost-benefit analysis. Finally, the last step consists of selecting the best alternative solution.

3 3 Case-study The case-study is the water distribution system of Caféde depicted in Figure 1. Caféde is a rural village in Castelo Branco, Portugal, that supplies about m 3 /year to 256 clients through a 7.8 km distribution system. The network pipes were built in 1994, mostly made of PVC, with diameters of 63 and 90 mm. The trunk main (red line in Figure 1) delivers water in a storage tank with 75 m 3 capacity with a head that is insufficient to ensure the minimum pressure in high elevation nodes. To solve this problem, a pumping station with two small pumps working in parallel (P=2.2 kw) was installed, as illustrated in Figure 1. According to the water utility, the pumping station set point is Q=4 m 3 /h and H=46.7m. Flow direction Tank Figure 1. The Caféde rural area with a detail on the pumping station. The main performance indicators from the utility s assessment system, with the definition and reference values are presented in Table 1. Supplementary KPI related to energy efficiency and water quality were calculated to study the impact of energy efficiency and water quality. A hydraulic model was built using EPANET 2.0 [9] for simulating pressure and water age. Table 1. Key-Performance indicators from the utility s assessment system KPI (units) Definition Reference values Percentage of delivery points (one per [99,0; 100,0] service connection) that receive and are ]97,0; 99,0] likely to receive adequate pressure. ]0,0;97,0[ QS10 - Pressure of supply adequacy (%) Fi46 - Non-revenue water by volume (%) Ph5 - Standardised energy consumption (kwh/(m 3.100m)) E3 * *Supplementary indicators Percentage of the system input volume that corresponds to non-revenue water. Average pumping energy consumption in the system per 1m 3 at 100 m of head. Ratio of total energy in excess. [0,0; 20,0] [20,0; 30,0] [30,0; 100,0] [0,27; 0,40] ]0,40; 0,54] ]0,54; + [ [0; 1[ [1; 2[ [2; + [ Water age (h) * Average retention time in the network -

4 4 Results 4.1 Water-energy loss diagnosis The summary of the performance indicators used in the water-energy loss diagnosis is presented in Table 2. The pressure indicator QS10 has an unsatisfactory value, showing that the pumping station is generating excessive pressures in low elevation nodes. Non-revenue water (Fi46), also unsatisfactory, indicates that 36% of the water is not billed. The utility attributes this to real losses (pipe bursts associated with high pressure in some nodes) and apparent losses (unauthorized consumption and old flow meters). Regarding energy efficiency, Ph5 is 1.44 kwh/(m 3.100m) meaning that the pumping station has an average global efficiency of 19%, which is unsatisfactory. The indicator E3 is 3.2, meaning that the energy in excess represents 3 times the minimum required energy. According to the utility, water quality in the network complies with current European standards for water intended for human consumption. The computed average water age at the demand nodes of the network is of 51.0 h (Table 2) of which about 38.0 h are spent at the storage tank. Although reference values for water age have not been established, higher values have been observed in other small systems [11]. This, along with the quality control results, suggests that the obtained average water age value is satisfactory and that similar or smaller values indicate a good performance. Table 2. Summary of the water-energy loss diagnosis (initial situation) Objective Water losses Energy efficiency KPI QS10 Fi46 Ph5 E3 Water quality Water age (h) Value Definition of alternative solutions The main alternative solutions studied by the water utility are described below: Alt1. Status quo maintaining the current operation and maintenance practices. Alt2. Pump efficiencyimprovement+alc changing the pumping station to increase its efficiency to 75%, coupled with active leakage control (ALC). Alt.3. Layout change+alc changing the network layout by connecting the distribution system directly to the transmission system, coupled with active leakage control (ALC). The first alternative (Alt.1) consists of reacting upon pipe bursts. The second alternative (Alt. 2) is equipment-driven and will focus on improving the pumping station s efficiency and campaigns of active leakage control based on minimum night consumption analysis, therefore reducing the energy consumption and energy costs and water losses. The third alternative (Alt. 3) is systemdriven consisting of the construction of a 1 km pipe, the de-activation of the storage tank and of the pumping station and also including active leakage control to reduce water losses. This will reduce the system s resilience, since the system storage capacity will be reduced.

5 4.3 Comparison of alternative solutions The alternative solutions have been compared using the same performance indicators as in the diagnosis (Table 3). Results show that the status-quo alternative will keep all the KPI at an unsatisfactory service level, as expected. Table 3. Comparison of performance indicators in alternative solutions (evolution from short- to long-term is marked with ). Objective Water losses Energy efficiency Water quality PI QS10 Fi46 Ph5 E3 Water Age (h) Alt. 1 - Status-quo Alt Pump eff. improvement+alc Alt. 3 - Layout change+alc Comparing alternatives 2 and 3, the main differences occur for energy efficiency and water quality. Since Alt. 3 consists of de-activating the pumping stations, the KPI Ph5 is non-existent, meaning that energy consumption is totally reduced. Water age is almost five times lower in Alt. 3, since there is no water stagnation in the storage tank, which suggests that chlorine residual levels in the network will be higher. To complement the comparison of alternative solutions, a cost-benefit analysis has been carried out (Table 4), based on the water utility s assessments. The investment costs considered in Alt. 2 refer to changing the pumping station to a more efficient one. Investment costs in Alt. 3 refer to the construction of 1 km pipe and the installation of a pressure-reducing valve. Energy costs were provided by the water utility for Alt. 1 and estimated for Alt. 2 using an average energy cost of 0.25 /kwh (including fixed and variable costs). Water losses costs were estimated based on the reduction of water loss volume predicted by the utility multiplied by the average cost of water, 0.59 /m 3 (water paid by the utility to the water supply provider). No maintenance costs have been considered. Payback period for the investments in Alt. 2 and 3 were calculated assuming a discount rate of 6%. The benefits in this analysis are the economic savings that can be achieved in relation to the status-quo scenario. Table 4 presents the cost-benefit analysis of the studied solutions. The economic benefit from reducing energy costs in Alt. 2 is paid in 8 years. In Alt. 3, the benefit from the complete elimination of energy costs and the significant reduction of water losses costs turns the investment feasible with a slightly higher payback period of 13 years. Table 4. Cost-benefit analysis Investment costs ( ) Energy costs ( /year) Water losses costs ( /year) Alt. 1 - Status-quo Alt. 2 - Pump eff. Improvement+ALC Alt. 3 - Layout change+alc Payback period (years)

6 4.4 Selection of the best alternative solution The alternatives have been ranked by standardizing each KPI in the assessment system according to the established reference values and Alt. 3 was selected as the best solution. Despite the advantages of reduced energy costs and water losses, this solution decreased the system s storage capacity and, thus, its reliability. This fact has postponed the implementation of this alternative for some time. The utility opted to keep a by-pass in the storage tank. In the case of an emergency, the utility will need to disinfect the pipe and the storage tank and will be able to reestablish the water supply in approximately six hours, which is an acceptable time. After implementing the layout change, pressure was reduced in almost all nodes and its distribution throughout the network is more homogeneous (Figure 3). (a) (b) Figure 2. Pressure at the nodes and velocity in the pipes at 3 am of the case study network in the status-quo (a) and layout change, including the PRV installed (b). In addition to lowering the average water age in the system, the implementation of the alternative solution also eliminated a pipe with very low velocities (below 0.03 m/s), thus diminishing water stagnation and loose deposits build-up potential [12].

7 Energy (kwh/year) 1 st International WDSA / CCWI 2018 Joint Conference, Kingston, Ontario, Canada July 23-25, Discussion Figure 3 shows the energy balance components related to energy inefficiencies and recovered energy for each alternative solution. The analysis of Pumping Station Inefficiencies clearly shows that Alt. 2 is better than Alt. 1 and that overall Alt. 3 is better, since no electric energy is being consumed in pumps. Energy associated with water losses is considerably lower for alternatives 2 and 3, while Surplus energy is lower for Alt. 3 since the layout change reduced the pressures in the network, therefore reducing the energy delivered in excess to the consumers. Continuous and singular headlosses increase for alt.3, meaning that a significant amount of potential energy is being dissipated in the pressure-reducing valves Pumping Station Inefficiencies Energy assoc. water losses Surplus Energy Continuous and singular headlosses Energy balance component Recovered energy Alt.1 - Status-quo Alt.2 - Pump eff. Improvement+ALC Alt.3 - Layout change+alc Alt. 4 - Alt3+Picoturbine installation Figure 3. Energy balance components for each alternative solution Recovering valve headlosses can be achieved through the installation of a picoturbine as a bypass in the existing valves. A pictoturbine, as suggested by the name, is a turbine that provides a small power (<25W) that can be used to charge 12V batteries. For instance, it can be designed to supply the power necessary to keep the remote controls and pressure regulators running, which removes the need to periodically replace batteries. This has been successfully implemented in Segovia, Spain [13] in a system with a pressure drop of 18 m and an average flow of 1l/s. Therefore, a new alternative that combines Alt. 3 and includes the picoturbine installation was also preliminarily explored (Alt.4). The results of recovered energy in Figure 3 were obtained assuming a turbine with an efficiency of 75%. This solution will be studied more thoroughly in the near future, along with a cost-benefit analysis. 6 Conclusions This paper focuses on the analysis of alternative solutions for a rural water distribution system in Portugal. The assessment showed high water losses due to ageing infrastructure, high pressures in some network nodes due to topography and high energy inefficiencies (a pumping station with an efficiency of 19%). Three alternative solutions have been studied to improve the system s efficiency. The best alternative consisted of changing the network layout for a higher elevation point and included the installation of two pressure-reducing valves (PRV). With this alternative, energy costs were totally reduced as well as the respective GHG emissions, pressure adequacy

8 improved in network nodes, reducing real losses, and water quality was also improved, reducing water age in the system. This solution was not obvious at first intuitively changing the pumping station for a more efficient one appeared to be better. A deeper analysis into the energy balance components shows that a significant potential energy is being dissipated in the PRV. This energy could theoretically be recovered by installing a picoturbine along with the PRV. Recovered energy can be used to charge 12V batteries in the monitoring system. This option will be further developed. Overall, this paper shows that thinking outside of the box and searching for unconventional solutions might result in a more efficient and economic performance and with less environmental impact. The fact that the case-study is a small system is just a context. The water-energy loss assessment methodology is systemic and straightforward and, therefore, can be successfully applied elsewhere. 7 Acknowledgements The authors would like to acknowledge the Fundação para a Ciência e a Tecnologia (FCT) for the PhD Grant PD/BD/105968/ References [1] D. Loureiro et al., Implementing tactical plans to improve water-energy loss management, Water Sci. Technol. Water Supply, vol. 16, no. 5, [2] C. Cherchi, M. Badruzzaman, J. Oppenheimer, C. M. Bros, and J. G. Jacangelo, Energy and water quality management systems for water utility s operations: A review, J. Environ. Manage., vol. 153, pp , Apr [3] D. J. Vicente, L. Garrote, R. Sánchez, and D. Santillán, Pressure Management in Water Distribution Systems: Current Status, Proposals, and Future Trends, J. Water Resour. Plan. Manag., vol. 142, no. 2, p , Feb [4] P. W. Jowitt and G. Germanopoulos, Optimal Pump Scheduling in Water Supply Networks, J. Water Resour. Plan. Manag., vol. 118, no. 4, pp , Jul [5] D. Loureiro, A. Mamade, R. Ribeiro, P. Vieira, H. Alegre, and S. T. Coelho, Implementing waterenergy loss management in water supply systems through a collaborative project, in IWA Water Loss, [6] A. Lambert and W. H. Hirner, IWSA Blue Pages, Losses from Water Supply Syst. Stand. Terminol. Perform. Meas., [7] A. Mamade, D. Loureiro, H. Alegre, and D. Covas, A comprehensive and well tested energy balance for water supply systems, Urban Water J., vol. 14, no. 8, [8] A. Mamade, D. Loureiro, H. Alegre, and D. Covas, Top-Down and Bottom-Up Approaches for Water-Energy Balance in Portuguese Supply Systems, Water, vol. 10, no [9] L. A. Rossman, Epanet 2 Users Manual, U.S. Environmental Protection Agency, vol [10] H.D.R. Engineering, Handbook of Energy Auditing of Water Systems, p. 109, [11] American Water Works Association, Effects of Water Age on Distribution System Water Quality, USEPA, pp. 1 17, [12] A. Poças et al., Pilot studies on discolouration loose deposits build-up, Urban Water J., vol. 12, no. 8, pp , Nov [13] Tecnoturbines, Picoturbine with remote monitoring for ACUAES, [Online]. Available: