Pressure Management in Water Distribution Networks for Water and Infrastructure Sustainable Use

Transcription

1 Pressure Management in Water Distribution Networks for Water and Infrastructure Sustainable Use Mathieu Laneuville, Engineer Quebec Ministry of Municipal Affairs This article is a translation of the French Article "Gestion de la pression d eau dans les réseaux de distribution pour une utilisation durable de l eau et des infrastructures" published by Mathieu Laneuville in Vecteur Environnement in May 2015, The author hereby confirms that he is entitled to grant this permission for copies to be made available free of charge for reading and/or downloading from the LEAKSSuite website. Reduce leakage rate, reduce number of new leaks and asset life extension: these are three major benefits offered by water Pressure Management in water distribution networks and whose impact was evaluated in a residential area in the city of Saint-Jean-sur-Richelieu (Province of Quebec, Canada). Context As part of the Quebec Water Efficiency Strategy (the Strategy), municipalities are led, by 2017, to reduce water losses in the distribution network of drinking water to a maximum of 20% of the amount of distributed water and 15 cubic meters per day per kilometer of mains (m 3 / d / km). However, the 2012 annual Report of the Strategy indicates that further efforts should be put in with potential water losses estimated at 26% of the amount of distributed water and 31 m 3 / d / km (MAMOT, 2014). In Saint-Jean-sur-Richelieu, the 2013 water balance shows water losses of about 23% and 18 m 3 / d / km. Therefore, to achieve the objectives of the Strategy, the City, which serves about people, wagers on Pressure Management. Principal methods of intervention To reduce real water losses, the International Water Association (IWA) and the American Water Works Association (AWWA) recommend the use of one or more intervention methods that are presented in the arrows of Figure 1. These methods are Pressure Management, active leakage control, asset management and the speed and quality of repairs. As shown in Figure 1, knowing that there are Unavoidable Annual Real Losses (white rectangle), the goal of intervention methods (four arrows) is to reduce the Current Annual Real Losses (dark gray rectangle) to an economic level of Real Losses (light gray rectangle). Most methods presented in Figure 1 are generally known, but only applied to a certain level within Quebec municipalities. Indeed, Pressure Management remains an underdeveloped solution at the present time since its recent international expansion and its limited broadcast in Quebec. However, some municipalities such as Laval and Saint-Georges-de-Beauce have already implemented some controls for Pressure Management and others like Montreal and Saint-Jean-sur-Richelieu are to implement solutions for Pressure Management.

2 2 Losses flex with pressure Pressure Management Unavoidable Annual Real Losses (This reference value varies with pressure) Real Losses in this range are not technically recoverable Speed and Quality of repairs Real Losses in this range are not economic to recover Active Leakage Control Economically Recoverable Annual Real Losses Current Annual Real Losses Pipeline and Asset Management Selection, Installation, Maintenance, Renewal, Replacement Economic Level of Real Losses Figure 1: Four principal methods of intervention to reduce the real water losses (AWWA, 2015, adapted from Lambert et al., 1999)

3 3 To whom does the Pressure Management apply? Pressure Management aims to minimize unnecessary excessive pressure in some places and at certain times while maintaining the levels of service required to meet the standards of fire protection and water quality. Any or all of the following criteria can present sufficient justification to proceed with a Pressure Management scheme. 1. Ease of implementation a. Pressure optimization possible at certain times To be able to do so, it is possible to add electronic actuators on the existing pressure regulating valves (PRV) or to add frequency variator (FV) on existing pumps whom allow to optimize pressure at certain times. A PRV generally works in one of these control modes: Fixed Outlet, Time-Based Control and Flow- Based Control. For example, Time-Based Control is used in Saint-Georges-de-Beauce to reduce pressure of 34 kpa (5 psi) at night which is when water demand is low. Moreover, Flow-Based Control, which is used in Laval and is expected to be used in Montreal and Saint-Jean-sur-Richelieu, allows optimal management because the pressure is modulated at any time based on the water demand. Thus, when there is strong demand, the pressure is increased to meet the needs and when demand decreases, the pressure is adjusted to not provide unnecessary excessive pressure. b. Pressure optimization possible at certain places 2. High repair rate To do so, Pressure Management Areas (PMAs) are created by the use of existing pressure regulating chambers. In municipalities serving people or more, as in Montreal, Saint-Georges-de-Beauce and Saint-Jean-sur-Richelieu, Pressure Management is generally accompanied by a sectorization of the network to target areas where implementation is more feasible and the number of leak occurences are the highest. When possible, as in the city of Laval, pressure optimization can be done on the entire network. Moreover, when the rate of repairs is high, a small pressure reduction on the entire network can be more cost-effective and easier to maintain than a large pressure reduction on a sector of the network. a. More than 20 repairs per 100 km of mains per year (excluding repairs on fire hydrants and valves). According to estimations based on limited international studies, the influence of pressure reduction is negligible if the rate is less than or equal to 10 repairs per 100 km of mains per year for infrastructure in good condition b. More than 5 repairs per 1000 public municipal service connections per year (excluding repairs on stop-taps).

4 4 According to estimations based on limited international studies, the influence of pressure reduction is negligible if the rate is less than or equal to 2.3 repairs per 1000 public service connections per year for infrastructure in good condition. 3. High potential water loss (active leak control and reduction of repair time are recommended in parallel) a. More than 15 m 3 / d per km of mains For municipalities with fewer than 20 service connections per km, the critical quantity of water loss is established at 15 m 3 / d / km. b. More than 375 L / d per service connection For municipalities with more than 20 service connections per km, the critical quantity of water loss is established at 375 L / d per service connection. In Saint-Jean-sur-Richelieu, it is the ease of implementation that has been the predominant criterion. This choice has the advantage of minimizing implementation costs and build experience in the areas where the application is simple, but has the disadvantage of limiting the benefits. Besides, here are the characteristics of the distribution network of the residential sector studied and shown in Figure 2: an inlet point which is the water treatment plant and from where it is possible to optimize the pressure at certain times in the study area by adding FV on existing pumps; an outlet point which is the exported water to the Sainte-Anne water tank with a capacity of about 400 m 3 ; the closure of three existing valves can isolate the residential sector from the neighboring industrial sector to be able to create the residential PMA about 104 km of mains (about 60% of the mains are flexible and 40% are rigid); approximately service connections, which represents an average of 45 service connections per kilometer; potential water losses estimated at 295 liters per service connection per day, which represents an Infrastructure Leakage Index (ILI) of about 4. The snapshot ILI represents the ratio of Current Losses on Unavoidable Losses based on analysis of night flows; an average repair rate in the 5 past years of 14 repairs per 100 km of mains per year and of 1 repair per public service connections per year. The very low repair rate on service connections could be explained by the leak detection program done by the City which concentrates on listening at fire hydrants and not service connections.

5 Figure 2: Plan of the distribution network studied in Saint-Jean-sur-Richelieu 5

6 6 What are the benefits of Pressure Management? This section presents the three main benefits of Pressure Management and their positive impacts seen in a residential area in Saint-Jean-sur-Richelieu. 1. Reduce the leakage rate The Pressure Management is the preventive method par excellence because it is the only one that reduces the flow of all types of leakage (background, unreported and reported) without replacing existing infrastructure (Thornton & Lambert, 2007). The definition and methods of intervention recommended for each type of leakage are presented in Figure 3. Figure 3: Types of leakage and intervention tools (Tardelli Filho, 2006)

7 7 To be able to quantify the influence of the pressure on the leakage rate, the use of Equation 2.1 is recommended by the IWA Water Loss Specialist Group (Thornton, 2003, p. 43): Q 1 /Q 0 = (P 1 /P 0 ) N1 (2.1) According to this equation, if the pressure varies from P 0 to P 1, the leakage rate Q varies from Q 0 to Q 1 according to the value of the exponent N1. Thus, the greater the value of N1 is, the higher the pressure influences the leakage rate. For example, N1 value can be of 0.5 on a fixed area of a thick rigid pipe and of 1.5 on a variable longitudinal of a flexible pipe (Thornton, Sturm and Kunkel, 2008, p. 142). Hundreds of field tests have been made internationally to calculate the N1 exponent and they suggest an average value of 1. Thus, a 10% pressure reduction would reduce water loss from leaks by 10%. In Quebec, a first test to calculate the N1 exponent was carried out in 2014 in a residential area in Saint-Jean-sur-Richelieu. During the test, the fire department was alerted. Thus, the chief of division coordinated the operation while an operator was available at all times to modulate the pressure at the water treatment plant and two public work employees were manipulating the valves on the network. To perform the test, the volume of water distributed was measured using an electromagnetic flowmeter which had its accuracy tested in advance with the volumetric method and had a deviation inferior to 3% (Reseau Environnement, 2013). In addition, as shown in Figure 4, a pressure gauge and a data logger mounted on the fire hydrant closest to the average zone point (AZP) were used to calculate the average pressure (Pav) of the zone. The AZP is located at the place where the pressure is closest to the Pav of the zone. The average zone pressure can be obtained by using a hydraulic model or simply by a calculation of the average elevation of the infrastructure (service connections or hydrants) in the area. An Excel spreadsheet facilitating the calculation is available from the author. Finally, the test required the temporary closure of three valves which had their seal tested beforehand. By reducing nocturnal pressure from 443 to 293 kpa (64 to 43 psi), the potential loss of water during the night on which the test was made have decreased from m 3 / h to m 3 / h which is a 31% reduction. Thus, the results of the test suggest a N1 value of 0.9, which is close to the average value of 1. The improvement of knowledge on night flows will allow to refine the results. By reducing pressure from 443 to 293 kpa (64 to 43 psi) between 23 pm and 5 am, the City would save about m 3 / year. Moreover, by estimating the variable costs of drinking water services, mainly of energy and chemical products, to 0.06 $ / m 3 (Sauve, 2011), the water savings would represent monetary savings of about $ / year. Furthermore, the City's water service in collaboration with the Fire Department is currently analyzing the possibility of reducing the average pressure from 443 kpa to 345 kpa (64 psi to 50 psi) from 5 am to 23 pm since the neighbor industry will not be supplied by the residential sector. To do this, a flow that is the sum of the maximum daily flow of the year and fire flow should be simulated in the critical sector to check if the pressure at that point will be higher than the minimum required pressure of 140 kpa which is 20 psi (MDDELCC, 2002).

8 8 Figure 4: Pressure gauge and data logger installed on the fire hydrant that is closest to the average zone point (AZP) in a residential area of Saint-Jean-sur-Richelieu By decreasing the pressure to 345 kpa for the day and to 293 kpa for the night, the savings linked to the reduction of leakage rate will represent about m 3 / year, which is $ / year. Take note that these savings will be 20% inferior if the active leak control and the delay of repairs of the City allowed to reduce the ILI to 3, which represents the achievable level by these two simple and economic methods of intervention. 2. Reduce the appearance of new leaks To know the influence of pressure on the frequency of appearance of new leaks on mains and service connections of a PMA, it is necessary to know the average number of repairs per year of the past five years before pressure reduction (FF 0 ). The FF 0 must be calculated separately for mains and service connections. In addition, the maximum pressure at the PRZ should be measured before (P max 0 ) and after (P max 1 ) the pressure reduction. Thereafter, the percentage of new leaks from mains and service connections may be obtained separately by using the equation 2.2 (Thornton and Lambert, 2012, p. 6): % of new leaks reduction = (1 FFip/FF0) x (1 (Pmax1/Pmax0) 3 ) (2.2) Depending on the use of this equation, the frequency of annual leaks independent of the pressure (FF ip ) can be estimated at 10 per 100 km of mains and 2.3 per service connections for infrastructure in good condition belonging to the municipality. In the residential sector studied in Saint-Jean-sur-Richelieu, the average number of repairs per year for the past five years is 14 on the 104 km of mains and 5 on the public service

9 9 connections. It is necessary to note that the leak detection performed by the City is a general survey (focuses on listening to hydrants) and not a comprehensive survey (focuses on hydrants, valves and service connections). Thus, only the reduction of bursts on mains is considered. By considering of an FF 0 of 14 on the mains and by reducing the maximum pressure at the average zone point from 443 to 345 kpa, 10 repairs on the mains would be avoided for the 5 next years. It is necessary to note that the reduction of repairs is likely to be greater in areas with a higher FF0 and that it is important to pay attention to pressure transients (water hammer) in order to eliminate them. By estimating the cost of a repair on a main to $, the monetary savings would be of about $ / year. 3. Asset life extension This is probably the most important benefit of Pressure Management, but it is currently the one that is the more difficult to quantify. This benefit is particularly important where the replacement of mains is carried out according to the number of repairs over a length of main and a time interval (Thornton and Lambert, 2005, p. 2). And this is the case in Quebec. At IWA, work is currently underway to develop a methodology to calculate the net present value of the savings due to asset life extension. Thus, the calculations performed for asbestos cement mains with variable remaining lifetimes, in a PMA in Australia, show that any reduction of the maximum pressure can be converted into a number of years of asset life extension. For example, a reduction of 196 kpa (28 psi) of the maximum pressure would extend the lifespan of asbestos cement mains by three years (Thornton and Lambert, 2012, pp. 9-10). In the residential sector of Saint-Jean-sur-Richelieu, the network length is 104 km, the replacement value of water mains is estimated at 900 $ / meter and the remaining lifespan of the water distribution network is estimated at 60 years. Thus, by dividing the replacement value of the mains of the sector by the remaining lifespan, the necessary provision of $ / year is obtained in order to ensure the sustainability of these infrastructures. By assuming that the Pressure Management extends the lifespan of a main by one year, the monetary savings would be of about $ / year. Preliminary profitability In the example of the residential sector of Saint-Jean-sur-Richelieu, reducing the average pressure to 345 kpa during daytime and to 293 kpa during night-time will annually generate water and money savings of about m 3 and $. The maximum pressure reduction from 443 to 345 kpa will reduce from 14 to 12 the average number of repairs per year on mains, which would represent a saving of $ per year. If this maximum pressure reduction extended by one year the life of distribution lines, the savings would be of about $ per year. Overall, the monetary savings are estimated at $ per year. To do Pressure Management in the residential sector, the City plans to conduct the following works by themselves (except for the instruments and automat that would be made by an extern specialist): Adding an actuator and electricity on a valve in an existing manhole ( $); New room with booster, FV and electricity ( $) New manhole with a 300 mm diameter valve, actuator and electricity ( $) Instrumentation and automat to optimize the pressure at distance ( $)

10 10 In sum, the estimated cost to implement the project is $. Thus, according to preliminary data and assumptions, the return on investment would be on a 3 year term. Complementarily, other benefits could be calculated such as a fastest detection of new leaks by night flow analysis of residential and industrial areas, the decrease in the number of insurance claims for damage caused by broken mains and the improved image of the municipality that sets an example with a good management of water and infrastructures. These benefits and the maintenance costs on the lifespan of the project should be taken in consideration on the final calculations of the profitability. Next steps To support municipalities wishing to do Pressure Management in their water distribution network, the author of this article is currently producing a guide and a simple Excel workbook that is adapted to the Quebec context in collaboration with the City of Montreal and Allan Lambert of the Water Loss Research & Analysis Ltd. The author invites you to contact him if you are interested in participating in the development of tools that will document the implementation process or to know the potential benefits of Pressure Management based on the settings of your network. Acknowledgements The author thanks Eric Desbiens of the city of Saint-Jean-sur-Richelieu, Jean Lamarre and Pascal Caron of the City of Montreal, Guy Bilodeau of the City of Saint-Georges-de-Beauce, Denis Allard of the City of Laval, Francois Payette and Ushanthan Murugananthan of the Quebec Ministry of Municipal Affairs, the members of the water efficiency committee of Reseau Environnement, the members of the AWWA Water Loss Control Committee and the members of the IWA Water Loss Specialist Group who commented this article. References AWWA (2015). Water audits and loss control programs. 4 th Association (in press). ed. Denver, American Water Works Brière, F. (2006). Distribution et collecte des eaux, 2e éd.: Presses internationales Polytechnique, 401 p. CERIU (2013). Guide d élaboration d un plan d intervention pour le renouvellement des conduites d eau potable, d égouts et des chaussées. 87 p. Lambert, A., TG Brown, M. Takizawa and D. Weimer. (1999). "A review of performance indicators for real Losses from water supply systems." AQUA, vol. 48, n o 6, p Consulted on January 23 rd, 2015: MAMOT. (2014). Rapport annuel de l usage de l eau potable. Consulted on January 23 rd, 2015: MDDELCC (2002). Directive 001 : Captage et distribution de l eau, 71 p. Consulted on January 23 rd, 2015: Réseau Environnement (2013). L économie d eau potable et les municipalités, Vol. 1, 4 th ed. 119 p. Consulted on January 23 rd, 2015: %20normal%20HD% pdf Sauvé, C. (2011). Mise à jour de l Évaluation économique de la Stratégie québécoise d économie d eau potable et du Rapport concernant l instauration d une tarification de l eau réalisés en 2006, 73 p. Consulted on January 23 rd, 2015:

11 pdf Tardelli Filho J. (2006). "Control of e ReduçãoPerdas". In Abastecimento de Água, 3rd ed. São Paulo: Departamento de Engenharia e HidráulicaSanitária, Polytechnic School of the University of São Paulo. Thornton, J. (2003). "Managing leakage by managing pressure: a practical approach" Water 21, p Thornton, J. and A. Lambert. (2005). " Progress in practical prediction of pressure: leakage, pressure: burst frequency and pressure: consumption relationships." IWA Leakage Conference. (Halifax, September 12-14, 2005). IWA Publishing. Consulted on January 23 rd, 2015: Halifax-2005U.pdf Thornton, J., R. Sturm and G. Kunkel (2008). Water Loss Control, 2nd ed., New York, McGraw- Hill, 632 p. Thornton, J. and A. Lambert. (2012). " Pressure: Bursts Relationships: Influence of Pipe Materials, Validation of Scheme Results, and Implications of Extended Asset Life ". In IWA Water Loss (Manila, Feb ). Consulted on January 23 rd, 2015: