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AUTOMATIC REAL-TIME CONTROL AND MANAGEMENT OF AN AQUEDUCT DISTRIBUTION NETWORK Matteo Frisinghelli Chiara Costisella
AUTHORS Matteo FRISINGHELLI – Water Manager, Novareti S.p.A. Chiara COSTISELLA - Water service - Operational support, Novareti S.p.A Novareti is the Dolomiti Energia Group company responsible for the management of network services. The company is Trentino leader in natural gas distribution with 290 million m3 a year distributed to a portfolio of nearly 150,000 gas customers in 108 municipalities; through cogeneration production it provides district heating of 1.6 million m3 to buildings and distributes almost 150 GWh of heat and steam every year; it manages over 1,200 km of water network through which almost 36 million m3 of water transit each year to 81,000 customers in 14 municipalities of Trentino province. www.novareti.eu
ENERGIA MEDIA Energia Media is a communication and relations agency that operates primarily in the energy, utility and smart city, and smart land sectors. It develops communication strategies, facilitates relations, and prepares content and information. www.energiamedia.it All the images and photographs in this document were properly acquired from databases. If the author feels that copyright laws have been violated, we ask that he report it to this address: comunicazione@energiamedia.it May 2018
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AUTOMATIC REAL-TIME CONTROL AND MANAGEMENT OF AN AQUEDUCT DISTRIBUTION NETWORK Matteo Frisinghelli Chiara Costisella
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INTRODUCTION Novareti S.p.A. manages various aqueducts, including that of the City of Trento. The city extends primarily along a valley floor; the numerous hillside villages are connected to the main network by means of catch basins and are already defined as water districts. The complexity of the system, with many essential interconnections, makes management very challenging: in the early years of the 2000s, with a view to optimized and increasingly efficient operation, Novareti implemented a hydraulic model of the entire aqueduct network, using the InfoWorks WS software distributed by HR Wallingford. The model was calibrated using the system measurements of Remote Monitoring and measures taken from ad hoc campaigns. The hydraulic model of the network is a powerful, essential instrument for ordinary and extraordinary management of the network: its excellent reliability, deriving from precise calibration, makes it usable as a base for strategic and design decisions; any work on the network or systems is simulated in advance to verify its impact on the entire system. Among the objectives that have characterized and required implementation of a simulation model from the outset was the analysis and optimization of the network, to determine whether there were margins for improvement in the management of pressures, pumping, and the various regulating systems that make up the aqueduct. One of the first elements revealed by an analysis of the simulation results (Figure 1) was the presence of an area in the valley floor network (along the fan of the Fersina torrent) that, since it was at higher elevations, was affected by low operating pressure, while the remaining network showed overpressure in certain areas necessary to ensure a minimum level of service to major users.
The minimum level of service is to ensure at least 7 m of water column (0.7 bar) on the highest floor of each residence. Overly low pressure, in fact, has a negative effect on usage of the service; at the same time, excessive pressure does not damage users, usually equipped with a pressure reducer, but is negative for the network structures: excessive pressure, in fact, places excessive stress on piping, valves, and joints, resulting in breaks. The result is a decline in the average life of the component assets of the aqueduct, resulting in higher costs of operation and break repair. Figure 1. Results of the modelling of the Trento network in terms of pressure: red and yellow areas are those with pressure below 2.5 bars, blue and violet with pressure above 4 bars
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In the 700 km of the Trento aqueduct network, with the physiological presence of a finite number of small holes, breaks or porosities, increased pressure causes the leakage of a greater quantity of water and thus the loss of the resource and waste of electric power. Since background losses, which represent the highest percentage of network losses, are difficult to detect, except with extensive, intensive leak detection campaigns, it is clearly essential to lower the pressure level of the network as much as possible, considering the direct proportionality between operating pressure and losses. All these considerations and analyses convinced the Water Service of Novareti to find design solutions that would reduce network pressure.
PROJECT TO OPTIMIZE THE TRENTO AQUEDUCT NETWORK The solution found by the technical staff of Novareti to reduce city pressure is to divide the network into a number of water districts, some real, i.e. regulated by pressure reduction valves, other virtual, i.e. only monitored by flow meters, useful for determining a water balance. In the real districts, pressure will be regulated based on water demand and time of day, to ensure a minimum level of service as all times without excessive pressure. The first real district, scheduled for completion in the first half of 2018, includes the area along the fan of the Fersina: in this way the pressure levels can be differentiated between the upper area of the Trento valley floor and the rest of the city. The new district will be supplied by the San DonĂ reservoir, which currently helps sustain the consumption of the entire valley floor along with the principal city reservoir (10,000 m3). A well controlled by a hydraulic valve will be created downstream from the reservoir and will regulate flow so as to maintain a pressure of 2.5 bars in the lowest point of the district. The San DonĂ reservoir receives water drawn from the underflow of the Fersina torrent, in a quantity that over 24 hours is greater than the consumption of the district; since this water is available by gravity, the
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project calls for the creation of a tail well with regulating valve, to allow the water to flow from the district to the rest of the city: in this way the water can be utilized without overflowing the reservoir. As things stand, the principal flow that supplies the valley floor of the Trento network, i.e. the flow out of the “10,000 m3” reservoir, is regulated by a regulating valve placed directly at the outlet of the reservoir: the flow is regulated automatically based on a pressure signal recorded in the area just before the historical centre. Since the pipe leaving the “10,000 m3” reservoir works in the initial portion by free flow (i.e. not under pressure), there is a structural delay between the change in pressure in the network and feedback regulation of the valve. Furthermore, the city of Trento extends along the axis of the Adige, so the northern area is higher that he southern area: this is the reason for low-pressure problems. To solve these problems, the Novareti project calls for shifting the primary regulation of pressure from the reservoir to the valley floor, creating a new installation: in this way, the entire pressure head provided by the distance in height with respect to the reservoir, around 50 m, can be utilized. The valve will work by modulating its opening as a function of the network pressure measured just downstream from it, with local electronics, so with greater precision and a practically instantaneous response to the demands of the network. Since the regulation will lower the pressure by approx. 1 bar, with an average transiting flow through the catch basin of around 300 l/s, the project was conceived with the installation of a regulating turbine, in parallel with the valve, that when required can produce electric power by exploiting the change in pressure. With these initial structural works, the two new districts (the area along the fan of the Fersina and the rest of the valley floor) will enjoy much more uniform pressure and better service; the pressure in most of the valley floor can also be reduced by 1 bar, with rather positive consequences in reducing losses and extending the useful life of the structure. Given the orographic conformation of the city, this first operational step will produce 8% of the benefits deriving from pressure regulation; each other real district to be created in the city will therefore bring positive, but lesser, effects: the refinement of the network structure will therefore progress gradually.
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IMPLEMENTATION OF THE REAL-TIME MODEL AND OF THE ADVANCED CONTROLLER When the structural works have been implemented (a new district for the area along the Fersina and a new main regulation plant), the system will be ready to receive high-level regulation, capable of adapting to all conditions and all stimuli coming from the network and from outside. The Trento network, in fact, is a rather impulsive system, if compared to many other aqueducts of equal size, and requires extreme expertise in management, but at the same time it offers large margins for improvement. Thus far, the criterion followed for operating the aqueduct is to ensure the water supply to the least favoured users, with an adequate margin of security: this affords an optimal service but leaves ample room for improvement that is not explored for fear of incurring inefficiencies. The parameter that plays a more or less important role in the hydraulic dynamic of an aqueduct is primarily the user consumption: this is not known a priori but can be determined rather precisely by analysing several years of consumption history. Since consumption also depends on weather conditions, such as rainfall, temperature, and sunlight, these data may be predicted and acquired by suitable weather stations. To take into account all the variables that affect the performance of an aqueduct and provide for its optimal regulation by acting on hundreds of devices (regulation valves, pumps, etc.), a controller is required that can rapidly develop solutions of maximum efficiency and prepare all the manoeuvres necessary to implement them. In an aqueduct context where service to users is essential, and where it is impossible to position a large number of sensors to acquire the status of the network in every crucial point, there must also be a real-time model: it will provide the controller with the status of the network at significant and important points. The real-time model will be a physical copy of the off-line model but will operate continuously; specifically, it will acquire all the hydraulic magnitudes of the system and develop a solution projected 2-3 hours into the future, predicting what the status of the network will be based on known parameters. If situations (future and virtual) of potential inefficiency are detected, an alarm will be generated that will be part of the contextual conditions of subsequent
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simulations. The acquisitions of data, or the real contextual conditions, will be repeated instantly and compared with the projections of the previous simulations by interpreting any deviations and making the necessary corrections. As the diagram in Figure 2 indicates, the controller will act at a higher level, acquiring in turn all the information coming from the network and from the simulations of the real-time model, and will develop the optimal solution, with the objective of minimizing network pressure (while maintaining the service level) in the various districts and making maximum use of renewable sources (in this case, photovoltaic panels at the principal well field and any hydroelectric production, after installation of the regulation turbine). Another highly important factor is to determine the daily water balance with a predetermined frequency for every district of the network and seek the minimum flow rate provided during the night: this magnitude, in fact, is the figure that best characterizes the level of losses in the various districts. The losses, in fact, appear as a more-or-less constant level within the daily supply, depending only on pressure. Figure 2. Operating logic of the APC system
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During the night, when consumption is much lower (except for fountains and a few other sporadic uses), the background losses represent a rather large portion of the supply, assuming the maximum weight at the minimum point, as mentioned earlier. The distribution of night-time minimums in the various districts, analysed over a number of days, may tell the system whether losses have arisen in any area of the network: when a significant increase in minimum supply is detected in a district, and it remains for several days, there is a high probability of a new loss. If it were actual consumption, in fact, it would be generalized in all the districts and then return to normal levels. This type of analysis is of fundamental importance, since it will automatically signal to the leak detection teams where to direct their detection, going directly to the target, in the district that has shown anomalies, with an increase in efficiency that may be described as historic.
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CONCLUSIONS The project to create such a sophisticated and ambitious instrument arises from the need of the utility to acquire the maximum technology to maximize the efficiency of increasingly complex systems, while containing operating costs, to increasingly invest in quality and service to users. It is estimated that, at the end of the work to create the districts, the pressure drop will reduce losses by 15% to 10%. This has all been possible through the work over time of the technical staff of Novareti, who have developed extremely solid, valuable databases (Digital Cartography and Remote Monitoring) that have made it possible to implement a precise off-line model and thus reliable real-time instruments. The next step, the introduction of an even higher-level controller, arises from the need to supervise more magnitudes and phenomena and ensure that all the variables, physical and virtual, will converge in solutions representing the possible optimum from the standpoints of energy, environment, and service. The instrument created will not be static but will evolve along with the physiological evolution of the network and will represent a new technological standard to apply gradually to all the aqueducts managed by Novareti.
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