Bogumil Ulanicki

Open and closed loop pressure control for leakage reduction

Abstract The UK water industry is addressing the major challenge of reducing leakage from water supply and distribution networks. It is widely accepted that a significant proportion of leakage is attributable to many small leaks (e.g., through fittings). Operational pressure control is a cost-effective action for reducing such leakage. This paper formulates and investigates methods for planning and implementation of on-line control strategies of predictive and feedback control for areas with many pressure reducing valves and many target points. The considered methods explicitly take into account a leakage model. The results are applied to an area with three pressure reducing valves and two target points.

Efficient energy management of a large-scale water supply system

Efficient energy management is important for water companies in order to meet economic and environmental targets. For many water supply systems, increased savings can only be accomplished by taking into account the non-linear characteristics of the system in terms of both heads and flows and mixed-integer decision variables. Scheduling must be achieved with complicated tariffs that are frequently changed throughout the year, as well as changes to the network structure. The article shows a case study for energy management of a large-scale network using the computer-aided water network engineering software called FINESSE. The network is a typical large-scale supply network supplying many towns and cities. The model of the network includes 4388 pipes, 35 pumps, 63 variable control valves, 10 non-return valves and 16 variable head reservoirs. The study resulted in a set of mixed-integer optimal schedules that achieved a 14% saving in electrical energy while satisfying operating constraints.

Pressure control in district metering areas with boundary and internal pressure reducing valves.

Despite operational improvements over the last 10-15 years, water utilities still are losing a significant amount of potable water from their networks through leakage. The leakage is managed on the one hand by reactive and proactive maintenance and on the other hand by pressure control to reduce background leakage from connection and joints. This paper is based on experience from the Process Control – Water Software Systems group which was involved in many pressure control projects and the current Neptune project (www.neptune.ac.uk). A fast and efficient method to calculate time schedules and flow modulation curves is presented. Both time and flow modulation can be applied to a single inlet DMA. Time modulation can be applied to a multi-inlet district metering area (DMA) but this is not always possible for flow modulation due to the risk of hunting. It is convenient to distinguish between boundary and internal pressure reducing valves (PRVs), the decision variable for a boundary valve is a PRV set-point whereas for the internal valves it is a valve resistance. The resistance is then automatically translated into a set-point for field implementation. The time modulation methodology is based on solving a nonlinear programming problem with equality constraints represented by a hydraulic model with a pressure dependent leakage term and inequality constraints representing operational requirements (e.g. pressure at critical nodes). The cost of boundary flows which include leakage flows is minimized. An extended content model with pressure dependent leakage is simulated to provide a starting point for quick convergence. Optimal time schedules are converted into flow modulation curves by plotting scatter plots of flows against heads. The algorithm has been implemented as a module in the FINESSE package and allows complete pressure control tasks to be solved. A user needs to provide an hydraulic model, leakage information and leakage characteristic – leakage area and the exponent in the pressure power law. The program calculates time schedules and also flow modulation curves for single and multi-inlet PRVs. Evaluation of optimal control strategies and benefit analysis in terms of leakage reduction for two case studies provided by Yorkshire Water Services is included.

Fast and Practical Method for Model Reduction of Large-Scale Water-Distribution Networks

AbstractThis paper presents a method for the reduction of network models described by a system of nonlinear algebraic equations. Such models are, for example, present when modeling water networks, electrical networks, and gas networks. The approach calculates a network model equivalent to the original one, but containing fewer components. This procedure has an advantage compared with straightforward linearization because the reduced nonlinear model preserves the nonlinearity of the original model and approximates the original model in a wide range of operating conditions. The method is applicable to hydraulic analysis and has been validated by simplifying many practical water network models for optimization studies.

Combined Energy and Pressure Management in Water Distribution Systems

In this paper a method is proposed for combined energy and pressure management via integration and coordination of pump scheduling with pressure control aspects. The proposed solution involves: formulation of an optimisation problem with the cost function being the total cost of water treatment and pumps energy usage, utilisation of an hydraulic model of the network with pressure dependent leakage, and inclusion of a PRV model with the PRV set-points included as a set of decision variables. Such problem formulation led to the optimizer attempting to reduce both energy usage and leakage. The developed algorithm has been integrated into a modelling, simulation and optimisation environment called FINESSE. The case study selected is a major water supply network, being part of Yorkshire Water Services, with a total average demand of 400 l/s.

Project Neptune: improved operation of water distribution networks

Water service providers (WSPs) in the UK have statutory obligations to supply drinking water to all customers that complies with increasingly stringent water quality regulations and minimum flow and pressure criteria. At the same time, the industry is required by regulators and investors to demonstrate increasing operational efficiency and to meet a wide range of performance criteria that are expected to improve year-on-year. Most WSPs have an ideal for improving the operation of their water supply systems based on increased knowledge and understanding of their assets and a shift to proactive management followed by steadily increasing degrees of system monitoring, automation and optimisation. The fundamental mission is, however, to ensure security of supply, with no interruptions and water quality of the highest standard at the tap. Unfortunately, advanced technologies required to fully understand, manage and automate water supply system operation either do not yet exist, are only partially evolved, or have not yet been reliably proven for live water distribution systems. It is this deficiency that the project NEPTUNE seeks to address by carrying out research into 3 main areas; these are: data and knowledge management; pressure management (including energy management); and the associated complex decision support systems on which to base interventions. The 3-year project started in April of 2007 and has already resulted in a number of research findings under the three main research priority areas (RPA). The paper summarises in greater detail the overall project objectives, the RPA activities and the areas of research innovation that are being undertaken in this major, UK collaborative study.

Rethinking Future of Utilities: Supplying All Services through One Sustainable Utility Infrastructure

Sustainable Utility Infrastructure Fatih Camci,†,* Bogumil Ulanicki,‡ Joby Boxall, Ruzanna Chitchyan, Liz Varga, and Ferhat Karaca† †IVHM Centre, Cranfield University, Bedford, U.K. ‡Department of Engineering, De Montfort University, U.K. Department of Civil and Structural Engineering, University of Sheffield, U.K. Department of Computer Science, University of Leicester, U.K. Complex Systems Research Centre, Cranfield School of Management, U.K.

PRESSURE AND LEAKAGE MANAGEMENT IN WATER DISTRIBUTION SYSTEMS VIA FLOW MODULATION PRVS

Globally, water demand is increasing while the recourses are diminishing therefore the leakage reduction in water distribution systems (WDSs) becomes an important objective for the water industry. The benefits of applying pressure control policy in WDS in order to reduce the leakage has been discussed in (Ulanicki et al. 2008). The pressure management via flow modulation has been applied and its benefits has been documented e.g. in (Yates and MacDonald 2007). Flow modulation PRVs can be operated either hydraulically (AbdelMeguid et al. 2009) or electronically to modulate the outlet pressure according to the demand level and required pressure at critical nodes. In this paper a genetic algorithm (GA) is used to calculate the coefficients of second order relationship between the flow and the optimal outlet pressure for a PRV. The method is implemented in Matlab linked to the EPAnet hydraulic simulator. The obtained curve can be subsequently implemented using a flow modulation controller (AbdelMeguid et al. 2009). The results of optimal PRV flow modulation via GA has been compared with the time schedule approach using a non-linear programming method described in (Ulanicki et al. 2008). The results of both techniques are very close to each other and resulted in almost the same amount of leakage reduction. The main advantage of the flow modulation in comparison to time schedules is that the modulation curve is calculated once and operates robustly over a wide range of demands. Although, the flow modulation is getting popular in the UK for single inlet district metering areas (DMAs), a special care must be taken for multi-inlet DMAs where interactions between inconsistent flow modulation curves may lead to hunting phenomena.

FEEDBACK RULES FOR OPERATION OF PUMPS IN A WATER SUPPLY SYSTEM CONSIDERING ELECTRICITY TARIFFS

The cost of energy used for pumping water constitutes a large proportion of operational expenditure for a water utility. Energy saving measures in water supply systems can be realized in different ways, by design of the system to be energy efficient, by proper maintenance of equipment especially pumps and by optimal control of the system. The cost of the pumping is a product of energy consumption and an electricity tariff. The energy can be reduced by pumping less water, lowering the head against which the water is pumped and by operating pumps near peak efficiency. The cost can also be reduced by re-scheduling the pumping from expensive to cheap tariff periods. Typically the real time control for time varying tariffs is implemented in a predictive control fashion, in which an optimal time schedule is calculated ahead over 24 hours period by a solver and recalculated at regular intervals e.g. 1 hour. In order to operate the scheme in real time the solver must be sufficiently fast and this may not always be possible for big water supply systems. In this paper a method to synthesize feedback control rules is proposed taking into account a time varying tariff. The rules are calculated off-line and then implemented in local PLCs or in a control room. Once the rules are implemented the response to the changing state of the water system is instantaneous. In this paper the feedback rules are calculated by a genetic algorithm. Each pump station has a rule described by two water levels in a downstream reservoir and two values of pump speed, for each tariff period. The lower and upper water levels of the downstream reservoir correspond to the pump being ON or OFF. The approach has been applied to a large scale water supply system and compared with the traditional time schedule approach. The achieved cost for the feedback control is only slightly higher than that for the time schedule approach. However, the feedback control by its nature is more robust and performs well in the presence of uncertainty in water demands and in inaccuracy of hydraulic models.

SYNTHESIS OF FEEDBACK CONTROL FOR PUMP OPERATION IN WATER DISTRIBUTION NETWORKS

Existing optimal scheduling packages for water distribution systems (WDS) calculate the time schedules for control elements such as pumps, valves and treatment works following the idea of open loop control. The calculations take into account the hydraulic model of WDS, operational constraints and the time dependent electrical tariff. The time horizon is typically one day or one week depending on the network storage capacity and the structure of the electrical tariff. If such a schedule is applied to a physical system the predicted and the physical reservoir levels diverge due to uncertain demands and as a result the calculations need to be repeated at some time using updated demand prediction and the current measured reservoir levels. The aim of this paper is to investigate the feasibility of synthesising continuous feedback from reservoir levels to pump and valve operation, taking into account the operational constraints and the electrical tariff. This attempt can be seen as a generalisation of a simple practical rule where a pump is controlled by the level of an associated reservoir, e.g. the rule ‘if the tank is full switch the pump OFF , if the tank is empty switch the pump ON’. The proposed methodology relies on preparing a control law in an off-line mode which is subsequently used in a real time situation. The traditional optimal scheduling problem is solved many times for typical initial reservoir levels in the system and a family of reservoir and corresponding control trajectories is generated. These trajectories are approximated by a hyper-surface which represents an optimal control law ready to use in the field. The control action will follow the sequence: log the time, measure the current reservoir levels, evaluate from the hyper-surface the corresponding operation for pumps and valves and finally apply the control action to the pumps and valves. The approach avoids time-consuming online-recalculation of pump schedules, and additionally the feedback control is much more robust with respect to uncertain demands. The limitation of the approach is dictated by the number of reservoirs and number of initial reservoir levels which need to be considered. In the worst case the computational complexity may increase exponentially with the number of reservoirs. Initially this approach was applied to a simple system containing a single reservoir fed by one pump station with a time varying tariff and subsequently to a medium-size system with four reservoirs and four pump stations.