Water Online the Magazine gives Water & Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.
Issue link: http://wateronline.epubxp.com/i/501621
• Reoptimizing solutions under alternative scenarios and perform- ing unlimited sensitivity analyses • Finding solutions that balance capital vs. operating costs or gray vs. green infrastructure • Staging to identify near-term projects that provide maximum value • Utilizing multiobjective optimization to develop trade-off curves for triple-bottom-line (TBL) objectives A 'Glass Box' Approach Innovative technologies are often misunderstood. By definition, they differ from the current approach to problem-solving. While the ODS approach has sometimes been called a "black box" approach, this is far from accurate. If anything, the ODS could be called a "glass box" approach. The ODS approach is transparent. It utilizes existing system simu- lation models, which in most cases are well understood and accepted by utility planners and managers. The ODS software instructs the system simulation model to create and evaluate many thousands of trial solutions. Trial solutions are automatically created using the range of alternative improvements it is allowed to consider, while the cost and performance of each trial solution (from a full simulation model run) are simultaneously evaluated based on the agreed unit costs and performance critieria. The inputs into the optimization model are straightforward. Whether for a single neighborhood or a citywide master plan, there are four basic types of input required for any optimization problem: 1. An up-to-date, calibrated system simulation model 2. Range of allowable decision options to be considered such as new pipe, storage, pump, regulator and plant locations and sizes, green infrastructure and inflow/infiltration removal options, and operating set points 3. Corresponding unit costs for the decision options, including energy and O&M; costs 4. List of design and performance criteria or service levels to be met, such as minimum pressures, maximum velocities, minimum drawdown for tanks to exercise, and overflow and surcharge levels The results from an optimization run are output as the optimized plan or design that can be saved separately as a simulation model. With the ODS approach, the designs can also be modified manually, which permits the modeler to make changes based on engineering judgment and then quickly run a simulation to check and report out both cost and performance on any number of designs. The knowl- edge of the engineer and planner are amplified in an ODS approach, enabling a broader range of their choices to be evaluated and allowing for extensive sensitivity analyses. Sample ODS Case Studies Several case studies illustrate how the ODS approach is being used by both small and large municipal utilities across the U.S. Bend, OR, optimized its Water System Master Plan in 2009-10. Based on that project's success, the city required an ODS approach be used by the consultant team to optimize its Comprehensive Sewer Master Plan in 2013-14. South Bend, IN, utilized an ODS approach in the development of its CSO Long Term Control Plan (LTCP) in 2011-12. In 2014, the Los Angeles Bureau of Sanitation and a large Texas city stormwater management group each completed demonstration studies on limited areas of their systems to better learn about the ODS approach and its ability to inform their decision-making process. The following brief descriptions highlight key aspects of these optimization projects, all of which were completed utilizing Optimatics' Optimizer ODS software tools. Bend, OR, Operations Optimization. As part of its overall Water Master Plan, the city requested an optimization of existing system operations aimed at reducing pumping energy costs in summer and improving reservoir storage turnover in winter to enhance system water quality. Annual pumping energy costs totaled approximately $700,000, with the majority of the cost coming from pumping groundwater to supplement the lower cost surface water supply in summer. The first step was to select typical summer and winter periods simulating the historical operation in the model and performing energy usage and cost calculations as a baseline. The ODS software was then formulated to investigate various operating options, including pump trigger levels and pressure-reducing valve (PRV) settings that might reduce costs. The optimization identified revised operating strategies that led to a 23 percent reduction in energy usage for the summer period. The operating changes included restricting flow into key reser- voirs during periods of high demand to reduce peak flows in transmis- sion lines, adjusting PRV settings to increase flow transfers from the surface water supply, and boosting surface water between zones rather than pumping groundwater at higher heads — all changes that were discussed and endorsed by the operations group. In addition to reducing energy usage, the charts in Figure 1 illustrate how restricting flow from the Outback surface water source to the Awbrey Reservoir and forcing the level to vary over a wider range mini- mizes peak flows from the surface water facility and increases the overall average utilization of the lower-cost surface water. South Bend, IN, CSO LTCP Optimization. South Bend's consent decree negotiations with the U.S. EPA and the Department of Justice concluded in December 2011. Prior to that, the city requested that its existing CSO LTCP be optimized using the ODS approach to see if WORKFORCEPLANNING Baseline Scenario Optimized Strategy Figure 1. Improved reservoir exercising and more constant surface water supply 30 wateronline.com ■ Water Innovations