EVALUATION OF ENERGY SAVING ALTERNATIVES AT MADISON WATER UTILITY
EXECUTIVE SUMMARY Introduction: In 2013, Madison Water Utility (MWU) consumed 19,660,250 kWh of energy to pump just over 10 million gallons of water (PSC 2013). Numerous benefits are observed by a utility when energy savings measures are implemented, with benefits being economic, environmental, operational, and customer relations in nature. Research performed for this project was aimed at identifying energy conserving practices, and applying them to Madison Water Utility?s system to observe the greatest energy savings. The objectives of the research are: 1. A system-wide variable frequency drive (VFD) study aimed at determining which wells in MWU?s system have characteristics that are ideal for future VFD installations 2. A system demand study in Pressure Zone 4, to characterize the impacts of peak demand periods on annual energy use 3. A hydraulic modeling study of Pressure Zone 4, aimed at estimating the energy savings produced by capital improvements and modifications to hydraulic operations within the zone. Background: On average, drinking water utilities are allocating 30-40% of their total annual operating budget to energy use, of which 94% or more can be attributed to pumping (Hamilton et al. 2009 and Elliot et al. 2003). Energy intensity can be defined as the amount of energy required to pump, treat, and deliver water to the customer?s tap. Energy intensity is a metric used to benchmark utilities on, and is reported as kilowatt-hours per thousand gallons pumped (kWh/kgal). In 2013, Madison Water Utility consumed 1.95 kWh/kgal, close to the Wisconsin groundwater utility average of 1.94 kWh/kgal (PSC 2013). However, energy savings are attainable, with estimates by the Water Research Foundation (WRF) predicting 10-30% savings by all water utilities (WRF 2011). Energy consumption by pumping systems can be divided into two categories: energy consumed by components that are lifting water, and excess energy consumed due to inefficiencies. Deep well pumps and booster pumps lift water from the ground to the distribution system where it can flow into customer?s taps, consuming large amounts of energy to complete this process. Along the way, energy inefficiencies accumulate, requiring more energy to deliver water than would otherwise be needed. Inefficiencies may include friction, an improperly sized pump, elevated water pressure at a tap, or an aging motor that is no longer operating at its maximum efficiency. To combat high energy use, energy conservation practices including variable frequency drive (VFD) installation, hydraulic grade line management, and flow distribution analyses were tested. Furthermore, pipe modification to reduce headloss, demand reductions to conserve water, and well refurbishment to improve efficiency were examined. Finally, off-peak pumping was tested to determine feasibility and potential energy savings of running pumps at night when energy rates are lowest. Methods: Three studies were performed with the goal of minimizing energy use in as many ways as possible. Much of the analysis revolved around Pressure Zone 4 (PZ4), while the remaining analysis was performed on previously tested wells. The VFD study used previously collected data by Baniel (2013) to group wells according to specific capacity, a well property that defines the amount of drawdown for a given flow rate. Wells were grouped into low, medium, and high specific capacities, and a representative from each group was analyzed for energy savings and payback. This study allowed for the selection of a group of wells with which to implement VFDs in the future. The energy use characterization of various system demands study utilized MWU?s supervisory control and data acquisition (SCADA) system and Madison Gas and Electric (MG&E) as data sources. Analysis of SCADA data was performed to identify flow ranges, or flow bins, where energy use was high. The hydraulic modeling software H2OMAP Water GIS was then used to test the energy use in each flow bin in Pressure Zone 4, attempting to identify flow bins which were consuming large quantities of energy. The study allowed for energy conservation measures to be specifically applied and optimized in flow bins of interest. The final study revolved around PZ4, specifically Unit Wells 9 and 31. Again, the hydraulic modeling software H2OMAP Water GIS was used to test (1) the optimal VFD speed of the UW31 deep well pump, (2) off-peak pumping feasibility, (3) optimal flow distribution between the two wells, and (4) optimal hydraulic grade line. Significant input data was required to test the various scenarios including pump curves, MG&E rates, PZ4 demands, and information about the proposed well (UW31). Energy use and predicted savings were identified for each model variable, then payback of the option was determined to identify the economic feasibility. This study provided estimates of how to operate PZ4 in the most energy efficient manner. Results: Results of the VFD study outlined the projected energy savings of high, medium, and low specific capacity site of Madison Water Utility. It was found that high specific capacity sites (>21.1 gpm/ft) generally had low energy use, low head savings, and low cost savings. Medium specific capacity sites (13.8 ? 21.1 gpm/ft) were found to have higher energy use than high specific capacity sites, on average, with greater potential for head savings. Large energy savings were found to be possible in some cases, with payback periods between 5 and 10 years being possible. Low specific capacity well sites (<13.8 gpm/ft) were considered the best candidates for VFD installations due to the head savings potential and paybacks less than 10 years. The characterization of energy use for varying system demand outlined distribution system flow conditions that were accounting for the largest energy use. From 2008 to 2013, 86% of flow events in Pressure Zone 4 fell between 1.00 and 1.75 MGD. Energy use and cost expenditures associated with this flow bin were both 85% of the total, implying that energy conservation techniques should be designed to be optimized in these flow ranges. The flow range covering 1.50 to 1.75 MGD was found to have the largest disparity between the number of events that fell into the flow range during the study year, and the percentage of total energy use the flow range accounted for. In total, 18% of flow events fell between 1.50 and 1.75 MGD, accounting for 23% of the energy use and 21% of the cost. Energy use and cost of differing well combinations were tested in Pressure Zone 4, including UW9 only, UW31 only, and UW9/UW31 concurrent operation. It was found that UW9 only operation dominated the other options in terms of low energy use and cost. Specific capacity was found to be the major driver in this difference as total deep well pumping head at UW9 and UW31 were 70 feet different. The hydraulic modeling software H2OMAP Water GIS was used to analyze PZ4 with several variables. VFD speed was the first parameter modified, and was applied to the UW31 deep well pump. Predicted and modeled energy use was lowest at an 80% VFD speed, savings nearly $15,000/year and 24,000 kWh/year from the no variable frequency drive case. Off-peak pumping was found to be possible in PZ4 with the construction of the proposed UW31 reservoir. Unit Well 9 and 31 deep well pumps operated off-peak resulted in 12 increased pump starts per week between the two pumps, increasing energy use 1% from non-peak pumping. Cost savings of $6,000/year were predicted at an 80% VFD speed as determined in the VFD study under average system demand conditions. High and low demand conditions, representing summer and winter, yielded similar cost savings. Optimizing flow distribution between UW9 and UW31 was performed, and found that UW9 only operation was best from a cost and energy perspective. Unit Well 9 and 31 concurrent operation was found to be best operationally as fire flow demands could be met, and water age goals were met. Hydraulic grade line of Pressure Zone 4 was also examined in the model. It was found that head reductions saved energy and money, 33,000 kWh/year and $4,000/year respectively, for a 30 foot HGL reduction. As a result, customer tap pressures in some areas of PZ4 became too low. Modifications to the pressure zone to improve pressure in these areas would be needed, but economics suggested the payback period to implement the modifications was greater than 25 years. Conclusions: It can be concluded from the VFD study that as specific capacity was decreased, the percent of head savings increased for a given flow reduction. This implies low specific capacity wells should be considered good candidates for VFD installation, while high specific capacity wells should be considered bad candidates in terms of head savings. VFD installation on high specific capacity wells was found to provide operational benefits to MWU including reduction of pump starts. Selection of pumps that are oversized with respect to flow, and undersized with respect to pumping head were found to produce more energy savings than a pump selected at the BEP. Operation of wells with the lowest pumping heads were found to yield the lowest energy operation for the utility. Results from the flow bin study has shown the occurrence of high demand flow events to be infrequent, and thus not contributing significantly to yearly cost expenditures by MWU. The extreme events accounted for less than 1% of yearly cost and energy. System demand conditions between 1.00 and 1.75 MGD were found to account for 85% of costs and energy use, thus reduction of flow events in this flow bin will have the largest impact on energy savings. Energy and cost characterization has shown that operation of Unit Well 9 alone in PZ4 produced the lowest yearly energy consumption and yearly cost. Model use in simulating PZ4 found that UW31 should be operated at an 80% VFD speed to maximize energy savings. Construction of UW31 will allow for the implementation of off-peak pumping, providing 6% cost savings in the pressure zone. Optimal distribution of flow between both wells in Pressure Zone 4 was found to be 40% UW31 and 60% UW9. Modifying the hydraulic grade line of PZ4 was found to be prohibitive due to economic and pressure reasons. It can be concluded that MWU?s policy of designing pipe segments to handle fire flow has prevented large headloss in the distribution system. Because of this, pipe modifications to reduce headloss have been found to be economically inferior to alternative energy saving measures due to the limited energy savings available. Recommendations: ? Do not install VFDs on high specific capacity wells to generate head and energy savings. Operational benefits such as reduction of pump starts may however result from VFD installations. ? Install VFDs on medium specific capacity wells, specifically Wells 11, 16, and 20. ? Install VFDs on low specific capacity wells, specifically Wells 13, 18, 19, 24, and 27. ? Size deep well pumps with high specific capacities to operate at the BEP, and medium and low specific capacities to operate to the right and below the BEP to maximize efficiency. ? Design energy conservation measures for system demand conditions between 1.00 and 1.75 MGD. ? Implement off-peak pumping in PZ4, except in very high demand conditions (>2.1MGD); Pressure Zones 7, 8, 9, and 10 all have similar characteristics and off-peak pumping should be tested in these zones. ? Operate UW9 and UW31 between a 60/40 operation and 75/25 operation to combat seasonal demand fluctuations, to maintain hydraulic residence time, and energy conservation guidelines by MWU. A 60/40 operation works during all seasons. ? Do not perform hydraulic grade line reductions in PZ4 due to pressure concerns. ? Do not perform pipe modifications in PZ4 to save energy, but only for operational reasons such as improved flow conditions. ? Continue flow reduction efforts as they have been found to conserve energy and water. ? Continue use of the hydraulic modeling software due to the benefits of energy analyses it can perform prior to implementing options, especially on small pressure zones and preliminary testing of alternatives.