New SCADA Technology Saves City Energy Costs
The multitude of aging infrastructure problems that face cities and counties throughout the country coupled with rising energy costs and crippled budgets combine to create what seems to be an insurmountable barrier for forward thinking water utilities. But a central Florida city looked beyond these hurdles and applied a unique technology to simultaneously address all of these issues.
Winter Park is a beautiful community that is the quiet antithesis of the nearby hustle and bustle of Orlando. Gourmet restaurants, high-end designer shops and boutiques, art galleries and museums attract crowds of upscale visitors. Residents maintain majestic homes in the city's historic district, set among towering oaks and lush foliage. Much of the city's half century-old wastewater collection system runs under the quaint, brick-lined streets that house the many downtown businesses and homes and host the nationally acclaimed Winter Park Art Festival each Spring. This “sacred economic corridor” of shops, restaurants and other businesses is the heart and soul of the city.
The city's wastewater collection system has been strained by the tremendous growth that has characterized central Florida for the past few decades. Orange County, where Winter Park is located, has experienced a population increase of over 400% since the 1960 census. Sewer mains in downtown Winter Park are now forced to accommodate flows that far exceed their designers' expectations.
Utility director, David Zusi (standing) and city electrician Nollie Parrish consult a map of the city's collections system.
A few years ago, Winter Park was faced with a dilemma. Their collection mains were being strained by increasing daily demands and the city was delivering ungainly peak flows to the regional wastewater treatment plant that threatened to exceed its capacity. The obvious solution was to replace the mains with newer, larger ones and build a flow equalization basin that would allow the city to store some of its peak flow influent to avoid overflowing the head works at the WWTP.
But two major barriers stood in the way. First, of course, was cost.
Like many Florida cities, Winter Park was dealing with an ever-constricting budgetary dilemma. Property tax revenues were falling and as a result, many cities froze or cut utility spending for all but the most basic or urgent needs. At the same time, energy costs to operate the utility were steadily increasing, taking up larger and larger chunks of their budget. The funds simply did not exist.
The second barrier was the “sacred economic corridor.” Replacing the existing collection mains through the city's center would involve digging up the brick-lined streets and completely disrupting the business district. The utility knew they would face serious opposition from anxious business owners, residents and city officials even if the budget dollars could somehow be acquired.
City utility director, David Zusi, PE, began to investigate a new technology offered by the manufacturer of their existing SCADA system, Data Flow Systems. DFS had added a complementary capability to their SCADA system they referred to as “SymphonyTM – Harmonious Pump and Flow Management.” It was designed to synchronize and coordinate pump station operations to level out sewerage flows, extend the life of existing collection mains and reduce peak inflows into the WWTP. An especially problematic pressurized force main was selected to test the new technology.
This force main consists of a master pump station that receives inflow from 19 various sized duplex pump stations, nine of which pump directly into the force main. These pump stations' operations are totally independent of each other.
As with most wastewater collection systems, the pumps at each site are activated by local sensors that start the pumps whenever the well level indicates they're needed. But most wastewater is generated during a few peak periods of the day – notably in the morning when families are rising and businesses are opening and again in the evening when families return home. Since there was no coordination among the pumping sites, it was not unusual for many or most of the pump stations to run at the same time.
When multiple pump stations on a single force main run simultaneously, problems occur. Pressure in the main increases. When pumps have to work against high head pressures, they can't operate at full efficiency. The pumps run under stress and take longer to complete a pump-down cycle. Lift stations that have smaller horsepower pumps face additional problems. When head pressures reach a certain level, smaller pumps spin uselessly, “dead-heading,” and unable to force wastewater into the main until pressures fall to a level at which they can make some headway. This situation has several detrimental results.
First, it wastes energy. Pumps draw more power when they fight against high pressure and it takes longer for each pump to complete a pump-down cycle. Energy expense already occupies a prominent spot in a utility's operating budget without having pumps run so inefficiently. Second, since the pumps run longer and under greater stress, pump maintenance is adversely affected, resulting in higher repair costs and an increase in service call-outs. Third, a 50 year-old force main that operates under pressures that are much greater than the designers ever imagined is simply a disaster waiting to happen. And finally, the huge spikes in wastewater production can provide a surge that the regional wastewater treatment plant is unable to accommodate.
City electrician, Nollie Parrish, makes an adjustment at a lift station remote terminal unit.
Zusi assigned the city's lead electrician, Nollie Parish, to work with one of DFS' field engineers to begin the project. The team extracted data from Winter Park's SCADA system to determine in-flows, out-flows, pump run times and cycles in a 24-hour period. An evaluation of the data revealed that their system suffered from this typical, asynchronous pumping syndrome. Periods during which many pumps on the pressure main ran simultaneously were frequently followed by periods during which no pumps ran at all, adding to the inefficiency of the system. Both the force main and the treatment plant into which it pumps, were capable of handling the total amount that flows through the system over the course of 24hours. However, those periods of peak flow that sent the main pressures dangerously high and threatened to overflow the treatment plant's head works, had to be controlled.
The Symphony system uses the SCADA communications between pump stations to minimize those instances when multiple stations pump simultaneously and to take advantage of the times when no pumps are running. Parrish used the extracted SCADA system data to establish priority levels among the pump stations and influence the operations at each site. Symphony does not control the pumps, but “suggests” when individual sites should pump or not pump, always manipulating the stations within normal operating parameters. By managing the pumping activity on a minute-by-minute basis, pump station operations began to synchronize. Peak flows were reduced and pumps began operating more efficiently. When a lift station does not fight against overwhelming head pressures, the pumps don't work as hard and they complete their cycles in a faster and more-efficient manner. The intended result was to lower energy consumption and wear and tear on pumps, lessen the number of maintenance call-outs and reduce stress on an aging sewer main.
The second stage of the technique is meant to reduce the peak flow of wastewater that passes through the collection system to the WWTP. While many city sewage mains can handle the average daily flow within their systems, it is the peak flow hours that test capacities and force municipalities to consider the expensive and disruptive chore of enlarging collection mains and constructing surge tanks. If peak flows can be flattened during the high usage periods of the day, the collection system capacity is effectively expanded and the need to enlarge the collection mains can be delayed.
The Symphony system anticipated peak usage periods and prepped the collection system so that it was better prepared to deal with the surge. In the hours prior to the anticipated peak when the collections system is practically idle, the SCADA system methodically prompted each lift station to pump down to its lowest level. By "squeezing the sponge," and emptying the collections system prior to the peak of wastewater generation, the system effectively took a part of the peak flow and moved it forward in time, leaving more room in the collections system to handle the coming surge. When the peak flow into the WWTP evened out, the plant operated more efficiently.
When the initial test was complete, data from the SCADA system was used to compare the before and after results of the Symphony implementation. The data showed that pump stations that did not have to fight against high head pressures were able to complete their cycles in about two-thirds of the time – 34 percent less - than it took to accomplish the same results the previous year. Lower pump run times and efficient pump operations lowered energy consumption at the test lift stations by a stunning 42 percent. Only half as many lift station maintenance visits were required and the system shaved a sufficient amount off the peak hour flows to help normalize WWTP operations.
But some of the greatest benefits to the city may not be immediately measured like pump run times or energy dollars saved.
The act of leveling the flows and emptying of the collections system prior to peak periods created an virtual expansion of the system's capacity. An analysis of before and after data indicated that the peak flow and the average flow per minute were diminished enough to allow over 100 new meter connections on this single force main, based on the equivalent resident connection of 350 gallons per day. This added capacity will delay the disruption and expense that will result from tearing up the city's streets to install larger collection mains.
The population in Winter Park will continue to grow and energy costs will continue to escalate. And no amount of technology will change the fact that the city's collection mains have a finite life expectancy and, one day, will be replaced. But by squeezing every capability from the city's SCADA system, Winter Park has taken a first step to reduce their energy appetite and has allowed their brick-lined streets to remain quiet a bit longer.
Steve Whitlock has spent more than 22 years in the water and wastewater industry and is vice president of customer relations at Data Flow Systems of Melbourne, Fla.
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This article originally appeared in Remote Site & Equipment Management
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