One of the most important concerns facing all pump users is finding new avenues for increasing efficiency, and taking a systems approach can illuminate areas for improvement in both performance and cost. In this month’s SWPA Insight, a trio of SWPA members—Chris Caldwell of pump manufacturer Sulzer Pumps, Jack Creamer of component/controls manufacturer Schneider Electric, and consulting engineer Ernie Sturtz of CDM Smith—offer different perspectives on the “pieces” required to create a Systems Approach, with one common goal: everything working together.
WHAT IS THE SYSTEMS APPROACH?
What is the “systems approach” and how can it benefit the design engineer, manufacturer, sales representative, contractor, and end user? The key issue lies in how lift stations are typically constructed, that is by the lowest bidder, working from standard or cookie cutter documents. Many times, drawings are not to scale and the contractor or builder must be an expert in assembling the numerous parts and pieces that make up even the simplest duplex submersible pumping station. In that case, the contractor must turn to the (low-bid) supplier of the pumping equipment and attempt to get as much system responsibility as possible included in a purchase order or purchase contract.
The constructor of a facility designed using the “systems approach” as the basic philosophy will avoid many of the pitfalls inherent in the often-convoluted “low-bid” approach, but how far should the designer take this approach in creating lift or pumping station construction projects? The answer depends on a number of factors, such as the complexity of the system(s), the sophistication level of the contractors who are likely to bid the project, and the capability of the local manufacturer’s representatives.
The most complex systems may include several pumping stations on a common manifold. For such systems, hydraulic analysis software is necessary to select the pumping equipment. In addition, because of the potential for improper operation, bidding restrictions to a few pre-selected manufacturers are justified. At a minimum, the scope of supply should include pumps and guide-rails, access frames and covers (hatches), motor controls, and pump station control systems. The scope can be expanded to include access hatches over a valve vault (if included in the design), variable frequency drives, pre-cast concrete wet well and valve vault, and all accessories, such as discharge gauges, check valves, plug valves, piping, etc. In the end, the goal is a quality project with no insurmountable issues during construction and successful operation with minimal call-backs after completion. The proper application of a systems approach can help all involved parties to reach this goal.
The systems approach typically includes a combination of the Pump, the Motor, and the Controls; each component being important is it can contribute to the efficiency of the overall installation. Pump efficiencies have not historically been standards based, but with the recent DOE definition of “minimum pump efficiency,” that will change as Pump Manufacturers will be driven to design pumps to minimum efficiency quidelines. Motors also play a critical role, and have for some time have had definitions relate to efficiency level, with “Premium Efficiency Motors” gaining market presence in the pump system approach. On the controls side, there are two distinct solutions that both contribute to the Pump Systems efficiency. On one hand, for pump systems that have been oversized to meet anticipated future growth, and for systems that have varying duty cycles (two good examples being buildings and swimming pools, VFDs can provide the mechanism to optimum performance). Controls can also provide system monitoring functions to ensure that pumps are operating at the optimal point. Time can reduce pump operating efficiency for example with impeller wear. Monitoring energy consumed provides feedback on such events and allows the end user to better maintain optimal operating performance.
WHY IS IT IMPORTANT TO INCORPORATE IT INTO PUMPING SYSTEM OPERATION?
Even a well-designed pumping system can become ineffective, inefficient, or unreliable if operated incorrectly. The Systems Approach goes beyond the design and construction of the pumping system, to incorporate proper and efficient operation of the system for long term success. Since system operators may not be aware of the optimum way to operate the system, and the limitations that exist in the mechanical and electrical components, it is critical that system operation be considered part of the design and commissioning of the system. Operational guidelines such as min and max speeds, flows, pressures, and temperatures, and well as wet well elevation levels, cycle time, alternation, and operation during emergencies must be documented for the operator. This way, there is no mystery about the capabilities and optimum operational parameters of the system.
HOW IS “BOTTOM LINE” PERFORMANCE OPTIMIZED THROUGH THE SYSTEMS APPROACH?
The ultimate goal of any pumping system is to move the liquid at the lowest possible cost and with the highest possible reliability. In wastewater systems, moving the liquid is simply a matter of getting it from point A to point B in an acceptable amount of time. In many other applications, the pumping system supplies liquid to a process, and therefore must be carefully controlled to prevent the adverse effects of over or under pumping. The systems approach requires that each component be selected and evaluated for suitability for the particular purpose, with an eye toward creating an efficient, reliable system at a reasonable cost. Examples of this include whether or not to use a VFD to control the speed of the pump, what type of pump and impeller design is most suitable for the application, and proper selection of piping, valves, and other components. As much as proper selection of system components will yield an efficient and reliable system which will accomplish the pumping task, failure to consider each and every component in the system can result in inefficiency, lack of reliability, and failure of the pumping system to accomplish the goal.
WHAT ARE SOME OF THE KEY BENEFITS OF THE SYSTEMS APPROACH IN PUMPING SYSTEMS?
- Determines the System Responsibility Unit responsibility eliminates the questioning of cause of failure and isolates it under the auspices of a single source.
- Reduces the time element for repairs.
- Promotes proper design and can establish a standard format for submittals and approvals.
- Optimizes performance of the pumping systems.
Certainly there are two key benefits—energy savings and system optimization/maintenance. Regarding energy, VFDs can ensure that pumping systems are both operating at the BEP as well as help to optimize applications where pumps operate with varying duty cycles. The later being significant in applications such as buildings where you typically find both peak and non-peak operating cycles. During the peak cycle the VFD can ensure operation at optimal load, but during off peak cycles, the VFD can adjust the pump to meet lower demand criteria. As many pumps represent variable torque loads, the energy savings is significant! A lesser known, but potentially equal impact of the systems approach is that the controls can provide system feedback, on energy consumption for example. This allows the end user to implement a preventative/predictive maintenance approach and avoid system shutdown.
WHAT ARE SOME OF THE STANDARDS THAT APPLY FOR USING THIS APPROACH?
- “10 States Standards,” “Policies for the Design, Review, and Approval of Plans and Specifications for Wastewater Collection and Treatment Facilities,” A Report of the Wastewater Committee of the Great Lakes—Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers.
- Hydraulic Institute Standards ANSI/HI 11.6-Latest.
There are various systems evolving to help drive the system approach. Two of the more recent ones include the DOE Pump Efficiency standards and the AHRI1260 VFD efficiency testing process. Both of these address the pump system approach and will drive all manufacturers towards a pump system view. Optimizing the system, as well as the individual components that make up the system. ◆
For More Information:
SWPA will be hosting a two day Pumping Systems and Controls Training Seminar on April 20-21, 2015, in Chicago. For more information, contact SWPA headquarters at 847.681.1868 or visit www.swpa.org.
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MODERN PUMPING TODAY, February 2016
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