By Mike Pemberton and Joananne Bachmann
Pumps are the second most widely used machine in the world after motors, with their purchase and operation entailing significant expenses for most facilities. However, it is common practice for pumping system design and procurement to be based primarily upon the initial purchase cost of the equipment. Often such decisions, particularly with new systems, are under the control of the engineering contractor—who has few incentives in the world of fixed price contracts to embrace energy efficient pump system designs.
Depending on the application and operating environment, the initial pump purchase is small in relation to overall pumping systems costs. Energy, maintenance and other operating costs far outweigh initial expenditures. Therefore, it makes economic sense to consider these lifetime costs in addition to original pump pricing when designing and procuring pumping systems.1
Subsequently, each year the number of retrofit optimization opportunities greatly exceed the number of new system installations with the bulk of potential savings lying within the enhancement of existing control systems, pumps or both. As a result, the average energy savings potential through economically viable pump system optimization projects is approximately 20%, although certain installations can realize even greater savings ranging from 25% to 50%. This potential represents significant cost savings in addition to energy efficiency improvements that normally coincide with improved reliability, productivity and reduced environmental costs.
However, the numerous benefits derived through the optimization of existing systems should also not be ignored. For a given new system, the potential savings in energy and life cycle costs are far greater than in a given existing system of similar size and application. One reason for this is the opportunity to optimize piping system designs. Other aspects of the pump system can also be better tailored to the system requirements in the design of new systems.
In 2007, the U.S. Department of Energy (DoE) “Save Energy Now” Program identified more than $5 million in cost savings with just 31 pumping system assessments looking at only two or three systems per plant. In addition, a recent industrial motor systems market opportunities assessment by the DoE also reviewed motor energy consumption and savings by numerous industry groups. Among the findings was the realization that pump system optimization practices could greatly increase organizational cost savings since pump systems make up 25% of the motor opportunities in these companies.
However, this process must begin with the proper assessment of pump system costs. For example, the average plant today, based on kilowatt-hour cost increases since 1998, spends more than $1.4 million per year on pump system energy. As a result, the average savings achieved from the optimization of pumping systems can potentially be valued at $350,000 per year. In larger facilities, these savings could even run into the millions of dollars.
A Systems Approach
A systems approach, which analyzes both the supply and demand sides of a pumping system and how they interact, almost always produces greater energy and cost savings than the optimization of components alone. For example, a survey of only the components of a pumping system may reveal opportunities for an energy efficient motor, replacement of a leaking valve, and adjustment to the energy management system to precisely align the pump operation hours to the schedule of the end-use process. In comparison, analysis of the pumping system using a systems approach could identify a varying load profile that could best be met through a two-pump arrangement or adjustable speed drives, resulting in a 50% to 60% savings.
In fact, approximately 75% of the total life cycle cost of a typical pumping system is accounted for in energy and maintenance costs. (This will vary significantly by application.) To maximize pump system efficiency, the pump must be operated at its Best Efficiency Point (BEP). According to Hydraulic Institute standards, “the BEP is the rate of flow and head at which the pump efficiency is at maximum.” 2,3
A systems approach to new pumping system design is equally important, and often overlooked. A recent survey of seven pump manufacturers revealed a significant lack of understanding on the part of pump specifiers and purchasers regarding the proper application of pumps.4 These pump manufacturers were asked “What percentage of the pumps your company sells are incorrectly specified by the contractor or owner/operator?” Of the five manufacturers that responded with a percentage, three indicated a value of 60% or greater, and one indicated that 30% to 40% were incorrectly specified. A follow-up question asked “Of the pumps that are incorrectly specified, what percentage is a result of inaccurate operating point specifications (i.e., rate of flow, required pressure, and net positive suction head)?” The answers varied between “most” to 90%. Misapplication of pumps has a direct affect on pumping system operating costs. A pump forced to operate away from its BEP increases energy and maintenance costs, and shortens the life expectancy of that pump.
Pumping System Efficiency
New solutions for increasing pumping system efficiencies can provide significant economic opportunities for reducing energy consumption. For instance, the over-sizing and under-sizing of pump systems during the purchasing and installation processes can create numerous issues. This is because centrifugal pumps alone:
• Consume 20% to 60% of plant motor energy;
• Have the highest process equipment maintenance cost; and
• Remain a major source of process leaks and fugitive emissions.
However, a recent paper by the ARC Advisory Group revealed that while American industry spent millions of dollars on information systems to review production management and asset management processes, major assets such as pumps, fans, blowers, etc. were disconnected from the process. Companies have little real time data on the performance of these assets and up to 60% of scheduled maintenance checks on valves and motors are unnecessary due to the lack of performance data.5
This can be easily remedied with low-cost Internet-based technologies as well as other methods, which can now provide an integrated view of pump system efficiencies that include a review of chips or variable speed drives, operational conditions and process parameters like flow and pressure. Among these technologies are low cost, wireless predictive condition monitoring systems that provide continuous online machine monitoring as well as intelligent flow systems that work with any pump using variable frequency drive (VFD) controller and control software to provide advanced process control, enhanced reliability through failure prevention, reduced life cycle costs and up to 65% lower energy costs.
To further highlight the need for enhanced pump system optimization processes, in 1996 a Finnish Technical Research Center report, “Expert Systems for Diagnosis and Performance of Centrifugal Pumps,” revealed the average pumping efficiency, across the 20 plants and 1,690 pumps studied, was less than 40%, with 10% of pumps operating below 10%. Pump oversizing and throttled valves were identified as the two major contributors to this sizeable efficiency loss.6
Pump systems optimization is all about maximizing efficiency. This includes modifying pumps mechanically to achieve best efficiencies for the longest possible period of times.
Unfortunately, industrial practices have included the oversizing of pumps to accommodate increased production expectations or excessive safety margins. As a result, pumping systems that may have been purchased at exceptional prices could actually be operating with extremely high maintenance and energy costs since they were not optimized initially to run at best efficiency.
A pump costing $100,000 to purchase and install could actually end up costing up to $435,000 a year, once you factor in the energy, maintenance and other costs involved when you analyze the life cycle costs of a pumping system. This is a considerable expense since optimum pump sizing as well as use of variable speed can provide significant pump savings. In addition, the proper pump system design choices on the front end could also reduce plant building and operation costs since the entire process includes the installation and maintenance of less equipment, valves, bypass lines.
As for existing facilities, many pump systems can be modified through control or mechanically re-engineered with paybacks periods that usually range from six to 24 months. Variable speed drives, whether electrical or mechanical, also account for only 4% of motor energy usage, while the potential exists to apply its use up to 25%.
Anecdotal evidence indicates that about 75% of all pumping systems are oversized. This inefficient condition may result from conservative design, design for anticipated system capacity increases, or a decrease in the output demand. Other factors include the propensity of everyone involved in the design process to overestimate current and future needs with the inclusion of larger-than-necessary margins.
Typical indications of an oversized system include frequent on/off cycling, highly throttled valves, or heavy reliance on bypass lines. Possible improvements include trimming the existing pump impeller, installing a smaller impeller, removing stages of the pump (if a multistage pump), replacing the unit with a smaller pump, or reducing the pump speed. An engineering analysis can identify practical alternatives, and a life cycle analysis can then be employed to determine the most economical option. Proper sizing results not only improve energy efficiency, but also have a positive effect on other factors in the life cycle cost equation. A properly sized system operates close to its BEP, resulting in lower maintenance costs, longer equipment life (increased mean time between failure), and reduced downtime expenses.
End users frequently install VFDs to control motors on pumping systems with variable loads. The VFDs often result in substantial energy and maintenance savings, but it is important to note that not all applications are appropriate for VFDs, particularly systems with substantial static head.7 A systems analysis will typically identify whether a VFD is appropriate for a particular application. Flow control alternatives such as impeller trimming and multiple pump arrangements may be more effective and economical.8
Life Cycle Costing (LCC)
A greater understanding of all the components that make up the total cost of pumping system ownership will provide insights into opportunities for significantly reducing energy, maintenance, and other operational costs. LCC analysis management tools can help companies realize these opportunities. The analysis takes into consideration the costs to purchase, install, operate, maintain and dispose of all components of the system. Determining the LCC of a system involves following a methodology to identify and quantify all of the components of the LCC equation. When used as a comparison tool between possible design or overhaul alternatives, the LCC process will identify the most cost effective solution within the limits of the available data.
In applying the evaluation process, or in selecting pumps and other equipment, the best information concerning the intended output and operation of the plant must be established. If bad or imprecise information is used then a bad or imprecise assessment will result. The LCC process offers a way to predict the most cost-effective solution; it does not guarantee a particular result but allows plant personnel to make reasonable comparisons between alternate solutions within the limits of the available data.
Pumping systems often have a lifespan of 15 to 20 years. Some cost elements will be incurred at the outset and others will be incurred at various times throughout the lives of the different solutions being evaluated. It is therefore necessary to calculate a present or discounted value of the LCC to accurately assess the different solutions.
To make the most of an LCC analysis, it is best to evaluate alternative system solutions. For a majority of facilities, the lifetime energy and/or maintenance costs will dominate the life cycle costs. It is important to determine the current cost of energy and the expected annual energy price escalation for the estimated life, along with expected maintenance labor and material costs. Other factors, such as the life time costs of downtime, decommissioning and environmental protection, can often be estimated based on historical data for the facility. In some processes, down time costs can be more significant than the energy or maintenance elements of the equation. Therefore, careful consideration should be given to productivity losses due to down time.
In 2001, the Hydraulic Institute (HI) and Europump produced “Pump Life Cycle Costs: A Guide to Life Cycle Cost Analysis for Pumping Systems” to help facilities calculate in-depth life cycle costing for pumping systems as well as provide substantial technical guidance on new pumping system designs and assessments for existing system enhancements.
Pump optimization practices on a facility-wide basis can increase plant profitability and asset reliability. Commonly, opportunities exist when companies look beyond components and at a total systems approach to pump system optimization. Improper sizing, the failure to review whole system operations, inflexible process changes in a mechanical world and quick speed design fixes are all culprits of inefficient operations that waste both money and energy.
Pump Systems Matter (PSM), a nonprofit educational organization, was specifically created by HI in 2005 to help facilities decrease energy costs, optimize pumping systems and gain a more competitive business advantage through strategic, broad-based energy efficiency management tools.
An increasing number of PSM sponsors, as well as the DoE, now offer system assessments of plant operations to identify potential energy savings and areas for process and/or performance improvement.
By 2015, PSM sponsors hope “end users will understand the value of—and the demand for—pump system optimization services, and that the supply chain will understand the value of offering these services on a competitive basis.”
1 Hydraulic Institute and Europump, “Pump Life Cycle Costs: A Guide to Life Cycle Cost Analysis for Pumping Systems,” 2001.
2 Hydraulic Institute, ANSI/HI 9.6.3 –1997, Centrifugal & Vertical Pumps for Allowable Operating Region 1997.
3 Hydraulic Institute, ANSI/HI L 1 – 1.2, Centrifugal Pumps for Nomenclature & Definitions, 2000.
4 Walters, Trey, “The Cost of Incorrectly Specified Pumps – and Ideas on How to Reduce It,” Presentation given at Hydraulic Institute Annual Meeting. February 22, 2005.
5 ARC Advisory Group, “Strategies to Drive Manufacturing Efficiency on the Production Floor,” (David Clayton), 2000.
6 Finnish Technical Research Center, “Ex-pert Systems for Diagnosis and Perfor-mance of Centrifugal Pumps,” 1996.
7 Hovstadius, Gunnar, “Economical Aspects of Variable Speed Drives in Pumping Systems,” 1999 International Energy Technology Conference. Houston, Texas.
8 Pump Systems Matter & Hydraulic Institute, “Optimizing Pumping Systems: A Guide For Improved Energy Efficiency, Reliability & Profitability,” 2008.
Pemberton is performance services manager, ITT Corp.–Industrial Process, a charter sponsor of Pump Systems Matter. Bachmann is project and marketing manager, Pump Systems Matter, a nonprofit educational organization. This article has been published with permission of the Hydraulic Institute and is excerpted from the original paper, available in its complete form at www.pumps.org.