Improved pump efficiency goes right to the bottom line

If we were told that we could lower our home energy bills by up to 50%, most of us would jump at the opportunity. That could mean an extra $1,000 in our pockets, instead of in the pocket of the utility company — a significant annual saving. Look at a similar industrial plant scenario. Many industries are extremely pump intensive.


If we were told that we could lower our home energy bills by up to 50%, most of us would jump at the opportunity. That could mean an extra $1,000 in our pockets, instead of in the pocket of the utility company — a significant annual saving.

Look at a similar industrial plant scenario. Many industries are extremely pump intensive. A typical process plant can have a pump population of up to 2,000 units. Optimizing pumping system efficiency has the potential to achieve up to a 50% improvement in energy and maintenance costs while improving pump and process reliability. On 2,000 units, averaging 50 hp at a cost of $.08/kWh hr, the savings could be dramatic (Fig. 1).

There are numerous consultants ready to help conduct plant assessments and realize maximum savings. But, there are also things that can be done today and everyday to start saving dollars immediately through greater pump efficiency.

Pump selection

Bigger is not always better. Standard practice has been to oversize a pump to ensure adequate pumping capacity during peak demand periods. Today however, in an era of oil at more than $60 a barrel and rising, energy costs are pounding company profits, making energy conservation a priority.

According to a recent report, average pumping efficiency across 20 plant locations and 1,700 pumps studied was less than 40%. Pump oversizing and throttled valves were two major contributors to this sizeable efficiency loss. Besides hindering overall plant efficiency, poor pump performance can result in increased downtime, collateral damage to equipment and higher maintenance costs.

Improving pumping efficiency

The initial price of a pump is typically less than 15% of the cost of ownership. The life cycle cost (LCC) of a 50-hp pump, which includes the costs to install, operate, maintain and decommission the system, is several times the initial purchase price. In general, energy accounts for about 30% of LCC costs with maintenance reaching as high as 40%. Over a 20-year period, combined energy and maintenance costs may exceed the initial pump purchase price by a factor of 10. Pump system operating cost can be dramatically reduced through efficiency improvements.

Pumping system efficiency is affected by several factors including:

  • Efficiency of pump and system components

  • Overall system design

  • Efficient pump control

  • Efficient drives

  • Appropriate maintenance cycles.

    • When performing pumping system assessments, the following pump symptoms are good indicators of potential energy-saving opportunities:

      • Throttled valves

      • Bypass lines normally open

      • Multiple parallel pump systems with the same number of pumps always operating

      • Constant pump operation in a batch environment

      • Presence of cavitation noise.

        • Operate at the highest efficiency

          The growing use of variable frequency drives (VFDs), particularly intelligent drives for pump control, is a major departure from the standard operating practice of using valves as the final control element for fluid flow. Historically, VFDs were used in pump applications where conventional control strategies did not work well or to lower energy usage.

          The term "intelligent pump" is somewhat of a misnomer as the intelligence actually resides in the pump drive's microprocessor (Fig. 2). Intelligent drives allow the pump to operate near its best efficiency point (BEP) and protect the pump from mechanical damage when it moves away from BEP. Recent studies reveal that pump operation near the BEP provides dramatic improvements in pump efficiency and operating reliability.

          VFDs allow pumps to run at slower speeds with trimmed impellers to contribute to pump reliability and a significant improvement in mean time between failures. In new applications, variable speed drives are often less expensive to purchase and install than flow control valves. Subsequently, when combined with lower energy and maintenance costs the total LCC of a given pumping system can be significantly reduced.

          Depending on their type, pumps have mechanical designs that allow high-efficiency operation. When applied, the design goal is to size the pump to operate near it's BEP under normal operating conditions. However, large swings in demand and load requirements often change with time. As a result, sizing a fixed-speed pump to operate near its BEP is similar to shooting at a moving target.

          By controlling the speed of a motor in real-time, VFDs are able to adjust energy use according to system needs. By varying motor speed to meet the exact process demand, VFDs eliminate excess energy used when running a motor at a fixed speed. By optimizing pump performance, case studies have shown up to 50% or greater reductions in energy use. Also, the excess energy in fixed-speed systems, not used for moving fluid, is often dissipated into the piping infrastructure and can contribute to lower equipment reliability.

          Maintaining pump efficiency

          Some suggestions for maintaining the efficiency and savings in pump operations are:

          • Adjust for wear. The efficiency of pumps can be affected by normal wear, opening the clearances between the impeller and casing or wear plate. Be sure to select an adjustable clearance-type pump and maintain the specified clearance.

          • Buy original equipment replacement parts. Manufacturing tolerances and techniques are critical to efficient pump operation and are maintained by OEMs.

          • Operate at the best efficiency point. Not only will the pump operate at peak efficiency but this will reduce wear on bearings and seals.

          • Lubricate per OEM recommendations. Just as with any rotating mechanical device, proper lubrication reduces friction and wear.

          • Increase driver efficiency. Depending on the age of the pumping unit, the electric motor may be the biggest saving source. If the pump is in good condition, consider swapping out the motor. A new, high-efficiency unit could pay for itself through efficiency improvement and extended service life.

            • Document savings

              Establishing and maintaining a pump efficiency improvement program is great, but proving its value to plant management is the real brass ring. Develop a database of every pumping unit and benchmark the pump population. Do the calculation to determine a pump's current efficiency.

              Efficiency.= Capacity (gpm) x Head (ft)

              3960 x Horsepower

              Document the changes made through retrofits, upgrading, VFD installations, etc. Give progress reports to management. It will help sell future requirements for capital that will save even more dollars (Fig. 3)

              The Bottom Line...

              • Improving pump efficiency can cut costs by up to 50%.

              • VFDs help pumps operate at their best efficiency point.

              • Documenting savings helps sell future pump improvements.

                • Questions about increasing pump efficiency may be directed to Mike Pemberton at (205) 822-7433. Article edited by Joseph L. Foszcz, Senior Editor, (630) 288-8776, .

                  Flow demand vs. required control valve or VFD settings

                  Flow rate, gpm Duty cycle, % of time Control valve dP setting, psid & pump % of BEP VFD setting, rpm & pump % of BEP

                  ISA speakers to cover wide range of topics

                  Automation and control professionals will gather in Chicago Oct. 25 through Oct. 27 for ISA Expo 2005 at McCormick Place. Besides being a venue for the exchange of ideas and a chance to preview the latest innovations, ISA also will offer a series of technical presentations and insights from some of the industry's top experts.

                  Rockwell Automation vice president Kevin Roach will speak Tuesday, Oct. 25 at 8:30 a.m. on the vision for a seamless integration between the plant floor and business systems through the use of management enterprise software. Roach, chairman of the Management Enterprise Software Association, will discuss the kinds of returns that can be realized through the deployment of a comprehensive MES solution.

                  Jeff Harrow , author and editor of the Web-based multimedia technology journal, The Harrow Technology Report, will address the Expo on Wednesday, Oct. 26 at 8:30 a.m. on the technological advances that have changed work, home and social life in the computer age. He'll offer a view of the next technologies that will change the way we live and work, and how the pace of those changes will continue to accelerate.

                  James Durkin , vice president engineering, global supply chain for Kraft's global engineering function will discuss the issues of feeding the world safely, securely and cost effectively at his presentation on Thursday, Oct. 27 at 8:30 a.m. Durkin will look at those issues from his perspective in a global food company, focusing on key drivers in the industry and the important role that engineering plays in meeting those needs. He will also address key issues with security, reliability and how vendors can help meet food industry needs.

                  PLANT ENGINEERING magazine is one of the endorsing publications of the annual ISA Expo, which is presented by The Instrumentation, Systems and Automation Society . For more information, or to register, go to the Expo Website at

                  Nilfisk offering free onsite assessment

                  Industrial vacuum cleaner manufacturer Nilfisk-Advance America announces the launch of its new free onsite needs assessment service. The free assessment delivers a comprehensive evaluation of existing cleaning processes, identifies outstanding and unmet needs, and recommends improvements as warranted.

                  "Our customers led the way with this initiative," said Paul Miller

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