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Operators Forum: Pump Myths Debunked

Setting the record straight on system design, setup, and maintenance 
By Peter Gaydon , Wastewater News

Pump system misconceptions create missed opportunities for greater efficiency and cost savings. 

With pumps typically accounting for 40% of the energy use in industrial fluid systems, facilities cannot afford misunderstandings around the technology and its requirements. Whether for food and beverage production, wastewater disposal, or anything in between, designing your fluid system with these five truths can make the critical difference in operational success. 

 MYTH 1: Buying and installing the system is the most expensive part of pump system ownership. 

 TRUTH: Many people assume that the initial purchase and installation costs are the most expensive aspect of a pump system’s complete life-cycle cost. In reality, energy and maintenance are responsible for the lion’s share of system expenses. A typical pump system, for example, often boasts a lengthy lifespan of more than 20 years. Throughout this period of ownership, it is likely that 65% or more of costs will go toward keeping it operational (energy and maintenance). The original purchase and install make up less than 20% of costs. Choosing a less expensive system or installation process can result in an even greater disparity in these percentages. Considering this ratio, it is important to understand total life-cycle cost and how purchasing the most efficient pump that is properly selected and controlled for the system will cut costs over time versus getting hung up on the initial price tag. 

 MYTH 2: Pumps are often the source of an entire system’s operational inefficiency. 

 TRUTH: As with many technologies, efficiencies — and a lack thereof — stem not only from efficient equipment design but also from proper sizing and operating methods. Inherently, pumps offer relatively high efficiencies, however, their operational efficiency is tied to system design and operation. For example, the most efficient possible pump could be used and operated at its best efficiency point, but if the system requires less flow or pressure than the efficient pump is providing, the system is operating inefficiently. Remember, the operational requirements that draw energy, such as flowrate and pressure, are requirements of the system. System design should precede pump selection and include careful considerations around how the setup uses energy, identifying ideal pump size and flowrates. Understanding what level of pressure — or head — the specific system requires, and how it will vary over time, will guide optimal pump selection and control. After these system requirements have been considered, the Hydraulic Institute (HI; Parsippany, New Jersey) Energy Rating Program provides a resource to select the most efficient pumps, comparing energy consumption rates for pumps and systems in the marketplace and advising on potential power savings from system upgrades and changes. Using such resources, along with a system-focused approach, will yield the greatest improvements in energy and maintenance efficiencies. 

 MYTH 3: The technology used for pump systems is dated and unsophisticated. 

 TRUTH: Today’s pumps are not your grandfather’s pumps. Technology has advanced to make pumps — and their interaction with the system — increasingly agile and intelligent. The introduction of smart pumps creates an adaptive system that knows the pump’s performance parameters, analyzes activity and can adjust pump operations in response to demand. Using these learnings and adjusting the control can minimize downtime and increase efficiency (i.e., automatically changing control pressure setting based on a building’s actual heating or cooling demand). 

 MYTH 4: Pumps are typically unnecessarily oversized. 

 TRUTH: If and when pumps are “oversized,” meaning a safety factor is built in, it is to account for uncertainty in flow and pressure requirements, and sometimes future demands. It is important to consider this uncertainty because having a pump that is undersized for the demand will result in poor utility. In these cases, close management at commissioning can ensure that unnecessary power consumption is not occurring. 

To limit the effect of an oversized pump, implement proper commissioning when the pump is installed and determine if the system can be balanced to limit flowrates, if a smaller impeller will reduce power consumption or if a control setting can be adjusted and still meet the system requirements. In systems that have variable conditions, it is likely advantageous to purchase a pump that includes a variable frequency drive, which can also help with oversizing by reducing the maximum operating speed to meet the system’s actual requirements. 

 MYTH 5: Variable speed drives always increase pump efficiency. 

 TRUTH: When variable conditions exist, think of throttling the pump flowrate with a control valve akin to adjusting speed in the car with the brake, but not taking a foot off the accelerator. There is no question that variable speed pumping can boost system efficiency, but a common misconception is that simply adding a variable frequency drive is enough to improve system efficiency. In truth, there are a few more boxes to check when implementing the functionality. Does the system require variable operation? Does the system contain instrumentation to measure the system variable (i.e., pressure, flow, power, temperature, etc.) and feedback so that speed can be adjusted to meet a set point for this variable? Adding a variable speed drive to a pump without these considerations will not result in energy savings. Instead, approach this technology with a sense of how it will fall into your complete system and plans for extracting the right information. 

 Facility designers, managers, engineers, and other pump system professionals can lean on industry authorities, such as the Hydraulic Institute, for the latest guidance in pump selection, optimization, and critical standards for operational efficiency. As the industry continues to evolve and adapt to heightened production demands and changing regulations, having a keen understanding of pump technology will foster a more cost-effective, responsible operation. 

 Peter Gaydon is the Director of Technical Affairs for the Hydraulic Institute (Parsippany, New Jersey). 

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Originally appeared in the November 2021 issue of Water Environment & Technology magazine. Reprinted with permission from the Water Environment Federation. All rights reserved.