Efficiency matters in a water system, not only in terms of operational costs, but also in terms of installation and long-term system maintenance. While efficient solutions deliver positive financial benefits, steady operation, and consistent performance are non-negotiable. So, how do pump professionals and installers ensure they are maximizing efficiency without compromising reliability? From the pump-motor assembly to controls and wire, each component contributes to overall system efficiency. How these components work together can also boost efficiency and minimize downtime.
What is Wire-to-Water Efficiency?
Wire-to-water efficiency is the measure of the efficiency of a pump and motor together, as well as the pipe, controls, and wire necessary to complete the operation. It’s the overall efficiency of the entire system. The goal is to pick the right size for each component since oversizing leads to waste. Installers must manage performance needs with the customer’s budget to get the best possible operating system for their application. If a recommended operating system is outside the customer’s budget, an installer needs to be able to understand and explain the benefits of additional expenditures. For example, could the new system lead to better performance, less downtime, and less money spent on operating costs?
Targeting the Best Efficiency Point for Your Application
When considering a pump’s efficiency, installers can look at two things: the pump’s label and the manufacturer’s pump curve.
Beginning in 2020, the U.S. Department of Energy required all pump manufacturers to list the PEI (Pump Efficiency Index) on certain pumps’ labels alongside the pump family/model designation and the pump impeller diameter. These labels give installers a clear method to compare the efficiency of one pump to another initially.
In addition to the pump label, pump manufacturers calculate a pump curve showing the pump's best efficiency point at various flows. To properly size a pump, installers need to consider the factors shown on the pump curve, including the total dynamic head and the desired flow rate (GPM). Overestimating or underestimating the total dynamic head or the GPM needed to accomplish the job could cause significant effects on the optimization of the system. The pump curve maps out these efficiency points. The closer the pump’s BEP (best efficiency point) to the desired conditions, the better. If the desired operating point is too far to the left of the BEP, it could cause motor power overload, high flow velocity wear, cavitation, higher than desired radial loads, shaft deflection, turbulence, and erosion of the component parts of the pump. Too far to the right of the BEP could result in vibration, high temperature, excess recirculation, cavitation, or extremely low efficiency. All of these can reduce the lifespan of the system.
Online tools can help streamline the sizing process, quickly present options, and instill confidence that the most efficient solution has been selected within the pump’s recommended operating range.
Looking Beyond Motor Rating: Materials & Design
Motor efficiency will vary between manufacturers based on construction materials and design. Generally, tighter manufacturing tolerances yield a more efficient product. A poor design will cause losses in heat, vibration, and suboptimal energy conversion.
Similar to the pump efficiency standards, a manufacturer cannot simply place a sticker on a motor and say it’s “Premium Efficient.” Independent trade organizations, like the National Electrical Manufacturers Association (NEMA) and the Hydraulic Institute, test and verify efficiencies claimed by manufacturers. Efficiency information for motors can be found on manufacturer websites and through the Hydraulic Institute.
Another consideration when selecting a motor is the motor’s technology. For example, submersible motors can employ highly efficient permanent magnet (PM) operation. Permanent magnet motors are lighter and smaller than AC induction motors, which can ease the installation. PM motors do not have “slip” and operate at synchronous speeds. This means there will be more output when using a PM motor as compared to a typical three-phase induction motor. Users also benefit from possible energy savings of up to 20% compared to a standard induction. Since PM motors are more efficient and require less power than a comparable AC induction motor, installers can use smaller gauge wire for the same horsepower. This equates to considerable cost savings for the wire. While the initial cost of these motors is higher than that of a traditional AC induction motor, operational and wire savings can overcome this.
Driving System Optimization with VFDs
Another component that can maximize the efficiency of a pumping system is a VFD (variable frequency drive). With a VFD, users can regulate the system speed, providing precise adjustment of the flow, built in motor protection based on motor current and temperature, as well as other inputs depending on the options selected.
This ability to increase or decrease motor speed delivers incredible efficiency benefits. If the pump doesn’t always need to run at maximum flow, a VFD can be used to reduce the speed automatically. This can equate to considerable energy cost savings. For example, by reducing the speed of a 10-horsepower motor from 1800 RPM to 1500 RPM (approx. 17% speed reduction), the horsepower requirement goes down to 5.78 horsepower. Now, approximately half of the available horsepower is used – equating to energy savings. Here’s another example of how those numbers add up using a 100-horsepower motor.
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The average cost of operating a 100-horsepower system at full capacity is $100,300 (590,000 kWh x US average of $0.17 per kWh).
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Running the same motor/pump at a reduced speed using a VFD would cost about $39,100. (230,000 kWh).
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Equates to savings of $61,200 per year.
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Since the average cost of a 100-horsepower variable frequency drive package is about $25,000, the drive would pay for itself in about six months.
Application-driven drives, starters, and protection options that require minimal adjustments are ideal for simplified installation and can deliver operational cost savings.
Evaluating Every Component: How Wire, Tank, & Piping Size Make a Big Difference
Installers should also consider components such as tank size, wire size, and piping when choosing a system for optimum efficiency.
A properly sized tank will mean fewer on/off cycles. A tank that’s too small could cause more starts than the motor is rated for. Over-cycling any system can lead to premature failure of one or more system components. Energy consumption is also a factor when it comes to excess starts and stops due to the inrush currents, which will add to overall energy usage.
The type of motor chosen will affect the wire requirements, efficiency, and cost. A 15-horsepower single-phase motor with a 4AWG wire can only run a maximum of 270 feet. For a longer run, the wire gauge size must be increased, significantly raising the cost. In comparison, a 15-horsepower three-phase induction motor with a 4AWG wire size can run up to 520 feet. By selecting a three-phase motor instead of a single-phase motor, the length that a particular wire gauge would be acceptable can be doubled. (Refer to all local and NEC requirements for the application.)
Proper pipe size is also an important part of the size and design of a system, and it can lead to a potential reduction in horsepower requirements. Using a 1.5-inch diameter PVC pipe instead of a 1-inch pipe will decrease pipe friction losses and head by approximately 10 times. For a 20 gallon per minute application, if a 1-inch schedule 80 PVC plastic pipe is used, head loss for 100-feet is 31.26-feet. If the pipe size is increased to 1.5-inch, head loss for the same 100 feet of pipe is only 3.51-feet. By increasing the pipe size by just a ½-inch in this example, head loss is reduced by a factor of 10. This can drastically affect the pump size and horsepower required for the pump application. Proper pipe sizing not only improves the performance point on the curve but can also change the horsepower of the pump needed, improving electrical consumption and making the overall system more efficient.
Efficiency matters in a water system, not only in terms of operational costs but also in terms of installation and long-term system maintenance.
Single Source Benefits: Optimized from Installation to Operation to Expansion
Obtaining components from a single manufacturer can enhance the entire system's efficiency from the initial order through to operation and maintenance. During the selection process, online manufacturer specification tools can identify the best component combinations for the application, offering insights into options for optimizing operational efficiencies and extending system lifespan. Manufacturers often design and test components to work harmoniously, enabling streamlined installation and operation. In the future, if the system requires expansion or service, the OEM can recommend the most suitable replacement parts or scalable components that can be integrated efficiently.
Conclusion
Reducing horsepower requirements goes a long way toward maximizing pumping system efficiency, and every component in the system contributes to this. Wire size, piping, a VFD, motor type, and more should all be considered. In some cases, spending a little more upfront can save installers and water professionals time and money in the future.