Every pump industry professional faces the challenge of choosing the most efficient system for a particular application. This process is complicated by the uncertainties of efficiency regulations, mandates and parameters, especially when efficiencies alone do not tell the whole story. Sometimes the most efficient motor is not the best choice. By using two simple calculations, pumping professionals can determine the best motor\'97as well as the best pump and drive—for each application. To help both consumers and installers, nearly every product sold today features an energy cost or energy star rating. Industry standards and regulations developed by a coalition of industry experts help control these ratings, including multinational organizations such as The National Electrical Manufacturers Association (NEMA) and International Electrotechnical Commission (IEC).
Consider more than the efficiency rating to select the most cost-effective system for the pumping application.
06/04/2015
Image 1. Analyze both the capital expenditure and the total energy cost of the pumping system to identify the motor that is truly the most efficient for an application. (Images and graphics courtesy of Franklin Electric)
The goal of these organizations is to help individuals and power companies save money on energy and infrastructure costs by reducing confusion in methods of measurement and providing consistency in terminology and product labeling. This standardization minimizes incorrect measurements, misleading nomenclature and false competitive advantages. All reputable manufacturers support and collaborate with agencies like NEMA and IEC to maintain the professional standards of the organization. For this reason, users must ensure all of their products adhere to these standards.
Pump users often gravitate toward motors that report the highest efficiencies because they believe this decision will lead to future cost savings. This, however, is not always the case and is another reason end users must check the standards first. Companies that do not adhere to the standards could label their products as "super efficient," for example, or make similar false claims.
In many cases, the terms used on product labels are convoluted. For example, a company could invest in the original design of a 100-horsepower (HP) system, increase its efficiency by 16 percent and label it "super efficient." According to the standards, however, this improvement in design does not meet the criteria for premium efficiency. While the new product is 54 percent efficient compared with the previous product that was only 38 percent efficient, the minimum efficiency required for a premium label is 68 percent. Despite the fact that this product has been improved, it still does not meet the premium efficiency requirements. In this way, agencies and certifying bodies prevent manufacturers from making claims that do not meet the standards.
While understanding standard efficiencies is a vital part of choosing equipment, end users must go beyond efficiencies to select the ideal motor for an application. For example, submersible motors are generally 80 percent efficient, while similar surface motors are 90 percent efficient. Based on these numbers alone, one would assume that a submersible motor is less efficient. This, however, is not necessarily the case. Incorporating pump end efficiency in the assessment and evaluating horsepower requirements based on motor speed is vital.
Two simple calculations can help end users go beyond basic efficiencies to select the ideal motor for a particular pumping application.
Figure 1. When analyzing pump efficiency, look at the head point of an efficiency curve rather than solely using the BEP that most pumps list.
Analyzing these values closely is important because they represent a cost position. Looking only at total system product efficiency as noted above ignores the energy consumed by the system. Differences in speed and HP can result in higher energy costs, even when the efficiency ratings seem to indicate high efficiency.
Figure 2. The Application, Installation & Maintenance Manual (AIM) manual is one of the many places that you can obtain accurate motor efficiency information. Product efficiency information from online resources are typically more accurate because they can be updated more frequently.
Users must also consider the needs of their applications. Some systems may run for only a couple of months out of the year, while others may run every day to supply water to a city/municipal system. For systems that will run for years, the cost of operation is paramount. While the energy cost for a continuous run system will be much higher than that of a short run, the savings calculation is similar. The amount of savings will be diminished by the amount of run time.
Image 2. The submersible motor shown here may actually be a more efficient option than a surface motor, depending on the pump and drive/control it is paired with.
The more efficient pumping system consumes more watts and costs more to operate, so it might not necessarily be the best choice for a continuous run application. When choosing a pumping system, determining motor and pump efficiencies is an important preliminary step. But when calculating the final system cost, users must include both the capital expenditure and the energy cost of the system. In many cases, the most efficient system may not be the most cost-effective system.
Measuring efficiency and energy cost offers more insight into total cost of ownership.
To learn more about industry standards, visit nema.org or iec.ch