Consider more than the efficiency rating to select the most cost-effective system for the pumping application.
by Mike Stockman
June 4, 2015

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).

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)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.

Step 1. Measure WWE

The first step is to measure true efficiency by analyzing the complete wire to water efficiency (WWE) of the pumping system (see Equation 1).

WWE = [(motor efficiency) x (pump efficiency) x (control/drive efficiency)] x 100
Equation 1

One-hundred percent efficiency is impossible if any component within a system is less than 100 percent efficient. Consider the following examples.

Example 1. 50-HP, 2 Pole (3,600 RPM) pumping system:
The system has an 84 percent efficient motor, 45 percent efficient pump and 99 percent efficient control/drive. Its WWE is 37.42 percent (see Equation 2).

(0.84 motor x 0.45 pump x 0.99 control/drive) x 100 = 37.42% WWE
Equation 2

Example 2. 60-HP, 4 Pole (1,800 RPM) pumping system:
This system has a 90 percent efficient motor, 76 percent efficient pump and the same 99 percent efficient control/drive. Its WWE is 67.72 percent (see Equation 3).

(0.90 motor x 0.76 pump x 0.99 control/drive) x 100 = 67.72% WWE
Equation 3

Every motor and pump manufacturer is required to publish full load efficiency data for standard rated products. Be aware of data accuracy, and note that Web- or app-based sources for efficiency ratings are generally updated more frequently than printed documents are.

As the industry evolves, changes are inevitable. A subtle change has a multiplicative effect on total system efficiency. For this reason, end users should research the same efficiency data for pumps and controls/drives.