• Longer Life – Energy efficient motors dissipate less heat compared to standard motors, as they are more efficient. Use of
energy efficient fans keeps the motor at a lower temperature.
This increases the life of the insulation and windings, besides
increasing the overall life of the motor.
• Lower Operating Cost – The total energy cost of energy
efficient motors during its life cycle is much lower when compared to conventional motors.
• Other benefits – better tolerance to thermal and electrical
stresses, ability to operate at higher temperatures, ability to
withstand abnormal operating conditions such as low voltage,
high voltage or phase imbalance.
The advantages of energy efficient motors as defined above are
accurate. Now let’s look at some other statements that are being
made regarding premium efficient motors:
• Utility rebates
• Reduced load
• Energy Savings
Since the implementation of the EISA standard most if not all
utilities have eliminated the rebate for premium efficient motors.
Why? Because it is now mandated by the federal government.
Will the premium efficient motor reduce loading, will it save
After this lengthy explanation on premium efficient motors, we
can get to System Efficiency.
• Motors meeting higher efficiencies tend to run faster than
their less efficient counterparts.
• Matching speeds to applications need (pump flow, fan cfm) is
• Drives may be required, which offers the opportunity to increase system efficiency in applications with variable output
• In some cases, mounting dimensions for motor into machinery may be slightly different.
The following is a case study that graphically illustrates the
impact of a premium efficient motor in a centrifugal pumping
The spreadsheet (previous page) provides four separate
scenarios for reducing energy consumption in a cooling tower
pumping system. The system portrayed is a typical closed loop
configuration where the discharge is being throttled over a range
of operation. The system in this example operates 24/7, 365 day
a year and at this particular load point 70 percent of the time or
6,250 hours per year.
Columns one and two indicate the various components factored
into the system efficiency calculation. Column A is the base condition where the system operates 50 percent of the time. You will
note the component efficiencies for the VFD and gearbox at 100
percent since they were not utilized. Under the based condition
the total power required is approximately 1,777 hp, almost 356 hp
is being lost (wasted) across a control valve. In addition the pump
is operating back on the curve at 65 percent efficiency. Under
these conditions the total system efficiency is 49 percent.
Column B provides the new operating conditions with the ad-
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