In 1994, electric motor-driven systems used in industrial processes consumed
679 billion kWh— 23 percent of all electricity sold in the United
States and 64 percent of electricity within the industrial sector. The
U.S. Department of Energy (DOE) has worked for years to encourage plant
operators to not only install energy efficient motors but also manage
and operate motors appropriately.
The presentation and workshop materials developed as part of the Illinois
IOF program are intended to clarify energy efficiency issues regarding
motors and then to provide the equations and tools necessary to quantify
the energy and cost savings potential for properly selecting and operating
energy efficiency motors.
Motors Efficiency
Today, motor manufacturers are required to meet standard efficiency levels
for their products. However, plant operators should consider investing
in high-efficiency or premium-efficiency motors. The following table outlines
the efficiency gains over standard motors.
Often, upgrading motors with high efficiency models does not reap sufficient
energy savings to justify the initial investment. The Illinois IOF program
does recommend that plant managers purchase high efficiency motors when
replacing burned out motors. Motor applications with high annual operating
hours are the best candidates for premium efficiency models.
The presentation developed for the Illinois IOF program outlines a methodology
for calculating potential savings.
MotorMaster+ Software
The Illinois IOF program recommends that all companies use the MotorMaster+
software to manage their motor equipment inventories. With a catalog of
over 20,000 AC motors, this tool helps facilities select appropriate motor
replacements, upgrades and control devices. It can compliment other preventative
maintenance programs and provide efficiency analyses, savings evaluations
and reporting capabilities.
Visit the U.S. DOE Best Practices website to download this free software:
MotorMaster+
4.0
Motor Management
Most people think of efficiency ratings when considering energy conservation
for motors. However, recent studies have revealed that most efficiency
improvements can be obtained through system optimization and proper motor
management.
Oversized Motors: Many motors are oversized for the application
and operate at part load conditions. Large motors (>75hp) can operate
efficiently down to 20% of full load, but smaller motors lose efficiency
below 30% or 40% load. Load can easily be measured with a standard amp
or power meter.
Voltage variations: Three phase motors operate best
when voltage is balanced across all three legs. More importantly, motors
with imbalanced voltage feeds suffer from maintenance problems and poor
torque performance.
Variable Speed Drives (VSDs)
Often system loads on pump and fan motors vary frequently during normal
operation. Sometimes flow is modulated through inlet vanes and throttling
valves or outlet dampers and bypass valves. Instead, plant operators should
consider modulating the speed of the pump or fan with variable speed drives.
The following tables outline the potential energy savings from variable
speed drives compared to other flow control strategies at variable speeds.
NOTE: These tables apply only to dynamic pressure head applications with
high friction losses. Static pressure head systems also save energy but
with a linear relationship between speed and power.
