Green initiatives are more than the right thing to do. Given budgetary pressures and an emphasis on increased efficiency, they make good economic sense.
Strategically managing power can yield significant advantages—energy savings, improved sustainability, cost reductions. Among the technologies helping us to meet energy challenges while addressing efficiency and reliability concerns are variable-frequency drives (VFDs).
Driving Energy Efficiency, Delivering Savings
VFDs can achieve significant energy savings and extend the life of mechanical systems. By closely matching a motor's speed to output requirements, drives help you to use only the energy you need, yielding system energy savings of 10 to 50 percent. Further, drives can be used to gradually accelerate motors or pumps, helping to protect assets and extend equipment life. In terms of both hardware and software, today's VFDs are able to generate more energy savings than previously possible.
Hardware Advances Improve Efficiency
Advances in capacitor technology are yielding net energy savings while limiting toxins. Traditionally, drives have utilized electrolytic capacitors to store energy and act as a filter for current pulses. Electrolytic capacitors leak electrolytes into landfills, produce unnecessary heat, and are less efficient than newer technology. Today's advanced drives are constructed with thin metalized-film capacitors that are non-toxic and Restriction of Hazardous Substances-compliant. Additionally, metalized-film capacitors do not require recharging, even after years of sitting on a shelf. They are self-healing, preventing hot spots, extending shelf life, and decreasing heat loss.
New capacitors lose less power, are more efficient, and produce less heat within a drive package. Because heat can significantly limit drive life, drives utilizing thin-film technology tend to last longer.
Software Advancements Fuel Energy Savings
Significant changes in software functionality are contributing to the improved energy savings achievable with today's drives. Advanced algorithms, heat-management systems, and enhanced functionality are making drives more efficient.
Energy-Control Algorithms Deliver
With advanced algorithms, the operating point of a drive and motor system can be adjusted dynamically in response to load conditions, reducing motor losses and improving efficiency. As a result, energy savings in both variable-torque and constant-torque applications can be improved significantly; typically, energy savings would not be realized in constant-torque applications with a VFD.
Using a drive for light-load conditions—typical of pumping and other variable-torque applications—can result in energy savings. For example, in a 50-hp application, $10,000 to $28,000 in energy savings can be achieved over the life of one of today's drives. By using drives with advanced efficiency algorithms, customers can save 0.5 to 10 percent more than they can with traditional drives.
Managing Heat to Increase Savings
Drives use internal fans to cool themselves. Traditionally, the fans are programed to run at full speed whenever a drive is energized. Newer drives monitor heat-sink temperature and control fans to receive only the amount of cooling that is necessary. Closely matching cooling requirements to fan speed can reduce the energy needed to control fans by 20 to 60 percent. Less loss means increased energy savings for drive users.
Saving Energy in Sleep Mode
In run mode, a drive consumes energy—even if a zero-speed reference is given. Some drive manufacturers offer an enhanced sleep function, which allows a drive to shut down when it is not needed. This can be useful in an application involving a fan or pump, in which a drive's internal proportional–integral–derivative (PID) loop controls speed.
A PID loop uses a set point and system feedback to determine speed. When feedback from a remote sensor indicates low or zero speed is required, a drive is able to turn off a motor by removing the run command. The drive returns to run mode when the system indicates a higher speed is required. Simply put, this functionality allows a drive to be better tuned to actual energy needs, tapering system requirements during off hours and on weekends and holidays, allowing customers to see significant savings on their energy bill.
Sustainability by Design
Drive technology continues to become smarter and more efficient with innovative motor-control developments. Significant incremental system savings can be achieved without hardware additions or advanced setup requirements.
According to the U.S. Department of Energy, motor-driven equipment, such as pumps, fans, and compressors, consumes about 16 percent of the energy used in U.S. industrial applications. This amounts to $30 billion annually. For variable-speed applications, installing a VFD with the latest motor-control technology is a simple and cost-effective way to yield significant energy savings.
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Bill Genaw is a product manager for Eaton. An electrical engineer by training, he has extensive experience in the design and implementation of motor and control equipment. Eaton is a global company helping customers better utilize electrical, hydraulic, and mechanical power by focusing on energy-efficient solutions.