Variable-frequency drives from Saftronics installed at Unilever safely convert old, power-hungry AC motors into energysparing equipment that requires 50% less electricity.
VARIABLE-FREQUENCY DRIVES (VFDS) safely convert old, power-hungry ac motors into energy-sparing equipment. Attached to existing motors that power blowers, pumps, and fans — and installed under the guidance of experienced energyservices companies (ESCOs) — these VFDs decrease the need for electricity by 50% or more. They also ease maintenance demands by prolonging motor life.
At consumer-goods supplier Unilever's plant in Edgewater, N.J., for instance, a VFD retrofit yielded projected energy savings of 67% — accounting for an annualized cost savings of $86,708. And a calculated ROI of 111% enabled payoff within nine months of installation.
VFDs are electroniccontrol systems that manipulate the speed of AC induction motors by changing the frequency and voltage supplied to them. Motor speed, and therefore efficiency, is optimized to fit demands and is determined via sensor (in most cases, from a buildingautomation system) input. Most drives are programmable so the user can also dial-in operation conditions suitable for the application.
"If you look at heating and air-conditioning loads in a building, it's like a bell-shaped curve — you only need 100% flow about 5% of the time, depending on what part of the country in which you live," says Bob Hughes, president of Industrial Systems Group, an ESCO serving the East Coast. "A VFD gives you the ability to dynamically balance your system so the motor handles the load using less horsepower."
If a shop is putting in new motors, fitting any VFD is usually not a concern. But if it's a retrofit, as with Unilever, there can be problems with burning out the primary winding of the insulation. However, one company, Saftronics, makes some VFDs with soft switching that work with any existing motor in the field without damaging it.
Saftronics' VFD uses pulse-width modulation, employing microprocessorbasedalgorithms and soft-switching gate control that lower a motor's peak terminal voltage to reduce overheating and prolong its life.
To further extract efficiency gains from older motors, Saftronics VFDs incorporate Smart Bypass — a control system that lets the motor operate directly from the AC line instead of from a solid-state controller when 100% speed is required. Smart Bypass monitors the load and transfers to bypass when demand exceeds a userprogrammable limit. By doing so, it achieves an additional 3% to 5% energy savings.
"Once the Saftronics equipment is integrated into a plant's HVAC system, then it's a hands-off process," says Hughes. "Set in motion, it becomes transparent. It's really that good."
FORT MYERS, FLA.