According to the company, large fans are traditionally driven with a.c. induction motors, and variable frequency drives (VFDs) are the standard choice when variable airflow is needed. Such components are known in the industry and can be cost competitive. However, the company says, problems arise from miniaturization of VFDs that have insufficient output filters. Motor winding failures and arcing in the ball bearings can occur within a few months of operation. In addition, VFDs can excite disturbing resonances in the fan structure.
Another option is an EC (electronically commutated brushless) motor system. The horsepower range of EC motors has increased to a maximum of about 3/4 hp in recent years. The motors' superior efficiency, added control, and flawless reliability are said to offer interesting solutions to HVAC projects. However, there is an added complexity when EC drive electronics are remote from the motors.
The company says its latest EC motor generation addresses this problem. All electronics are now completely within the envelope of the fan motors. The OEM or the contractor simply applies the a.c. power and either a 0- to 10-V or RS485 control signal. Some EC motors even have a controller for a PID closed-loop process control internally on board. An advanced commutation method assures extremely smooth fan operation. In addition, the EC motor performance range has been extended to 4 hp (3 kW) / 177 lb-in (20 Nm). The company says that this new range of EC motors helps to meet tough noise and efficiency specs for rooftop condensers and air-handling units.
ebm-papst Industries, Inc.