Developed by Control Resources of Littleton, MA, U.S., the microprocessor-based VFD uses onboard programming, which allows for the setting of various parameters. Motor speed can be based on several control inputs, including control signal (4 to 20 mA, 2 to 10 V d.c.), remote temperature sensor (thermistor), 0- to 18-V d.c. transducer, and modbus or I2C communication link.

In addition to flexibility, the company says the drive offers acoustical noise reduction, energy savings, and greater product reliability. Nate Lavoie, vice president of Engineering, explains that the noise reduction is achieved by sensing temperature and automatically slowing the fans down when full cooling power is not necessary. “We call this adaptive cooling—more cooling air when you need it, less noise when you don’t,” he says.

The energy savings comes from the drive’s variable-speed control technology, which only runs the device at the speed necessary for the desired result. This not only saves energy, but increases reliability. By running the fans at lower speeds, bearings typically last longer and the motor runs cooler, reducing the possibility of failure.

As a result, Mr. Lavoie says Stratus is beneficial in applications where variable-speed control can be used to save energy and regulate environmental conditions. Ideal uses include HVAC applications such as the fan control on burners for hot-water heating systems, fan control in forced-air heating systems, and controlling air-conditioning compressors. Other possibilities include fan control in range hoods, indoor pools and spas, attic/whole house fans, and medical equipment.

A common application, Mr. Lavoie says, is ventilating fans in commercial buildings and schools, where fans are switched on and off by individuals in each room. “Often when the fans are switched on, they are left on over night and on weekends. By adding temperature-based variable-speed control with set temperature settings, the fans run only at the speed necessary to maintain a set temperature range and automatically turn off below a set temperature,” he explains.

“When the fans are on, they only run at full speed when absolutely necessary as opposed to running at full speed all the time,” Mr. Lavoie continues. “The fan, an inherent air flow regulator, becomes a temperature regulator.” Resulting advantages include a constant temperature in each room, extend fan life due to running at reduced speeds, and energy savings compared to fans running at constant full speed.