Understanding Occupancy-Sensor Technology
April 21, 2009
This is Chris Matt, Associate Editor of Maintenance Solutions magazine. Today’s tip is understanding your options when specifying occupancy sensors.
To eliminate energy waste, most energy codes require some way to automatically shut off lights when not in use, either based on a schedule or on occupancy. Occupancy sensors are lighting controls that automatically turn off lights in unoccupied spaces, reducing energy costs by reducing energy waste.
Occupancy sensors use different technologies — including passive infrared, ultrasonic and dual-technology — to detect the presence or absence of occupants in a space. Passive-infrared sensors require a direct line of sight between the sensor and occupants in a space. Because of this requirement, managers can strictly define the sensor’s coverage.
Ultrasonic sensors detect the presence of people by sending out ultrasonic sound waves into a space and measuring the speed at which they return. They look for frequency changes caused by a moving person.
Dual-technology sensors use both passive infrared and ultrasonic technologies, activating the lights only when both technologies detect the presence of occupants. This setup virtually eliminates the possibility of false-on problems, and requiring either technology to hold the lights on significantly reduces the possibility of false-off problems.
Appropriate applications for dual technology include classrooms, conference rooms and spaces where a higher degree of detection is desirable.
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