- Occupancy and vacancy sensors save energy by automatically adjusting lights as needed.
- Sensor types include infrared and ultrasonic, and both wall- and ceiling-mounted units are available.
- Careful placement and tuning are necessary to ensure sensor performance and optimize savings.
Lighting accounts for 40 percent of the electricity used in commercial buildings. Despite the attention paid to efficiency upgrades, great opportunities exist for reducing energy use by simply turning lights off or dimming them as needed. While energy savings can be achieved through education and incentives, it's often difficult to get staff or building occupants to cooperate. An automated lighting control system using occupancy or vacancy sensors is more effective in many cases.
Selection and placement
Proper selection and placement of occupancy or vacancy sensors results in a system that building occupants view as an improvement. Occupancy sensors automatically turn off lights after occupants leave a room and automatically turn them on as occupants enter. Vacancy sensors save even more energy because they turn lights on to reduced brightness levels. However, inappropriate application of these sensors can limit the amount of energy savings and lead to poor, or even unsafe, lighting conditions.
There are two major types of sensors; each has strengths and weaknesses to consider:
- Infrared sensors detect motion from a heat source (such as a person) and therefore need to see the occupant, so they usually don't perform well in restroom stalls or office cubicles. Also, minimal motions (such as typing on a keyboard) aren't always be detected.
- Ultrasonic models detect motion from objects using a form of radar and are good at sensing small movements. They also don't need to see the occupant directly. However, since ultrasonic waves bounce off room surfaces, any movement will alter their return patterns.
Occupancy or vacancy sensors may not be a good fit for every part of your facility. Start by identifying spaces that are unoccupied on a regular basis, such as executive offices, copy rooms, restrooms and conference rooms. Selection of appropriate spaces requires an accurate understanding of how the spaces is used.
For existing buildings, you should measure and document space occupancy by using sophisticated data recorders or by simply having someone walk around at regular intervals to see which spaces are occupied. For high-intensity discharge lamps, occupancy sensors require specially designed stepped-dimming systems.
Installation and coverage
Occupancy and vacancy sensors are available as wall- or ceiling-mounted units. To avoid false detection with ceiling-mounted sensors, it's important to specify a viewing range that matches the application. For example, a hallway sensor should look in two directions but not into an office, while a conference room sensor should pick up motion from anywhere in the room. Some of the most common failures of occupancy control systems are from inadequate sensor coverage or improper tuning of a sensor's sensitivity.
Coverage area of sensors depends on the room arrangement, room geometry, the presence of partitions, type of sensor, location of sensor, sensitivity setting and type of motion. Ultrasonic sensors cover a wider range than infrared sensors, but are more prone to false triggering from air motion. Ceiling-mounted models may cover 250 to 2,000 square feet, while wall-mounted sensors may cover 300 to 7,500 square feet. Larger areas are covered by integrating multiple sensors. Each sensor has controls to adjust the time interval before lights are turned off—typically ranging from 1 to 15 minutes.
Save energy with sensors
When properly installed and located, occupancy and vacancy sensors can significantly reduce your lighting costs, while maintaining comfort, safety and security in your facility.
Image source: iStock
Content provided for SCE&G customers, Powered by Questline RelationshipBuilder. © Questline Inc.