Occupancy Sensors: Steps for Success

Jan. 22, 2007
An element of any successful lighting-control system, occupancy sensors are reliable and energy efficient when installed correctly

Lighting experts agree: An integrated lighting-control system is the best way to maximize occupant comfort and energy savings, and occupancy sensors can help you achieve a balance between these two goals. Once thought of as “those things you have to wave your hand in front of,” the correct application and installation of occupancy sensors can make your facility’s system more reliable and sustainable.

Why does my facility need occupancy sensors?
The most common and convincing argument for installing sensors is sustainable as well as cost effective: managing your energy usage. Just how much can you save in energy costs? “Generally, 20- to 30-percent savings over purely manual control is a realistic expectation for both new construction and retrofits. In the case of a retrofit, if the sensors are installed along with more energy-efficient lighting fixtures, the combined savings can be even more dramatic - 50 to 70 percent, depending on the type of lights that are being replaced,” claims Rich Westrick, director of embedded controls at Conyers, GA-based Lithonia Lighting.

Where can I best utilize occupancy sensors?
Offices where employees are often coming and going in the evenings and over the weekends are a perfect candidate. The ideal places for sensors in schools are gymnasiums and stack areas in libraries. With 24/7 occupancy and many unused aisles and areas, warehouses are another type of facility that can see significant energy savings from sensors. However, every building can benefit from the use of occupancy sensors in some capacity. Restrooms, copier rooms, hallways, and storage areas are all strong applications for the technology.

How do I choose the right type of sensor?
There are three main types of occupancy sensors. Passive infrared (PIR) occupancy sensors detect body temperature in a room, but require a clear line of sight to operate most effectively within their 15-foot field of view. They are best utilized in small enclosed spaces like private offices. Using high-frequency sound to detect motion, ultrasonic sensors can “hear” around corners, through walls, and through other objects, but are the most sensitive to false triggers by vibrations (such as those from an HVAC system). Ultrasonic sensors are well suited for larger spaces with multiple obstructions and for low-motion areas such as restrooms. The third type - dual technology - has a higher price point, but the fewest instances of false triggering because it combines PIR and ultrasonic methods. “We recommend dual technology in conference rooms or large executive offices,” says Jon Null, director of marketing for occupancy sensors at Santa Clara, CA-based Watt Stopper/Legrand.

Once you have chosen the right type of occupancy sensor for your application, make sure it is installed in the correct location. Use wall-mounted sensors in smaller spaces (bathrooms, offices, copier rooms) and ceiling-mounted sensors in larger areas with high lighting loads (open offices).

In addition to choosing the right type of sensor, train your maintenance staff and building occupants to keep the devices operational and to report any instances of false triggering. “When [the technology] is applied right - and that really falls on the building manager - then the false offs and false ons are minimized, and they’re very reliable devices that last a long time,” says Null.

How reliable are they - really?
Past reliability concerns have turned off some building professionals, but experts stress that choosing the right sensor for the application will ensure effectiveness. For example, installing a PIR occupancy sensor in a bathroom might leave an occupant in the dark if partitions interfere with the direct line of sight that is necessary between the sensor and the occupant. “Improved technology has helped prevent such problems. “[Some occupancy sensors] will learn from their own mistakes, so to speak,” says Ken Walma, product manager for Coopersburg, PA-based Lutron Electronics Inc. “If they see themselves tripping on and off, over and over again, they’ll adjust themselves to not do so as much.” Westrick adds, “This allows [sensors] to work much more reliably and in a wider variety of installations with less hassle than they could in the past.”

Lighting experts emphasize that occupancy sensors are only the first step in making your lighting system more sustainable. Integrating other technologies (such as daylighting, personal controls, and dimming) can further reduce energy usage.

Anne K. Goedken ([email protected]) is new products editor at Buildings magazine.

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