The North Carolina State energy office reports that the typical office spends 29 percent of its electrical energy costs on lighting. Occupancy sensors can reduce these charges by 50 percent or more, at a savings of 5 to 20 cents per square foot. Additional applications for occupancy sensors include increased security and reduced light pollution.
There are three common types of occupancy sensors used today, according to Michael Jouaneh, marketing manager for Lutron Electronics Co. Inc., Coopersburg, Pa. Ceiling-mounted sensors are used typically in larger spaces with ceilings less than 12 feet high, wall-mounted sensors for spaces with pendant light fixtures or ceilings more than 12 feet high, and wall-switch models that replace standard on/off light switches for smaller, enclosed spaces.
“Occupancy sensors are ideal for spaces where the automatic shutting off of light is desirable, such as classrooms, meeting rooms, lobbies, open and private office spaces, restrooms and storage areas,” Jouaneh said.
The technologies that drive occupancy sensors include passive infrared (PIR), ultrasonic and a combination of the two, according to Bob Freshman, marketing manager for Leviton Manufacturing Co. Inc., Little Neck, N.Y. PIR sensors detect differences in temperature between the person and the space and are best used for detecting major movements, while ultrasonic sensors emit very high-frequency sound waves and measure the echo to determine if a space is occupied.
“Ultrasonic sensors are more sensitive to small movements, such as someone sitting at a desk and typing,” Freshman said.
The combination, or multitech, sensor uses PIR technology to turn lights on in the space, and ultrasonic technology for maximum reliability during occupancy.
“With dual-technology sensors, the user can choose which technology should be used to detect movement and which technology is used to maintain lighting. Such flexibility is great for use in conference rooms or classrooms,” said Ed Uftring, product manager for Watt Stopper/Legrand, Santa Clara, Calif.,
For residential applications, occupancy sensors allow users to either turn lights on and off automatically or to turn lights on manually and off automatically, said Cheryl Samartano, residential lighting controls product manager, Leviton.
Occupancy sensors save building owners significant energy, often with a payback of less than two years, Uftring said.
In outdoor applications, such as parking lots, they also serve a safety function, potentially saving lives and money from a law suit.
Other benefits of using occupancy sensors are convenience and compliance with energy codes, Jouaneh said.
“Occupancy sensors save energy by ensuring that lights are not left on when a space is unoccupied. They add convenience by automatically turning lights on or off, depending on occupancy. And they comply with building energy codes by meeting automatic lighting shutoff mandates,” he said.
“In addition to reduced energy costs, occupancy sensors help businesses, in some cases, become eligible for government rebates,” Uftring said.
On the national level, the Energy Policy Act of 2005 created accelerated tax deductions for using energy-efficient lighting or control technologies, such as occupancy sensors, in new construction and retrofit applications; 2007’s Energy Independence and Security Act extended these deductions until 2013. California’s Title 24, which specifies lighting power density maximums, is quickly becoming a guideline across the nation for mandating energy efficiency, according to Freshman, and applies to both residential and commercial applications.
“Title 24 requires newly constructed home be wired with high-efficacy lighting, such as fluorescent, compact fluorescent or high-intensity discharge (HID) lamps. If nonhigh-efficacy lighting has been installed, a manual on/automatic off occupancy sensor switch or a dimmer switch must be installed to comply with the standard,” Samartano said.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 90.1 has been adopted by most states and specifies the amount of wattage per square foot required for lighting to achieve high--efficiency levels.
“Occupancy sensors, daylight harvesting and relay controls are some of the ways buildings can comply with mandated energy-efficiency building codes,” Freshman said.
Wireless technology is the next major advancement for occupancy sensors, which allows the sensor to communicate through a radio signal to a wall switch with a built-in radio receiver. The sensor is placed on the ceiling and the standard light switch is replaced with a compatible dimmer or switch.
“The biggest cost for retrofitting a building for occupancy sensors is the materials and labor to run wires. If that cost is eliminated, the entire installation can be accomplished in about a quarter of the time and at about half the cost,” Freshman said.
BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 or firstname.lastname@example.org.