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Occupancy-Sensor Savings


Occupancy sensors are rapidly becoming a standard feature in new buildings (and a successful addon in retrofits) across the commercial sector, and retail is no exception. By turning off the lights when a space is unoccupied, occupancy sensors eliminate wasted energy. According to the U.S. Environmental Protection Agency (EPA), the savings can range from 30% to 90% in restrooms, 45% to 80% in storage areas and up to 50% in offices.

In addition, occupancy sensors can enhance security and reduce light pollution, a growing concern throughout the nation, by reducing the use of outdoor illumination.

Occupancy sensors provide higher energy savings in spaces that are used either infrequently (left unoccupied for two or more hours per day) or unpredictably. In retail facilities, these include restrooms, offices, break rooms, warehouses, back rooms and storage areas.

There are three main types of sensors. The most popular methods are passiveinfrared (PIR) and ultrasonic. A third—dual-technology sensors—utilizes both methods. Each sensor type has features that make it more suitable for some applications than others. As a result, it’s important to match the technology to the specific application, taking into account the area to be lit and the types of surfaces in the space.

Here is a brief overview of the different sensor types, and some application tips from the Lighting Controls Association (LCA), an adjunct of the National Electrical Manufacturers Association (NEMA), Rosslyn, Va.:

PIR sensors sense the difference in heat emitted by humans in motion from that of the background space. These sensors detect motion within a field of view that requires a line of sight. They cannot “see” through obstacles and have limited sensitivity to minor hand movement at distances greater than 15 ft.

PIR sensors are best-suited for smaller, enclosed spaces (wall-switch sensors), spaces where the sensor has a view of the activity (wall- and ceiling-mounted sensors), and outdoor areas and warehouse aisles;

Lights OFF

Impressive energy savings are not the only factor driving the use of occupancy sensors. All state energy codes in the United States are required to be at least as stringent as the ASHRAE/IES 90.1-1999 standard, which requires, with few exceptions, automatic shut-off of lighting in commercial buildings greater than 5,000 sq. ft. There are two options for providing the automatic shut-off: programmable timescheduling devices or occupancy sensors.

Ultrasonic occupancy sensors utilize the Doppler principle to detect occupancy by emitting an ultrasonic high-frequency signal throughout a space. They sense the frequency of the reflected signal and interpret a change in frequency as motion in the space. These sensors do not require a direct line of sight. Instead, they can “see” around corners and objects. This technology has proven to be the most effective method for detecting small body movements, according to the LCA.

Ultrasonic sensors are most suitable for restrooms, spaces with obstacles and open spaces. They are incompatible in spaces with high ceilings (greater than 14 ft.), spaces with high levels of air flow, and open spaces that require selective coverage, such as control of individual warehouse aisles; and

Dual-technology sensors employ both PIR and ultrasonic technologies, activating the lights only when both technologies detect the presence of people, which virtually eliminates the possibility of false-on and significantly reduces the change of false-off. They are most suited for applications where a higher degree of detection is desirable, such as conference rooms.

All sensors should activate the lights as soon as a person enters the space, but should not monitor the area outside the door to avoid nuisance switching.

Once the right sensor technology has been selected, it’s crucial to determine the coverage pattern, or the range and coverage area for the sensor based on the desired level of sensitivity. Improper coordination between required coverage area and required sensitivity is a leading cause of application problems.

In a small space, for example, one sensor may easily provide sufficient coverage. In a large space, it is recommended to partition the lighting load into zones, with each zone controlled by one sensor.

Other critical steps to effective performance include:

Mounting: Determine whether the sensor should be installed at the wall switch, wall/corner, ceiling or task; and

Layout: Sensors should be located so they have the least possibility of nuisance switching. They should also activate the lights as soon as the person enters the space, and have a permanent unobstructed line of sight to the task areas.

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