Consulting-Specifying Engineer - June 2008 - (Page 67)

Equipment Lifecycles Specify the optimal occupancy sensor Consideration of each application will maximize energy savings and occupant satisfaction. BY ERIC FOURNIER, Product Manager, Watt Stopper/Legrand, Santa Clara, Calif. ccupancy sensors are proven energy savers that meet code requirements, facilitate sustainable construction, and provide convenient lighting control. But with the breadth of products now available, how does one select the right sensor for a given application? Because sensor selection is key to proper operation and occupant satisfaction, this is an important question. To choose the optimal sensor, a specifier must consider certain characteristics of the space that will be controlled, as well as how occupants will use To choose the optimal lighting the space. sensor, a specifier must consider Occupancy senhow occupants will use the space. sors use passive infrared (PIR) technology, ultrasonic technology, or both technologies to detect motion. Traditional occupancy sensors turn lighting on when a space becomes occupied and provide energy savings by turning lights off, following a time delay, after the space becomes unoccupied. Greater energy savings are achieved by providing a switch for the user and configuring the occupancy sensor for manual on-operation. This way, the lights are turned on only if they are needed. Space evaluation Identifying the ideal occupancy sensor for a particular application begins with examining the size and shape of the area to be sensed, O including determining the location of the work area(s), furniture, partitions, suspended lighting fixtures, doors, windows, and HVAC ducts and fans. Ceiling height also is important, as is knowing what kind of activity will occur in the space. Understanding how sensing technologies detect motion helps recognize why different sensors work best under different circumstances. PIR technology detects occupancy by sensing the differences in the heat emitted by humans in motion from that of the background space. PIR technology requires an unobstructed line of sight for proper sensing. This characteristic creates the opportunity to cut off coverage and prevent sensing of adjacent areas. PIR sensors are a good choice for individual offices, spaces with unobstructed views, and spaces with high ceilings, including lobbies and warehouses. Ultrasonic technology uses the Doppler principle to detect occupancy; ultrasonic waves are emitted throughout a space, and shifts in the returning waves indicate motion. Because ultrasonic coverage does not have a clear cut-off and can see past partial obstructions, these sensors are ideal for areas with partitions and enclosed spaces with normal height ceilings. Use ultrasonic sensors for groups of office cubicles, multi-stall restrooms, and enclosed hallways and stairwells. High levels of airflow can disrupt ultrasonic sensing, so these sensors should be located at least 6 ft. from HVAC ducts. Consulting-Specifying Engineer • JUNE 2008 67

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Consulting-Specifying Engineer - June 2008 Contents Viewpoint Letters News M/E Roundtable No Gambling Allowed on Smoke Control in Las Vegas Be Prepared: Hospital Protections for Catastrophic Events Ready for Retail Commissioning Documents: Necessary Evil Codes & Standards Codes & Standards Case Study Equipment Lifecycles New Products Advertiser Index Green Space

Consulting-Specifying Engineer - June 2008

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