Occupancy Sensors/Motion Detectors Explained by Engineers
Posted on Thu, Jan 19, 2012 @ 10:15 AM
Sarah Douglass
sdouglass@tesengineering.com
ASHRAE 90.1 requires any building larger than 5000 square feet have interior lighting controlled to shut off in all spaces automatically. Examples of an automatic control device include a time-of-day device like a time clock, a central lighting control signal, an energy management system, or an occupancy sensor. Occupancy sensors are one of the most commonly used devices for controlling interior lighting and meet the requirements of ASHRAE 90.1.
Passive infrared (PIR) occupancy sensors sense heat and motion in a space and adjust the lights accordingly. These sensors require a direct line of sight and have a limited sensitivity of 15 feet or less. An alternative to this type of device is ultrasonic sensors. They emit a high frequency signal that senses sound and motion. These sensors are able to see around corners and objects, allowing them to have coverage up to 25 feet.
High-mounted sensors are another option and can be mounted on the ceiling, high on the wall, or in a corner. These are used in large areas that may contain obstacles, corridors, or aisles. These sensors are 2 to 3 times more costly to install, but are very economical if used to control several large zones.
Wall-mounted sensors are usually used in small, enclosed spaces since they require a direct line of sight between the sensor and the task area. These sensors are inexpensive and very easy to install. Workspace sensors are used in individual cubicles. They are connected to the power strip within the cubicle and are used to control lights as well as plug in loads such as radios or heaters.
Small spaces may only require one sensor while larger areas may need several sensors, each covering a different own zone. Coverage zones of a large area should overlap by 20% in order to ensure the system will not result in false on/offs. Each sensor has adjustable time delays and sensitivities, allowing the coverage system to be customized to the space it is in. Time delays of 15 minutes are usually recommended and sensitivities must not be set too high or else the sensor will pick up changes that do not require the lights to turn on.
Choosing the correct sensor and technology are very important when using occupancy sensors to control lighting within an area. TES Engineering is happy to assist you with your next lighting project. Click below to talk with an engineer today.
