12/03/2001

Occupancy Sensors

Take Control - Part 2 of 4

Contributors: James Earl  
 

Improved technology has made occupancy sensors the most popular component light control solution on the market. Both ceiling-mounted or wall-box occupancy sensors survey a room through passive infrared, ultrasonic, or a combination of the two technologies (dual-technology) to determine if a space is occupied. If the sensor does not detect the presence of anyone after a preset amount of time, the sensor will turn off the lights. When the space detects an occupant, lighting will resume.

"Occupancy sensors are very effective at what they do, if they are applied properly," says Baselici. Selection of the right type of sensors and their mounting location can mean the difference between a major annoyance and a valued energy saver. Passive infrared (PIR) occupancy sensors respond to the heat energy emitted by humans and adjust lighting according to the detection of occupants in a space. PIR sensors must have an unobstructed "line of sight" to determine occupancy. For example, a wall-box PIR occupancy sensor in a restroom will not "sense" individuals behind partition walls. These sensors are most often employed in corridors, lobbies, or copy areas where large movements are common.

Conversely, ultrasonic occupancy sensors detect occupancy by emitting sound waves (at high, inaudible frequencies) that are reflected from a room's surfaces back to the sensor. When there is motion in the space, the frequency of these reflected waves is altered and lights are activated. Ultrasonic sensors are more capable of detecting occupancy in areas with partitions and other obstructions. However, the situation has to meet certain requirements (such as an enclosed space with hard surfaces that will easily reflect sound waves). The benefit of ultrasonic sensors is their ability to detect small movement, like a person sitting at a desk typing. However, small air currents moving a curtain can also trigger the system to activate lighting in an unoccupied space.

Dual-technology occupancy sensors combine both infrared and ultrasonic technology at a higher cost. Thought to be "the best of both worlds," dual-technology sensors minimize false on/offs.

Retrofit in some applications can be as simple as replacing a manual on/off switch with a wall-box occupancy sensor. "If you can replace a wall switch with an occupancy sensor, you can typically pay that back in three years," explains Alfred R. Borden IV, IALD member and president of The Lighting Practice, Philadelphia. Regardless of whether wall-box or ceiling-mounted sensors are selected for a space, serious consideration needs to be given to the sensors' area of coverage and coverage pattern. Borden suggests that 30 days after an installation, sensors should be checked and adjusted to make sure that they are working as intended.

Figure 2: Operating Cost Comparison: Private Office, 128 sq. ft.
Performance
Base Case
Occupancy Sensors
Daylighting
Occupancy Sensors + Daylighting
Annual Energy Use*
450 kWh
340 kWh
330 kWh
250 kWh
Annual Energy Cost
$33
$24
$24
$18
Annual Energy Cost Savings
-
$9
$9
$15
* Average daily "on" hours for wall switch is 14.7. Average daily occupied hours for the office is 12.9.
Source: US Dept of Energy

Figure 3: Operating Cost Comparison: Open Office Area, 1,000 sq. ft.
Performance
Base Case
Time Scheduling
Occupancy Sensors
Daylighting
Time Scheduling + Daylighting
Annual Energy Use*
5,700 kWh
5,100 kWh
5,000 kWh
4,200 kWh
3,700 kWh
Annual Energy Cost
$340
$305
$300
$250
$220
Annual Energy Cost Savings
-
$35
$40
$90
$120
* Average daily "on" hours for wall switch is 9.1. Average daily occupied hours for the office is 6.8.
Source: US Dept of Energy
 

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When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.

Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.


Mitsubishi Electric’s H2i R2-Series heat pumps provide 100% heating capacity down to 0° F and simultaneous heating and cooling down to -4° F delivering year-round comfort, regardless of climate zone.

 
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