Occupancy Sensors

Occupancy sensors reduce energy consumption by only activating lighting if people are present. They use a variety of techniques or a combination of detection mechanisms such as infrared, acoustic, microwave or ultrasound to sense human presence.

The primary role of occupancy sensors is to save money. This point is of primary consideration because the occupancy sensor must pay for itself through savings in electricity. There is no point in installing occupancy sensors merely to “go green” as the manufacture of the sensors produces a carbon footprint in itself.

An occupancy sensor consists of a motion detector to sense human presence, a switch to turn the lights on and a timer to keep the lights on after movement has been sensed. Size, shape and positioning can include:

• Ceiling mount (for multi-lamp control).
• External luminaire mount (for individual lamp control).
• Internal luminaire mount (for individual lamp control behind lens).
• Wall switch mount (replaces wall switch).

A complete sensor unit usually consists of a motion detector, a photocell, a timer and a switching relay. Three user adjustable controls are usually provided: sensitivity, photocell lux level and time delay.

Installation criteria

Consider the mode of occupation, i.e. predicted traffic and direction of movement. Small movements are always difficult to detect and in such instances, the time setting should be set on maximum. Do not install sensors in spaces where there are extremely low levels of occupant motion.

Wall-mounted sensors are better suited for smaller rooms such as offices or restrooms, and equipment rooms (such as printer or copier rooms) where people are only likely to be present for short times after they walk by the sensor. In an open-plan office or where the lighting load is higher, mount the sensor in the ceiling.

Install sensors carefully. Sensors are easy to spot and people might be tempted to adjust, steal, or vandalise them, or they may just try to fool the sensors into perceiving a human presence when a space is unoccupied. Position the sensors carefully and train building occupants on their purpose to ensure continued energy savings.

Involve building personnel in planning for the sensors. Understand local occupancy patterns. Occupancy sensors generate the greatest savings in spaces where occupancy is unpredictable or intermittent.

Train maintenance personnel and office occupants to keep sensors operational rather than disconnecting them as problems occur.

Determine the range of detection coverage. Position sensors so they only “see” the area intended to be observed – the most common cause of false triggering is incorrect positioning. Line of sight must be maintained between the sensor and the occupant except in the case of an enclosed space with hard surfaces covered by a microwave sensor. View the sensor specifications to determine the amount of coverage that will be provided to the space by the sensor. This will aid with choosing the number of sensors required to cover an area properly and where to place them.

Position sensors away from air ducts and windows. Do not install sensors within 2 – 2,5 m of HVAC outlets or heating blowers.

Calibrate the sensor. It will be provided with manufacturer-default settings for sensitivity to magnitude of motion and time delay before switching the lights off. The default time delay may be from 30 seconds to 15 minutes. Calibrate the sensor to specific conditions in the space for best performance.