Incorporate
Occupancy Controls in Zones
with Intermittent Use
Use occupancy
sensors to control lighting, heating and cooling according to
motion detected within an intermittently occupied area. Occupancy
sensors can save up to 80% of the lighting and HVAC energy when
properly applied. There are three basic sensor technologies:
infrared, ultrasonic, and acoustic.
Infrared
(IR) technology senses body heat. IR requires a straight “line-of-sight”
in order to operate properly. IR is ideal for small offices
and other regularly shaped rooms as well as high spaces (auditoriums,
open classrooms, large open offices with low or no partitions,
factories and other large work facilities).
Ultrasonic
(US) technology emits a high-frequency sound that reflects off
room surfaces. US sensors have good sensitivity and range where
small motions must be detected. They suit irregularly shaped
spaces and room obstructions such as medium to high partitions,
large furniture or structural columns. Due to the high sensitivity
associated with US, air currents or other small movements produced
by the ventilation system or motion in adjacent spaces may trigger
false-on conditions, requiring attentive calibration.
Ultrasonic
sensors are available in a variety of frequencies; be sure to
note any other ultrasonic emitting equipment on the job and
specify a distinct frequency for each controller. Check that
sensor frequency does not overlap hearing-aid frequency.
Acoustic
or audible sensors rely on voices, machinery sounds, keyboard
tapping and other typical daily noises. Background noise, such
as a constant hum, and low-level noise are ignored. This technology
works well in areas with high partitions or other obstructions,
or high air movement within the space during unoccupied periods,
such as kitchens and large washrooms.
Dual or
triple technology sensors are available, as are intelligent
sensors that self-adjust to occupancy data collected in a prescribed
“learning period”. These sensors also reduce false-on
and -off conditions. However, they must still be properly located,
adjusted and calibrated in commissioning, and regularly maintained.
Sensors
have a field of view. Take care in locating the mounting position
to cover the occupied area of interest according to the manufacturer’s
recommendations; the correct position will vary with the sensor’s
coverage pattern. Over-coverage can result in false-on signals;
under-coverage can result in false-off.
Two commissioning
adjustments are critical for energy savings and occupant satisfaction:
- time-out
– how long equipment will remain on after last detection
of motion. This will vary with the space use, and should be
adjusted after occupancy.
- sensitivity
– how small a change in infrared heat, movement or noise
is required to trigger the sensor. Adjustment is important
to prevent false-on and false-off signals.
These should
be adjusted after lamps and sensors are installed, room furnishings
are in place, fluorescent lamps have burned-in for 100 hours,
and HVAC systems are operating.
Important
options available include:
- manual-on/automatic-off
with manual-off option – requires occupant to physically
turn the equipment on initially. Equipment and be turned off
either automatically or manually.
- lights-out
warning – an audible or visible (lights flicker) indicator
that lights will be turning off in one minute (time should
be adjustable).
- coverage
mask – to allow certain areas to be deleted from the
coverage of the sensor, to prevent false-on.
- combined
daylight sensor and control.
Cautions
- It is
hard to predict “dead spots” (areas where sensor
cannot detect) without knowing furniture location.
- Commissioning
is critical for proper operation and energy savings.
- System
must be periodically maintained and tested.
- Hours
of fluorescent lamp life will be reduced (up to 40%), but
calendar lamp life will be extended.
- Occupant
education is often required, especially during “learning
period” of intelligent sensors.
