Innovations in Comfort, Efficiency, and Safety Solutions.
|Impact of lighting control schemes
on occupant satisfaction and energy
|Sara Gilani, Postdoctoral Fellow
William O'Brien, Associate Professor
long-term study of a new academic building with advanced control
hardware at Carleton University revealed that the overhead
occupancy-based lights in private offices were on 1.6 times as long as
the occupants were present. This motivated us to investigate: why the
lights were on so long, what the corresponding energy implications
were, whether the occupants were satisfied with the lighting controls
and whether the controls could be modified to improve occupant
satisfaction and energy performance simultaneously.
A five-month monitoring study of the existing lighting control scheme showed that many occupants were dissatisfied with the lighting control scheme because it was set to turn on lights automatically despite the good daylight spaces. Many of the occupants took their own interventions without contacting facilities management. A quick modification to the control logic (approximately five minutes per office), whereby DIP switches on each light switch device were changed, yielded energy savings of over 60% while greatly improving occupant satisfaction (based on measurements of one additional year). Aside from the specific findings, this study also revealed the importance of 1) centralizing all building controls functionality (including lighting) into a single building automation system; (2) subtle controls decisions’ impact on overall building energy performance and occupant satisfaction; and (3) continuous monitoring of building performance to identify issues and opportunities.
Hall (formerly River Building) at Carleton University in Ottawa, Canada
is a 17,000 m2 academic building with a variety of functions including
lecture halls, conference spaces, and private offices. It features
dozens of highly daylit private offices around the east, south, and
west-facing facades (Figure 1).
2015, we noticed that occupancy-based lights in the private offices
were on for much of the day, regardless of occupancy. To investigate
the cause of this energy-adverse observation, we performed a monitoring
study. The building is equipped with state-of-the-art controls
equipment (including a DNS-L24 (Figure 2) in every office). However,
the lighting controls in Richcraft Hall are decoupled from the central
building automation system (BAS). To monitor lighting use, we affixed
light state data loggers to the lamps in 25 offices (Figure 3). This
approach required us to manually install the devices, obtain consent
from all office occupants, and collect and post-process frequent data
collection. We collected data for 15 months starting in March 2016.
by the light use monitoring, the lead researcher collected numerous
anecdotes of unsatisfied occupants, as indicated by the photographic
evidence in Figure 4. In contrast to the frequent-cited complaint that
lights automatically turn off as a result of automation (e.g., daylight
or vacancy-based control), Richcraft Hall occupants tended to be
annoyed that the lights were automatically turning on despite often
having ample daylight. The original controls were set to turn on the
lights upon detected occupancy and turn them off 15 minutes after the
last detected motion, during the five-month study period (and since
building occupancy five years earlier).
results of the five-month monitoring study indicated that for the 25
offices, the median ratio of lights on to occupied period was 1.6. In
other words, the lights were on at least 60% longer than necessary (if
the lights were on for all occupied periods). And in fact, most
occupants did not want the lights on even during occupied periods. The
reason for this ratio being above 1.0 is that these occupants routinely
leave their office for meetings and to teach the class. Thus, each
departure event was associated with as much as 15 minutes when the
occupant was not present.
Following the study period, the lead researcher switched
the lighting controls to manual-on/vacancy-off after 30 minutes. In
other words, the occupant must turn on the lights manually, and the
lights turn off after 30 minutes of no detected occupancy. The 30
minutes is used to prevent false negative presence states where the
occupancy sensor fails to detect a near-motionless occupant. The
lighting control product in use required us to change in position of
several DIP switches which we accessed under the cover of the light switch
in each office. However, for the sake of reducing disruptiveness and
manual labour, it would have been ideal if we could make the change
the modification to the controls, the lighting use in the 25 offices
was monitored for an additional 10 months ending in June 2017. The data
show that the simple change of control schemes reduced energy use by an
average of 62% (Figure 5). Moreover, some occupants did not use lights
at all for certain months.
the lead researcher met with the occupants, most occupants revealed
that they are more satisfied with the post-intervention lighting
controls. Only two of the occupants expressed a preference for the
initial controls, as they liked to be able to walk into their offices
with their hands full and not need to turn on the lights manually.
Key lessons learned
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