ASHRAE Journal - September 2013 - 47

Technical FeaTure
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commissioning authority should also ensure proper
training of the building owner or operator to ensure
persistent savings. User interfaces, calibration steps
and equipment locations must all be taught and well documented to the operator during this training step, allowing them to make ongoing adjustments for occupant
complaints and building modifications.
Calibration and functional testing controls are steps in
this commissioning process that are critical to successful implementation and energy savings.6 Calibration
is sometimes blended into the functional testing task,
though ideally the calibration would be finished and
then separate functional tests completed to ensure steps
from installation to calibration were done correctly.7 In
an ideal process, the contractor would complete start-up
and calibration, and a commissioning authority would
simply verify that the calibration and necessary illumination tests had occurred. In practice, it is most important that somebody at the very least calibrates the system.
Most of the system problems that we encountered could
be solved if this process was completed. In fact, as part
of our study we went back to each system and recommissioned them to measure the impact on performance.
Primarily, we followed the recommended calibration processes to adjust the daylight sensor and controller settings
to achieve adequate light levels at the critical work plane*
with minimum possible energy consumed. This process
aims to optimize the settings in Table 1. All that is needed
for the process is knowledge of the controls (including
locations), design illumination targets, and a light meter
for determining that design illumination is met.
Our study found that with these steps in place these
systems save substantial energy, and can be economically justified. More importantly, the study showed that
these key commissioning steps were critical to making
the technology justifiable.

What We Did
The Spaces
We began our study by locating buildings throughout
Minnesota and Wisconsin that used daylighting controls.
Of a larger sample set that included a range of building
types, we chose 20 spaces for in-depth study. The spaces
were chosen to be significantly different in orientation, usage, and perceived level of commissioning in an
attempt to achieve a diverse sampling of spaces.

Table 1 Six key items to be adjusted during daylighting control calibration.
SenSor locaTion

Sensor Should be Located Over a Workplane

SenSor orienTaTion

Sensor Should See Reflective, Representative Space

SenSor Shielding

Sensor Should Not Receive Direct Light

gain

Tune to Design Light Level + Lumen Depreciation

Fade raTe

Fade Rate Should be Long (~1 Minute)

deadband (iF STepped)

Deadband Should be Long (Several Minutes)

Data Collection
We collected data over three separate periods of time
to demonstrate the effect of commissioning. In Period
1, the control system was monitored in its as-found
state. In Period 2, the daylighting controls were disabled (other lighting controls remained functional)
such that the system would behave as if it never had
daylighting controls. Then, prior to Period 3, we completed a basic recommissioning of the system, with
the help of knowledgeable technicians. This process
included calibration of the key items discussed previously, and listed in Table 1.
In each space we installed continuous monitoring
equipment to collect several data points across all periods, beginning on Jan. 13, 2012, and concluding at the
end of Period 3 on July 10, 2012. For more information
regarding our monitored spaces and data points, refer to
our full report.4

Methodology and Analysis
Two different savings metrics were key outcomes of
this study: the energy savings from a typical daylighting
control system (measured in Period 1) and the energy
savings from a fully commissioned system (Period 3).
We calculated each metric for the luminaires controlled
by the daylighting control system. The measured lighting energy power was calculated using monitored
electrical current, along with spot measurements of
voltage and power factor. This calculation is represented in Figure 1, in which the energy usage of Period 1
and Period 3 is shown in yellow, while the energy savings is shown in orange. Recall that the energy savings
in Period 3 includes additional savings realized by full
commissioning.
But the primary goal of our study was not to look at the
architectural or lighting design impacts on daylighting

*The critical work plane is the location that receives the least daylight within the zone of controlled light.
Septem ber 2013

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