afst.bundel 8 MEI 07 - Technische Universiteit Eindhoven

Figure 2 Mixing range of Dynamic Lighting system and the CIE daylight
locus
also disrupt the required CCT-curve.
Based on this observation, the aim of this project was to
quantify the amount and colour of daylight that reaches the
work plane of a standard open plan office over the course of one
year, and to assess whether or not it is possible to maintain the
Dynamic Lighting curves. This data was obtained for different
window orientations and sizes, and repeated for four geographical
locations in Europe (approximately 1,000 km apart).
Automatic blinds blocked out any direct sunlight, and standard
clear glazing was applied.
The amount of daylight was accurately simulated with DAYSIM,
an add-on program to Radiance that efficiently calculates the
work plane illuminance for any location and geometry.
Additionally, one-year measurements of the daylight CCT in
Lyon, France (courtesy of ENTPE) were processed and analysed
to obtain factual values for the bandwidth of daylight CCT over
the course of one year. In these measurements, the daylight
CCT was logged every 10 minutes for 12 months and for four
orientations.
After the amount and colour of daylight had been quantified,
day-by-day curves were constructed that evaluated: (1) how much
the lighting system could be dimmed in response to the influx
of daylight, i.e. the daily energy savings; and (2) if it was
possible to maintain the CCT-curve by adapting the CCT of the
lighting system in response to the colour of daylight. These
results were then contrasted to a less complex energy saving
solution: time switching, which simply turns off the lighting
system when a threshold-value is crossed. From this analysis
several implementation strategies for Dynamic Lighting systems
in daylit offices were put together.
Conclusions
First, it was found that with daylight responsive control the
Dynamic Lighting illuminance curve could be maintained very
Figure 3 Calculation of average illumination of the control area of a light
sensor
well in the second and third zone behind the window over a
long period of time. Energy savings up to 67% are achievable in
these zones. However, in the first zone behind the window it
was found to be much more difficult to maintain the illuminance
curve. This is because the system is dimmed completely over
long periods of time, resulting in an illuminance curve that
follows the colour and luminance of the sky. It is therefore
better to use a different lighting concept for this zone, for
instance a regular 500 lx lighting solution. It is not possible to
maintain the correlated colour temperature curve by mixing
daylight with the artificial light. This curve is disrupted too
much by daylight to maintain over long periods of time.
Second, the results of this study indicate that with time switching,
comprising a much simpler modification of the original
lighting system, it is also possible to use Dynamic Lighting in
daylit offices. This method does not use real-time measurements
but uses a pre-set condition for each month: the lighting system
either provides the Dynamic Lighting curve for the whole
month, or it provides a constant output of 500 lx.
This resulted in far lower annual energy savings (up to 12%) for
the second and third zone behind the window. Similarly to the
first strategy, it is also better to use a regular lighting solution
for the zone directly behind the window since this the Dynamic
Lighting curve cannot be realised for the larger part of the year.
Also, it is not possible to maintain the required CCT curve.
In general, therefore, it can be concluded that Dynamic Lighting
can be successfully implemented in daylit offices bearing in
mind that: (1) it cannot be used in zones directly behind the
window, and (2) the correlated colour temperature cannot be
controlled. With a simple modification of the original system it
is possible to achieve small energy savings. A drawback of this
method is that the illuminance curve is always distorted by
daylight. With a more complex modification of the original
system it is possible to achieve larger energy savings, while
maintaining the illuminance curve very accurately.
afstudeerbundel faculteit bouwkunde
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