Ingineria Iluminatului - Journal of Lighting Engineering - Prof. Florin ...

Annual autonomy in daylight
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
300 lx
The impact of sun shading devices on the
availability of daylight during the year is presented
on Figures 4 and 5 for two thresholds of lighting
adequacy: 500lx and 300lx respectively. For all
kinds of solar control the availability of daylight is
slightly affected on areas near the window and
close to the rear wall of the model. This is because
the areas along the window receive more daylight
than needed, while on areas close to the rear wall
the daylight levels are formed mainly by the
internal reflections and are not influenced by
exterior elements at a great extend.
When 500lx are regarded as the threshold, the
energy demands of Mod-1 are considerably
increased in the center of the space; the period with
daylight autonomy is decreased by 50% with
respect to the reference case Mod-0. For the same
threshold, the central area of Mod-2 is autonomous
only for the 10% of the annual working hours.
Additionally, the central and rear areas of Mod-3
need artificial lighting during the entire annual
occupancy of the office.
If the activity conducted on the central areas
requires 300lx, the decrease on daylight availability
of Mod-1 with respect to the base case accounts for
27%. Daylight levels prevailing on the center of
Mod-2 are adequate for 40% of the annual
occupancy hours. For Mod-3 daylight autonomy is
restricted to only 10% of the working hours.
Distance from window [m]
Mod-0
Mod-1
Mod-2
Mod-3
0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0
Figure 5 The availability of daylight across the working plane of the examined models, when the threshold for
illuminance is considered equal 300lx.
3.2 Assessment of the thermal conditions
The assessment of the impact of the examined
shading devices on the formation of the indoor
thermal environment was based on the estimation
of the thermal loads (heating and cooling) required
for the achievement of comfort conditions in the
interior of each model. The desired indoor
temperature during the working hours (09:00-
17:00) was considered equal to 20 o C in winter and
26 o C in summer and was achieved with the
operation of the heating and cooling system. The
ventilation rate was set to the minimum required
for office buildings (2ACH) [7], while especially
for the summer period it was assumed that the
openings would allow the inflow of exterior air in
case that the ambient air temperature ranged in
levels lower than the ones prevailing indoors.
Main factors determining the indoor thermal
environment are the properties of the elements of
the building envelope. In Greece thermal protection
was introduced in buildings in the early 80s; the
examined building was erected in the late 50s and
therefore its envelope is not thermally insulated.
The load bearing structure consists of beams and
pillars made of reinforced concrete and the external
masonry is double brickwork. The lack of thermal
insulation and the large opening surfaces result in
extended heat losses during the winter months and
high indoor temperatures in summer. For that
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