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

assumed that the slats are adjusted to eliminate
direct transmission of solar beam, as well as
that the slats are perpendicular to the solar
beams. The shading provided by the interior
blinds was estimated on the basis on EN 13363,
according to which the visible transmittance of
an assembly composed by clear glazing and
interior blinds with a slat inclination of 45 o is
considerably decreased [3], resulting in a
glazing transmittance equal to 40% and total
solar energy transmittance equal to 0,45. These
values were incorporated in the description of
Model-3. In order to extract comparable results
for the thermal simulation, it was assumed that
the U-value of the glazing of Model-2 and
Model-3 remained unaffected.
The analysis of the conditions prevailing on the
reference model (Mod-0) and the models of the parametric
study (Mod-1 to Mod-3) included both thermal and
daylight aspects and was conducted by means of
simulating programs.
More specifically, the computer program ADELINE
was used for daylight estimations. The calculation
technique used in ADELINE is based on the exchange of
radiation flux between surfaces (radiosity method), in
which space surfaces are divided into a mesh of small
elements and the amount of light distributed from one
mesh element to another is calculated [4]. Main criteria for
the analysis were the average values and the distribution of
daylight factor, as well as the estimation of the percentage
of time during which autonomy in lighting was achieved
calculated on an annual basis.
Thermal conditions were simulated with SUNCODE,
an hourly simulation model, which incorporates detailed
solar algorithms designed for use in multi-zone structures
and is appropriate for most residential and small
commercial buildings [5]. The estimated differences in the
loads covering the heating and cooling requirements
between the examined models were the criteria for the
assessment of thermal conditions.
By the comparative analysis of the results, the impact
of sun shading on thermal and daylight performance is
highlighted and the assessment of the optimal selection for
sun protection for each case is enabled.
3. Parametric study
3.1 Assessment of the daylight conditions
The evaluation of the daylight conditions was based on
quantitative criteria: daylight factor is regarded as the
most appropriate indicator for the adequacy of lighting
indoors. It represents the illuminance at a specified point
indoors, expressed as a percentage of the simultaneous
horizontal illuminance outdoors under an overcast sky.
The orientation of the opening does not play an
important role on the determination of daylight factor,
since the standardized overcast sky presents only
altitudinal asymmetry, featured by illuminance at the
zenith three times greater than on the horizon [6]. On the
contrary, differentiations on the angular height of the
visible sky patch and on the glazing transmittance
influence the daylight factor patterns significantly.
The mean value of daylight factor prevailing on the
working plane of the models is presented on Figure 2.
In the case of a horizontal projection (Mod-1), the
daylight factor is reduced by 14,5% compared to the
relevant conditions prevailing on the unobstructed
reference Mod-0. The basis of daylight reduction is
depicted from the distribution of daylight factor across
the symmetry axis of the working plane of the
examined modules, which is displayed on Figure 3. For
Mod-1, areas along the opening receive less daylight
than the respective surfaces of reference case Mod-0.
The effect of the overhang is obvious in areas with
depth reaching the center of the space. On the contrary,
there is not any remarkable differentiation in daylight
factor on areas located close to the rear wall. This is
due to the fact that the overhang blocks the view of the
Mean daylight factor [%]
8%
7%
6%
5%
4%
3%
2%
1%
0%
4,9%
4,2%
2,7%
2,2%
Mod-0 Mod-1 Mod-2 Mod-3
Type of shading device
Reference case Overhang
Reflective glazing Venetian Blinds
Figure 2 The average daylight factor prevailing on the
working plane of the examined models.
3
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