S o l a r – o p t i c a l P r o p e r t i e s o f V e n e t i a n B l i n d s
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Results and Discussion
Figures 6-10 show the comparison of the computed blind solar transmittance with in situ
experimental data. For each simulation run, the slat was divided into five equal elements
and the profile angle of the incident solar beam radiation specified. For the calculation of
the profile angle, ASHRAE (2001) procedure has been used.
Figure 6 shows the venetian blind transmittance obtained numerically and experimentally
at 10h and 14h near the autumnal equinox and under clear sky conditions, for different
slat angles (0º, 30º, 45º, 60º and 90º). As expected, as the slat angle increases the blind
solar transmittance decreases. The numerical results agreed quite well with the
experimental ones at 10h, whereas some discrepancies were found for slat angles of 45º
and 60º at 14h. As referred before, during the morning the incident radiation on the east-
facing fenestration system has both direct and diffuse components and during the
afternoon it mostly comes from diffuse radiation. Therefore, the numerical model predicts
better the total (direct + diffuse) blind transmittance than the diffuse blind transmittance.
Figure 6: Comparison between numerical and experimental results of venetian blind solar
transmittance at 10h and 14h for different slat angles.
The same conclusion can be drawn from Figures 7, which shows the measured and
predicted solar transmittance for the venetian blind oriented at 0º, 30º, 45º and 90º slat
angles, respectively. Similar discrepancies between numerical and experimental results
were also found in Chantrasrisalai and Fisher (2006) and Chaiyapinunt and Worasinchai
(2009) studies when incident solar radiation is mostly diffuse.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
15
30
45
60
75
90
Slat angle
ψ
(º)
Venetian blind transmittance
Exp10h
Num10h
Exp14h
Num14h
