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
321
a.
b.
c.
d.
Figure 1: Experimental setup and measurements instruments: LI-COR LI-200 (a and b) and
Kipp&Zonen CMP3 (c) pyranometers and Campbell CR10X datalogger (d).
The incident solar radiation (
I
) was measured with a Kipp&Zonen CMP3 pyranometer
(Fig. 1c) installed in front of the venetian blind (represented as sensor 1 in Figs. 2a and
2b). The transmitted radiation (
G
2
) through the venetian blind was obtained by a
pyranometer LI-COR LI-200 installed behind the venetian blind (sensor 2 in Figs. 2a and
1b). In order to take into account slats dirtiness and dust accumulation, the reflectance
of the slats was measured in situ by using another pyranometer LI-COR LI-200 also
installed in front of the venetian blind, but now facing indoors (sensor 3 in Figs. 2b and
1a). Slats reflectance of 0.40 was then obtained as the ratio between the reflected
radiation measured by sensor 3 (
G
1
) when the blind is fully closed (
ψ
= 90
°
or -90
°
), and
the incident solar radiation (
I
) measured by sensor 1– Fig. 2b. All measured results are
expressed in terms of the venetian blind solar transmittance which was calculated as the
ratio of the transmitted (
G
2
, measured by sensor 2) to the incident radiation (
I
, measured
by sensor 1).
a.
b.
Figure 2: Measurement position of vertical irradiances with piranometers to calculate, respectively,
the solar transmittance (a) and slats’ reflectance (b).
The experiments were performed near the autumnal equinox and under clear sky
conditions. Since the monitored venetian blind is facing east, it receives both direct and
diffuse radiation in the morning and only diffuse radiation in the afternoon.
Numerical Modelling
As solar radiation is partitioned into direct and diffuse components, the optical properties
should account for all combinations that can be established between the incident flux
and flux that results from the transmission, reflection and absorption processes. T
he
direct component passes in part directly through the blind assembly without hitting the
slats (direct-to-direct) and the rest indirectly by reflection and transmission through the
slats (direct-to-diffuse). These scattered reflection and transmission are uniformly diffuse
1
2
1
3
ext.
int.
ext.
int.
