Z E M C H 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e
324
The back-side diffuse-to-diffuse solar blind properties are calculated in a similar way by
setting an unit source flux to the back opening element (
S
2
= 1) and the other
S
i
equal to
zero. The back-side transmittance and reflectance will be now equal to
G
1
and
G
2
,
respectively.
Figure 4: Direct-to-difuse (a) and diffuse-to-diffuse (b) slat surface discretization into n=5 equal
elements.
Blind Control Strategy
Venetian blinds can help to control overheating, daylighting and glare, which is important
for energy savings and to improve the comfort of occupants. Although the admission of
daylight increases occupants’ performance, productivity and satisfaction, it can also
cause glare. Besides that, the slats orientation should be adjusted in such a way that the
passive solar gains in winter would be increased and in summer reduced. As a result, a
compromise between daylighting and thermal requirements has to be met.
A blind control strategy based on the profile angle of sun and a proper slat’s angle that
avoid direct solar radiation (and hence glare) while maximizing daylight and views to the
outside should be implemented. In this blind control strategy the ideal slat angle
corresponds to the cut-off angle (
ψ
cut-off
–
Fig.5), which is the maximum open position of
slats which completely block direct radiation, whilst enabling the transmission of as much
diffuse radiation as possible to indoors. A similar control strategy has been adopted by
Pfrommer et al. (1996) and Zhang and Birru (2012). The cut-off angle can be determined
by setting equation 1 equal to zero, i.e.:
φ
φ
ψ
−
=
−
cos
L
D sina
b
b
off
cut
(11)
D
m
L
b
φ
b
ψ
cut-off
Figure 5: Cut-off angle of slats for blind control strategy.
ψ
L -m
L
b
m
...
φ
3,b
...
1
3,f
n,b
D
n,f
b
2
b
I
D
D
L
1
3,f
L /N
...
n,f
b
b
3,b
ψ
2
...
n,b
b
a.
b.
