Environmental Engineering Reference
In-Depth Information
Estimation of the degree of shading of diffuse irradiance
For the estimation of the degree of shading of diffuse irradiance, the object
polygon is considered as being projected on a hemisphere. The objects
represented by the object polygon block the diffuse irradiation that passes
through the object polygon on the hemisphere. As a simple example, Figure
2.23 shows a polygon with four points, with two of them on the horizontal
ground plane. The two remaining points define the polygon clearly.
γ
(
α
) =
m
•
α
+
n
describes the connecting line of the points
p
1
and
p
2
for
α
1
≠
α
2
as well as
γ
1
> 0 and
γ
2
> 0. The parameters
m
and
n
of this line are:
γγ
2
-
1
γα γ α
1
•
2
-
2
•
1
m
=
and
n =
αα
2
-
1
2
-
αα
1
Assuming an isotropic intensity distribution, the diffuse irradiance
E
diff,hor,A
i
through the area
A
i
on a horizontal surface becomes:
(2.38)
Figure 2.23
Two Points, the Horizontal Meridian and Two Polar Meridians
Define the Polygon Area
