Agriculture Reference
In-Depth Information
(a)
90
Tr ansmission
80
70
60
50
40
30
20
Reflection
10
Absorption
0
05
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
Angle of incidence
(b)
Used PE thermal film
New PE thermal film
Used PE three-layer film
New PE three-layer film
0
20
40
60
80
0.2 mm thickness
Tr ansmissivity (%)
Fig. 4.5.
(a) Influence of the angle of incidence of direct radiation on the transmission, reflection and
absorption of a greenhouse covering material. (b) Transmissivity of diffuse solar radiation of different
greenhouse covering materials (Montero
et al
., 2001).
that is converted into diffuse radiation
when passing through a film (Papadakis
et al
., 2000). On sunny days, with a diffu-
sive film (Fig. 4.6), the diffuse radiation
inside a greenhouse can be three or four
times higher than the outside diffuse
radiation (Baille
et al
., 2003; see Appendix
1 section A.3.1).
The transmission characteristics are
altered by the presence of condensation
and water vapour on the film, depending
on the shape that the condensed vapour
