Utilisation of Passive Solar Energy - Renewable Energy: Technology, Economics and Environment - page 109

Table 3.2 Diffuse g -values and U -values of different glazing types and transparent thermal
materials /3-4/

Diffuse
g -value

U -value
glazing

in W/(m 2 K)

Insulating glazing (4 + 16 + 4 mm, air)
Thermal insulation double-glazing (4 + 14 + 4 mm, argon)
Thermal insulation double-glazing (4 + 14 + 4 mm, xenon)
Thermal insulation triple-glazing with argon filling
Thermal insulation triple-glazing with krypton filling
Thermal insulation triple-glazing with xenon filling
10 cm plastic capillaries, one cover pane
10 cm plastic honeycombs, one cover pane
10 cm glass capillaries, two panes
2.4 cm granular aerogel, two panes filled with air
2 cm evacuated (100 mbar) aerogel plate, two panes

3.00
1.30
0.90
0.80
0.70
0.40
0.90
0.90
0.97
0.90
0.50
The diffuse g -values were measured for a 4 mm front pane, poor in iron, whereas for the U -values an
average sample temperature of 10 °C has been assumed.

0.65
0.60
0.58
0.44
0.44
0.42
0.67
0.71
0.65
0.50
0.60

However, the diffuse g -values indicated in Table 3.3 only apply to the glazing
itself. For window calculation the frame thus needs to be deducted from the win-
dow surface. For large-surface windows the U -value of a window U w includes a
30 % frame surface. For smaller windows the U w - value needs to be recalculated
by means of the thermal transmittance coefficient ( U -value) for both frame and
glass pane, and additional thermal losses due to connecting sections have to be
considered.

Table 3.3 Diffuse g -value ( g diffuse ), U -value of the window ( U w ) and equivalent U -values
( U eq ) corresponding to different glazing types (see /3-5/)

g diffuse U w eq

(south)

U eq
(east/west)

U eq
(north)

in W/(m 2 K)

Simple glazing
Double-glazing (air 4 + 12 + 4 mm)
Double-glazing with thermal insulation
and argon filling (6 + 15 + 6 mm)
Triple-glazing with thermal insulation and
krypton filling (4 + 8 + 4 + 8 + 4 mm)
Triple-glazing with thermal insulation
and xenon filling (4 + 16 + 4 + 16 + 4 mm)

0.87
0.78
0.60
0.48
0.46

5.8
2.9
1.5
0.9
0.6

3.7
1.0
0.1
-0.3
-0.5

4.4
1.6
0.5
0.1
-0.2

5.0
2.2
0.9
0.4
0.2

The g -value (energy transmittance factor) of a glass pane is additionally re-
duced by dust on the glass pane F D and possible fixed shading F S and flexible
shading F C . Even for frequently cleaned surfaces, due to dust, a reduction of the
g -value by 5 % has to be assumed /3-6/. The value needs to be further reduced to