Solar energy use in buildings - Solar Energy Sciences and Engineering Applications - page 594

Figure 18.3.2 Irradiance G, absorption α G and secondary heat flows of single glazing outward and
inward.

difference between pane surface T s and room air T i or outside air T o . Temperature
differences between the outside and inside surface are neglected.

Q i
A w =

Q o
A w =

h i ( T s − T i ) h o ( T s − T o ) (18.3.3)

From the heat flow balance, first determine the pane surface temperature T s :

αG = ( h i + h o ) T s − h i T i − h o T o

(18.3.4)

αG + h i T i + h o T o

⇒ T s =

h i + h o

With this pane temperature T s , the heat flow inward can be calculated:
Q i
A w =

h i
h i +

h i ( T s − T i ) = ( αG − h o ( T i − T o ))

h o

h i
h i +

1

(18.3.5)

=

h o αG
secondary heatflow

− ( T i − T o )

1
h i

1
h o

+

Transmission losses

Transmission heat losses of the glazing are calculated separately via the
U-value. Thus, for the definition of the secondary heat emission degree q i , the ambient
temperature can be set equal to the outside temperature The result for q i is:

Q i /A w
G

h i
h i +

q i = = α for T i = T o (18.3.6)

h o

For double-glazing, the characteristic values are calculated similarly, although an
additional heat balance for the outside pane must now be created. The absorption