Case
Table 3 . The thermal characteristics of air cavities for the double window cases
Glazing system
External window
Internal window
Distance between the external and internal windows [ mm ]
Effective thermal conductivity ( W∙m ‐1 ∙K ‐1 )
Thermal resistance |
( RR ss , m 2 ∙K∙W ‐1 ) |
|
ISO
15099
|
ISO
10077‐1
|
CFD |
|
|
0.219 |
1 |
A |
D |
88 |
0.4333 |
0.203 |
|
|
2 |
E |
E |
88 |
0.4252 |
0.207 |
|
0.219 |
3 |
A |
D |
88 |
0.4333 |
0.203 |
|
0.219 |
4 |
A |
A |
88 |
0.4577 |
0.194 |
|
0.219 |
5 |
F |
F |
94 |
0.4489 |
0.209 |
N / A |
0.220 |
6 |
Upper
Lower
|
B
C
|
B |
70.6
94.5
|
0.3475
0.4649
|
0.203
0.203
|
0.216 |
7 |
Upper
Lower
|
A
C
|
A |
70.6
94.5
|
0.3607
0.4867
|
0.196
0.194
|
0.216 |
2.4 . Calculation of the thermal transmittance of a double window
Generally , the thermal transmittance of a window can be calculated according to ISO 15099 and 10077 . In this study , ISO 15099 and 10077 are considered as the procedures for calculating the U‐value of windows , and , if ISO 10077 is chosen , the linear thermal transmittance shall be calculated . The preferred method of establishing values of the linear thermal transmittance is by numerical calculations with formulas in accordance with ISO 10077‐2 ; however , when the results of a detailed calculation are not available , ISO 10077‐1 provides default values of the linear thermal transmittance for typical combinations of frames , glazing , and spacers that can be used . The values in Table 3 are used when the thermal transmittance of a double window is calculated .
ISO 15099 includes the procedure for calculating thermal transmittance , in which the effect of three‐dimensional heat transfer in frames and glazing units is not considered . In this procedure , the linear thermal transmittance and frame thermal transmittance , UU � , shall be calculated ; however , there is an alternative procedure for calculating these values , which are used in area‐based calculations and by WINDOW / THERM . In this case , the following equation shall be used to calculate the total thermal transmittance :
UU � � ∑ UU ��AA � � ∑ AA �� AA � � ∑ UU �� AA � � ∑ UU ��� AA ��� � ∑ UU �� AA ��
AA �
.
Using this method , it is unnecessary to determine the linear thermal transmittance . Instead , the glass area , AA �� , is divided into the center‐glass area , AA � , plus the edge‐glass area , AA � , and one additional value of thermal transmittance , UU �� , is used to characterize the edge‐glass area . In this study , the thermal resistance of glazing system in Table 3 are used when seven cases of double window are calculated for the thermal transmittance . If dividers are present , then the divider area , AA ��� , and the divider thermal transmittance , UU ��� , are calculated as well as the corresponding divider edge area , AA �� , and thermal transmittance , UU �� .
165 ZEMCH 2019 International Conference l Seoul , Korea