Glass and thermal insulation
2008
Technical Advisory Service
Thermal
Insulation
Acoustic
Insulation
Solar
Control
Safety
Aesthetic
and decoration
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC Flat Glass Europe range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Introduction
high t°
low t°
Introduction
20°C
0°C
Necessary power
?
P = S (m²) x DT (°C) x Ug (W/m² °C)
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Conduction, convection and radiancy
Conduction
Convection
Radiancy
Conduction, convection and radiancy
Outdoor
temperature :
Tout
Indoor
temperature :
Tin
Radiation
Radiation
Conduction
Convection
Convection
(and conduction)
Ug-value =
(and conduction)
Heat loss
Temperature difference
(W/m².K)
Conduction, convection and radiancy
Intensity
(W/m²)
1.5
Energy
UV
Light
Short infra red
1.0
0.5
0
0 280 380
780
2500
Wavelength
(nm)
Conduction, convection and radiancy
Solar spectrum :
UV
: 280 tot 380 nm 
Light
: 380 tot 780 nm 
50% energy
Short I.R. : 780 tot 2500 nm 
45% energy
5%
energy
Conduction, convection and radiancy
Solar
radiancy
V
is
ib
le
Radiators
Close
IR
Radio
waves
Long IR
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
Regulation
Single glazing
4
glass = 1 W/(m K)
alu = 160 W/(m K)
insulating material  0,065 W/(m K)
: thermal conductivity
Single glazing
4
19 mm
glass = 1 W/(m² K)
insulator < 0,065 W/(m² K)
Ug = 5,8
W/(m² K)
Ug = 5,4
W/(m² K)
Single glazing
6.00
U (W/m²K)
5,8
5.50
5,4
5.00
4.50
4
5
6
8
10
12
Glass thickness (mm)
15
19
Single glazing
700 mm
Ug = 1.1 W/(m² K)
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 High output double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Double glazing
glass = 1 W/(m² K)
air = 0,025 W/(m² K)
Ug = 5,8 W/(m² K)
Ug = 2,9 W/(m²
K)
Double glazing
U (W/m² K)
4,00
3,00
2,9
2,00
1,00
4
6
8
10
12
14
16
18
Width of the spacer (mm)
20
22
24
Double glazing - composition
Thermobel
Air
Float
Float
Butyl
Spacer
Dryer
Sealing
Double glazing - composition
 2 glazings
 Spacer
 Gas
 Dryer for absorbing humidity
 Primary barrier of sealing (humidity) :
– Butyl
 Secondary barrier of sealing (sealing) :
– Polyurethane
– Silicone
Double glazing
Ar
Kr
Ug = 2,9
W/(m² K)
Ug  2,6 W/(m² K)
Double glazing
3,50
4-x-4 air
4-x-4 argon
U (W/m² K)
4-x-4 krypton
3,00
2,50
2,00
4
6
8
10
12
14
16
Width of spacer (mm)
18
20
22
24
Double glazing
Ug = 2,9
W/(m² K)
Ug  2,0 W/(m² K)
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Double glazing
Outside
Inside
UV, visible,
short IR
Long IR >
2500 nm
Double glazing
Long IR > 2500 nm
en=0.89
en =0.89
Double glazing
 Glass is not transparent to long IR
 Glass then absorbs the heat which tries to
leave the building
 In winter, when it is colder outside than
inside, the major part of this absorptive
energy is re-emitted towards outside
Low e double glazing
Heat
LowE
coating
Ug = 2,9
W/(m² K)
Ug = 1,4 to 2,0
W/(m² K)
Low e double glazing
Low emissivity coating :
n=0.15 to 0.02
Long IR > 2500 nm
en =0.89
Low e double glazing
UV, visible,
short IR
Long IR > 2500 nm
en =0.89
Low e double glazing
 The low-e coating forces the reemission of
the absorbed heat by glass towards the
interior
 I.e. that it behaves as a mirror which reflects
the heat which tries to leave the building
 On the other hand, it does not prevent the
solar radiation from penetrating in the
building
Low e double glazing
 Physically :
– Glass is opaque to long IR (ET = 0)
– From where the result of a heating of glass and
reemission
– The low-e coating forces the reeimisson
towards outside
e = AE = 1 – TR – RE = 1 – RE
 The lower is emissivity, the higher is the
energy reemission towards the interior
Low e double glazing
Clear glazing : emissivity e = 0,89
Coatings :
 pyrolithic low-e: e about 0,15 to 0,30
 Vacuum (magnetron): e about 0,02 à 0,1
Low e double glazing
3,50
4-x-4 air e = 0,89
0,15
4-x-4 air / ee == 0,15
0,05
4-x-4 air / ee == 0,05
U (W/m² K)
3,00
2,50
2,00
1,50
1,00
4
6
8
10
12
14
16
Width of spacer (mm)
18
20
22
24
Double glazing with Warm Edge spacer
The metallic spacer (alu, steel, …) is replaced by
a plastic spacer (eventually reinforced).
Double glazing with Warm Edge spacer
Advantages:
 Improvement of the U-value of the frame (not
the glazing)  economy of energy
 The surface temperature is more uniform
 better comfort
Without Warm Egde
With Warm Edge
Low e double glazing
In short :
– Thickness of glass : insignificant
– Gas (argon): small improvement
– Low emissivity coatings
 Big improvement
 Low e double glazing
– Warm-Edge spacer
 Improvement of the insulation of the frame
Double glazing
In short :
Ar
Ug = 5,8
W/(m² K)
Ug = 2,9
W/(m² K)
Ug from 1,4 to
2,0 W/(m² K)
Ug = 1,1
W/(m² K)
Triple glazing
Ar
Ar
Kr
Kr
Ug from 0,5 to 0,9 W/(m² K)
Thermal losses of a dwelling...
Roof : 20%
Walls : 25%
Ground : 20%
Windows account for about 35% !
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Temperature of surface and comfort
17,3°
18,5
°
20°
12,8°
5,6°
0°
Planibel
4 mm
Outside
Thermobel
Thermobel
Top N+
4-12-4 mm 4-15 ar-4 mm
Ug =5,8 Ug = 2,9 Ug = 1,1
Thermobel
Triple
4-15 ar-4
-15 ar-4
Ug = 0,6
Inside
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Technology
1970
Dial Sputtering
1980
1990
2000
Gold Thermoplus
Lodelinsart
Magnetron sputtering
Single silver Thermobel
(Plus, Top, Top N, Energy)
Top N+, Top NT, Energy N
Lodelinsart / Tiel / Teplice
Pyrolytic (Spray)
Thermoplus Comfort
Moustier
Pyrolytic (CVD)
K Glass
Moustier
1970
1980
1990
Planibel G
2000
AGC range – low-e coatings
Magnetron
Pyrolytic
Neutral low-e
glas
(Planibel Top)
(Planibel Plus)
Planibel Top N+
Planibel Top NT
Planibel (K glass)
Planibel G
Neutral low-e
and solar
control glass
Planibel Energy N
Planibel Energy
NT
Solar control
glass
Stopray
Sunergy
AGC range – Thermobel
 Ug = 2,8 W/m²K
 LT = 81 % - SF = 77 %
 Dimensions max : 3210 mm x 6000 mm
 Thicknesses : 4 to 19 mm
 Processings : tempering, laminating, silk
screening, bending
AGC range – Thermobel
Alternatives
 Thermobel cross bars
 Thermobel luxaclair
AGC range – Thermobel Top N+
 LT = 78 % - SF = 60 %
 Top N+ (ar): Ug = 1,3 – 1,1 W/m²K
 Dimensions max: 3210 mm x 6000 mm
 Standard thicknesses: 4 - 5 - 6 - 8 - 10 - 12 mm
 Processings: laminating
AGC range – Thermobel Top NT
 LT = 79 % - SF = 66 %
 air: Ug = 1,7 – 1,5 W/m²K
 ar : Ug = 1,3 – 1,2 W/m²K
 Dimensions max: 3210 mm x 6000 mm
t° out = 0°C
t° in = 20°C
 Standard thicknesses : 4 – 6 – 8 – 10 mm
 Transformations : tempering,
t° of inner
laminating
sheet =
17.3°C
AGC range – Thermobel Energy N
 LT = 71 % - SF = 42 %
 ar: Ug = 1,2 – 1,1 W/m²K
 Dimensions max: 3210 mm x 6000 mm
out6
= 0°C
t° inmm
= 20°C
 Standard thicknesses : 4t° –
– 8 – 10
 Processings : laminating
t° of inner
sheet =
17.3°C
AGC range – Thermobel Energy NT
 LT = 74 % - SF = 45 %
 ar: Ug = 1,2 – 1,0 W/m²K
 Dimensions max: 3210 mm x 6000 mm
= 20°C
 Standard thicknesses: 4 t°–out6=–0°C8 – 10t° in
mm
 Processings: tempering, laminating
t° of inner
sheet =
17.3°C
AGC range – Thermobel Warm E
 Double glazing with Warm Edge spacer
 Available with Top N, Energy N, Stopray, …
 Maximum dimensions: 3000 x 1800
t° out = 0°C
t° of inner
sheet =
17.3°C
t° in = 20°C
AGC range – Planibel G
 Dimensions max: 3210 mm x 6000 mm
 Standard thicknesses : 4 – 6 mm
 Transformations: tempering, laminating,
bending
t° out = 0°C
t° of inner
sheet =
17.3°C
t° in = 20°C
AGC range – Planibel G
 In simple glazing :
– LT = 80 % - SF = 71 %
– Ug = 3,7 W/m²K
 In double glazing :
– LT = 74 % - SF = 73 %
– Ug (air) = 1,9 – 1,8 W/m²K
t° out = 0°C
– Ug (ar) = 1,6 – 1,5 W/m²K
t° of inner
sheet =
17.3°C
t° in = 20°C
AGC range - Summary
Raw glass
Planibel
Insulating glazing
4/15 air/4
4/15 ar/4
Thermobel
Ug = 2,8
SF
77
Planibel Top N
Thermobel Top N+
Ug = 1,4
Thermobel Top N+
Ug = 1,1
64
Planibel Top NT
Thermobel Top N+
Ug = 1,5
Thermobel Top N+
Ug = 1,2
66
Thermobel Energy N
Ug = 1,4
Thermobel Energy N
Ug = 1,1
42
Thermobel Energy NT
Ug = 1,4
Thermobel Energy NT
Ug = 1,0
45
Planibel Energy N
Planibel Energy NT
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Condensation
 In the spacer  Glazing to be replaced
Condensation
 On the inside surface
 Very rare with DG and low-e DG
 Sign of interior climate too wet and/or building
not enough heated
Condensation
 On the outside surface
DGU
low e DGU
Condensation
Condensation
 On the outside surface
 Unavoidable phenomenon, occuring sometimes the
morning, after cold nigth without clouds
 Is the mark of the very goog insulating level of the
glazing
 Similar to condenstation on the windscreen of cars
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Calculation of the Ug-value of a glazing (EN
673)
Single glazing :
1
1 d 1
  
Ug he  hi
 he = coefficient of surface heat exchange between the wall and
the external environment = 1/8 W/(m² K)
 hi = coefficient of surface heat exchange between the wall and
interior environment = 1/23 W/(m² K)
 d = glass thickness (m);
  = thermal conductivity of a glass = 1 W/(m K)
Calculation of the Ug-value of a glazing
(EN 673)
Double glazing
with :
1
1 d1 1 d 2 1
   

Ug he  hs  hi
5,14
B
hs 
 Nu
1
1
s

1
e1
e2
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Calculation of the Uw-value of a window
Uglazing
Spacer
Uframe
Calculation of the Uw-value of a window
Calculation of the Uw-value of a window
(EN ISO 10077-1)
Uw 
A g  U g  A f  U f  lg  ψ
Ag  Af
 = 0 to 0,06 ((metallic spacer) in function of the frame type
 = 0.05 (Uframe  2.0)
 to calculate for Warm edge spacer (EN ISO 10077-2)
Calculation of the Uw-value of a window
(EN ISO 10077)
 Example of calculation: Comparison between
traditional and Warm E spacer
Wood
PVC
Alu
Uf = 1.4
W/(m².K)
Uf = 1.9
W/(m².K)
Uf = 2.0
W/(m².K)
Metallic spacer
1.43
1.58
1.70
Warm E
1.36
1.51
1.56
0.07
4.9 %
0.07
4.4 %
0.14
8.2 %
Amelioration
W/(m².K)
%
Calculation for window 1.23 x 1.48 m with Thermobel Starlite N 1.2 W/(m².K)
Calculation of the Uw-value of a window
(EN ISO 10077)
 Exemple of calculation: Influence of the
surface of the window and Warm E
Dimensions
Surface
Uw aluminium window
Amelior.
Uw
Amelior.
Uw
(mm)
(m²)
Metallic spacer
Warm E
W/(m².K)
%
910 x 1100
1.00
1.84
1.67
0.17
9.2
1230 x 1480
1.82
1.70
1.56
0.14
8.2
1580 x 1900
3.00
1.60
1.49
0.11
6.8
Glazing
: Thermobel Starlite N
Ratio glass/frame
: 70 / 30
Glass and thermal insulation
 Introduction
 Convection, conduction and radiancy
 Single glazing
 Double glazing
 Low e double glazing
 Temperature of surface and comfort
 AGC range
 Condensation
 Calculation of the Ug-value of a glazing
 Calculation of the Uw-value of a window
 Regulation
Regulation
Most countries have a thermal regulation giving:
 maximum Uw-value for the frame or the glass
 maximum U-value for the building
 maximum energy consumption
…
Example: Regulation in Belgium
Thermal regulations of the Regions
 Uw value of the window to be respected
Wallonie
Flandres
Bruxelles
Since 09/96
Since 01/06
Since 01/2000
3,5 W/m² K
2,5 W/m² K
2,5 W/m² K
+ glass 1,6 W/(m²K)
 K level to be respected for the building
Example: Regulation in Belgium
Example of Uwindow
Uframe
Uglazing
5,8
2,9
1,8
1,1
Wood
1,8
4,65
2,72
2,01
1,52
PVC
2,8
4.95
3,02
2,31
1,82
Alu
3,5
5,23
3,20
2,43
1,91
Thermal
Insulation
Acoustic
Insulation
Solar
Control
Safety
Aesthetic and
decoration
Solar control coating
Silicone resistant
to UV
Safety :
Laminated glass
Acoustic
insulation :
Laminated glass
and assymetric
DG
Therma insulation
low-e coating