Transcript Definition - YourGlass.com

Evaluation of risk of
breakage by thermal shock
2008
Technical Advisory Service
Thermal shock
 Definition
 Parameters of influence
 Method of calculation
 Example of calculation
Thermal shock - Definition
 A breaking by thermal shock occurs when
there is a too high difference of temperature
between two point of a annealed glass.
 Indeed, if the temperature of the glass
increases, this glass expands.
 Reminder : Coefficient of linear expansion :
9.10-6 m/(m °C)
Ex: T° difference of 50°C for a 2 m glass
 9.10-6 m/(m °C) x 50°C x 2 m = 0,0009 m = 0,9 mm
Thermal shock - Definition
 This phenomenon does not present a problem
if the increase in temperature is uniform on all
the glazing and if the movement is not
blocked.
 On the other hand, if the border of the glazing
remains cold, it will prevent the hot part from
dilating freely and it results the beginning
traction constraints.
 At a certain difference of temperature
between two points of a same glazing, there is
a risk of thermal breakage.
Thermal shock
Thermal shock
Thermal shock
Thermal shock
 Thermal breakage starts allways at the edge
of the glass, perpendicular to the edge and
the 2 faces.
 The breakage can be single or multiple.
Thermal shock
Thermal shock
 Definition
 Parameters of influence
 Method of calculation
 Example of calculation
Thermal shock – Parameters of influence
 Climatic conditions
 Parameters depending of the glazing and
its setting
 Outside « architectural » parameters
 Inside « architectural » parameters
Thermal shock – Parameters of influence
 Climatic conditions :
– Daily difference of temperature (°C)
– Solar intensity (W/m²)
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
– Nature of glass  Energy absorption (EA)
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
– Type of setting and colour of the frame
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
–
–
–
–
–
–
–
–
–
–
Structural glazing
VGG
Alu with thermal break
Dark alu without thermal break
Middle alu without thermal break
Wood or PVC
Clear alu without thermal break
Dark steel
Clear steel
Concrete/Masonry
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
– State of the glass edges : damaged edges or
presenting chips increase the risk of thermal
breaking, these one starting from these weak
points.
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
– Use of TV or sliding frame with Low E
Toughened or heat
strengthened glass
Thermal shock – Parameters of influence
Thermal shock – Parameters of influence
 Parameters depending of the glazing and
its setting
– Glass in a roof
Outside
temperature
Inside
temperature
Thermal shock – Parameters of influence
 Outside « architectural » parameters
– Exposure of
hemisphere)
the
facade
(in
the
Northern
Thermal shock – Parameters of influence
Solar flow in summer
800
East
West
700
Flow (W/m²)
600
500
South
400
300
200
100
0
4
6
8
10
12
14
Time (hour)
16
18
20
22
Thermal shock – Parameters of influence
Solar flow in autumn and in spring
800
South
700
West
East
Flow (W/m²)
600
500
400
300
200
100
0
4
6
8
10
12
14
Time (hour)
16
18
20
22
Thermal shock – Parameters of influence
 Outside « architectural » parameters
– Eventual shadows on the glazing (eaves of a
building, blind) and letting only one part of the
glazing in the shadow.
Thermal shock – Parameters of influence
Thermal shock – Parameters of influence
Thermal shock – Parameters of influence
Thermal shock – Parameters of influence
more and more
dangerous
Thermal shock – Parameters of influence
 Inside « architectural » parameters
– Presence of blinds
– Proximity of heating appliances
– Proximity of the inside aeration forcing air
system (hot or cold) on the glazing
– Inside ceiling
– Proximity of a dark object behind the glazing
Thermal shock – Parameters of influence
Thermal shock – Parameters of influence
Minimum distance 20 cm
Liquid temperature max 65°C
Thermal shock – Parameters of influence
h
L
Risk if L < h
Thermal shock
 Definition
 Parameters of influence
 Method of calculation
 Example of calculation
Thermal shock – « Glass in building » method
1°) Basic calculation of Dt :
SV:
Dt = I . AE
he + hi
With
DV:
+ A . he
he + hi
I = solar intensity (750 à 850 W/m²)
A = maximum daily t° range (10 à 13 °C)
Dte = …
Dti = …
Thermal shock – « Glass in building » method
2°) Influence of the inside blinds :
Dt1 = Dt + Dt’
Thermal shock – « Glass in building » method
2°) Influence of the inside blinds : Values of Dt’
Simple glazing
Ventilated
space
Non ventilated
space
Open weave
3°C
6°C
Closed weave
4°C
7°C
Venetian blinds
5°C
8°C
Thermal shock – « Glass in building » method
2°) Influence of the inside blinds : Values of Dt’
Double
glazing
Outside glazing
Ventilat
ed
space
Inside glazing
Non
Non
ventilat Ventilated
ventilated
ed
space
space
space
Open
weave
2°C
4°C
4°C
8°C
Closed
weave
3°C
5°C
5°C
9°C
Venetian
blinds
4°C
6°C
6°C
10°C
Thermal shock – « Glass in building » method
3°) Influence of the frame :
Dt2 = Dt1 x f1
Thermal shock – « Glass in building » method
3°) Influence of the frame :
Type of frame
f1
Concrete
1
Clear steel
0,9
Dark steel
0,8
Steel with thermal break
0,8
Clear alu without thermal break
0,8
Wood of PVC
0,75
Dark alu without thermal break
0,7
Alu with thermal break
0,7
Structural glazing
0,5
Thermal shock – « Glass in building » method
4°) Influence of the outside shadows :
Dt3 = Dt2 x f2
Thermal shock – « Glass in building » method
4°) Influence of the outside shadows
Sort of shadow
SV and outside
glass of DG
Inside glass
of DG
1,2
1,1
1,5
1,2
Thermal shock – « Glass in building » method
 Stress in the glass :
s = E . e = E .  . DT3 = 0,63 . DT3
 Criteria of acceptability :
– DT3 < 30°C 
OK
– DT3 > 30°C 
a thermal treatment
(toughened or heat
strengthened) is necessary
Thermal shock – « Glass in building » method
 Notes :
– Thermal treatment can be toughened or heat
strengthened glass
– Advantage of a toughned glass : it is a safety glass
against injuries too
– Advantage or a heat strengthened glass : does not
present a risk of spontaneous breakin and so, no
heat soak treatment is needed
Thermal shock – « Glass in building » method
 Notes :
– The edge treatment is not considered as a good
solution to prevent of the risk of thermal shock
– The spandrels must always be tempered
Thermal shock
 Definition
 Parameters of influence
 Method of calculation
 Example of calculation
Thermal shock – Example of calculation
 Example of a calculation :
– 6 mm Stopsol Supersilver Dark Blue pos.2
12 mm air
6 mm Planibel clear
– AEe = 55
– AEi = 4
Thermal shock – Example of calculation
 Example of a calculation :
– 6 mm Stopsol supersilver Dark Blue pos.2
12 mm air
6 mm Planibel clear
– Setting in an aluminium frame with thermal break
and outside shadow
 DTe = 33,5 °C
 DTi = 13,0 °C
 The glass outside must be tempered
Thermal shock – Example of calculation
 Example of a calculation :
– 6 mm Stopsol supersilver Dark Blue pos.2
12 mm air
6 mm Planibel clear
– Setting in Structural glazing without shadow nor
blind
 DTe = 17,6 °C
 DTi = 8,5 °C
 A thermal treatment is not necessary
Evaluation of risk of thermal choc for vision double glazing (FIV 01)
Version 3.0 - 08/2003
Project and location
Asked by
Remarks
TAS DAYS 2
Glazing characteristics
Composition
6 mm Stopsol Supersilver Dark Blue #2 - 12 mm air - 6 mm Planibel
Length
1000
mm
Width
1000
mm
ext EA
55
%
int EA
4
%
U
2.9
W/(m²K)
Climatic conditions
temp. var.
sun int.
12
750
°C
W/m²
Frame characteristics
Type of setting
Type of window
Structural Glazing 4 sides
Structural Glazing
Exterior environment
Internal blind
No internal blind
External environment
Horizontal mullion
Vertical mullion
Shadow - Blind
0
mm
0
mm
No shadow or blind
Calculated maximum temperature difference in the glass lites
Basis
Correction factors
DT
DT
Glazing
Blinds
Frame
Shade
DT'
[°C]
f1
f2
[°C]
Outer
31.9
0
0.50
1.1
17.6
Inner
15.4
0
0.50
1.1
8.5
Thermal treatment
not necessary
not necessary
Thermal shock – Method « Glass in building »
 Advantages:
– Simple, proven and safety
 Disadvantages:
– Does not allow the calculation of triple glazing
and double skin façades