evaluation of risk of breakage by thermal shock 2008 technical advisory service
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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 the facade (in the Northern
hemisphere)
Solar flow in summer
0
100
200
300
400
500
600
700
800
4 6 8 10 12 14 16 18 20 22
Time (hour)
Flo
w (
W/m
²)
East West
South
Thermal shock – Parameters of influence
0
100
200
300
400
500
600
700
800
4 6 8 10 12 14 16 18 20 22
Time (hour)
Flo
w (
W/m
²)
East
South
West
Solar flow in autumn and in spring
Thermal shock – Parameters of influence
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
1°) Basic calculation of t :
SV: t = I . AE + A . he
he + hi he + hi
With I = solar intensity (750 à 850 W/m²) A = maximum daily t° range (10 à 13 °C)
DV: te = …
ti = …
Thermal shock – « Glass in building » method
2°) Influence of the inside blinds :
t1 = t + t’
Thermal shock – « Glass in building » method
2°) Influence of the inside blinds : Values of t’
Simple glazingVentilated
spaceNon 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 t’
Double glazing
Outside glazing Inside glazing
Ventilated
space
Non ventilat
ed space
Ventilated space
Non ventilated 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 :
t2 = t1 x f1
Thermal shock – « Glass in building » method
3°) Influence of the frame :
Thermal shock – « Glass in building » method
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
4°) Influence of the outside shadows :
t3 = t2 x f2
Thermal shock – « Glass in building » method
4°) Influence of the outside shadows
Thermal shock – « Glass in building » method
Sort of shadowSV and outside
glass of DGInside glass of
DG
1,2 1,1
1,5 1,2
Criteria of acceptability :
– T3 < 30°C OK
– T3 > 30°C a thermal treatment
(toughened or heat
strengthened) is
necessary
Thermal shock – « Glass in building » method
Stress in the glass :
= E . = E . . T3 = 0,63 . T3
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 – « Glass in building » method
Thermal shock
Definition
Parameters of influence
Method of calculation
Example of calculation
Example of a calculation :
– 6 mm Stopsol Supersilver Dark Blue pos.212 mm air6 mm Planibel clear
– AEe = 55
– AEi = 4
Thermal shock – Example of calculation
Example of a calculation :
– 6 mm Stopsol supersilver Dark Blue pos.212 mm air6 mm Planibel clear
– Setting in an aluminium frame with thermal break and
outside shadow
Te = 33,5 °C
Ti = 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.212 mm air6 mm Planibel clear
– Setting in Structural glazing without shadow nor
blind
Te = 17,6 °C
Ti = 8,5 °C
A thermal treatment is not necessary
Thermal shock – Example of calculation
Version 3.0 - 08/2003
Project and locationAsked by TAS DAYS 2Remarks
Glazing characteristicsComposition 6 mm Stopsol Supersilver Dark Blue #2 - 12 mm air - 6 mm PlanibelLength 1000 mmWidth 1000 mmext EA 55 %int EA 4 %U 2.9 W/(m²K)
Climatic conditionstemp. var. 12 °Csun int. 750 W/m²
Frame characteristicsType of setting Structural Glazing 4 sidesType of window Structural Glazing
Exterior environmentInternal blind No internal blind
External environmentHorizontal mullion 0 mmVertical mullion 0 mmShadow - Blind No shadow or blind
Calculated maximum temperature difference in the glass litesBasis Correction factors
Glazing T Blinds Frame Shade T Thermal treatment
[°C] T' f1 f2 [°C]Outer 31.9 0 0.50 1.1 17.6 not necessary
Inner 15.4 0 0.50 1.1 8.5 not necessary
The calculations in this sheet are only valid for the specific project above, and not for any other project.
When drawing up the said calculations, Glaverbel used its actual knowledge and as a basis the information given to it
by the customer, who expressly recognizes that this is comprehensive and true.
The customer undertakes in addition to respect fully and in good faith the recommendations made by Glaverbel
as well as the rules of the art and the standards of approved institutes, professionnal institutes and organizations
or other similar bodies, which are in force.
This sheet may only be used or exploited by the customer who asked for this document, and exclusively
for the purposes for which is was requested.
Furthermore, in the case of sliding frame with low-e glass, the 2 central glass (compared with the 4 glasses,
when the frame is open) must be tempered.
DR Page 1 of 1
Evaluation of risk of thermal choc for vision double glazing (FIV 01)
Advantages:
– Simple, proven and safety
Thermal shock – Method « Glass in building »
Disadvantages:
– Does not allow the calculation of triple glazing and double skin façades
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