Evaluation of risk of breakage by thermal shock 2008

1. Evaluation of risk of breakage by thermal shock 2008 Technical Advisory Service

2. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

3. 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

4. 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.

5. Thermal shock

6. Thermal shock

7. Thermal shock

8. 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.

9. Thermal shock

10. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

11. Thermal shock – Parameters of influence • Climatic conditions • Parameters depending of the glazing and its setting • Outside « architectural » parameters • Inside « architectural » parameters

12. Thermal shock – Parameters of influence • Climatic conditions : • Daily difference of temperature (°C) • Solar intensity (W/m²)

13. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Nature of glass  Energy absorption (EA)

14. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Type of setting and colour of the frame

15. 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

16. 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.

17. 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

18. Thermal shock – Parameters of influence

19. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Glass in a roof Inside temperature Outside temperature

20. Thermal shock – Parameters of influence • Outside « architectural » parameters • Exposure of the facade (in the Northern hemisphere)

21. Thermal shock – Parameters of influence

22. Thermal shock – Parameters of influence

23. 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.

24. Thermal shock – Parameters of influence

25. Thermal shock – Parameters of influence

26. Thermal shock – Parameters of influence

27. Thermal shock – Parameters of influence

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29. 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

30. Thermal shock – Parameters of influence

31. Thermal shock – Parameters of influence Minimum distance 20 cm Liquid temperature max 65°C

32. Thermal shock – Parameters of influence h L Risk if L < h

33. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

34. Thermal shock – « Glass in building » method 1°) Basic calculation of Dt : SV: Dt = 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: Dte = … Dti = …

35. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Dt1 = Dt + Dt’

36. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Values of Dt’

37. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Values of Dt’

38. Thermal shock – « Glass in building » method 3°) Influence of the frame : Dt2 = Dt1 x f1

39. Thermal shock – « Glass in building » method 3°) Influence of the frame :

40. Thermal shock – « Glass in building » method 4°) Influence of the outside shadows : Dt3 = Dt2 x f2

41. Thermal shock – « Glass in building » method 4°) Influence of the outside shadows

42. Thermal shock – « Glass in building » method • Stress in the glass : • s = E . e = E . a . DT3 = 0,63 . DT3 • Criteria of acceptability : • DT3 < 30°C  OK • DT3 > 30°C  a thermal treatment (toughened or heat strengthened) is necessary

43. 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

44. 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

45. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

47. Thermal shock – Example of calculation • Example of a calculation : • 6 mm Stopsol Supersilver Dark Blue pos.212 mm air6 mm Planibel clear • AEe = 55 • AEi = 4

48. 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 • DTe = 33,5 °C • DTi = 13,0 °C •  The glass outside must be tempered

49. 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 • DTe = 17,6 °C • DTi = 8,5 °C •  A thermal treatment is not necessary