Chapter 17 Glass and Glazing

1. Chapter 17 Glass and Glazing

2. Glass • Benefits of Using Glass • Allows entry of natural light • Provide “views” of exterior environment • Entry of sunlight provides warmth • Disadvantages and/or Design Considerations • Limits occupant’s privacy • Lower resistance to thermal transmission • heat in the summer & • Cold in the winter • Initial & operating costs

3. Glass History Material used for Centuries • Early Processes (10th Century) • Crown Glass • Heated glass blown into sphere • Reheated & spun on “punty”(rod) • Sphere becomes a “disk” • Cooled & cut into pieces • Cylinder glass • Heated glass blown into sphere • Swung like a pendulum • Elongated into a cylinder • Ends cut off, split lengthwise • Reheated, opened, flattened into rectangular sheet • Cut into pieces • Neither had high “optical” quality

4. Glass History (cont.) • Plate Glass • Introduced in the 17th Century • Process • Molten glass cast into frames • Spread into sheets by rollers • Cooled • Each side ground / polished • Larger sheets of High optical quality • Costly (until process was mechanized)

5. Glass History (cont.) • Drawn Glass • Replaced cylinder glass, early 20th century • Flat sheets of glass drawn directly from a molten glass container • Production Process • Continuous production line - highly mechanized • Drawn glass • Ground & Polished (plate) • To finished sheets of glass

6. Glass History (cont.) • Float Glass • Process invented in 1959 in England (produced in US, 1963) • Has become a worldwide standard • Largely replaced drawn & plate glass • Production Process (Glass “floated” across a bath of molten tin)

7. Ribbon of Float Glass • Process Benefits • Surfaces parallel • High Optical Quality • (Comparable to Plate) • Brilliant Surface Finish • Economical • Virtually all flat glass produced

8. Terminology • Glazing - “...installation of a transparent material (usually glass) into an opening” • I.E. “Glass & Glazing” • Glazier • A glass installer • Lites (lights) • Individual pieces of glass

9. Glass as a Material • Major ingredient - Sand (silicon dioxide) • Strength • Individual fibers stronger than steel, but less stiff • In larger sheets - microscopic imperfections inherent with manufacturing process significantly reduce its strength • Cracks propagate from these imperfections near the point of maximum tension • Types of Breakage • Thermal Stress Breaks • Mechanical Stress Breaks

10. Glass Thicknesses • Range of Thicknesses • 3/32” Single strength • 1/8” Double strength • Up to 1”+ • Thickness Required is Determined by: • Size of Glass Lites (span) • Maximum Design (Wind) Loading • Acceptable Breakage Rate (most always some breakage)

11. Wind TestingCommon on tall Buildings - Purpose: Establish expected loads Mockup for a 24 Story Condo

12. Tempered Glass • Ordinary Glass - Annealed • glass cooled slowly under controlled conditions to avoid internal stresses • Tempered Glass • Annealed glass that is: • Reheated • Surfaces cooled rapidly, core cooled more slowly • Induces permanent compressive stresses in edges & faces and tensile stresses in the core • Result: • 4 times as strong in bending • More resistant to thermal stress & impact

13. Tempered Glass • When Tempered Glass Breaks: • The sudden release of the internal stresses: • Produces small square edged particles (as opposed to sharp, jagged pieces) • Strength & breakage characteristics make it well suited for: • Exterior Doors • Floor to Ceiling Sheets of Glass • All-Glass Doors, Glass walls (ex; handball courts), basketball backboards • Disadvantages • More Costly • Process may cause noticeable distortions • Cutting & Drilling must be prior to tempering

14. Uses of Tempered Glass

15. Heat-Strengthened Glass • Substitute for Tempered Glass • Lower Cost, but • Less of the desirable qualities of tempered • Lower strength • Less desirable breakage characteristics • Process Similar, however • Lower induced stresses • Less strength (only twice annealed) • Breakage characteristics more similar to annealed

16. Laminated Glass • Sandwiching • Transparent interlayer (PVB) • Between layers of glass (can be multiple layers) • Bonded under heat & pressure • PVB - Polyvinyl Butyral • Soft interlayer • Can be clear, colored, and/or patterned • Improves resistance to sound transmission • Upon breakage - PVB holds pieces of glass together • Uses? • Skylights (overhead glazing) • Reduce noise (hospitals, classrooms, etc.) • Security glass (typically has multiple layers) Glass PVB Layer

17. Skylight @ the Bellagio Hotel

18. Hurricane Resistant Glass Large Missile Impact Test Laminated and Tempered

19. Fire Rated Glass • Required for: • Fire rated doors • Rated Window and wall assemblies • Glass Types • Specially Tempered Glass (rated for 20 minutes) • Wired Glass (mesh of wire in glass, rated for 45min.) • most common, but • changes the appearance of the opening • Optical Quality Ceramics (20min. to 3hr)

20. Wire Glass

21. Spandrel Glass • Interior face • Ceramic based paints w/ pigmented glass particles (frits) applied • Heated / Tempered to form a ceramic coating • Opaque Lite • Match or contrast other glass • Often tempered - resist thermal stresses behind light • Purpose • Conceal structure behind glass / curtainwall

22. Spandrel Glass (view from the inside)

23. Spandrel Glass (view from the outside)

24. Spandrel Glass

25. Tinted & Reflective Glass • Why tint or apply a reflective coating to glass? • Reduce glare from sunlight • Reduce solar heat gain • Architectural look - Aesthetics

26. Clear Float Glass Sunlight 85% +/- sunlight enters Reflected Sunlight Absorbed & Reradiated as Heat Outside Inside

27. Tinted Glass Sunlight 14% to 75% Reflected • Result: • Lower Cooling Costs • Less “sunlight” • Glare for people • Fading FF&E Reradiated Reradiated Outside Inside

28. Tinted Glass • Process • Chemical elements added to the molten glass • Colors available • Grays, bronzes, blues, greens, golds, etc.

29. Clear (untinted) Glass

30. Lightly tinted glass

31. Lightly tinted glass

32. Tinted glass

33. Reflective Glass • Thin films of metal or metal oxide placed on the surface of the glass • Film purpose: • Reflect sunlight • Reduce solar heat gain • Changes Appearance • Colored Mirror effect • Can be placed on either face, • However, often on the inside face Glass Reflective Film

34. Reflective Glass

35. Reflective Glass

36. Reflective Glass

37. Shading Coefficient • “Ration of total solar heat gain through a particular glass compared to heat gain through double-strength clear glass.” • Shading Coefficient = Heat gain of a Glass type Heat gain thru Clear (double-strength) • Tinted glass range: .5 to .8 • Reflective glass range .3 to .7

38. Visible Transmittance • “Measures the transparency of glass to visible light (rather than solar heat gain) • Ranges: • Clear Glass .9 • Tinted & Reflective < .9

39. Glazing Luminous Efficacy (Ke) • Ke = Visible Transmittance Shading Coefficient • High Ke • High amount of solar heat blocked while • Considerable amount of sunlight allowed to enter • Green & blue glass • Low Ke • Similar amounts of solar heat & sunlight blocked • Darker interior (less light) • Bronze, gold, & grays

40. Glass & Thermal Transmission “Well” Insulated Wall Single Pane Glass 1” Polystyrene Thermal Transmission 1/5 of Glass 1/20 of Glass Disadvantage of Glass: Higher Initial & Operating Costs, Reduced Comfort

41. Insulating Glass • Two or more sheets of glass separated by an air space • Double Glazing: Two (2) sheets • Triple Glazing: Three (3) sheets (somewhat uncommon) • Primary purpose of additional sheets of glass • Improve insulating value - reduce thermal transmission • Two (2) sheets - cuts heat loss in half (1/3 for 3 sheets) • Increases initial cost but: • Reduces operating costs • Increases comfort • Provides additional architectural options

42. Insulating Glass Air Space • Spacer (Spline) • Separates the glass • Often Metallic • Air Space • Dry Air or • Inert Gas (such as Argon) • Sealant • “Seals” Unit • Prevent air escape & • moisture penetration • Glass • Clear, reflective and/or tinted Glass Spacer Sealant

43. Insulated Glass (tinted)

44. Insulated Glass (tinted)

45. Metal Spline

46. Low-Emissivity GlassLow-E Glass Insulated Glass • Improves thermal performance • Ultra-thin, transparent, metallic coating • Generally placed on: • The #2 or #3 position in insulating glass or • The #4 position in laminated glass • Reflects selected wavelengths of light & heat radiation • Allows entry of most short-wave (sunlight) • Reflects most longer-wave infrared radiation from objects and humans inside the building • Result: • Reduced heating & cooling load, increased comfort inside 1 2 3 4

47. Thermal Performance Data Obtained from PPG Glass 13% Improvement Add Argon 6% Improvement Add “special” spacer 33% Improvement Add Low-E Glass Clear, insulated, alum. spacer, air filled

48. Glass with Changing Properties • Thermochromic glass (darker when warmed by the sun) • Photochromic (darker when exposed to bright light) • Electrochromic (changes transparency with electricity) • Photovoltaic (generates electricity from sunlight)

49. Self-Cleaning Glass • Proprietary product w/ coating of titanium oxide • Catalyst allowing sunlight to turn organic dirty into carbon dioxide and water • Plastic Glazing Sheet • Materials – acrylic & polycarbonate • More expensive, higher coefficients of thermal expansion

50. Glazing - Small Lights • Design Considerations • Low stresses from wind loading • Low stresses from thermal expansion / contraction Glazier’s points & Putty Wood Stop Snap-in Glazing Beads & Synthetic Rubber Gaskets