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Chapter 17 Glass and Glazing

Chapter 17 Glass and Glazing. 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

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Chapter 17 Glass and Glazing

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  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

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