Glass And Window Repair Glossary For A Modern Glass Company
There are many terms that are unique to the glass industry which can be confusing the first time you hear or see them. Below are glass definitions that might be helpful. See our library of custom decorative glass images also.
Note: For ease of description the surfaces of a double paned unit are named according to the following convention: Surface #1 (facing outside), Surface #2 (inside of outside pane), Surface #3 (outside of inside pane) and Surface #4 (inside surface of inside pane). Applying the corresponding nomenclature for triple paned units results in surfaces #1 through #6.
Beveled glass is usually made by taking one-quarter inch-thick clear glass and creating a one-inch bevel on one side around the entire periphery. These bevels act as prisms in the sunlight creating an interesting color diffraction which both highlights the glasswork and provides a spectrum of colors which would ordinarily be absent in clear float glass.
The heat and sound insulation of glazing may also be improved by the use of a film or coating applied to its surface. This film is typically made of polyester or metal, and may give the window a reflective appearance or a one-way mirror effect. It may be used on single-glazed windows as an alternative to insulated glazing, or on surfaces #1, #2 or #3 (or combinations there of) of insulated glazing to further improve its effectiveness. Such coatings may reduce fading of fabric and improve safety in case of breakage. Glass performance is measured in two ways: Solar Heat Gain Co-efficient (SHGC), which expresses the proportion of incidental solar thermal radiation that is transmitted by the glass and Visible Transmittance, which describes the amount of visible light that is conducted through the glass between the exterior and interior surfaces. Both of these properties can be independently altered by different coatings.
For ease of description the surfaces of a double paned unit are named according to the following convention: Surface #1 (facing outside), Surface #2 (inside of outside pane), Surface #3 (outside of inside pane) and Surface #4 (inside surface of inside pane). Applying the corresponding nomenclature for triple paned units results in surfaces #1 through #6.
IGUs are manufactured on a made to order basis on factory production lines. The width and height dimensions, the thickness of the glass panes and the type of glass for each pane as well as the overall thickness of the unit must be supplied to the manufacturer. On the assembly line, spacers of specific thicknesses are cut and assembled into the required overall width and height dimensions and filled with desiccant. On a parallel line, glass panes are cut to size and washed to be optically clear. An adhesive sealant (polyisobutylene or PIB for short) is applied to the face of the spacer on each side and the panes pressed against the spacer. If the unit is gas filled, two holes are drilled into the spacer of the assembled unit, lines are attached to draw out the air out of the space and replacing it with the desired gas. The lines are then removed and holes sealed to contain the gas. The more modern technique is to use an online gas filler, which eliminates the need to drill holes in the spacer. The units are then sealed on the edge side using either polysulphide or silicone sealant or similar material to prevent humid outside air from entering the unit. The desiccant will remove traces of humidity from the air space so that no water appears on the inside faces of the glass panes facing the air space during cold weather. Some manufacturers have developed specific processes that combine the spacer and desiccant into a single step application system.
The double glazed window was invented in 1930s, and was commonly available in USA in the 1950s under the Thermopane TM brand name, registered in 1941 by Libbey-Owens-Ford Glass Company. After so many decades, the manufacturing process is well established. The brand name Thermopane has entered the vocabulary of the glazing industry as the equivalent name for an IGU. Materials which can be used for double glazing are versatile and include aluminum, PVC, and timber.
Glass is used to provide light and allow a view from either side to the other side. While the composition and manufacturing of glass is covered elsewhere, for the purposes of this article, its importance to the construction is its dimensional stability over a wide temperature range. Insulated Glass Units (IGUs) are manufactured with glass in range of thickness from 3 mm to 10 mm or more in special applications. Laminated or tempered glass may also be used as part of the construction. Most units are manufactured with the same thickness of glass used on both panes but special applications such as acoustic attenuation or security may require wide ranges of thicknesses to be incorporated in the same unit.
To reduce shear effects on the sealed unit (a major cause of premature failure), manufacturers use a rule of thumb that permits a difference of 1 mm between panes of glass used in the unit and still maintain the warranty for the unit. For example, a unit may be ordered with a 4 mm pane on the exterior and a 3 mm pane on the interior. These variations are allowed for architectural and cost reasons. Other combinations can be specified and produced but the manufacturer may reserve the right to limit the term of the warranty or refuse to warranty the unit altogether. The performance of glass cna be modified through the use of the following: Tinted Glass, Coated Glass, Low-Emissivity Glass, Spacer, Construction, Thermal Performance and Heat Insulating Properties.
Heat Insulating Properties
The effectiveness of insulated glass can be expressed as an R-value. The higher the R-value, the greater is its resistance to heat transfer. A standard IGU consisting of clear uncoated panes of glass (or lites) with air in the cavity between the lites has an R-value of 2, or 0.35 K·m2/W (2 h·ft2·°F/BTU).
Using imperial units, a rule of thumb in standard IGU construction is that each change in the component of the IGU results in an increase of 1 R-value to the efficiency of the unit. Adding Argon gas increases the efficiency to about R-3. Using low emissivity glass on surface #2 will add another R-value. Properly designed triple glazed IGUs with low emissivity coatings on surfaces #2 and #4 and filled with argon gas in the cavities result in IG units with R-values as high as R-5. Certain vacuum insulated glass units (VIG) or multi-chambered IG units using coated plastic films result in R-values as high as R-12.5
Insulated Glazing Unit or Insulating Glass Unit (commonly referred to as IGU) IGU made of glass is called insulated glass, which refers to heat insulation, not sound or electricity. A less accurate term is “insulating glass,” since the glass itself has no insulative properties. It is the air space between the glass layers (lites) that provides the insulation.
It is important that the air remains as immobile as possible to prevent convection currents transferring heat across the insulating gap. This limits the thickness of the air gap used and is the reason for triple glazing. Read More
Radius Grid Work
All of our SDL muttons can be used to build radius grid windows with the exception of contour grid material.
The South is full of beautiful historic homes and commercial buildings many of which are now being restored by dedicated preservationists. A full restoration requires glass that mirrors the original stock and at American Insulated Glass we provide just that. Read More
SDL (Simulated Divided Lite) Glass We offer a broad range of mutton options within our SDL product line. Sample are available as computer screen images vary by manufacturer. Read More
SDL (Simulated Divided Lite) Glass
We offer a broad range of mutton options within our SDL product line. Samples are available as computer screen images vary by manufacturer.
|Dull White||5/8”13/16”5/8” Contour Profile|
|Bright White||1/2”5/8”13/16”1” Contour Profile|
The glass panes are separated by a “spacer”. A spacer is the component, or piece, used in window manufacturing that separates the two panes of glass in an insulating glass (IG) system, and seals the gas space between them. Historically, spacers were made primarily of metal, which manufacturers thought provided more durability for their windows. However, metal spacers act as a heat conductor, undermining the ability of the IGU to reduce heat flow. This may result in water or ice forming at the bottom of the sealed unit because of the heating/cooling loss through the window. To reduce heat transfer through the spacer and increase overall thermal performance, the spacer may be constructed of a less-conductive material such as structural foam.
Typically, spacers are filled with or contain desiccant to remove moisture trapped in the gas space during manufacturing, thereby lowering the dew point of the gas in that space, and preventing condensation from forming on surface #2 when the outside glass pane temperature falls.
New technology has emerged to combat the heat loss from traditional spacer bars.
The maximum insulating efficiency of a standard IGU is determined by the thickness of the space containing the gas or vacuum. Too little space between the panes of glass results in conductive heat loss between the panes (the inside surface of one pane cools the surface of the other pane) while too wide a gap results in convection current losses (gas begins to circulate because of temperature differences and transfers heat between the panes). For further information, see the article heat flow. Typically, most sealed units achieve maximum insulating values using a gas space of between 5/8 to 3/4” (16–19 mm) when measured at the centre of the IGU. When combined with the thickness of the glass panes being used, this can result in an overall thickness of the IGU of between 7/8 and 1” for 3 mm glass (22–25 mm) to 1½” (28–31 mm ) for 1/4” plate glass.
IGU thickness is a compromise between maximizing insulating value and the ability of the framing system used to carry the unit. Some residential and most commercial glazing systems can accommodate the ideal thickness of a double paned unit. Issues arise with the use of triple glazing to further reduce heat loss in an IGU. The combination of thickness and weight results in units that are too unwieldy for most residential or commercial glazing systems, particularly if these panes are contained in moving frames or sashes.
These issues can be solved in various ways. A product known as Vacuum Insulated Glass (VIG), or evacuated glazing, can be used to drastically reduce heat loss due to convection and conduction. These VIG units have most of the air removed from the space between the panes, leaving a nearly-complete vacuum. VIG units which are currently on the market are hermetically sealed along their perimeter with solder glass, that is, a glass frit having a reduced melting point. Such a glass seal is rigid, and will experience increasing stress as the outer pane temperature rises or falls relative to that of the inner pane. Rigid seal glazing is generally restricted to applications for which the temperature differential across the VIG will NOT exceed 35 °C (63 °F), such as warmer climates where air conditioning costs are significant but temperature differentials remain within the warranted range.
Vacuum technology is also used in some non-transparent insulation products called vacuum insulated panels.
A more practical alternative is to replace air in the space with a heavy gas that is more viscous than oxygen and nitrogen. Higher viscosity reduces convective heat transfer. Argon (argon has a thermal conductivity 67% that of air), krypton (krypton has about half the conductivity of argon) or xenon to increase the insulating performance. These gases are used because they are non-toxic, clear, odorless, chemically inert, and commercially available because of their widespread application in industry. These gases have a higher density compared to air but have higher costs. In general, the more effective a fill gas is at its optimum thickness, the thinner the optimum thickness is. For example, the optimum thickness for krypton is lower than for argon, and lower for argon than for air. However, since it is difficult to determine whether the gas in an IGU has become mixed with air at time of manufacture (or becomes mixed with air once installed), many designers prefer to use thicker gaps than would be optimum for the fill gas if it were pure. Argon is commonly used in insulated glazing as it is the most affordable. Krypton, which is considerably more expensive, is not generally used except to produce very thin double glazing units or relatively thin, or extremely high performance triple glazed units. Xenon has found very little application in IGUs because of cost.
While clear glass is the most common glass component of IGUs, tinted glass may be used to reduce solar heat gain or as an architectural feature. The principal colors available are bronze, gray and green. The degree of tint depends on both the composition of the glass and the thickness of the coating. Tinted glass is usually placed on the exterior of the IGU. It almost always requires heat-treatment to reduce potential thermal stress and breakage and tends to re-radiate the absorbed heat.
U-Factor – The U-Factor (BTU/hr/ft2/°F) measures the rate of heat Loss through a window. The lower the U-Factor, the better the window is at reducing heat loss. Solar Heat Gain Coefficient (SHGC) – T he Solar Heat Gain
Coefficient measures the amount of solar heat that passes through a window. The lower theSHGC, the better the window is at blocking heat from the sun.
Visible Transmittance (VT) – Visible Transmittance measures how much visible light passes through a window compared to the amount that would pass through an open hole of the same size. The higher the VT, the more light is transmitted. A low VT often increases the amount of artificial light needed which leads to an increase in energy costs. A VT of 60 percent or more often appears clear, while a VT below 50 percent begins to look dark and/or reflective. Fading Transmission (Tdw) – Fading transmission measures the amount of fading-causing solar energy that enters through a window. The lower the Tdw value, the better the window is at protecting against fading. Insulating Glass – Insulating glass features two panes of glass separated by a spacer. The dead air space between the panes creates an insulating barrier and helps to reduce sound transmission. Warm-edge Spacers – Warm-edge spacers are manufactured from low-conductivity material. They can improve the U-Factor of a window by 10 percent and increase the glass edge temperature by almost 5°F, helping reduce condensation. Low-Emissivity (Low-E) Coated – A metal or metallic oxide layer applied to the surface of the glass that lowers the window’s U-Factor. The coating blocks long wave infrared inside and short wave solar heat outside. This results in keeping heat inside during the winter and outside during the summer, reducing air conditioning or heating demand, thus lowering energy costs. It also reduces winter condensation because of higher indoor glass temperatures and blocks harmful ultraviolet rays, lowering the Tdw, without blocking as much VT as tints do. Argon is a gas used to fill the airspace between panes of insulating low-E glass. It may increase insulating performance by slowing the transfer of energy through the window, therefore lowering the window’s U-Factor. Because the amount of argon in a unit may deplete over time, the insulating performance attributed solely to argon may diminish over time. Capillary/breather tubes are required on units with glass 12” and less in width or height and units shipped over high elevations. The capillary/breather tubes allow the unit to adjust to changes in pressure. Argon gas is not an option when capillary/breather tubes are used. Tinted Glass glass can lower the S HGC of a window significantly and can help control glare. Keep in mind that while blocking the sun’s rays, tinting also reduces VT.