Insulating glass ( IG ), better known as double glazing (or double panel , and more glass three times folding/pane), consisting of two or three glass panels separated by a vacuum or a filled gas to reduce heat transfer in part of the building envelope.
Insulating glass units (IGUs) are produced with glass in the thickness range from 3 to 10 mm (1/8 "to 3/8") or more in special applications. Laminated or tempered glass can also be used as part of construction. Most units are manufactured with the same glass thickness used on both panels but special applications such as acoustic or safety attenuation may require a wide range of thicknesses to be combined in the same unit.
Video Insulated glazing
Jendela double-hung dan storm
The insulating glass is an evolution of the old technology known as double-hinged windows and storm windows. Traditional double-hung windows use one glass panel to separate interior and exterior spaces.
- In summer, a window screen will be installed on the exterior above a double-hung window to prevent animals and insects.
- In winter, the screen is removed and replaced with a storm window, which creates a two-tier separation between the interior and exterior spaces, improving window insulation in winter. To allow storm window ventilation can be hung from loop removable hinges and swung using a folding metal arm. No screening is usually possible with an open storm window, although in winter, insects are usually inactive.
Traditional storm windows and storm screens are relatively time-consuming and labor-intensive, requiring the removal and storage of storm windows in the spring, and reinstallation in autumn and screen storage. The heavily shaded window frame and glass frame made his successor on the upper floors of tall, high-rise buildings that required repeatedly climbing up the ladder with every window and trying to hold the window in place while securing the retaining clips around the edges. However, the current reproduction of an old-style storm window can be made with removable glass in the replaceable bottom panel with a removable screen when desired. This eliminates the need to change the entire storm window according to the season.
Insulated glazing forms a very compact multi-layer sandwich from the air and glass, which eliminates the need for storm windows. The display can also be installed year-round with insulated glass, and can be mounted in a way that allows installation and discharge from inside the building, thus eliminating the requirement to climb the outside of the house to open a window. It is possible to retrofit insulated glazing into traditional double-hung frames, although this would require significant modification of the wood being framed due to the increased thickness of the IG assemblies.
Modern window units with IG typically actually replace older double-hung units, and include nother improvements such as better sealing between the top and bottom windows, and a spring-operated heavy balancer that eliminates the need for hanging loads that big inside the wall. in addition to windows, allowing more insulation around the windows and reducing air leakage, providing strong protection against the sun and will keep the house cool in summer and warm in winter. This spring-operated balancing mechanism also usually allows the top of the window to swing in, allowing cleaning of the outside of the IG window from within the building.
Maps Insulated glazing
Spacer
The glass panel is separated by "spacer". The spacer, also known as the warm edge, is the part that separates the two glass panels in an insulating glass system, and seals the gas chamber between the two. Historically, spacers were made primarily of metals and fibers, which, according to manufacturers, provide more durability.
However, the metal spacer conducts heat (unless the metal is thermally enhanced), impairs the ability of the insulated glass unit (IGU) to reduce heat flow. It may also result in water or ice being formed at the bottom of the sealed unit due to the sharp temperature difference between the window and the surrounding air. To reduce heat transfer through the spacer and improve overall thermal performance, manufacturers can make spacers out of less conductive materials such as structural foams. An aluminum spacer that also contains a highly structural thermal barrier reduces condensation on the glass surface and improves the insulation, as measured by the overall U-value.
- Spacers that reduce heat flow in glass configurations may also have characteristics for silencers where external interference is a problem.
- Typically, spacers are filled or contain dryers to remove moisture trapped in the gas chamber during manufacture, thereby lowering the dew point of the gas in the chamber, and preventing condensation from forming on surface # 2 when the temperature of the outer glass panel falls.
- New technologies have emerged to cope with heat loss from traditional spacer bars, including improved structural performance and long-term durability of improved metal (aluminum with thermal barrier) and foam spacers.
Construction
IGUs are often made on order for factory production lines, but standard units are also available. The width and height dimensions, the thickness of the glass panel and the type of glass for each panel and the overall thickness of the unit shall be supplied to the manufacturer. On an assembly line, a certain thickness spacer is cut and assembled into the required width and height dimensions and filled with the dryer. On parallel lines, glass panels are cut to size and washed to be optically clear.
Adhesive sealant (polyisobutylene) is applied to the spacer face on each side and the panel is pressed into the spacer. If the unit is filled with gas, two holes are drilled into the assembled unit spacer, the lines are fixed to draw air out of space and replace it (or leave only a vacuum) with the desired gas. The stripes are then removed and sealed holes contain gas. A more modern technique is to use an online gas filler, which eliminates the need to drill a hole in the spacer. The units are then sealed on the edges using either polysulfide or silicone sealant or similar material to prevent moisture from entering the unit. The desiccant will remove traces of moisture from the air chamber so that no water appears on the inner face (without condensation) from the glass panels facing the air space during cold weather. Some manufacturers have developed special processes that incorporate spacers and desiccants into single-step application systems.
The insulating glass unit, consisting of two glass panels tied together into one unit with a seal between the edges of the panel, was patented in the United States by Thomas Stetson in 1865. It developed into a commercial product in the 1930s, when several patents were filed, and a product announced by Libbey-Owens-Ford Glass Company in 1944. Their products were sold under the brand name Thermopane, which had been registered as a trademark in 1941. Thermopane technology differs significantly from contemporary IGUs. Both glass panels are welded together by a glass seal, and two panels are separated by less than 0.5 inches (1.3 cm) typical of a modern unit. The Thermopane brand name has entered the glass industry vocabulary as a generic brand for every IGU.
Thermal performance
The maximum insulation efficiency of a standard IGU is determined by the thickness of the chamber. Typically, the most sealed units achieve maximum insulation values ​​using 16-19 mm (0.63-0.75 inches) space when measured at the IGU center.
The thickness of IGU is a compromise between maximizing the value of isolation and the capability of the framing system used to carry the unit. Some of the most residential and commercial glass systems can accommodate the ideal thickness of a double-paned unit. Problems arise with the use of triple glazing to further reduce heat loss in IGU. The combination of thickness and weight results in units that are too heavy for most residential or commercial glass systems, especially if these panels are contained within a moving frame or belt.
This trade-off does not apply to insulated glass vacuum (VIG), or evacuated glass, such as heat loss due to convection removed, leaving radiation loss and conduction through the edge seal and required supporting pillars above the face area. This VIG unit has most of the air expelled from the space between the panels, leaving a nearly complete vacuum. The VIG units that are currently on the market are tightly sealed around them with stained glass, ie glass frit (powder glass) which has a reduced melting point heated to join the component. This creates a stressed glass seal with increased temperature differences across the unit. This stress can limit the maximum permissible temperature differential. One manufacturer recommends 35 Â ° C. Close pillars are needed to strengthen the glass to withstand atmospheric pressure. Pillar distance and insulating limit diameters achieved by available designs from the 1990s to R = 4.7 hours Ã, Â ° FÃ, Â · ft2/BTU (0.83 m2Ã, Â · K/W) were no better than a high quality double glazed glass insulation glass unit. The product recently claimed the performance of R = 14 hours Ã, Â ° FÃ, Â · ft2/BTU (2.5 m2Ã, Â · K/W) that exceeds three glass insulated glass units. The necessary internal pillars exclude applications where views are obstructed through the desired glass unit, which is mostly residential and commercial windows, and refrigerated food display cabinets.
Vacuum technology is also used in some non-transparent insulation products called isolated vacuum panels.
The old-established way to improve insulation performance is to replace air in space with lower thermal conductivity gas. Convective heat transfer gas is a function of specific viscosity and heat. Monoatomic gases such as argon, krypton and xenon are often used because (at normal temperatures) they do not carry heat in rotation mode, resulting in lower heat capacity than poly-atom gases. Argon has 67% thermal conductivity of air, krypton has about half the argon conductivity. Argon is almost 1% of the atmosphere and is isolated with moderate costs. Krypton and xenon are just atmospheric trace components and very expensive. All these "noble" gases are non-toxic, clear, odorless, chemically inert, and commercially available for their widespread application in the industry. Some manufacturers also offer sulfur hexafluoride as an insulating gas, primarily to isolate the sound. It has only 2/3 of argon conductivity, but is stable, cheap and solid. However, sulfur hexafluoride is a very powerful greenhouse gas that contributes to global warming. In Europe, SF
6 under the F-Gas directive which prohibits or controls its use for some applications. Since 1 January 2006, SF
6 is prohibited as a tracking gas and in all applications except high voltage switchgear.
In general, the more effective gas is in the optimum thickness, the thinner the optimum thickness. For example, the optimal thickness for krypton is lower than argon, and lower for argon than air. However, since it is difficult to determine whether the gas in the IGU has been mixed with air at the time of manufacture (or to be mixed with air after installation), many designers prefer to use thicker gaps than to optimally fill the gas if pure. Argon is commonly used in insulated glass because it is the most affordable. Krypton, which is much more expensive, is generally not used except for producing very thin double glass units or triple-glazed units with very high performance. Xenon has found very few applications in IGU due to cost.
Properties of heat insulation
The effectiveness of insulated glasses can be expressed as R-values. The higher the R value, the greater its resistance to heat transfer. The standard IGU consisting of uncoated glass panels (or lamps) with air inside the cavity between the lamps usually has a R value of 0.35 K Â · m 2 /W.
Using the US customary unit, the rule of thumb in standard IGU construction is that any change in the IGU component 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. A properly designed triple-glazed IGU with low emissivity coating on surfaces # 2 and # 4 and filled with argon gas in the cavity produces an IG unit with R-values ​​as high as R-5. Certain vacuum insulation glass units (VIGU) or multi-space IG units using coated plastic films produce R-values ​​as high as R-12.5
An additional layer of glass provides an opportunity for better insulation. While standard double glazing is most widely used, triple glazing is not common, and quadruple glass is produced for very cold environments such as Alaska. Even quintuple glazing (four cavities, five panes) is available - with a mid-pane insulation factor equivalent to a wall.
Acoustic isolation properties
In some situations, insulation refers to noise mitigation. In these circumstances, a large air space improves the quality of sound insulation or sound transmission class. Asymmetrical double glass, using different glass thickness than conventional symmetrical systems (same glass thickness used for both lamps) will enhance the acoustic attenuation properties of the IGU. If standard air space is used, sulfur hexafluoride may be used to replace or increase inert gas and improve the performance of acoustic attenuation.
Variations of other glass materials affect acoustics. The most widely used glass configurations for sound absorbers include laminated glass with varying thickness of interlayer and glass thickness. Including thermal aluminum air pressure barrier, thermal enhancement of thermal insulating glass can improve acoustic performance by reducing the transmission of exterior noise sources in the fenestration system.
Reviewing the components of glass systems, including airspace materials used in insulating glass, can ensure an overall increase in voice transmission.
Longevity
The life of the IGU varies depending on the quality of the material used, the gap size between the inner and outer panels, the temperature difference, the workmanship and the mounting location in both the facing direction and geographic location, as well as the treatment received by the unit. IG units typically last from 10 to 25 years, with windows facing the equator often lasting less than 12 years. IGU usually carries a warranty for 10 to 20 years depending on the manufacturer. If IGU is changed (such as installation of a solar control film) the warranty may be canceled by the manufacturer.
The Insulating Glass Manufacturers Alliance (IGMA) conducted an extensive study to characterize the failure of commercial insulation glass units over a 25 year period.
For standard construction IG units, condensation collects between layers of glass when the perimeter seal has failed and when the desiccant has become saturated, and generally can only be removed by replacing the IGU. Seal failure and subsequent replacements result in significant factors in overall cost of having an IGU.
The large temperature difference between the inner and outer panels squeezes the spacer adhesive, which can eventually fail. Units with small gaps between panels are more susceptible to failure due to increased stress.
Changes in atmospheric pressure combined with wet weather can, in rare cases, eventually lead to filling the gap with water.
Flexible sealing surfaces prevent infiltration around the window unit may also degrade or tear or break. Replacement of this seal is difficult, because the IG window generally uses extruded channel frames without screws or seal retaining plates. Instead, the edge seal is mounted by pushing the one-way flexible lips shaped arrow into the slot on the extruded conduit, and often can not be easily extracted from the extruded slot for replacement.
In Canada, since the early 1990s, there have been several companies offering failed IG unit services. They provide open ventilation to the atmosphere with drilling holes in glass and/or spacer. This solution often reverses visible condensation, but can not clean the interior surfaces of glass and staining that may occur after long-term exposure to moisture. They may offer a warranty of 5 to 20 years. This solution lowers the value of window isolation, but it can be a "green" solution when windows are still in good condition. If the IG unit has a gas fill (eg argon or krypton or mixture) the gas is naturally lost and the R value suffers.
Since 2004, there have also been several companies offering the same restoration process for failed double-glazed units in the UK, and there is one company that offers the recovery of failed IG units in Ireland since 2010.
Thermal stress breakage
The cracking of thermal stress is no different for insulated glass and uninsulated glazes. Temperature difference in the glass panel surface can cause glass cracking. This usually happens where the glass is partially shaded and one part is heated in the sun. Colored glass increases thermal heating and stress, while annealing reduces the internal stress built into the glass during manufacturing leaving more available power to withstand thermal cracks.
Thermal expansion creates internal stress, or stress, in which the expanded warm material is retrained by a cooler material. Cracks may form when the voltage exceeds the strength of the material and the cracks will propagate until the stress at the tip of the crack is below the strength of the material. Usually cracks start and spread from the edge of a thin shaded piece where the material is weak and the tension is spread over a small glass volume compared to the open area. The thickness of the glass has no direct effect on the thermal crack in windows because both the thermal pressure and material strength are proportional to the thickness. While thicker glass will have more power remaining after supporting wind loads, it's usually only a significant factor for large glass units in tall buildings and winds increasing heat dissipation. Increased resistance to cracked glass in heavy commercial and residential commercial applications is more reliably the result of using tempered glass to meet building security codes that require its use to reduce injury severity when damaged. The cutting edge trim should be reduced by pre-wastage and that removes the stress concentration made during glass cutting and which significantly increases the voltage required to initiate the slit from the edge. The cost for treating tempered glass is much greater than the cost difference between glass 1/8 "(3mm) and 3/16" (5mm) or 1/4 "(6.5mm) materials, encouraging glaziers to suggest replacing cracked glass with thicker. Glass can also avoid disclosing to customers that tempered glass should be used initially.
Estimating heat loss from double-glazed windows
Given the thermal properties of sling, frame, and threshold, and the dimensions of glass and thermal properties of glass, the rate of heat transfer for a given window and a series of conditions can be calculated. This can be calculated in kW (kilowatt), but more useful for cost benefit calculations can be expressed as kWh pa (kilowatt hours per year), based on the general condition for a year for a particular location.
Glass panels in double glass windows transmit heat in both directions by radiation, through glass by conduction and across the gap between the panels by convection, by conduction through the frame, and by infiltration around the perimeter seals and the ranch seals into the building. The actual rate will vary with conditions throughout the year, and while solar may be much welcomed in winter (depending on the local climate), it can lead to an increase in the cost of air conditioning in the summer. Unwanted heat transfer can be reduced by for example using curtains at night in winter and using sun shades during the day in summer. In an effort to provide a useful comparison between alternative window construction, the British Fortration Rating Council has defined the "Window Energy Rating" WER, ranging from A to the best up to B and C etc. This takes into account the combination of heat loss. through the window (U value, opposite of R-value), solar gain (g value), and loss through air leakage around frame (L value). For example, A Rated window will benefit from heat generated from solar heat due to loss in other ways (but most of this advantage will occur during the summer, when heat may not be required by building occupants.). This provides better thermal performance than ordinary walls.
See also
- Wall curtain
- Passive solar design
- Window
References
- The Chemical Handbook & amp; Physics, 62, CRC Press, ISBN 0-8493-0462-8
External links
- Media related to Insulated glazing in Wikimedia Commons
Source of the article : Wikipedia
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