Simplified view of the components of solar heat gain. Heat gain includes the transmitted solar energy and the inward flowing component of absorbed radiation.
The second major energy-performance characteristic of windows is the ability to control solar heat gain through the glazing. Solar heat gain through windows is a significant factor in determining the cooling load of many commercial buildings. The origin of solar heat gain is the direct and diffuse radiation coming from the sun and the sky (or reflected from the ground and other surfaces). Some radiation is directly transmitted through the glazing to the building interior, and some may be absorbed in the glazing and indirectly admitted to the inside. Some radiation absorbed by the frame will also contribute to overall window solar heat gain factor. Other thermal (nonsolar) heat transfer effects are included in the U-factor of the window.
Center-of-glass solar heat gain values of double pane units
Window standards are now moving away from a previous standard referred to as Shading Coefficient (SC) to Solar Heat Gain Coefficient (SHGC), which is defined as that fraction of incident solar radiation that actually enters a building through the entire window assembly as heat gain. To perform an approximate conversion from SC to SHGC, multiply the SC value by 0.87.
The SHGC is also affected by shading from the frame as well as the ratio of glazing and frame. The SHGC is expressed as a dimensionless number from 0 to 1. A high coefficient signifies high heat gain, while a low coefficient means low heat gain.
Solar heat gain is influenced by the glazing type, the number of panes, and any glass coatings. Solar heat gain of glazing ranges from above 80% for uncoated water-white clear glass to less than 20% for highly reflective coatings on tinted glass. A typical double-pane IGU has a SHGC of around 0.70. This value decreases somewhat by adding a low-E coating and decreased substantially when adding a tint (see figure to the right). Since the area of a frame has a very low SHGC, the overall window SHGC is lower than the center-of-glass value.
Visible Transmittance (VT or Tvis)
Visible transmittance) is the amount of light in the visible portion of the spectrum that passes through a glazing material. A higher VT means there is more daylight in a space which, if designed properly, can offset electric lighting and its associated cooling loads. Visible transmittance is influenced by the glazing type, the number of panes, and any glass coatings. Visible transmittance of glazing ranges from above 90% for uncoated water-white clear glass to less than 10% for highly reflective coatingson tinted glass. A typical double-pane IGU had a VT of around 78%. This value decreases somewhat by adding a low-E coating and decreased substantially when adding a tint (see figure to the right). VT values for the whole window are always less than center-of-glass values since the VT of the frame is.
Light-to-Solar-Gain Ratio
In the past, windows that reduced solar gain (with tints and coatings) also reduced visible transmittance. However, new high-performance tinted glass and low-solar-gain low-E coatings have made it possible to reduce solar heat gain with little reduction in visible transmittance. Because the concept of separating solar gain control and light control is so important, measures have been developed to reflect this. The LSG ratio is defined as a ratio between visible transmittance (VT) and solar heat gain coefficient (SHGC).
Light-to-Solar-Gain Ratio
In the past, windows that reduced solar gain (with tints and coatings) also reduced visible transmittance. However, new high-performance tinted glass and low-solar-gain low-E coatings have made it possible to reduce solar heat gain with little reduction in visible transmittance. Because the concept of separating solar gain control and light control is so important, measures have been developed to reflect this. The LSG ratio is defined as a ratio between visible transmittance (VT) and solar heat gain coefficient (SHGC).
The image illustrates the center-of-glass properties for the options used in the Facade Design Tool. A double-glazed unit with clear glass (B) has a visible transmittance (VT) of 0.79 and a solar heat gain coefficient (SHGC) of 0.70, so the LSG is VT/SHGC = 1.12. Bronze-tinted glass in a double-glazed unit (C) has a visible transmittance of 0.45 and a solar heat gain coefficient of 0.50, which results in an LSG ratio of 0.89. This illustrates that while the bronze tint lowers the SHGC, it lowers the VT even more compared to clear glass. The double-glazed unit with a high-performance tint (E) has a relatively high VT of 0.52 but a lower SHGC of 0.29, resulting in an LSG of 1.80—significantly better than the bronze tint. A clear double-glazed unit with a low-solar-gain low-E coating (H) reduces the SHGC significantly, to 0.27, but retains a relatively high VT of 0.64, producing an LSG ratio of 2.4—far superior to those for clear or tinted glass.
U-factor (Insulating Value)
For windows, a principle energy concern is their ability to control heat loss. Heat flows from warmer to cooler bodies, thus from the inside face of a window to the outside in winter, reversing direction in summer. Overall heat flow from the warmer to cooler side of a window unit is a complex interaction of all three basic heat transfer mechanisms—conduction, convection, and long-wave radiation (see figure to the right). A window assembly's capacity to resist this heat transfer is referred to as its insulating value, or u-factor.
Conduction occurs directly through glass, and the air cavity within double-glazed IGUs, as well as through a window's spacers and frames. Some frame materials, like wood, have relatively low conduction rates. The higher conduction rates of other materials, like metals, have to be mitigated with discontinuities, or thermal breaks, in the frame to avoid energy loss.
Convection within a window unit occurs in three places: the interior and exterior glazing surfaces, and within the air cavity between glazing layers. On the interior, a cold interior glazing surface chills the adjacent air. This denser cold air then falls, starting a convection current. People often perceive this air flow as a draft caused by leaky windows, instead of recognizing that the remedy correctly lies with a window that provides a warmer glass surface (see figure to the right). On the exterior, the air film against the glazing contributes to the window's insulating value. As wind blows (convection), the effectiveness of this air film is diminished, contributing to a higher heat rate loss. Within the air cavity, temperature-induced convection currents facilitate heat transfer. By adjusting the cavity width, adding more cavities, or choosing a gas fill that insulates better than air, windows can be designed to reduce this effect.
All objects emit invisible thermal radiation, with warmer objects emitting more than colder ones. Through radiant exchange, the objects in the room, and especially the people (who are often the warmest objects), radiate their heat to the colder window. People often feel the chill from this radiant heat loss, especially on the exposed skin of their hands and faces, but they attribute the chill to cool room air rather than to a cold window surface. Similarly, if the glass temperature is higher than skin temperature, which occurs when the sun shines on heat-absorbing glass, heat will be radiated from the glass to the body, potentially producing thermal discomfort.
Determining Insulating Value
The U-factor (also referred to as U-value) is the standard way to quantify overall heat flow. For windows, it expresses the total heat transfer coefficient of the system (in Btu/hr-sf-°F), and includes conductive, convective, and radiative heat transfer. It represents the heat flow per hour (in Btus per hour or watts) through each square foot of window for a 1 degree Fahrenheit temperature difference between the indoor and outdoor air temperature. The insulating value or R-value (resistance to heat transfer) is the reciprocal of the total U-factor (R=1/U). The higher the R-value of a material, the higher the insulating value; the smaller the U-factor, the lower the rate of heat flow.
Given that the thermal properties and the various materials within a window unit, the U-factor is commonly expressed in two ways:
- The U-factor of the total window assembly combines the insulating value of the glazing proper, the edge effects in the IGU, and the window frame and sash.
- The center-of-glass U-factor assumes that heat flows perpendicular to the window plane, without addressing the impact of the frame edge effects and material.
The U-factor of the glazing portion of the window unit is affected primarily by the total number of glazing layers (panes), their dimension, the type of gas within their cavity, and the characteristic of coatings on the various glazing surfaces. As windows are complex three-dimensional assemblies, in which materials and cross sections change in a relatively short distance, it is limiting, however, to simply consider glazing. For example, metal spacers at the edge of an IGU have a much higher heat flow than the center of the insulating glass, which causes increased heat loss along the outer edge of the glass.
Overall U-factor
The relative impact of these "edge effects" becomes more important as the insulating value of the entire assembly increases, and in small units where the ratio of edge to center-of-glass area is high. Since the U-factors vary for the glass, edge-of-glass zone, and frame, it can be misleading to compare the U-factors of windows from different manufacturers if they are not carefully and consistently described. Calculation methods developed by the National Fenestration Rating Council(NFRC) address this concern.
In addition to the thermal properties of window assembly materials, weather conditions, such as interior/exterior temperature differential and wind speed, also impact U-factor. Window manufacturers typically list a winter U-factor for determined under relatively harsh conditions: 15 mph wind, 70 degrees Fahrenheit indoors, 0 degrees Fahrenheit outdoors. A specific set of assumptions and procedures must be followed to calculate the overall U-factor of a window unit using the NFRC method. For instance, the NFRC values are for a standard window size-the actual U-factor of a specific unit varies with size. Originally developed for manufactured window units, new methods are available to determine the U-factor of site-built assemblies.
The U-factor of a window unit is rated based on a vertical position. A change in mounting angle affects a window's U-factor. The same unit installed on a sloped roof at 20° from horizontal would have a U-factor 10–20% higher than in the vertical position (under winter conditions).
Low-E Coatings
When heat or light energy is absorbed by glass, it is either convected away by moving air or reradiated by the glass surface. The ability of a material to radiate energy is called its emissivity. All materials, including windows, emit (or radiate) heat in the form of long-wave, far-infrared energy depending on their temperature. This emission of radiant heat is one of the important components of heat transfer for a window. Thus reducing the window's emittance can greatly improve its insulating properties.
Standard clear glass has an emittance of 0.84 over the long-wave portion of the spectrum, meaning that it emits 84% of the energy possible for an object at its temperature. It also means that 84% of the long-wave radiation striking the surface of the glass is absorbed and only 16% is reflected . By comparison, low-E glass coatings can have an emittance as low as 0.04. Such glazing would emit only 4% of the energy possible at its temperature, and thus reflect 96% of the incident long-wave, infrared radiation. Window manufacturers' product information may not list emittance ratings. Rather, the effect of the low-E coating is incorporated into the U-factor for the unit or glazing assembly.
The solar reflectance of low-E coatings can be manipulated to include specific parts of the visible and infrared spectrum. This is the origin of the term spectrally selective coatings, which selects specific portions of the energy spectrum, so that desirable wavelengths of energy are transmitted and others specifically reflected. A glazing material can then be designed to optimize energy flows for solar heating, daylighting, and cooling.
(Spectral transmittance curves for glazings with low-emittance coatings (Source: Lawrence Berkeley National Laboratory).
With conventional clear glazing, a significant amount of solar radiation passes through the window, and heat from objects within the space is reradiated back into the glass, then from the glass to the outside of the window. A glazing design for maximizing energy efficiency during underheated periods would ideally allow all of the solar spectrum to pass through, but would block the reradiation of heat from the inside of the space. The first low-E coatings, intended mainly for residential applications, were designed to have a high solar heat gain coefficient and a high visible transmittance to allow the maximum amount of sunlight into the interior while reducing the U-factor significantly. A glazing designed to minimize summer heat gains, but allow for some daylighting, would allow most visible light through, but would block all other portions of the solar spectrum, including ultraviolet and near-infrared radiation, as well as long-wave heat radiated from outside objects, such as pavement and adjacent buildings. These second-generation low-E coatings still maintain a low U-factor, but are designed to reflect the solar near-infrared radiation, thus reducing the total SHGC while providing high levels of daylight transmission (see figure to the right).
Low-solar-gain coatings reduce the beneficial solar gain that could be used to offset heating loads, but in most commercial buildings this is significantly outweighed by the solar control benefits. In commercial buildings, it is common to apply low-E coatings to both tinted and clear glass. While the tint lowers the visible transmittance somewhat, it contributes to solar heat gain reduction and glare control. Low-E coatings can be formulated to have a broad range of solar control characteristics while maintaining a low U-factor.
There are two basic processes for making low-E coatings—sputtered and pyrolytic. Sputtered coatings are multilayered coatings that are typically comprised of metals, metal oxides, and metal nitrides. These materials are deposited on glass or plastic film in a vacuum chamber in a process called physical vapor deposition. Although these coatings range from three to possibly more than thirteen layers, the total thickness of a sputtered coating is only one ten thousandth the thickness of a human hair. Sputtered coatings often use one or more layers of silver to achieve their heat reflecting properties. Since silver is an inherently soft material that is susceptible to corrosion, the silver layer(s) must be surrounded by other materials that act as barrier layers to minimize the effects of humidity and physical contact. Historically, sputtered coatings were described as soft-coat low-E? because they offered little resistance to chemical or mechanical attack. While advances in material science have significantly improved the chemical and mechanical durability of some sputtered coatings, the glass industry continues to generically refer to sputter coat products as "soft-coat low-E."
Most sputtered coatings are not sufficiently durable to be used in monolithic applications; however, when the coated surface is positioned facing the air space of a sealed insulating glass unit, the coating should last as long as the sealed glass unit. Sputtered coatings have emittance as low as 0.02 which are substantially lower than those for pyrolytic coatings.
A typical pyrolytic coating is a metallic oxide, most commonly tin oxide with some additives, which is bonded to the glass while it is in a semi-molten state. The process by which the coating is applied to the glass is called chemical vapor deposition. The result is a baked-on surface layer that is quite hard and thus very durable, which is why pyrolytic low-E is sometimes referred to as "hard-coat low-E." A pyrolytic coating can be ten to twenty times thicker than a sputtered coating but is still extremely thin. Pyrolytic coatings can be exposed to air and cleaned with traditional glass cleaning products and techniques without damaging the coating.
Because of their inherent chemical and mechanical durability, pyrolytic coatings may be used in monolithic applications, subject to manufacturer approval. They are also used in multi-layer window systems where there is air flow between the glazings as well as with non-sealed glazed units. In general, though, pyrolytic low-E is most commonly used in sealed insulating glass units with the low-E surface facing the sealed air space
Low-solar-gain low-E coatings on plastic films can also be applied to existing glass as a retrofit measure, thus reducing the SHGC of an existing clear glass considerably while maintaining a high visible transmittance and lower U-factor. Other conventional tinted and reflective films will also reduce the SHGC but at the cost of lower visible transmittance. Reflective mirror-like metallic films can also decrease the U-factor, since the surface facing the room has a lower emittance than uncoated glass.
Reflective Coatings
As the SHGC falls in single-pane tinted glazings, the daylight transmission (VT) drops even faster, and there are practical limits on how low the SHGC can be made using tints. If larger reductions are desired, a reflective coating can be used to lower the solar heat gain coefficient by increasing the surface reflectivity of the material. These coatings usually consist of thin metallic or metal oxide layers. The reflective coatings come in various metallic colors—silver, gold, bronze—and they can be applied to clear or tinted glazing. The solar heat gain coefficient can be reduced by varying degrees, depending on the thickness and reflectivity of the coating, and its location in the glazing system. Some reflective coatings are durable and can be applied to exposed surfaces; others must be protected in sealed insulating glass units. The emittance of the coating creates modest changes in the U-factor (see figure to the right).
Similar to tinted films in retrofit situations, reflective coatings may be applied to the inner glass surface of an existing window by means of an adhesive-bonded, metallic-coated plastic film. The applied films are effective at reducing solar gains but are not as durable as some types of coated glass. As with tinted glazing, the visible transmittance of a reflective glazing usually declines more than the solar heat gain coefficient. Reflective glazings are usually used in commercial buildings for large windows, for hot climates, or for windows with substantial solar heat gains. Reflective glazing is also used by many architects because of its glare control and uniform, exterior appearance.
Special consideration should always be given to the effect of the reflective glazing on the outside. Acting like a mirror, the reflective glass intensifies the sun's effects, and should be avoided (or is not permitted by local zoning regulations) in some locations because of its impact on adjacent buildings. It is also important to remember that reflective glass acts like a mirror on the side facing the light. Thus, a reflective window that acts like a mirror to the outside during the day will look like a mirror on the inside during the night. These coatings will not provide visual privacy at night if interior lights are on.
Center-of-glass values of double pane units with and without reflective coating.
Tinted Glazing
Glass is available in a number of tints which absorb a portion of the solar heat and block daylight. Tinting changes the color of the window and can increase visual privacy. The primary uses for tinted glass are reducing glare from the bright outdoors and reducing the amount of solar energy transmitted through the glass.
Tinted glazings retain their transparency from the inside, although the brightness of the outward view is reduced and the color is changed. The most common colors are neutral gray, bronze, and blue-green, which do not greatly alter the perceived color of the view and tend to blend well with other architectural colors.
Tinted glass is made by altering the chemical formulation of the glass with special inorganic additives. The color is durable and does not change over time. Its color and density changes with the thickness of the glass. Coatings can also be applied after manufacture. Every change in color or combination of different glass types affects visible transmittance, solar heat gain coefficient,reflectivity, and other properties. Glass manufacturers list these properties for every color, thickness, and assembly of glass type they produce.
Tinted glazings are specially formulated to maximize their absorption across some or all of the solar spectrum and are often referred to as heat-absorbing. All of the absorbed solar energy is initially transformed into heat within the glass, thus raising the glass temperature. Depending upon climatic conditions, up to 50% of the heat absorbed in a single pane of tinted glass may then be transferred to the inside via radiation and convection. Thus, there may be only a modest reduction in overall solar heat gain compared to other glazings. This heat gain from absorption that is transmitted to the room leads to discomfort near tinted windows as well. Heat-absorbing glass provides more effective sun control when used as the outer layer of a double-pane window. Traditional tinted glazing, bronze and gray, often force a trade-off between visible light and solar gain. There is a greater reduction in visible transmittance than in solar heat gain coefficient (see figure to the right). This can decrease glare by reducing the apparent brightness of the glass surface, but it also diminishes the amount of daylight entering the room. For windows where daylighting is desirable, it may be more satisfactory to use a high-performance tint or coating along with other means of controlling glare. Tinted glazings can provide a measure of visual privacy during the day, when they reduce visibility from the outdoors. However, at night the effect is reversed and it is more difficult to see outdoors from the inside, especially if the tint is combined with a reflective coating.
To address the problem of reducing daylight with traditional tinted glazing, glass manufacturers have developed high-performance tinted glass that is sometimes referred to as spectrally selective. This glass preferentially transmits the daylight portion of the solar spectrum but absorbs the near-infrared part of sunlight. This is accomplished with special additives during the float glass process. Like other tinted glass, it is durable and can be used in both monolithic and multiple-glazed window applications.
Spectrally selective glazings have a light blue or light green tint and have higher visible transmittance values than traditional bronze- or gray-tinted glass, but have lower solar heat gain coefficients. Because they are absorptive, they are best used as the outside glazing in a double-glazed unit. They can also be combined with low-E coatings to enhance their performance further. High-performance tinted glazings provide a substantial improvement over conventional clear, bronze, and gray glass, and a modest improvement over the existing green and blue-green color-tinted glasses that already have some selectivity.
Tinted glazing is more common in commercial windows than in residential windows. In retrofit situations, when windows are not being replaced, tinted plastic film may be applied to the inside surface of the glazing. The applied tinted films provide some reduction in solar gain compared to clear glass but are not as effective as spectrally selective films or reflective glue-on films, and are not as durable as tinted glass.
Laminated Glass
Laminated glass consists of a tough plastic interlayer made of polyvinyl butyral (PVB) bonded between two panes of glass under heat and pressure. Once sealed, the glass sandwich behaves as a single unit and looks like normal glass. Laminated glass provides durability, high performance, and multifunctional benefits while preserving aesthetic appearance.
Similar to car windshield glass, laminated glass may crack upon impact, but the glass fragments tend to adhere to the plastic interlayer rather than falling free and potentially causing injury. Laminated glass resolves many design problems, offering increased protection from the effects of disasters such as hurricanes, earthquakes, and bomb blasts.
Annealed, heat-strengthened, or tempered glass can be used to produce laminated glass; the glass layers may be of equal or unequal thickness. With respect to solar control, laminated glass retains the characteristics of the glass making up the assembly (see figure to the right). Reflective coatings and frit patterns may also be applied within a laminated glass sandwich. Laminated glass can also be used as a component of an insulated glazing unit.
Single-pane laminated glass with a spectrally selective low-E sputtered coating on plastic film sandwiched between two panes of glass offers the energy performance of single-pane, spectrally selective glass and the safety protection of laminated glass. However, in this configuration, since the low-E surface is not exposed to an air space, the lower emittance has no effect on the glazing U-factor and SHGC. With double-pane laminated glass, the full benefit of the low-E coating can be realized by placing the coating on one of the glass surfaces facing the air space.
Glass has inherently poor acoustic properties, but laminated glass, alone or combined with additional glass plies to form a sealed, insulating glass unit, outperforms other glazing assemblies. Laminated glass reduces noise transmission due to the PVB layer's sound-dampening characteristics.
Solar Control Window Film
Solar control window film reduces solar heat gain by reflection and absorption. As they also block solar heat gain in winter months, these films are ideal for cooling-dominated climates. Window films can be tinted for solar heat and glare control, but some recent window film options reflect solar heat while maintaining a relatively clear appearance. The lower a film's solar heat gain coefficient (SHGC), the less solar heat it transmits. The higher the visible transmittance (VT) number, the more light is transmitted. Window film does not provide substantial insulating benefits. To find certified window films, visit the NFRC's Certified Products Directory.
Window film often is applied to the room-side glass surface of windows. Since window film absorbs the portion of solar heat that it does not reflect or transmit, it increases the glass temperature and may cause thermal stress on the glass or insulated glazing seals, particularly on sunny but cold days. Before installing window film, be sure to check whether this interferes with the warranty conditions for your windows and whether self-installation would meet the window film's warranty requirements. Before having window film installed, it is advisable to have a window film professional check your windows' location, type and condition to match the appropriate film to the glass type. For more information on the factors to take into account when installing window film, check the Window Film Information Center by the International Window Film Association.
Manufacturer: Saint-Gobain Solar Gard LLC
| Film Series/Model Number | CPD Number | Film Tint | Film Location | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar Gard Silver AG 25 | SGF-K-001 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Autumn Bronze 30 | SGF-K-002 | BZ | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Hilite 70 | SGF-K-003 | CL | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 8mil Hilite 70 | SGF-K-004 | CL | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Silver 20 | SGF-K-005 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 10mil Silver 20 | SGF-K-006 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 4mil Silver 20 | SGF-K-007 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 8mil Silver 20 | SGF-K-008 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Silver 35 | SGF-K-009 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 8mil Silver 35 | SGF-K-010 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Silver 50 | SGF-K-011 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Slate 10 | SGF-K-012 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Slate 20 | SGF-K-013 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Slate 30 | SGF-K-014 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Slate 40 | SGF-K-015 | GY | Interior | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Thermal and Solar
Where glazing is to be used in applications where energy conservation is important, the thermal transmittance (U-value), light transmission (%), light reflectance and solar factor (g-value) properties of the glass and coatings should be specified. Testing in accordance with BS EN 410, BS EN 673 and BS EN 12898 is specified within the product conformity standards for most glasses to be used in construction.
We carry out testing in accordance with these standards and our Notified Body status allows measurements to contribute towards Attestation of Conformity (AoC), and ultimately CE marking. See our other notified body services for the initial type testing of glass construction products.
Gas Concentration
We are also able to measure the argon gas concentration using non-destructive methods on insulating glass units sent to our laboratory. The gas concentration can be compared with the requirements in BS EN 1279 part 3 Long term test method and requirements for gas leakage rate and for gas concentration tolerances. This service forms part of our overall product verification service where specified product performance can be compared with delivered product performance in buildings. Argon gas is primarily used to reduce heat loss in insulating units and the concentration level has a direct impact on the thermal performance and running costs of a building.
Standards
- BS EN 410, 'Glass in building. Determination of luminous and solar characteristics of glazing';
- BS EN 673, 'Glass in building. Determination of thermal transmittance (U value). Calculation method';
- BS EN 12898, 'Glass in building. Determination of the emissivity';
- ISO 9050:2003, 'Glass in building. Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors';
- BS ISO 13837:2008, 'Road vehicles. Safety glazing materials. Method for the determination of solar transmittance';
- BS EN 1279-3:2002, 'Glass in building. Insulating glass unitsLong term test method and requirements for gas leakage rate and for gas concentration tolerances'.
By: - M Z HAQUE
MBA, M.Ed, B.Ed, B.Sc (Math)
MBA, M.Ed, B.Ed, B.Sc (Math)
source:-1)http://www.glass-ts.com/thermal-and-solar?gclid=CJrx-6CDgLwCFcoE4god2GMAbA
2) http://www.commercialwindows.org/films.php
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