An extensive selection of glass-related terms and phrases are defined.
The acoustic performance of windows and glazing assemblies may be defined by a number of terms; the most common being the acoustic performance measured at octave centre frequencies of 125, 250, 500, 1000, 2000 and 4000 Hertz. The attenuation of various glass configurations needs to be established by measurement and used as a guide to the acoustic attenuation performance of the glass. There are also single figure acoustic indices, the two most commonly used being the weighted reduction, Rw, which includes a correction for the varying sensitivity of the human ear at different frequencies and traffic noise reduction, RA,tr, which is relative to a standard traffic noise spectrum. The above terms have now been integrated into a single number quantity in accordance with EN ISO 717-1, which defines three terms as follows;
Where Rw is called the weighted sound reduction index, which takes account of the human ears sensitivity to a range of frequencies and may be used to compare the performance of alternative products. C is the adaptation term for pink noise, which considers higher frequencies and is determined by the equation
(Rw + C) = RA
Ctr is the adaptation term for the traffic noise spectrum, which considers lower frequencies and is determined by the equation
(Rw + Ctr) = RA,tr
For further information regarding acoustic performance solutions and Guardian's range of laminated glass products with special sound control features please refer to our specific documents which can be obtained from our Guardian technical centers or from your local sales representative.
Float glass (also called “flat” glass) that has not been heat-strengthened or tempered is “annealed glass.”
Annealing float glass is the process of controlled cooling to prevent residual stress in the glass and is an inherent operation of the float glass manufacturing process. Annealed glass can be cut, machined, drilled, edged and polished.
The ability of transmitted daylight through the glazing to portray a variety of colors compared to those seen under daylight without the glazing. Scale is 1 – 100.
For instance, a low CRI causes colors to appear washed out, while a high CRI causes colors to appear vibrant and natural.
In commercial glass, CRI indicates the effect the specific glass configuration has on the appearance of objects viewed through the glass.
A method of securing glass in a frame by use of a dry, preformed resilient gasket.
The condition of the edge of finished architectural glass products can impact the long-term structural performance of the glass system.
The following table of edge types is provided to help design professionals understand fabrication processes and typical applications for architectural glass.
All float glass contains some level of imperfection. One type of imperfection is nickel sulfide (NiS) inclusion. Most NiS inclusions are stable and cause no problems. There is, however, the potential for NiS inclusions that may cause spontaneous breakage in tempered glass without any load or thermal stress being applied.
Heat strengthened glass has been subjected to a heating and cooling cycle and is generally twice as strong as annealed glass of the same thickness and configuration. Heat strengthened glass must comply with all the requirements of EN 1863: Parts 1 & 2. Heat strengthened glass has greater resistance to thermal loads than annealed glass and, when broken in service, the fragments are typically larger than those of toughened glass. Heat strengthened glass is not a safety glass product as defined by European Building Regulations and Standards. This type of glass is intended for general glazing, where additional strength is required to withstand wind load and thermal stress. It does not require the strength of toughened glass, and is intended for applications that do not specifically require a safety glass product. Heat trengthened glass cannot be cut or drilled after heat strengthening and any alterations, such as edge-grinding, sandblasting or acid-etching, will weaken the glass and can cause premature failure.
The energy generated by radiated heat sources such as electric elements and any object that absorbs heat and reradiate that heat is producing long-wave infrared energy. An example of the latter is when short-wave energy from the sun is absorbed by glazing; it is converted into long-wave energy when radiated from the glazing.
Insulating glass (also referred to as insulated glass) refers to two or more lites of glass sealed around the edges with an air space between, to form a single unit.
Commonly referred to as an “IG unit,” insulating glass is the most effective way to reduce air-to-air heat transfer through the glazing. When used in conjunction with low emissivity and/or reflective glass coatings, IG units become effective means to conserve energy and comply with energy regulations.
Laminated glass consists of two or more lites permanently bonded together with one or more polyvinylbutyral (PVB) interlayers using heat and pressure. The glass and interlayers can be a variety of colours and thicknesses designed to meet relevant building code standards and requirements as necessary. Laminated glass can be broken, but the fragments will tend to adhere to the plastic (PVB) interlayer and remain largely intact, reducing the risk of injury. Laminated glass is considered "safety glass" because it meets the requirements of the various European Building Regulations and Standards. Heat strengthened and toughened glass can be incorporated into laminated glass units to further strengthen the impact resistance. Bomb blast protection, the need for sound attenuation and ballistic or security concerns are all uses for laminated glass.
In Europe low E coatings are generally neutral in appearance and designed to reduce heat loss through the glass from inside the building. The coating reflects long-wave energy and subsequently reduces the u-value of the glass. Low e coatings may also be incorporated into solar control coatings to provide both benefits of retaining heat in the building and reflecting heat from the sun providing improved energy control.
Moiré is an optical phenomenon that may appear as a wavy, rippled or circular pattern under certain lighting conditions. Moiré patterns may be created when one pane with a repetitive pattern is placed over another and the two are not aligned. This may occur when the outer pane has a pattern which casts a shadow on a pane behind it which flood coated as in a spandrel. Another possibility under certain lighting conditions is a reflection from a glass surface in vision glazing.
A single pane of glass.
Glass with a coating applied at high temperature and fired into the surface of the glass during the float glass manufacturing process.
The ratio between daylight transmission and solar factor.
The solar factor ( total transmittance) of a glass relative to that of 3 mm clear float glass (0.87) and is used as a performance comparison. The lower the shading coefficient number, the lower the amount of solar heat transmitted. The short wave shading coefficient is the direct transmittance (T) of the glass as a factor of the solar factor or total transmittance ( g or TT) of 3 mm clear float glass (T÷0.87). The long wave-shading coefficient is the internally re-radiated energy that the glass has absorbed as a factor of the solar factor ( total transmittance) of 3 mm clear float glass. It is determined by subtracting the direct transmittance from the solar factor ( total transmittance) of the subject glass and then dividing by the solar factor ( total transmittance) of 3 mm clear float glass (g-T ÷ 0.87).
Tinted and/or coated glass that reduces the amount of solar heat gain into the building.
Radiant Energy from the sun having a wavelength range of 300 to 2500 nm, which includes ultraviolet ( 300 to 380 nm), visible light ( 380 to 780 nm) and near infrared energy ( 780 to 2500 nm).
The spacer in an insulating glass unit is at the perimeter between the panes and ensures a constant width of cavity. Standard spacer is constructed from either aluminium or stainless steel, but the recent development of warm edge spacers now includes open cell foams, polyamides, plastic, polyisobutylene and composite constructions.
Spandrel glass is the area of glass panels that conceal structural building components such as columns, floor slabs, heating, ventilating and air conditioning (HVAC) systems, electrical wiring, plumbing, etc. often contained within false ceilings on each floor of a building, spandrel glass is typically located between vision glasses on each floor.
High performance glazing that admits the highest possible levels of daylight, while preventing the transmission of as much solar heat as possible. By reducing solar heat gain in summer and preventing heat loss in winter, the buildings ongoing energy cost are reduced.
This is low E or solar control glass which has a coating applied through an off-line process. Glass is passed into a vacuum chamber where ionized gas bombards a metal target with ions. Atoms of the target material are vaporized and then deposited in a thin uniform film on the surface of the glass.
Strain pattern refers to a specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarised light (also referred to as "quench marks", "leopard spots" or anisotropy). The phenomena are caused by the localised stresses imparted by the rapid air cooling of the heat treatment process. Strain pattern is characteristic of heat treated glass and is not considered a defect.
Thermally tempered glass is approximately four times stronger than annealed glass of the same thickness and configuration, and must comply with the requirements of EN 12150: Parts 1 & 2. When broken, it will break into many relatively small fragments, which are less likely to cause serious injury. The typical process to produce thermally tempered glass involves heating the glass to over 600 degrees Celsius, then rapidly cooling to lock the glass surfaces in a state of compression and the core in a state of tension as shown in the diagram. Tempered glass is often referred to as "safety glass" because it meets the requirements of the various European Building Regulations and Standards that set standards for safety glass. This type of glass is intended for general glazing, and safety glazing such as in sliding doors, building entrances, bath and shower enclosures, interior partitions and other uses requiring increased strength and safety properties. Toughened glass cannot be further processed - such as cutting, drilling, edge grinding -after toughening and any alterations, such as sandblasting or acid-etching will weaken the glass and can cause premature failure.
Thermal breakage can be influenced by a number of factors. A critical factor in the early stages of glass selection is whether or not the glass will be shaded. When glass becomes partially shaded by buildings, overhangs or extensions, temperature differentials may become high within the glass resulting in excessive stress, which can result in thermal breakage. A thermal stress analysis should be completed for each project in order to determine whether the glass needs to be tempered or heat strengthened.
A body coloured glass which reduces both visible light and solar heat transmission. The solar heat absorption of body tinted glass is relatively high and it is prone to thermal overstressing so it often has to be tempered in order to prevent breakage.
Ultraviolet radiant energy from the sun having a wavelength ranfe of 300 to 380 nm.
The percentage of incident ultraviolet energy that is directly transmitted through the glass. Long-term exposure to UV light may result in fabric and pigment fading, plastic deterioration and changes to the appearance of many types of wood.
SunGuard provides solutions that will minimize the effects of long-term exposure to UV light.
Also called "U-value"
A measure of the heat gain or loss through glass due to the difference between indoor and outdoor air temperatures. It is also referred to as the overall coefficient of heat transfer. A lower U-factor indicates better insulating properties.
Radiant energy in the wavelength range of 380 to 780 nm with III. D65 and CIE 2 observer.
Warm edge spacer technology is another option for improving the thermal properties, reducing condensation and reducing u values in insulating glass units. There are a number of warm-edge spacer designs available, all of which thermally break the metal-to-glass contact point to some degree, while offering varying levels of structural integrity that may or may not be suitable for commercial applications. Warm-edge spacers can significantly reduce heat conduction when compared to conventional aluminium spacers.
Wind and snow loads are usually considered and calculated in accordance with local Standards and Regulations depending where the building is sited. Guardian is capable of determining the minimum thickness for the type of glass to be installed to resist the specified loads. These loads must be addressed in the early stages of design. Contact your Guardian representative or local technical department for assistance with wind and snow load analysis.