Glass. Double/Triple Glazing. Solar Control Double Glazing
Multi-layered, insulating glazing units are manufactured out of two or more sheets of glass – (1) (clear float glass, tinted and coated glass, rough cast and patterned glass) separated by one or more air- or gas-filled cavities. Multi-layered glazing units can, depending on the assembly, provide high thermal and/or sound insulation (e.g. sound-reducing units, solar protection units, heat-absorbing units, laminated glass with intermediate layers).
There is dried air or a special gas in the spaces between the glass sheets. Different edge treatments define three types of units: full glass edge welding – (1)A; edges welded together with inserts – (b)B; glued organic edge sealing – (1)C.
Solar Control Double Glazing. Solar control double glazing is characterised by a high light transmittance and an energy transmittance which is as low as possible. This is achieved by a very thin layer of precious metal deposited on the protected inside layer of one of the panes. Apart from its solar control qualities, solar control double glazing fulfils all the requirements of highly insulating double glazing, with к values up to 1.2W/m2K. The choice of a wide range of colours and colourless tones, augmented by the availability of colour-matched single- and double-glazed fagade panels, presents many design opportunities. Solar control glass can be combined with sound-reduction glass, armoured glass, laminated glass, safety glass or ornamental/cast glass as either internal or external sheets. A combination with wired glass is not possible.
Each glass type is identified by colour (as seen from the outside) as well as by a pair of values: the first is the light transmittance and the second the total energy transmittance, and both are given as percentages. Example: auresin (= blue) 40/26.
Light transmittance TL in the 380-780 nm (nanometres) wavelength band, based on the light sensitivity of the human eye (%).
Light reflection RL from outside and inside (%). Colour rendering index Ra:
- Ra >90 = very good colour rendering;
- Ra >80 = good colour rendering.
UV transmittance Tuv in the 320-2500nm wavelength band is the sum of the direct energy transmission and the secondary heat emission (= radiation and convection) towards the inside.
The b value is the mean transmittance factor of the sun's energy based on an energy transmission of a 3 mm thick single pane of glass of 87%. Accordingly:
where g is the total energy transmittance.
Selectivity code S. S = TL/g. A higher value for the selectivity code S shows a favourable relationship between light transmittance (TL) and the total energy transmittance (g).
The thermal transmittance к of a glazing unit indicates how much energy is lost through the glass. The lower this value, the lower the heat loss. The к value of conventional double-glazing units is greatly dependent on the distance between the two sheets of glass and the contents of the cavity (air or inert gas). With solar-control glass, an improved к value is achieved because of the precious metal layer. Standard к values are based on a glass spacing of 12 mm.
Generally, colour rendering seems unaltered when looking through a glass window from inside a room. However, if a direct comparison is made between looking through the glass and through an open window, the slight toning produced by most glass is perceptible. Depending on the type of glass, this is usually grey or brown. This difference can also be seen when looking from outside a room through two panes set at a corner. The interior colour climate is only marginally effected by solar-control glazing since the spectral qualities of the daylight barely change. Colour rendering is expressed by the R index.
Multifunctional Double-Glazing Units. Owing to the increasing demands being placed on fagade elements, glazing is required to provide a wide range of functions: thermal insulation, sound reduction, solar control, personal security, fire protection, aesthetic and design aspects, environmental protection and sustainability. These functions demand an increased protection element which cannot be provided by conventional double glazing.
Multifunctional double-glazing units can combine several protection properties, and it is technically possible to fulfil almost all of those listed above. However, a standard multifunctional double-glazing unit is not yet commercially available – (4).
Date added: 2023-01-01; views: 344;