The importance of glass
The type of glass employed in the construction of windows plays a substantial role in terms of
energetic and acoustic absorption. Its choice must be based on a few essential parameters.
Let us briefly analyse the two
concepts of energetic and acoustic absorption.
The energetic absorption
The sun energy reaches the Earth principally in the form of three different types of rays, differing from one another in their wave length. The wave length is the distance between one wave and the next wave, measured in millionths of millimetres (nm=nanometres). Imagine the concentric waves generated by a stone thrown into a pond: the wave length is the distance from the crest of one wave to the crest of the next wave:
ultraviolet rays: human eyes cannot see them. Their wave length ranges between 280 and 380 nm (nanometres). Ultraviolet rays account for roughly 3% of total sun rays.
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rays visible by human eyes (light): Their wave length ranges from 380 to 780 nm (nanometres), and they account for 54% of total sun rays.
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infrared rays: (invisible, they are perceived as heat), wave length between 780 and 2500 nm (nanometres). Their share amounts to 43% of total sun rays.
By means of physical or chemical industrial processes very thin layers (at an atomic level) of noble metals are deposited onto the inner side of glass, in order to control, limit or absorb the rays, to which the glass is exposed.
Picture: technical terms, possible results in absorption tests:
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Light transmission (TL): luminous flux transmitted through the window glass with respect to the incoming luminous flux;
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Direct energetic transmission (TED): fraction of energetic sun flux transmitted directly through the window glass;
- Energetic reflex (RE): fraction of energetic sun flux reflected by the window glass;
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Energetic absorption (AE): fraction of the energetic sun flux absorbed by the window glass (warming up of the glass);
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Sun factor (FS) or total energetic transmission: the sun factor is the result of the interaction between the total energetic flux penetrating through the window glass and the incoming energetic sun flux.
The _U"(k) coefficient
The coefficient of thermal transmittance
k indicates the amount of heat per time unit, expressed in Watt, transmitted through 1m2 of glass surface for every degree of difference between the inside and the outside of the surface itself. The lower the value for
k,.the more isolating the glass surface.
The noble metals deposited on the glass allow up to 97% internal thermal reflex and guarantee very low values for
k. Compared with traditional window glass, this means as much as a constantly pleasant indoor temperature in any season of the year.
A careful choice of glass may help saving up to 70% air conditioning costs and up to 60% heating costs, if compared to standard glass: Purchase expenses will be made up for very quickly and decidedly more comfortable living conditions are ensured over a long term period.
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