Energy Glazing
The 3rd generation energy glasses or the low-e glasses provide solar insulation letting the sunlight to go through the windows. This occurs due to the special coating of metals on the glass surface. This sort of coating on glasses consists of several metal oxides which reduce the transfer of heat from the inner side of the outer glasses and vice versa depending on the season. Therefore, during the summer they prevent the undesired heat to go through inside and during the winter the heat to go away. Also, in many cases the sun’s heat is not always undesirable, as in very cold climates.
It should be noted that energy glasses are never used by themselves, but in combination, depending on your needs and the money you can afford. For example, they may be combined with a triplex glass for more security or a triplex glass with acoustic membrane for better soundproofing. Also in some cases it may be used triple glazing too.
There are two kinds of energy glasses. Glasses of hard coating and soft coating. The glasses of hard coating are on the market for about 25 years, while in the Greek market we find them since 1997. They are produced by the chemical spraying method or otherwise the pyrolytic method, in other words this method is applied during the production of the glass when it is hot. The soft coating glasses were created after several years. They are produced completely differently from the ones of hard coating. In this case, the coating does not take place during the production of glass but later. This method is called natural spray method. The thickness of the coating is too thin (80-90nm) and consists of several films of metal oxides based on silver (Ag).
The most important indicators for the right choice of a glass are:
- 1. The U value or R value (W/m2 * K): The U value shows us how fast the heat is transferred between indoors and outdoors (in Watt) per m2 of a glass for heat difference of 1 Kelvin degree. Therefore, the lower is the rate of heat transfer (emissivity) the K follows.
- 2. Solar factor g: The solar factor. It is one of the most important indicators and expresses the percentage of the total solar energy that passes through the glass inwardly in relation to the amount of solar energy received. It is advisable for Greece, as the summer is very hot and lasts quite enough, the Solar Factor g should be in a low level.
- 3. Light Transmission LT: The optical transmittance. In case that we do not want all that heat from the sun during the summer but we just want the light then we should keep the LT high. A value of 65 % and more will be sufficient enough so as not to have the lights open in the house / shop.
- 4. Selectivity indicator (LT / g): It is a combination of the above that shows us the selectivity of a glass. That means how much light relative to the heat passes through the glass.
We can also improve the thermal insulation of a double glass by adding noble gases such as Argon inside the double glass and even better in combination with a gap of 16mm thickness that the energy glass perform better.
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