|
The windowpane – an important element of the window |
 |
The insulated glazing is a part of the window to which we normally give little attention. For many, the windowpane’s only demand is to guarantee to let light through. Nevertheless, it appears that modern insulated glazing creates a cozy feeling as well as brings clear energy savings.
Our presentation has the purpose to show briefly, the qualities of an insulated glazing and to answer which aspects you should pay attention to when choosing a concrete kind of glazing.
Construction of the insulated glazing
The insulating glazing consists of two windowpanes which are separated by a spacer, normally with a gap of 15-16 mms. The space between the panes, filled with dried air or argon gas, is to increase the thermal insulation effect. To avoid enclosed air from getting humid, the spacer is filled with a molecular sieve ‒ a solid hygroscopic device made from granulate material. Alongside the complete edges, the panes are connected to the spacer with sealing materials, which guarantees the tightness of the system and limits the penetration of steam inside.
|
|
Insulation glazing – Characteristics
Basic functions of the insulating glazing are, besides letting sunlight through the increased thermal and sound insulation, due to different pane combinations, are improved desired effect and additionally improved window qualities:
-
Improved thermal insulation. This characteristic is expressed by the coefficient U [W/m²K], which defines the heat transfer through the windowpanes; the smaller, the better. By using panes with a low-emissivity coating (noble metal oxides, which are applied in thin layers onto the pane), which keeps the warmth in the space between the panes, and by filling the space with argon gas we gain the thermal insulation effect. Such a windowpane reaches a coefficient of U = 3,0 [W/m²K]. The energy consumption (to compensate the energy loss, which escapes through the windowpanes) is reduced by 60 %.
Improved sound insulation. We attain this effect by the different pane thickness in the system, the enlargement of the space between the panes and the use of laminated panes with a sound-absorbing special foil. The problem of sound absorption is complicated – different sound frequencies are reduced on different levels, because of this there doesn’t exist a simple correlation between the application of the pane and the reduction of the respective sound. Sound-absorbing panes reduce the noise in a range of approx. 35-51 dB. This means a decrease of the noise level by a coefficient of 3.5 to 5, according to the rule, a decrease of the sound level of 10 dB accounts for the fact, that the sound is perceived around half as loud.
Reducing the risk of burglary. We attain this quality by using laminated security glass in the system which persists of two panes which are connected by a PVB-foil with very high tear strength. The security level depends on the pane thickness and number of foil layers which were used for the pane production – from O2 to P5.
Reducing the risk of injury – by using laminated or tempered glass
Decorations and visual protection. A broad range of ornaments and solar protection offers panes with the desired esthetic and visual protection.
The described qualities are not mutually exclusive, i.e., panes can be improved with thermal insulation and sound absorption which at the same time make a break-in more difficult.
Till this day, panes still have one weak point. Glass and metal (aluminum spacers) are good heat conductors, because of that in the area of the spacer, significant heat losses do appear at the so-called thermal bridge. For this problem, there is a modern solution ‒ the "warm edge” from materials with low conductivity.
The advantages of this spacer are evident:
1. Reduction of the thermal bridge
2. Energy savings up to 6‒7 %
3. Esthetic matt look without metal reflection
4. Almost total avoidance of steam condensation on the windowpane edges, which takes place under certain circumstances, due to the higher and stable temperature on the inside surface of the panes.
5. The same mechanical and heat resistance as aluminium spacers.
What aspects should be especially considered when choosing the glazing?
1. Needs and requirements must be exactly defined. By reference to these the desired glazing system can be selected.
2. It should be made sure that the glazing is from a well-known manufacturer – every company is obliged to mark its product on the spacer with the security sign "B", the name of the manufacturer and production date. It is even better if the exact product description is applied to spacer.
Special qualities of the insulation glazing
After purchasing a window, we can observe in some cases characteristics at the multiple insulating glazing which can look disconcerting. Nevertheless, this is not caused by glass mistakes. They normally result from the physical properties of the glass and the construction of the insulating glazing:
Interferences
With insulating glazing from floatglas, interferences can appear in the form of rainbow-like dots, edges and stripes.
These optical interferences are a typical phenomena if two or more a number of light waves meet at the same point. These can be observed in the form of weaker or more intensive color zones which change their position when pressure is applied to the pane. This physical effect is strengthened through the parallelism of the pane surfaces. Interferences appear accidentally and cannot be influenced.
Glass concavity and convexity
The windowpane system is closed by sealing contents of a certain volume of gas in the space between the panes. The final parameters of the gas are influenced crucially by the atmospheric pressure, absolute height above the sea level and the air temperature at the time and at the place of production. When installing the insulating glass on other heights, at a different temperature and different atmospheric it results in a concave and convex bending of the single pane and through this to an optical deformation.
Condensation of the steam on the exterior surfaces
Under certain conditions condensation can also appear with insulating glass on the exterior surfaces of the interior or exterior side. From the inside, the condensation depends on the U value, the air humidity, airflow and the outside temperature and inside temperature. When using a very good system of heat insulation, with high air humidity in proportion to the glass, higher air temperature and condensation is also possible on the outside pane surface.
Color deviations
The inherent color of the glass (color cast) depends on the glass thickness, production method and composition of the glass raw material. Color divergences can appear especially with repeat orders.
At the moment for the rating of insulating glazing the norm PN-B-13079 „ Glass in building, insulating glass“ is standard