Type of insulated glazing
Quadruple glazing (quadruple-pane insulating glazing) is a type of insulated glazing comprising four glass panes, commonly equipped with low emissivity coating and insulating gases in the cavities between the glass panes. Quadruple glazing is a subset of multipane (multilayer) glazing systems. Multipane glazing with up to six panes is commercially available.
Multipane glazing improves thermal comfort (by reducing downdraft convection currents adjacent to the windowpane), and it can reduce greenhouse gas emissions by minimising heating and cooling demand. Quadruple glazing may be required to achieve desired energy efficiency levels in Arctic regions, or to allow for higher glazing ratios in curtain walling without increasing winter heat loss. Quadruple glazing allows building glazing elements to be designed without modulated external sun-shading, given that the low thermal transmittance of having four or more glazing layers enables solar gain to be adequately managed directly by the window glazing itself. In Nordic countries, some existing buildings with triple glazing are being upgraded to glazing with four or more layers.
Features.
With quadruple glazing, the center-of-panel U-value (Ug) of 0.33 W/(m2K) [R-value 17] is readily achievable. With six-pane glazing, a Ug value as low as 0.24 W/(m2K) [R-value 24] was reported. This brings several advantages, such as:
Engineering.
Multipane glazing is often designed with thinner intermediate glass panes in order to save weight. To prevent intermediate panes from thermal stress cracking it is sometimes required to use heat-strengthened glass. With more than three glass panes, special care must be taken of the spacer and sealant temperatures as intermediate glass panes in contact with these glazing elements can readily exceed design temperature limits of respective materials due to solar radiation (irradiance) heating.
Solar irradiance heating of intermediate glass panes increases substantially with an increased number of glass panes. Multipane glazing must be carefully designed to account for the expansion of the insulating gases that are placed between the glass layers, because such gaseous expansion becomes an increasingly important consideration as the number of glass panes is increased. Special breather vents, as well as small vents communicating between the layer spaces, can be incorporated in order to manage this glass-bulging effect. Finite element analysis is often used to calculate appropriate glass sheets' strengths. Calculating static equilibrium with thin glass panes used in multipane glazing may involve nonlinear plate mechanics.
Performance.
Double-pane windows have been the industry standard for decades. They represent a vast improvement over single-pane windows but the potential for even greater energy savings with more highly insulating windows has been elusive. Recent price reductions in the thin glass used in both smartphones and flat-screen TVs, as well as in the krypton gas used in halogen lights, however, have made it possible to build lighter, high- efficiency quad-pane windows at a lower cost. Researchers from the National Renewable Energy Laboratory evaluated two configurations of Alpen High Performance (an American manufacturer) quad-pane windows at an office building at the Denver Federal Center. Both configurations have the same thickness and a comparable weight as a standard commercial double-pane window—one model uses two layers of film suspended between two panes of standard glass, the other replaces the film with two panes of ultra-thin glass. Researchers found that on average, quad-pane windows saved 24% heating and cooling energy compared with a high-performing double- pane window. For new construction and window replacements, the quad-pane windows have payback between one and six years, depending on climate zone and utility rates.
References.
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