Double Glazing
Double glazing refers to the fitting of window frames with two panes of glass, mounted together with a small space between the panes. The advantages of double-glazed windows are increased thermal protection, noise reduction, and better security. Triple glazing is possible with even greater benefits, however this increases the cost considerably, and most home window frames will not handle the additional thickness.
The glass panes, with a spacer around the edge to preserve the gap between them, are sealed together as a unit. This is commonly known as an IGU, an insulated glass unit. Usually a dessicant is included in the spacer to control condensation between the panes.
The space between the two panes of glass is filled with a gas of some type. This may simply be air. Even ordinary air increases the insulating power and reduces the passage of noise through windows. Insulation is increased because heat cannot be efficiently transferred from one glass pane to the other by either convection or radiation. The thickness of the gap must be carefully calculated to maximize the efficiency since a greater space increases convection and a narrower space increases radiation. Noise is reduced because sound travels at different speeds in the glass and the gas in the gap.
The most efficient double glazed window would be one that has a vacuum between the panes. However, the practical problems of structural stability caused by the outside pressure of the atmosphere limits vacuum IGUs to small sizes. A partial vacuum may be used which reduces heat transfer by means of both convection and conduction. This is generally called evacuated glazing.
Other gases which may be used to fill the gap are argon, krypton or xenon. All these are so-called "noble gases" which are not reactive with other elements. Argon is the most commonly used since it is the least expensive. Argon has two-thirds of the thermal conductivity of air, and krypton's is only half of argon's. Xenon is even more efficient. However the costs increase dramatically with each successively better gas. There are also problems with keeping the units sealed well enough to keep some air from mixing in anyway.
Another way to improve the efficiency of IGUs is by applying certain coatings on one of the glass surfaces. These coatings reflect light and heat, and also create attractive exteriors for commercial buildings.
Double glazed IGUs are used in a number of applications. They can be used in homes and commercial buildings to increase the efficiency of heating and cooling. They are often the best choice for greenhouses.
Double glazed windows also decrease the transmission of noise. If noise reduction is the goal, having two different thicknesses of glass, and increased width of the gap is the best choice. Laminated glass in the panes reduces noise even further.
Two panes of glass are more difficult to break than one. Double glazing improves the security of any building in which these type of windows are installed.
A homeowner who is planning to install replacement windows should carefully consider the reasons to use IGUs. All of the considerations for maximum efficiency of each application can be calculated mathematically. Reputable companies will use these formulas to provide the best windows for each application balanced against the costs of production. There may even be several options at various price levels.
The glass panes, with a spacer around the edge to preserve the gap between them, are sealed together as a unit. This is commonly known as an IGU, an insulated glass unit. Usually a dessicant is included in the spacer to control condensation between the panes.
The space between the two panes of glass is filled with a gas of some type. This may simply be air. Even ordinary air increases the insulating power and reduces the passage of noise through windows. Insulation is increased because heat cannot be efficiently transferred from one glass pane to the other by either convection or radiation. The thickness of the gap must be carefully calculated to maximize the efficiency since a greater space increases convection and a narrower space increases radiation. Noise is reduced because sound travels at different speeds in the glass and the gas in the gap.
The most efficient double glazed window would be one that has a vacuum between the panes. However, the practical problems of structural stability caused by the outside pressure of the atmosphere limits vacuum IGUs to small sizes. A partial vacuum may be used which reduces heat transfer by means of both convection and conduction. This is generally called evacuated glazing.
Other gases which may be used to fill the gap are argon, krypton or xenon. All these are so-called "noble gases" which are not reactive with other elements. Argon is the most commonly used since it is the least expensive. Argon has two-thirds of the thermal conductivity of air, and krypton's is only half of argon's. Xenon is even more efficient. However the costs increase dramatically with each successively better gas. There are also problems with keeping the units sealed well enough to keep some air from mixing in anyway.
Another way to improve the efficiency of IGUs is by applying certain coatings on one of the glass surfaces. These coatings reflect light and heat, and also create attractive exteriors for commercial buildings.
Double glazed IGUs are used in a number of applications. They can be used in homes and commercial buildings to increase the efficiency of heating and cooling. They are often the best choice for greenhouses.
Double glazed windows also decrease the transmission of noise. If noise reduction is the goal, having two different thicknesses of glass, and increased width of the gap is the best choice. Laminated glass in the panes reduces noise even further.
Two panes of glass are more difficult to break than one. Double glazing improves the security of any building in which these type of windows are installed.
A homeowner who is planning to install replacement windows should carefully consider the reasons to use IGUs. All of the considerations for maximum efficiency of each application can be calculated mathematically. Reputable companies will use these formulas to provide the best windows for each application balanced against the costs of production. There may even be several options at various price levels.
