Window Construction

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IGUs (Typical Window Construction)

Diagram of a Typical IGU (source: Matthew Tanteri)

The typical glazing module used in commercial building fenestration systems is called an Insulating Glazing Unit (IGU). An IGU is a sealed assembly of multiple glass lites held apart by spacer, sealed around the edge with an organic sealant, and filled with air, argon or krypton gas. The entire assembly is often characterized by the number of lites contained, e.g., double-glazed, triple-glazed, quadruple-glazed. The incorporation of the IGU into a building envelope requires it to be held in a frame or sash, or used frameless such as in a curtain wall assembly. Frame design (e.g., material, weight, use of thermal breaks) is an important factor in the overall thermal performance of a fenestration system. Using spacers made from low conductance materials help short-circuit conductive heat flow. Warm-edge spacers made of stainless steel offer improved thermal performance along the window edges. Desiccant filled spacers function to absorb internal moisture trapped inside the gas space during manufacturing. Space thickness and fill gas also determine the IGU insulation efficiency. Too little space results in conductive heat loss, while too much space can result in convective heat loss. For lower thermal conductance heavy gases, typically argon or krypton, replace air as a fill gas. Increasing the number of lites may improve some aspect of performance (e.g., thermal, acoustic, safety or security, however the trade-off of performance vs. weight is an important consideration. Using a suspended low-E film as the internal glazing layer of a triple-glazed unit is one means to achieve lower weight and enhanced thermal performance.

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Lead Author(s): Matthew Tanteri

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