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Building envelope

Reducing Cooling Loads: A Window Point of View

Windows and window treatments have a large influence on cooling loads. Therefore, careful selection of glazing, the use of window films, and proper use of shading devices can help users achieve significant reductions in cooling loads. Glazing Most large commercial buildings are dominated by cooling loads, so window selection for commercial buildings is usually an exercise in maximizing daylighting and keeping summer heat out. Today’s best windows block heat transfer more than five times better than single-pane glass, the standard windows of just two decades ago. High-performance windo…

Insulation Primer

Insulation is a material designed to slow down the flow of heat. In most North American regions, the primary function of insulation in the building envelope is to keep heat in, but insulation also plays an important role in keeping unwanted heat out in warmer months. Most insulation materials are lightweight fibrous or cellular materials that enclose air or gas pockets. Heat flows through these materials through conduction, convection, and radiation: Conduction occurs through both the gas and the solid material that separates pockets of gas. Insulation is most effective at stopping conduct…

Cool Roofs

Although most heat gain in a facility comes through the windows, eliminating heat gain through the exterior roof and walls can be a cost-effective and low-risk way to reduce cooling loads and peak demand. One of the most effective measures for commercial buildings is light-colored walls and roofs—the latter is commonly referred to as a cool roof. Using light-colored building surfaces is a time-honored means of keeping buildings cool in the Mediterranean region, the Caribbean, and other sun-drenched locales. Light-colored roofing materials with high reflectance (known as high albedo) c…

Air Leakage Control

Air leakage is a major source of heating load, but controlling air leakage is important for other reasons as well. Certain types of uncontrolled leakage result in moisture deposits in the building envelope. For example, when warm, moisture-laden air works its way out through the wall system, the moisture condenses on the cold outer wall panels, providing an opportunity for mold and mildew to grow, degrading insulation performance, and even causing structural damage. Air leakage can also contribute to occupant discomfort in perimeter spaces. Understanding the Basics Even if the building enve…

Windows

Windows, more formally referred to as glazing or fenestration, affect the daylight that can be effectively used in a building as well as heating and cooling loads. The windows you choose can make a significant difference in your energy consumption—in both new or retrofit situations, they can cut annual energy costs by up to 20 percent in perimeter zones if properly employed. Cooling represents the major energy load in most large commercial buildings, so glazing that transmits adequate light for daylight activity while minimizing solar heat transmission is usually best. In buildings where…

Window Film

A window film is a thin, transparent sheet that can be applied to the interior of a window to change its heat- and light-transmitting characteristics. Films reduce cooling loads, improve shatter resistance, block up to 99 percent of ultraviolet (UV) radiation, and reduce glare. Temperatures near the windows are reduced as well, which can increase occupant comfort. For retrofit applications, many of the benefits of window materials that control solar heat gain are available by applying window films to existing glazings (Figure 1). Typical films have a total thickness of 0.001 to 0.004 inc…

Insulation

Insulation can be one of the most important factors in improving energy efficiency in a building. It slows the flow of heat through a building envelope. Insulation not only saves money by reducing heating and cooling loads but also is a key factor in achieving comfortable living and working spaces. Insulation Ratings All insulation is rated according to its resistance to heat flow, measured in units of R-value in the United States. The inverse of thermal resistance is conductance, referred to as the U-value (U = 1/R), which in the United States is measured in units of Btu/square foot-°Fa…

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