ECM: Building Envelope

    B3. Install Window Sun Shades

    DescriptionPhoto: Window sun shades can reduce air conditioning needs.

    Solar radiation's heat gain through windows often accounts for 50 percent of air-conditioning load in the summertime. If no existing shading exists in air-conditioned spaces such as offices, community rooms, or lobbies, window shading should be considered.

    Applicability

    • Air-conditioned office and community space
    • Air-conditioned spaces without inter shades, blinds, or tinted glass
    • Air-conditioned spaces whose windows are not well-shaded by exterior trees, vegetation, or other buildings

    Types

    • Exterior shading
      • Architectural elements
        • Roof overhangs
        • Vertical shading devices
      • Awnings
      • Shading screens        
    • Interior shades
      • Blinds
      • Curtains
      • Sun screens
    • Tinted film

    ConsiderationsExterior shading on windows can improve comfort and reduce energy consumption.

    • Exterior shading should be engineered for correct summer solar angles to ensure effective shading.
    • Tinted film is fragile and should not be installed in areas where objects or people come into contact with windows.
    • Exterior shading devices should be designed to withstand snow loads.
    • Sunshades on south- and west-facing windows can be effective at improving comfort and reducing the need for air conditioning.
    • Windows manufactured with low-emissivity (often called low-e) films typically cost about 10 to 15 percent more than regular windows.
    • Window treatments do not reduce air leakage and infiltration

    Performance/Economics

    • Venetian blinds reflect 40 to 60 percent of the sun’s radiant energy. Low-e windows reduce energy costs by approximately 30 to 50 percent.
    • Window tinting can reduce solar energy gain 25 to 55 percent.
    • Vertical blinds reflect approximately 23 percent of the sun’s radiant energy.
    • Roller shades, depending on their composition, reflect 15 to 80 percent of the sun’s radiant energy. Overhangs are most effective at midday.

    Resources/Links

    Energy Conservation for Housing – A Workbook, HUD, September 1998. Pages 7-17 through 7-20 address energy-saving window sun shades.

    Window Treatments and Coverings. Part of the U.S. Department of Energy's Consumer's Guide.

    Using the Sun: Using Windows Wisely. Provides information on using film, indoor shading, and vegetation to reduce solar gain.

     

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