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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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