Energy Efficiency -Windows

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Energy Efficiency -Windows

• EGEE 102

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Savings with Efficient Windows in a Heating Season
http//www.efficientwindows.org/energycosts.html
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Cooling Season
http//www.efficientwindows.org/energycosts.html
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Heat losses through Doors and Windows

• Most window manufacturers label their windows
  with a U-value (conductance of heat, Btu/h F
  ft2)
• U-values are the reciprocals of R-values (h F
  ft2/Btu).
• The lower the U-value, the less heat is lost
  through the window

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Factors in Selecting Windows

• Solar heat gain coefficient (SHGC),
• Visible transmittance (VT), and
• Air leakage (AL).
• The type of window frame
• The degradation of fabrics by ultra-violet
  radiation

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Factors affecting the R-value of a window

• The type of glazing material (e.g., glass,
  plastic, treated glass)
• The number of layers of glass
• The size of the air space between the layers of
  glass
• The thermal resistance or conductance of the
  frame and spacer materials
• The "tightness" of the installation i.e., air
  leaks.

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Improved Comfort
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Advances in Window Technologies

• Low e-coatings
• Spectrally Selective Coatings
• Heat absorbing Glazing
• Reflective Coatings
• Gas fills

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Effect of Glazing

• Special thin coatings (metal oxide or
  semiconductor) that reduce heat transfer
• Soft and hard Coatings
• Cost 10-15 more
• Reduce Energy loss by 30-50

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Spectrally Selective Coatings

• These coatings filter out 40-70 of the heat
  normally transmitted through clear glass while
  allowing full amount of light to be transmitted
• Customizable
• Increase or decrease solar gains according to
  aesthetic and climatic effects
• Reduce 40 of the cooling requirements

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Gas Filed Windows

• Filling the space with a less conductive, more
  viscous, or slow-moving gas minimizes the
  convection currents within the space, conduction
  through the gas is reduced, and the overall
  transfer of heat between the inside and outside
  is reduced.
• Argon and Krypton gas with measurable improvement
  in thermal performance have been used.
• Argon gas filling provides an effective thermal
  resistance level of R-7 per inch, krypton gas
  provides R-12.5 per inch, and xenon gas provides
  R-20 per inch.

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Insulation Performance
Conventional
Advanced
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Smart Windows
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Normal Window

• Relative to all other glazing options,
  single-glazed with clear glass allows the highest
  transfer of energy (i.e. heat loss or heat gain
  depending on local climate conditions) while
  permitting the highest daylight transmission

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Triple-Glazed with Low-Solar-Gain Low-E
Glass(Spectrally Selective)

• Three glazing layers and two Low-E coatings, 1/2"
  argon gas or 1/4" krypton gas fill between
  glazings, and low-conductance edge spacers. The
  middle glazing layer can be glass or plastic
  film. Some windows use four glazing layers (two
  glass layers and two suspended plastic films).
  With this window, both Low-E coatings are
  spectrally selective in order to minimize solar
  heat gain. This window is best suited for
  climates with both significant heating and
  cooling loads.

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Improvement in Windows Resistance to Heat Flow
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Resources

• http//www.efficientwindows.org/glazing_single.htm
  l
• http//windows.lbl.gov/
• http//www.eren.doe.gov/erec/factsheets/eewindows.
  html