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Energy Efficiency -Windows EGEE 102 - PowerPoint PPT Presentation

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Energy Efficiency -Windows EGEE 102 Savings with Efficient Windows in a Heating Season Cooling Season Heat losses through Doors and Windows

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Savings with Efficient Windows in a Heating Season

EGEE 102

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Cooling Season

EGEE 102

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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

EGEE 102

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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

EGEE 102

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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.

EGEE 102

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Advances in Window Technologies

  • Low e-coatings

  • Spectrally Selective Coatings

  • Heat absorbing Glazing

  • Reflective Coatings

  • Gas fills

EGEE 102

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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%

EGEE 102

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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

EGEE 102

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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.

EGEE 102

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Insulation Performance

EGEE 102



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Smart Windows

EGEE 102

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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

EGEE 102

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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.

EGEE 102

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Net Energy








Net Energy






Double pane


Single pane

1970 1980 1990 2000 2010


Improvement in Windows’ Resistance to Heat Flow

EGEE 102

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EGEE 102