Energy Efficiency Windows EGEE 102 Savings with Efficient Windows in a Heating Season EGEE 102 2 http www efficientwindows org energycosts html Cooling Season http www efficientwindows org energycosts html EGEE 102 3 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 Rvalues h F ft2 Btu The lower the U value the less heat is lost through the window EGEE 102 4 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 ultraviolet radiation EGEE 102 5 Factors affecting the Rvalue 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 6 Improved Comfort EGEE 102 7 Advances in Window Technologies Low e coatings Spectrally Selective Coatings Heat absorbing Glazing Reflective Coatings Gas fills EGEE 102 8 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 9 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 10 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 11 Insulation Performance Conventional EGEE 102 Advanced 12 Smart Windows EGEE 102 13 Normal Window Relative to all other glazing options singleglazed 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 14 Triple Glazed with Low SolarGain 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 lowconductance 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 15 Improvement in Windows Resistance to Heat Flow Actual Net Energy Gain Net Energy Loss R 5 0 Superwindows R 2 5 Low E R 1 7 Double pane R 9 0 Superwindows R 7 0 Superwindows Projected R 0 5 Single pane 1970 1980 1990 Year EGEE 102 2000 2010 16 Resources http www efficientwindows org gl azing single html http windows lbl gov http www eren doe gov erec facts heets eewindows html EGEE 102 17