1.4.3 U-Value and R-Value
The U-factor (U-value) measures the rate of heat loss or how well a product prevents heat from escaping. The R-value measures resistance to heat transfer via conduction and expresses insulation value for most non-glazed materials, i.e. floor, wall, roof insulation and panels.
The U-value includes the thermal properties of the frame as well as the glazing. The insulating value is indicated by the R-value, which is the inverse of the U-factor. U-factor ratings generally fall between 0.20 and 1.20. The lower the U-factor, the greater a product’s resistance to heat flow and the better its insulating R-value. R-value is a measure of the insulation’s heat loss retardation and it indicates the thickness of the material / the thermal conductivity of the material.
To reduce U-factors, some manufacturers apply a low-E (low-emitting) coating to glazing surfaces. These low-E coatings reduce heat loss, improving both heating and cooling performance. Some window assembly strategies include using two or more layers of panes or films, low-conductance gas fills between the layers, and thermally improved edge spacers. Using triple glazed windows can lower the U-value by over 40% as compared to double glazed windows. (http://www.efficientwindows.org)
Significant cost reductions due to reduced solar loads (cooling mode) and heat loss (heating mode).
Energy savings due to reduced heating energy loss. Maximum protection from cold drafts near the exterior without compromising access to daylight and views.
Verify energy code requirements.
1.4.1 Solar Heat Gain Coefficient
1.4.2 Visible Light Transmittance
1.7.8 Passive Solar Heating
5.1.1 Energy Modeling