Both measures concentrate on enhancing the fenestration assemblies, including enhanced U-Factor
and Solar Heat Gain Coefficient (SHGC).
Walls and attics are rated with R-value, and windows are rated with U-factor
Simplified one-dimensional thermal models were developed to compute heat transfer and temperature distribution in TDD glazing panes, as well as the overall thermal performance characteristics (SHGC and U-factor
) under standard or design environmental conditions.
, the better the window is at preventing heat transfer through the window.
Take for example a window's U-factor
. It is used to measure its ability to conduct heat.
A typical double pane window has a U-factor
The curtainwall provides enhanced condensation performance and tow U-Factor
, along with panoramic, floor-to-ceiling views.
rating measures the efficiency of the windows.
Specific guidelines for U-factor
and solar heat gain coefficient (SHGC) of replacement glass; minimum R-values for insulation; exemptions for lighting replacements of less than 50% of a space, as well as bulb and ballast-only lighting alterations, so long as these don't result in increased power consumption; and requirements for door and roof replacements, as to when additional insulation is mandated, and when it is not.
This incentive includes replacement windows and doors, including sliding glass doors, with a U-factor
(a measure of the amount of heat that escapes from a room) and a Solar Heat Gain Coefficient (a measure of the amount of heat allowed to enter a room) each at or below 0.30.
The National Fenestration Rating Council is a good first stop, since o it rates windows on factors like air leakage and offers a U-factor
measurement of how well the window guards against heat loss.
When selecting windows, consider their insulation value (the U-factor
) and the solar heat gain coefficient (SHGC.) Advanced spectrally selective coatings allow light in, but not heat.