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Benefits: Improved Comfort

Comfort

Source: Lawrence Berkeley National Laboratory (Lyons and Arasteh).       

High performance windows with new glazing technologies not only reduce energy costs but make homes more comfortable as well. During cold weather, exterior temperatures drive interior glass surface temperatures down below the room air temperature; how low the glass temperature drops depends on the window's insulating quality. If people are exposed to the effects of a cold surface, they can experience significant radiant heat loss to that cold surface and they feel uncomfortable, even if the room air temperature is comfortable. When the interior glass surface temperature is 52°F or less, it is most likely that there will be discomfort. During warm weather, solar radiation can cause discomfort. Just as people turn up the heat to compensate for cold windows in cold weather, they may use air-conditioning to counter the effects of warm window surfaces and sunlight in summer.

Winter Thermal Comfort

Convective Loop

An older window with a lower glass temperature feels colder because more heat is radiated from a person's body to the window. Cold glass can also create uncomfortable drafts as air next to the window is cooled and drops to the floor. This sets up an air movement pattern that feels drafty and accelerates heat loss. High performance windows with lower U-factors will result in a higher interior window temperature in winter and thus greater comfort. Proper installation along with weatherstripping designed to seal tightly (for operable windows) will also improve comfort by reducing cold air leakage.

Probability of Discomfort

Source: Lawrence Berkeley National Laboratory (Lyons and Arasteh).

Summer Thermal Comfort

Solar Heat Gain

In summer, strong direct sunlight strikes people and interior surfaces, creating overheating and discomfort. Windows with low solar heat gain coefficients will reduce the solar radiation coming through the glass and associated discomfort. Low solar heat gain low-E glass (spectrally selective) reduces heat gain while still providing sufficient light and view.

Probability of Discomfort

Source: Lawrence Berkeley National Laboratory (Lyons and Arasteh).