Presents the results of a study aimed at quantifying the change in the U-factor caused by glass plate curvature in sealed, insulated (IG) glazing units. Studies curvature caused by barometric pressure and gas space temperature variations. Reviews briefly the equations governing glass plate deflections and heat transfer through IG units. Then examines the glass plate deflections and the resulting change in the U-factor of several IG units for ASHRAE type winter conditions. Also performs yearly simulations for Montreal and Toulouse to examine the combined effects of exterior temperature, barometric pressure and wind speed. These last results how that the U-factor of a particular IG unit (triple glazing, low emissivity with air) may vary up to 5% above and 10% below the yearly average.

KEYWORDS: year 1997, Glazing, triple glazing, transmittance, outdoor temperature, winds, pressure, air