An Analysis of Frame and Edge Heat Transfer in Residential Windows

New window technologies are reducing heat transfer through the glazed areas of windows. Low-emissivity (low-E) coatings reduce radiative heat transfer and low-conductivity gas fills (which replace the air between glazing layers) reduce conductive heat transfer. Given these advances in insulating glass technology, researchers and manufacturers are now beginning to focus their attention on reducing heat transfer through window edges. Old edge designs are now under scrutiny and new designs are being proposed.

This paper explores window material and design parameters which influence heat transfer using two-dimensional heat-transfer modeling with an advanced finite-element computer code (ANSYS). A comprehensive set of correlations, based on ANSYS parametrics, is then developed. These correlations are compared, whenever possible, to experimental results and will be incorporated into future versions of the WINDOW program. Glazing edge designs analyzed include both double-glazed and triple-glazed options with aluminum, steel, wood, fiberglass, butyl, and insulated spacers. Single and double seal design are also analyzed.