The selection of optimum pane spacing for glazing systems has been a topic of ongoing debate in the window manufacturing industry. Arguments are often based on speculation, intuition and results from tests not specifically designed to examine the effects of pane spacing. This study presents a set of measured centre-glass U-values taken from experiments where pane spacing was carefully varied while holding all remaining conditions unchanged. Heat flux measurements were made using a guarded heater plate apparatus. Glazing systems were all double glazed, air filled and tested in the vertical position.
Measured centre-glass U-values were compared to calculated U-values. These calculations were performed using a version of the VISION glazing system thermal analysis program which was modified in order to model the guarded heater plate test conditions. VISION runs were also carried out in order to predict the optimum pane spacing as a function of variations in glazing system design, fill gas type, weather condition, and the number of panes incorporated in the glazing system.
VISION results were combined with results of the window frame thermal analysis program, FRAME. FRAME was used to estimate the average edge-glass and frame U-values for several design options. The results of these calculations provide an estimate of the sensitivity of overall U-values to variations in pane spacing.Renewable Energy Branch of the Department of Energy Mines and Resources || Natural Sciences and Engineering Research Council of Canad
