Transient three-dimensional window thermal effects

Abstract

A model is developed, and checked experimentally, to allow reasonably accurate computer calculations for three-dimensional temperature distributions in sunlit, partly shaded windows. The time evolution of surface temperature profiles, the sideways heat flow to and from adjacent walls, and the heating due to solar absorption in the glazing can be calculated. To reduce computation time, only two layers of cells were taken for each glazing pane, and uniform heat transfer was assumed between the panes. Nevertheless, the calculations matched well with experimental temperatures obtained for nine different full-scale windows at different orientations in a rotatable test hut on 27 clear or nearly clear winter days. In some winter experiments, an average of 15% of the 24-hour heat loss through a south window went sideways to the adjacent walls, with a minimum of 10% near noon, and a maximum of 20% near midnight. Near noon, with an ambient temperature of — 7°C (20°F), the centre of the inside of a south-facing triple-glazed window was above room temperature, due to solar absorption in the glass. At the same time, the inside of the shaded edge of the glazing was below room temperature.