Consider the double-pane window of Problem 9.97, for which 1m x 1 m panes are separated by a 25-mm gap of atmospheric air. The window panes are approximately isothermal and separate quiescent room air at T_{∞, i} = 20°C from quiescent ambient air at T_{∞, o} = - 20°C.

(a) For glass panes of emissivity ε_g = 0.90, deter- mine the temperature of each pane and the rate of heat transfer through the window.

(b) Quantify the improvements in energy conservation that may be effected if the space between the panes is evacuated and/or a low emissivity coating (ε_c = 0.1) is applied to the surface of each pane adjoining the gap.