A thermopane window consists of two pieces of glass each 0.1\" thick separated b

Question

A thermopane window consists of two pieces of glass each 0.1" thick separated by a layer of dry,
stagnant air .4" thick.
• Find the resistance of a 4 ft × 3 ft thermopane window.
• Suppose the window is made by fastening an aluminum border .1" thick all around the edge.
Find the total resistance for this configuration.
• As an alternative to the aluminum, we might use a border of .75" thick white pine. Find the total
resistance for this configuration. (For white pine, "across the grain", k = .087 Btu/hr ft °F).
• Calculate the heat loss for the two windows and compare with that for a single pane of .1" glass.

Explanation / Answer

Thermopane Glass Thickness 0.1 0.00254 m Air 0.4 0.01016 m L 4 1.2192 m B 3 0.9144 m kg 0.869 W/mK ka 0.026 W/mK R1 0.002622 R2 0.350517 R3 0.002622 Total Resistance 0.355761 K/W Aluminium Border Glass Thickness 0.1 0.00254 m Air 0.4 0.01016 m L 4 1.21412 m B 3 0.90932 m kg 0.869 W/mK ka 0.026 W/mK kal 0.022 R1 0.002647 R2 0.350517 R3 0.002647 R4 0.103562 0.100914 Total Resistance 0.456726 K/W White Pine Border Glass Thickness 0.1 0.00254 m Air 0.4 0.01016 m L 4 1.20015 m B 3 0.89535 m kg 0.869 W/mK ka 0.026 W/mK kp 1.5047 W/mk R1 0.00272 R2 0.350517 R3 0.00272 R4 0.001514 -0.00121 Total Resistance 0.358677 K/W Single Pane Glass Thickness 0.1 0.00254 m Air 0.4 0.01016 m L 4 1.2192 m B 3 0.9144 m kg 0.869 ka 0.026 R1 0.002622 R2 0.350517 R3 Total Resistance 0.353139 K/W Temperature Diff 5 K Single Pane Heat Loss 15.78467 W/m Double Pane Heat Loss 15.66835 W/m

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