Energy conservation is important for houses. To what fraction is the heat transfer rate reduced by replacing a glass window 3 ft wide and 5 ft high with a smaller window 2 ft wide by 3 ft high? As a typical case, assume the outside temperature in the winter is 25°F and the inside temperature is 75°F. For this example assume U = 5.5 Btu/(hr)(ft2)(°F).

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Asked Jun 18, 2019
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Energy conservation is important for houses. To what fraction is the heat transfer rate reduced by replacing a glass window 3 ft wide and 5 ft high with a smaller window 2 ft wide by 3 ft high? As a typical case, assume the outside temperature in the winter is 25°F and the inside temperature is 75°F. For this example assume U = 5.5 Btu/(hr)(ft2)(°F).

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Expert Answer

Step 1

For convective heat transfer through the glass window of area A ft2 having convective heat transfer coefficient U Btu/(hr)(ft2)(°F), outside temperature as T1 (°F), and inside temperature as T2 (°F), the rate of heat transfer is calculated as:

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Q= UA(T-T) Btu/hr

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Step 2

Given information are:

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T 25 F T 75 F Btu U 5.5 (hr)(ft')('F) For glass window 1 45 ft b 3 ft For glass window 2, 3 ft b, 2 ft

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Step 3

Let the rate of heat transfer be Q1 for glass window 1....

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(5 ft)x (3 ft =15 ft

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