Consider a house whose walls are 12 ft high and 40 ft long. Two of the walls of the house have no windows, while each of the other two walls has four windows made of 0.25-in-thick glass (k = 0.45 Btu/h·ft·°F), 3 ft × 5 ft in size. The walls are certified to have an R-value of 19 (i.e., an L/k value of 19 h·ft²·°F/Btu). Disregarding any direct radiation gain or loss through the windows and taking the heat transfer coefficients at the inner and outer surfaces of the house to be 2 and 4 Btu/h·ft²·°F, respectively, determine the ratio of the heat transfer through the walls with and without windows.

Transcribed Image Text:

Attic space 12 ft 40 ft 40 ft Windows