A wall assembly (total area = 100 ft2)consists of 80 ft2 of opaque wall with an R- value of R- 20 and a 20 ft2 of window whose R- value is R- 2. The effective (overall)R- value of the entire wall assembly is approximately
A)R- 15.
B)R- 7.
C)R- 11.
D)R- 3.
E)none of the above.

Question

Quizplus · Accepted Answer

The effective R-value is calculated using the formula for parallel resistances: 1/R_total = (A1/R1 + A2/R2) / A_total. Substituting the given values: 1/R_total = (80/20 + 20/2) / 100 = 0.1425, so R_total ≈ 7.

A Wall Assembly (Total Area = 100 Ft2)consists of 80