I know what the answer is supposed to be, but I have no idea how to calculate th

Question

I know what the answer is supposed to be, but I have no idea how to calculate this. Please leave a detailed solution with all steps shown. Thank you!

17. The wall of a house consists of three layers: a wooden outer wall with an R factor of 1.0, a 3-in layer of fiberglass insulation with an R factor of 11. and a gypsum-board inner wall with an R factor of 0.33 (all R factors are in h - ft2 - Fdegree/Btu). When the temperature is 68degreeF inside the house and - 4.0degreeF outside, what is the rate of heat loss through an 8-ft by 15-ft section of this wall? 700 Btu/h 780 Btu/h 5.8 Btu/h 130Btu/h 350 Btu/h Ans: A

Explanation / Answer

heat flux = (delta T)/ R-factor

Total R-factor = 1 + 11+ 0.33 = 12.33 h.ft^2.F/Btu

delta T = 68-(-4) = 72 degree F

so, heat flux = (72 degree F)/(12.33 h.ft^2.F/Btu) = 5.8392 Btu/ft^2.h

Rate of heat loss = Heat flux* area of wall

(5.8392 Btu/ft^2.h)*(8*15 ft^2) = 700 Btu/h

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