Department of Natural Sciences
Clayton College & State University
Morrow, Georgia

February 10, 2009

SCI 1901E - Quiz 6

Name __________SOLUTION_____________

(09)    1.    Calculate the R-value for a wall of the following composition: 1/2" lapped wood siding, 2" hardwood plank, 4" of cellulose insulation and 1/2" sheetrock wall board.  A table of R-values is provided below:

material

thickness

R-value
(ft2·hr·°F/Btu)

hardwood

1"

0.91

softwood

1"

1.25

plywood

1/2"

0.62

sheetrock

1/2"

0.45

fiberglass insulation

3 1/2"

10.9

fiberglass insulation

6"

19.0

cellulose insulation

1"

3.7

wood sliding (lapped)

1/2"

0.81

 

Rtotal = Rlw + Rhp + Rci + Rsr

Rtotal = [ (0.81) + (2)(0.91) + (4)(3.7) + (0.45) ] ft2·hr·°F/Btu

Rtotal = 17.88 ft2·hr·°F/Btu ANS

 

(06)    2.    If the wall in problem 1 has dimensions of 15.0 ft by 8.0 ft, calculate rate of heat transfer by conduction through the wall when the indoor temperature is 70°F and the outdoor temperature is 20°F.

Awall = (15.0 ft)(8.0 ft) = 120 ft2

DT = 70°F - 20°F = 50°F

Qc / t = A DT / R

Qc / t = (120 ft2)(50°F) / (17.88 ft2·hr·°F/Btu)

Qc / t = 336 Btu / hr ANS