Question

1. A wall is made up of four elements, as follows:

½” wood siding R = 0.81
½” plywood sheathing R = 0.62
3½” fiberglass insulation R = 10.9
½” sheetrock R = 0.45
(Units of R-value are ft2-hr-oF/Btu)

A. What is the total R-value of the wall?
B. What is the R-Value if no insulation is installed?
C. In which direction (in or out) would the heat flow when the outside temperature is 90oF and the temperature inside is 70oF?

Answer 1

Part A)

Since all four resistors are made up of different elements and connected in series

SO in series the net resistance is given by

`R = R_1 + R_2 + R_3 + R_4`

`R = 0.81 + 0.62 + 10.9 + 0.45`

`R = 12.78`

Part B)

If insulation is removed then resistance due to three materials

`R = R_1 + R_2 + R_3`

`R = 0.81 + 0.62 + 0.45`

`R = 1.88`

Part c)

Heat will always flow from High temperature to low temperature

So here heat flow is from 90 degree F to 70 degree F

so it will flow from outside to inside