Finding the thickness

Greetings all,

would you please support me to solve this problem:

An extrior wall of house may be approximated by a  4 in brick with k = 0.7 w/m.k followed by 1.5 in layer of gypsum plaster ( k= 0.48 w/m.k ) what thickness of  loosely  packed rook wool insulation ( k= 0.065 w/ m.k) should be added to reduce the heat loss through the wall by 80 percent?

Saad85 said:

Greetings all,

would you please support me to solve this problem:

An extrior wall of house may be approximated by a  4 in brick with k = 0.7 w/m.k followed by 1.5 in layer of gypsum plaster ( k= 0.48 w/m.k ) what thickness of  loosely  packed rook wool insulation ( k= 0.065 w/ m.k) should be added to reduce the heat loss through the wall by 80 percent?

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You'll have to assume the addition of the wool layer doesn't change the surface temperatures of inner and outer faces of the wall.

if DeltaT is that temperature difference then:

q=DeltaT/R1          (1)

where R1 is the equivalent resistance of brick and gypsum without the wool. The other equation is:

0.2q = DeltaT/R2     (2)

where R2 is the equivalent resistance of brick, gypsum and wool. R2 will be an expression containing L_wool, the unknown  thickness of wool.

Now eliminate q from (1) and (2) and solve for L_wool. 

Thanks but I couldn't understand how to convert the thermal conductivity from SI to US , the thinkness needed in in

Then convert the brick and gypsum thicknesses to meters, proceed as above and obtain the required wool thickness in meters, and convert THAT to inches.

Also, check this out:

http://www.unitconversion.org/unit_converter/thermal-conductivity.html

Slay the P.E. said:

Then convert the brick and gypsum thicknesses to meters, proceed as above and obtain the required wool thickness in meters, and convert THAT to inches.

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Thanks a lot for your usual support 

Obviously everything Slay said is correct. But just in case, here's a detailed solution. Converting the 

Sheshtawy said:

Obviously everything Slay said is correct. But just in case, here's a detailed solution. Converting the 

View attachment 10135

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Thanks a lot your usual support your feedback is highly appreciated .

Saad85 said:

Thanks a lot your usual support your feedback is highly appreciated .

Click to expand...

My pleasure!