Question

A composite series wall has an inside surface temperature of 1600F and outside surface temperature of 500F. If it consists of 3.5 in. of mineral wool, 0.05 in. of plaster on the outside, and 0.75 in. of cork board on the inside, determine the heat loss in a 120 square foot of wall.

Answer 1

(All units will be converted to SI units)

The rate of heat conduction per unit area for a material of length L with temperature difference is given by the formula,

Therefore we can say that the thermal resistance of the material is ,

We will now calculate the thermal resistance of the materials,

Thermal resistance of 3.5 in mineral wool is, (k = 0.04 W/mK)

Thermal resistance for 0.05 in plaster is, (k = 0..28 W/mK)

Thermal resistance for 0.75 in cork board is, (k = 0.043 W/mK)

The total thermal resistance for the setup is,

The rate of heat going out per unit area is conduction is,

Therefore the rate of heat loss from 120 square foot wall is,

Hence the rate of heat loss is 2526.83 J/s.