Question

The composite walls of a building are made up of three materials. The inside layer of the walls is 1-cm thick wall board (kwb = 0.2 W/mK). The middle layer is 10 cm thick insulation (kI = 0.06 W/mK) and the outside layer is 3 cm of wood (kw = 0.15 W/mK). The total wall area is 350 m2. The outside air temperature is -10 oC and the inside air temperature is maintained at 20 oC. The inside and outside average convective heat transfer coefficients are 7 and 35 W/m2K, respectively. You are asked to: a. Sketch and label the thermal circuit diagram for the rate of heat transfer, q, from the inside of the room, through the composite walls and to the outside. Evaluate all individual thermal resistances, the total thermal resistance and the overall heat transfer coefficient. [10] b. Evaluate q. [2] c. Determine the unknown temperatures on both sides of the insulation layer. [3] Hint: Neglect radiation, contact resistance and conduction in air. The walls are large enough so that 1-dimensional conditions exist.

Answer 1