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A house has a roof (20 m wide x 30 m long) of a design similar to the one shown in the figure. Thermal conductivity of the roof materials are as follows: plaster board k = 0.22 W/m°C, insulation k = 0.038 W/m°C, and for air k = 0.026 W/m °C. The emissivity of the outer surface of the roof is 0.2 and the heat transfer coefficient by convection of the roof surface is 10 W/m². °C. The outer surface of the roof ceiling is maintained at 4.5 °C when outside ambient air is at 4°C. Assume sky temperature equals ambient temperature, determine: a- Heat transfer by convection from the roof surface. (5 marks) b- Heat transfer by radiation from the roof surface. (5 marks) c- Total heat loss from the roof. (3 marks) d- Total thermal resistance R of the roof structure (plaster board, insulation, and air space) assuming roof sheet thermal resistance is negligible. (6 marks) e- Temperature at point "x" on the inner side of the roof ceiling as shown in the figure. (6 marks) Outside air 4 °C 10 cm 15 cm Outer surface at 4.5 °C 1 cm Plaster board Air Roof sheet Insulation Inner surface of roof ceiling A house has a roof (20 m wide x 30 m long) of a design similar to the one shown in the figure. Thermal conductivity of the roof materials are as follows: plaster board k = 0.22 W/m°C, insulation k = 0.038 W/m°C, and for air k = 0.026 W/m °C. The emissivity of the outer surface of the roof is 0.2 and the heat transfer coefficient by convection of the roof surface is 10 W/m². °C. The outer surface of the roof ceiling is maintained at 4.5 °C when outside ambient air is at 4°C. Assume sky temperature equals ambient temperature, determine: a- Heat transfer by convection from the roof surface. (5 marks) b- Heat transfer by radiation from the roof surface. (5 marks) c- Total heat loss from the roof. (3 marks) d- Total thermal resistance R of the roof structure (plaster board, insulation, and air space) assuming roof sheet thermal resistance is negligible. (6 marks) e- Temperature at point "x" on the inner side of the roof ceiling as shown in the figure. (6 marks) Outside air 4 °C 10 cm 15 cm Outer surface at 4.5 °C 1 cm Plaster board Air Roof sheet Insulation Inner surface of roof ceiling

Answer rating: 100% (QA)

a Heat transfer by convection from the roof surface The heat transfer by convection can be calculated using the following formula Qconv h A Tsurface Tambient Where Qconv is the heat transfer by convec... View the full answer