Answer Happy

(a) Figure Q7 shows a cross sectional view of a roof. Using the dimensions in the figure and the thermal properties of the materials show that the overall U- value is approximately 0.180W/m2K [10 marks] Resistance of outside boundary layer........ ..0.13m2K/W Resistance of inside boundary layer. ..0.05m²K/W Thermal conductivity of roof tile. .1.19 W/mK Thermal conductivity of plywood.. .0.14 W/mK Thermal conductivity of insulation .... ...0.030 W/mK Thermal conductivity of plasterboard. ...0.160 W/mK (b) The roof in part (a) is covered with a uniform blanket of snow. Calculate the thickness of snow that would reduce the total U-value for the roof to 0.08W/m²K. [6 marks] Thermal conductivity of snow ....0.05 W/mK (c) The roof has a total area of 150m². Calculate the heat lost by conduction with and without the layer of snow on the roof [4 marks] Internal room temperature ..20°C External air temperature .-6°C Roof Tile 20mm 25mm 150mm Insulation 20mm Plasterboard 10mm Plywood