2. Compare the heat loss in W from two windows of a room, one having a single sheet of glass 4 mm thick while the other has two sheets of glass, 2 mm thick each, separated by 2 mm of air. The second window is called a thermopane. The window sizes are 1.5 m × 2 m. The air temperature in the room is 23°C and the outside temperature is -10°C. The average value of the thermal conductivity of glass is 0.96 W/m·K and that of air is 0.0257 W/m·K over this temperature range of interest. The heat transfer coefficient corresponding to slower moving air inside the room is 5 W/m2·K and that of the faster moving air outside is 25 W/m2·K. Consider the thin layer of air between the glass sheets to be stagnant.

Determine the time of the day and month of the year at which the peak sensible cooling load occurs for a top floor, north-eastern corner room of an office building in durban for the following conditions: floor area: 8 x 8 x 3 m east and north walls: 115 mm face brick (outside), 20 mm air space, 115 mm ordinary brick (inside) with 15 mm plaster roof construction: suspended plasterboard ceiling, 450 mm air space, 150 mm concrete, 75mm screed, waterproofing no heat transfer across other surfaces window area 3x 1,5 m high in north wall only. ordinary glass with venetian blinds. lights and occupants : from 07: 00 to 18: 00 average light density: 25 w/m2 number of occupants : 5 seated, light office work room temperature 24°c