A 50 mm × 45 mm × 20 mm cell phone charger has a surface temperature of Ts = 33°C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity ε = 0.92 and is subject to a free convection heat transfer coeffcient of h = 4.5 W/m2 ⋅K. The room air and wall temperatures are T[infinity] = 22°C and Tsur = 20°C, respectively. If electricity costs C = $0.18/kW ⋅ h, determine the daily cost of leaving the charger plugged in when not in use.

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