Question

A proposed building includes a 100m² atrium covered by a horizontal glass roof. the glass is 10mm thick, its albedo is 0.3, its thermal conductivity is 1.05WK^-1 m^-1 and its solar transmittance is 80%

If Ri is the constant normal incident solar irradiance of the glass at noon on a summer's day, the solar radiation (W/m^{2)
absorbed by the glass will be?}

Answer 1

albedo is the percentage of solar light reflected from the window, which is 30 % Ri =0.3Ri

so 70 % of the radiation is absorbed by the glass and reradiated. since the solar transmittance is 80 % , the radiation entered the room will be 0.8 x 0.7 x Ri = 0.56 Ri

The remaining is the absorption = Ri - 0.3Ri - 0.56 Ri = 0.14 Ri

Thermal conductivity = power/thickness of wall/(change in temperature) =1.05 WK-1 m-1

solar radiation absorbed = Thermal conductivity x thickness of wall / area x 0.14 Ri = 1.05 x 0.01/100 x 0.14 Ri

solar radiation absorbed = 1.47 x 10-5 W/m2