GATE 2021 AR – Question 55
A wall has external surface conductance 20 W/m²/°C, solar absorptance 0.66 and U-value 1.2 W/m²/°C. Find its solar-gain factor, to two decimals.
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Correct answer: 0.03 to 0.05
Explanation
The factor relating incident solar irradiance to transmitted heat gain in the source’s steady sol-air model is αU/ho. Substitute 0.66×1.2/20=0.0396, which rounds to 0.04. It is dimensionless; absorptance alone does not account for wall and external-film resistance.