In the context of building energy efficiency in a hot, tropical climate like Gujarat, a low ‘Solar Heat Gain Coefficient’ in architectural glass indicates what property?
- AThe glass permits maximum visible light while trapping indoor heat.
- BThe glass is highly efficient at insulating against conductive heat transfer in winter.
- CThe glass transmits a very small fraction of incident solar radiation as heat into the building interior.Correct
- DThe glass is highly absorptive, turning opaque when exposed to direct sunlight.
Solution
Concept
Solar Heat Gain Coefficient in architectural glass
Formula
SHGC = Solar Heat Transmitted / Incident Solar Radiation
Step-by-step solution
1. The Solar Heat Gain Coefficient (SHGC) represents the fraction of incident solar radiation admitted through fenestration as heat. 2. SHGC ranges between 0 and 1, where lower values signify reduced solar thermal transmission. 3. In warm tropical regions, glazing with a low SHGC admits natural daylight while reflecting or absorbing solar infrared heat. 4. Therefore, a low SHGC indicates that the glass transmits a very small fraction of incident solar radiation as heat. Answer: C
Explanation
The Solar Heat Gain Coefficient (SHGC) measures the fraction of incident solar radiation admitted through a window pane, both via direct transmission and inward heat release. In hot tropical climates, architectural glass with a low SHGC admits daylight while blocking the majority of solar thermal infrared radiation. This substantially reduces solar heat ingress and minimizes building air conditioning cooling loads.
Why the other options are wrong
A) Glass trapping indoor heat describes the greenhouse effect or high solar heat retention. B) Insulation against conductive heat transfer is governed by the U-factor, not SHGC. D) Photochromic glass turns dark in sunlight, which is distinct from the static SHGC rating.
Shortcut
Low SHGC = Low solar heat transmission into building (ideal for hot climates).
Common mistake
Confusing SHGC with U-value (conductive thermal transfer) or Visible Transmittance (light transmission).
Correct answer: C) The glass transmits a very small fraction of incident solar radiation as heat into the building interior.