West-Facing Glazing and Afternoon Overheating in a Composite-Climate Office
A 4-storey office building (G+3) in Jaipur, plot 40 m × 60 m, long axis east–west. The south façade has 30% window-to-wall ratio (WWR) with 1.5 m deep horizontal fins; the west façade has 60% WWR with no shading. A central courtyard is 12 m × 12 m. Measured summer indoor dry-bulb temperature at 3 p.m. is 34 °C when outdoor is 41 °C. Occupants report severe glare on the west side from 3 to 6 p.m. Envelope U-values: wall 0.50, roof 0.40, glazing 5.80 W/m²K. HVAC is sized at 120 W/m² and runs at 90% capacity. The client wants ECBC compliance and better comfort without increasing capital cost. The site has no space for external shading on the west boundary because of a 3 m setback. Internal blinds are already installed but ineffective.
1. Diagnose the dominant causes of afternoon overheating and glare, using the orientation, WWR, U-values and courtyard geometry. Rank them by likely impact.
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The west façade is the primary problem because it combines a high WWR (60%) with no external shading and a low-altitude afternoon sun. At 3–6 p.m. the sun strikes the west glass almost perpendicularly, so solar heat gain is high even though the glass area is smaller than the south wall. The glazing U-value of 5.80 W/m²K is also the weakest envelope element, so conduction adds to the load. Internal blinds are ineffective because they intercept radiation after it has already entered the room; they reduce glare but convert direct sun into diffuse heat inside the occupied zone. The south façade is better controlled: 30% WWR with 1.5 m fins reduces summer altitude sun. The courtyard helps diffuse light and may drive stack ventilation, but a 12 m × 12 m courtyard cannot shade a 60% west façade. Roof and wall U-values are moderate by Indian conditions. Ranking: (1) unshaded west glazing solar gain and glare; (2) high glazing U-value; (3) internal blinds trapping heat; (4) residual roof/wall conduction. The 3 m setback rules out large external fins, so the diagnosis must focus on glazing selection and WWR reduction.
2. Propose a cost-neutral or low-cost retrofit sequence that improves thermal and visual comfort. Justify each measure with a mechanism, not just a label.
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Sequence from highest impact per rupee: (1) Apply a spectrally selective solar-control film or low-e coating to the west glass. Mechanism: reduces solar heat gain coefficient (SHGC) and glare while retaining daylight; cost is low and reversible. (2) Replace 20–30% of the west vision glass with insulated spandrel panels or opaque infill. Mechanism: cuts both solar gain and conduction at the weakest orientation; cost can be offset by downsizing the HVAC upgrade. (3) Add 0.6 m deep vertical fins or a perforated screen within the 3 m setback. Mechanism: blocks low-angle west sun before it reaches the glass; the setback is sufficient for shallow fins. (4) Apply a cool-roof coating or additional roof insulation. Mechanism: reduces steady-state ceiling heat gain, which matters on upper floors. (5) Operate the courtyard as a night-flush and stack-ventilation path. Mechanism: lowers overnight slab temperature, reducing peak afternoon load. Internal blinds should remain only for glare control, not as the primary solar strategy. Verify with a calibrated energy model and a two-week post-retrofit monitoring period.
3. If the client insists on retaining the 60% west WWR, what alternative strategy would you recommend, and what evidence would you collect to prove it works?
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If the WWR must stay at 60%, use dynamic glazing or a double-skin façade rather than fixed clear glass. Electrochromic glazing can tint automatically when west irradiance exceeds a threshold, cutting SHGC and glare while preserving views at other times. A double-skin cavity with integrated blinds is another option: the cavity acts as a thermal buffer and the blinds are protected from wind, but it adds depth and maintenance. Because the 3 m setback prevents deep external fins, the strategy must be integrated into the façade thickness. Evidence to collect: (a) measured vertical illuminance and glare probability (DGP) at west workstations before and after; (b) surface temperatures of inner glass; (c) HVAC electrical demand at 3–6 p.m. over at least two weeks; (d) a calibrated energy model showing peak cooling reduction. If the measured DGP remains above the acceptable threshold or HVAC capacity is still exceeded, the client must accept WWR reduction or additional cooling. The evidence should be contractual, not anecdotal.