Energy-efficient thermal performance of walls and windows for four building orientations in four Indian climatic zones: A verified dynamic analysis of insulation, glazing type and glazing area

Facade design rules for Indian dwellings are still drawn largely from mid-latitude studies. This article presents a verified dynamic analysis of the thermal performance and energy requirements of external walls and windows for four orientations in New Delhi, Mumbai, Jaipur and Shimla, representing the composite, warm-humid, hot-dry and cold climatic zones of India. For design days on 15 December and 15 June, with boundary conditions built from climatological temperatures and a clear-sky irradiance model, transient conduction through uninsulated and externally insulated concrete walls was solved with an implicit finite-difference scheme verified against the exact harmonic solution (maximum deviation 0.12 W/m 2 ), and heat transmission through single and double clear glazing was computed with an angle-dependent optical model that reproduces reference glass properties. At Indian latitudes the summer facade problem is an east–west problem: in June the east and west walls receive 3.5 to 4.7 kWh/m 2 ·day against 1.3 to 1.8 kWh/m 2 ·day for the south wall, and west-wall sol-air temperatures reach 67.5 °C in New Delhi and 68.2 °C in Jaipur. A 6 cm external rock-wool layer reduces the daily transmission load by 81% and the swing of the inside heat flux by 92%, extends the time lag by 1 to 3 h and lowers the decrement factor to about 0.01; outer placement gives the smallest peak flux. Double glazing halves the night-time conductive loss and reduces the June solar gain of east and west windows by 24% to 27%. For an insulated facade with 40% glazing, double glazing reduces the December heating requirement by 49% to 55% (New Delhi, Jaipur, Shimla) and the June cooling requirement by 23% to 34% (New Delhi, Mumbai, Jaipur), saving up to 51 ₹/m 2 per month at current tariffs. The set-point, glass type and system efficiency dominate the uncertainty; absorptivity and wind speed contribute less than 8%. Orientation-specific glazing recommendations are derived for each zone and related to the Eco-Niwas Samhita.