Time-lagged thermal comfort response to solar geometry and sky regime in Indian composite-climate cities

Thermal comfort shapes HVAC set-points and architectural decisions to moderate solar heat gain through building form and operation. Geometry-based approaches derived from Olgyay, relate solar position to discomfort hours, often assume instantaneous thermal response, overlooking sky conditions and prior thermal states. This study models Effective Moisture Temperature (EMT) as a lagged response to solar altitude, solar azimuth, cloud opacity, and base temperature across 15 Indian composite-climate cities. Using 30-min data from 2021–2024, observations were grouped by four seasons and two diurnal phases. Linear regression models were tested for lags between 0 and 2.5 h and interpreted using standardized coefficients. Results show the longest lags during winter and monsoon. Solar altitude was the dominant driver in winter mornings, whereas base temperature governed most other periods. Winter response varied with latitude-driven solar angles, while monsoon lag depended on geographic location and associated cloud-cover. The study extends Olgyay’s framework by quantifying delayed responses and identifies that geometry, storage, and sky-regime dominate EMT patterns for passive-active design. These findings provide actionable lead times for architects, building operators, and HVAC designers during early decision making to anticipate peak discomfort and implement shading, ventilation, or cooling strategies that improve occupant comfort while reducing energy use.