Explaining the Functional Logic of Louvered Façades in a Hot-Arid Climate: Investigating the Role of Window-to-Wall Ratio and Louver Angle in Balancing Thermal Loads and Daylighting in Office Buildings in Kerman

Abstract

This study aimed to explain the hierarchy of effects of the window-to-wall ratio (WWR) and horizontal louver blade angle (Alpha) on the balance between annual heating–cooling load intensity and daylight performance in the south façade of a typical office cell in the hot-arid climate of Kerman. A quantitative, simulation-based, parametric, and multi-objective research design was adopted. The design space comprised a full-factorial combination of four variables—WWR, Alpha, Offset, and Spacing—generating 640 scenarios. Geometric modeling was performed in DesignBuilder, thermal calculations were conducted using EnergyPlus, and daylight performance was simulated with Radiance. The resulting database was audited and statistically analyzed in R. Annual heating–cooling load intensity was assessed as the thermal outcome, while spatial Daylight Autonomy (sDA), Useful Daylight Illuminance (UDI), and Annual Sunlight Exposure (ASE) represented daylight performance. Global sensitivity analysis using generalized additive models (GAM) and permutation importance was followed by Pareto-based multi-objective optimization. Global sensitivity analysis identified WWR as the dominant variable for annual heating–cooling load intensity (86.9% relative importance) and sDA (63.2%). Conversely, Alpha was the dominant determinant of ASE (58.4%) and UDI (63.4%), indicating its primary role in limiting direct solar exposure and improving useful daylight. WWR accounted for 39.2% of variation in ASE, while Alpha accounted for 34.6% of variation in sDA. Multi-objective optimization identified 44 non-dominated Pareto scenarios, confirming that no single-variable solution simultaneously optimized thermal and daylight objectives. Optimal louvered-façade performance is not achieved by maximizing transparency or excessively obstructing solar radiation; rather, it depends on coordinated adjustment of façade openness and solar filtration. WWR primarily determines the magnitude of thermal exposure and quantitative daylight availability, whereas Alpha primarily governs solar control and useful daylight quality. Accordingly, these variables should be treated as complementary and sequential design decisions within performance-based façade design.