Effect of external louvre shading system on indoor thermal environment in three climates

External louvre systems are widely used passive shading strategies, but their performance varies significantly with climate and geometry. However, limited studies have systematically compared the combined effects of louvre orientation, blade angle, and climate variability using consistent simulation and statistical approaches across multiple climatic contexts. This study investigates vertical and horizontal louvre systems in London, Chabahar, and Chittagong using simulation-based analysis with four blade angles (0°, 30°, 45°, and 60°), evaluated through seasonal, hourly, and statistical methods. Results indicate that increasing blade angle improves thermal performance in all climates, although the magnitude varies by climate and louvre orientation. Vertical louvres are more effective in hot climates, achieving up to 4.0°C and 3.2°C reductions in Chabahar and Chittagong, respectively. In contrast, horizontal louvres in London provide more stable indoor thermal conditions with reduced fluctuations, despite lower peak cooling performance. The 0° configuration is consistently the least effective across all cases. The study demonstrates that louvre performance is highly climate-dependent and that no single configuration is universally optimal. Vertical louvres are recommended for hot climates, while horizontal louvres are more suitable for temperate conditions.