Effect of straw bale insulation on indoor thermal comfort in school building under tropical climates

This study assesses the impact of straw bale insulation on indoor thermal comfort in school buildings, aiming to develop customized solutions for tropical climates. The approach involves simulations conducted with Design Builder software, powered by the Energy Plus engine, and validated through occupant feedback via survey (students and teachers) and field measurements using meteorological sensors. Initial findings revealed that school configurations failed to meet thermal comfort requirements during the hottest periods. Three scenarios were explored to mitigate this issue. The first focuses on adjusting the building orientation in 5° increments from 0° to 360°, while the second highlights walls and roof external insulation reinforced with straw bales, where the fibers are oriented perpendicular to the heat flow. The last scenario emphasizes the same insulation system with fibers facing parallel to the heat flow. Results indicate that orientation has a minor effect on temperature, with variations of approximately 0.2–0.3 °C depending on the angle. Orientations around 90° and 270° (East-West) tend to exacerbate thermal discomfort due to increased solar radiation in the morning and afternoon. In contrast, North-South orientations (0° and 180°) and slight deviations of ±15° provide better thermal comfort. The temperature reduction trend relative to insulation thickness shows a steady decrease in indoor temperatures as the insulation layer thickness increases. A more pronounced temperature drop is observed between 5 cm and 20 cm of insulation, while beyond 30 cm, the reduction stabilizes, suggesting a thermal saturation effect where additional insulation offers minimal improvement. Scenario 2 reaches a temperature gradient of 1.41 °C during November and December. In comparison with the original scenario, it observed a mean value of relative humidity deviation of +5.25 %, attesting to an enhancement in indoor freshness and a reduction in internal heat stress. Scenario 3 shows the same trend, a relative humidity deviation of +4.89 % and a temperature gradient of 1.35 °C. Scenario 2 demonstrates a slightly greater reduction than Scenario 3, due to straw fibers oriented perpendicularly to the heat flow, providing better thermal resistance compared to parallel fibers.