Evaluating Daylighting Gains from Window Geometry Reconfiguration in a Classroom under a Subtropical Climate

Daylighting is a key aspect of educational building design, supporting both visual comfort and energy efficiency. However, design practice often reduces the role of windows to aperture ratios, with limited attention to the influence of window geometry on daylight performance. This study investigates how different fenestration morphologies affect daylighting performance in a real university classroom located in southern Brazil. Two window configurations were compared: the existing irregular floor-to-ceiling design and a standardized rectangular layout, both maintaining equal glazing area (25 m², ≈20% of floor area). Annual climate-based simulations were conducted using daylight metrics defined in LM-83: spatial Daylight Autonomy (sDA300, 50%) and Annual Sunlight Exposure (ASE1000, 250h). Five glazing types with visible transmittance values of 88%, 87%, 76%, 52%, and 13% were tested. The standardized window layout consistently increased daylight availability, reaching sDA values up to 98%, but also led to high levels of overexposure, with ASE rising to 46%. In contrast, the irregular floor-to-ceiling configuration limited overexposure to a maximum of 23%, though daylight autonomy decreased substantially, in some cases to 41%. When assessed against LEED daylighting thresholds, neither configuration achieved full compliance: the standardized layout exceeded ASE limits, while the irregular geometry often fell below sDA requirements. To synthesize these trade-offs, a ranking framework was developed to enable comparisons across window geometries and glazing options. This research demonstrates that window geometry, independent of aperture ratio, is a decisive factor shaping daylight performance. By isolating morphology as a design variable, the study provides architects and designers with evidence-based guidance to balance daylight sufficiency and overexposure in educational spaces. These findings contribute to bridging the gap between performance-based simulation and architectural decision-making, offering actionable insights for both new classroom designs and retrofit strategies in existing buildings.