Evaluation and optimization of natural lighting in university classrooms: a case study in Tianjin, China

The classroom, as a space where students spend prolonged periods, is highly influenced by natural light conditions, and high-quality daylighting is essential for improving visual comfort and energy efficiency in architectural design. This study evaluates the daylighting performance of university classrooms in Tianjin, China, and proposes climate-responsive design strategies to improve indoor visual comfort and reduce artificial lighting demand. Tianjin, characterized by moderate solar radiation, represents typical daylight conditions in central and eastern China. However, existing studies often rely on meteorological data from other regions, leading to inaccuracies in local assessments. Field measurements were conducted in four typical classrooms located on the north and south sides of a university teaching building in Tianjin. Indoor illuminance was recorded at 30-minute intervals on September 16, 17, and 28, 2024 (near the autumnal equinox) using calibrated illuminance meters. To further assess daylighting performance and optimize design strategies, simulation models were developed using Grasshopper coupled with the Honeybee plugin. Key daylighting metrics, including illuminance levels, uniformity, and Useful Daylight Illuminance (UDI), were analyzed. The results indicate that the average indoor illuminance (<300 lx) in all classrooms at certain times of the day failed to meet the standard requirements, with poor spatial uniformity (<0.25). Insufficient illuminance is observed in zones distant from windows, while excessive illuminance (>3000 lx) in areas near windows introduces potential glare risks. Parametric simulations demonstrate that the integration of ceiling reflectors and horizontal reflective louvers in south-facing classrooms can achieve UDI autonomous coverage (300–3000 lx) across nearly 100% of the occupied area for over 50% of the occupancy period. For north-facing classrooms, the application of ceiling and external reflectors increases the annual average UDI by 5.1%. The study provides climate-responsive daylighting optimization strategies for the renovation of existing university classrooms in moderate solar radiation regions, offering practical design guidance for improving visual comfort and energy efficiency in architectural design. It should be noted that the performance of the proposed strategies is based on simulation results and requires further validation through long-term field measurements.

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