A Parametric Decision-Support Method for Window-to-Wall Ratio Based on Visual and Thermal Comfort

Buildings account for a substantial share of global energy consumption through heating, cooling, and lighting during the operational phase. The effective use of solar energy can improve visual and thermal comfort while reducing energy demand. Therefore, façade design decisions made during the early design stage are critical for building performance and occupant comfort. However, quantifying and balancing these competing demands remains a major challenge for designers. This study aims to develop a parametric method for determining a Window-to-Wall Ratio (WWR) range that satisfies both visual and thermal comfort while minimising heating and cooling energy demand. To this end, a parametric model of an office building was developed in Ankara, Türkiye. A total of 40 scenarios, comprising four façade orientations and ten incremental WWR variations, were evaluated through visual and thermal comfort simulations. The generated datasets were used in single- and multi-objective optimisation to identify the optimum WWR and a balanced WWR range, respectively. The results demonstrated that both façade orientation and WWR substantially influenced visual and thermal performance. In this case, the single-objective optimisation identified an optimum WWR of 0.20 under equal weighting, and the multi-objective optimisation determined a balanced range of 0.20–0.40. Within this range, the annual average Useful Daylight Illuminance (UDI) remained between 74% and 86%, while the total energy demand varied between 28.5 and 30.9 MWh. Owing to its parametric structure, the proposed method can be adapted to different building types, climates, and locations, offering designers a practical decision-support approach for balancing comfort and energy performance during the early design stages.