Optimizing Window Size for Effective Daylight Illumination in High-rise Buildings: A Case Study of Nib International Bank Head Office Addis Ababa, Ethiopia

Abstract

This study explores the optimal Window-to-Wall Ratio (WWR) for enhancing daylighting performance in such buildings based on their orientation. First measurements involved calculating the WWR of an existing bank building in all Cardinal direction, followed by lux meter readings taken in March a month marked by high solar intensity. Daylight levels were recorded in office spaces across various orientations (N, S, E, W, NE, SE, and SW). The study focused on floors 5 to 32 (Head Office of Nib Bank Building), where all windows are uniformly fitted with 5mm clear glass and aluminum frames, ensuring consistent glazing conditions for accurate analysis. As a result the measured WWRs, ranging from 55.56% to 57.03%, significantly exceed the LEED-recommended range of 25%?��?40%, indicating a strong focus on maximizing daylight penetration. Daylight illuminance was analyzed at 2-meter grid intervals on 3 points (A, B, C) at a height of 76 cm, with results compared to LEED daylighting criteria (sDA300/50%) and CIBSE standards, which recommend 300 lux for general office work and 500 lux for task-intensive activities. On grid points, such as A (14361963 lux) and B (704?��?830 lux), exceeded these standards. To compensate for Excessive daylight daylight, 50??50 cm ceiling panel lights are used with internal curtain to balance the light, with at least two per room and a total of 448 lights across the building. These fixtures consume 0.06 kWh each per hour, resulting in 26.88 kWh of hourly, 161.28 kWh daily, and approximately 58,867.2 kWh of annual energy consumption. The study conclude from the Simulation results WWRs of 30% for west and southwest orientations to reduce glare, 35% for northeast, and 40% for the remaining orientations to m