Assessment and prediction of daylight performance in high-rise office buildings

• Published in: The structural design of tall and special buildings 2008-12, Vol.17 (5), p.953-976
• Main Authors: Ko, Dong-Hwan, Elnimeiri, Mahjoub, Clark, Raymond J.
• Format: Article
• Language: English
• ISSN: 1541-7794; 1541-7808
• DOI: 10.1002/tal.474

Effective use of daylighting is an essential component to achieve a sustainable building design. In a tall building, the amount of useable space with a potential for the use of daylight is the space between the exterior wall and the core. This is commonly referred to as the ‘lease span’. Class A office buildings in the USA have typically utilized lease spans of around 45 ft (13·7 m), primarily due to efficiency of space usage. In Europe, however, lease spans in high‐rise office buildings have typically been shortened due to concerns of natural light penetrations and views. For instance, in Germany, the amount of leasable space per floor is less than in the USA. The maximum allowable depth of space in Germany is typically about 18 ft (5·5 m), whereas in the USA, as much as 50 ft (15 m) is no rarity. The lease span also has an impact on other items, such as the aspect ratio, floor‐to‐floor height, total height and total floor area. In this study, to assess and predict daylight performance, two different requirements were analysed: daylight factor (DF) and the daylight requirement of Leadership in Energy and Environmental Design (LEED) 2.2 green‐building rating system. The recommended average DF (DFave) ranges from 2 to 5% and LEED 2.2 requires that a minimum daylight illumination of 25 footcandles be achieved in at least 75% of all regularly occupied areas. This study conducted a series of computer simulations using RADIANCE to first show the effects of each of the fenestration parameters and then to provide an optimum effective aperture to meet the two daylight requirements in four lease span types ranging from 20 to 50 ft. As a final step, regression models and simple evaluation tools were developed to correlate the DF, daylight requirement in LEED 2.2 and the various fenestration parameters, such as window area, visible transmittance and lease span in four different cities (London, Chicago, Dubai and Bangkok). This paper provides a simplified method for evaluating indoor daylight performance to meet the two daylight requirements. This can be used as a pre‐design tool, not only to achieve more credits in LEED 2.2 green‐building rating systems, but also to evaluate based on DFave to ensure that the building meets the recommended level. Copyright © 2008 John Wiley & Sons, Ltd.