A rules of thumb-based design sequence for diffuse daylight

Abstract

This paper proposes and validates a daylighting design sequence for sidelit spaces. Since the design sequence uses the daylight factor as a performance metric, it is aimed towards spaces that primarily receive diffuse daylight. It should be complemented by a design analysis that looks at direct sunlight for glare and energy considerations. The sequence interconnects and refines earlier proposed rules of thumb and is intended to be used during the earliest design stages when concepts regarding programming, floor plans, massing and window areas are initially explored. All steps within the sequence were ‘validated’ using Radiance simulations of over 2300 sidelit spaces. During step one of the sequence the effective sky angles are calculated and target daylight factors are defined for all potential daylit zones within a building. In step two a refined version of the ‘daylight feasibility study’ is used to help the design team to identify building zones with high daylighting potential based on a target mean daylight factor criterion. During step three suitable interior room dimensions and surface reflectances are determined using a combination of the Lynes’ limiting depth, ‘no sky line’, and window-head-height rules of thumb. Step four provides a more accurate estimate of the required glazing area for each zone based on the Lynes daylight factor formula which is also validated as part of this work. The effect of external obstructions is considered throughout the process. The paper closes with a discussion of the merits of the design sequence compared to the glazing factor spreadsheet calculation method promoted by LEED-NC 2.2.