Development and evaluation of design tools for estimating the indoor daylight illuminance under the CIE standard skies
Student thesis: Master's Thesis
Daylight is a natural, free and non-depleted resource coming from the sun. Integrating daylight with architectural design not only enriches the built environment but also alleviates the problems in energy and pollution. To properly design buildings with satisfactory daylight environment, an accurate indoor daylight prediction is necessary. However, the tools available for this purpose are either not flexible enough to predict the daylight illuminance under non-overcast skies (daylight factor method) or too complicated to use during the initial stage (computer simulation). Therefore, it is essential to develop a simple daylight design tool suitable for all sky conditions. The primary aim of this study is to develop and evaluate a simple design tool for estimating indoor daylight illuminance under the CIE standard skies. The proposed method was then extended to the average daylight factor (DFave) determination and its performance was assessed. Also, computer simulation technique was employed to investigate the contributions of different components on the daylight available on the vertical façade. Traditionally, the indoor daylight illuminance is determined using daylight factor approach (DFA), which is computed under the International Commission on Illumination (CIE) overcast sky. The DFA gains the advantage of simplicity but is not flexible enough to predict the dynamic variations in daylight illuminance as the solar position and sky condition change under non-overcast sky. Instead, the daylight coefficient (DC) concept, which considers the changes in the luminance of the sky elements, offers an effective way for computing indoor daylight illuminances under various sky conditions and solar positions. Based on the DC concept, a simplified numerical method to compute daylight indoor illuminance under the CIE standard skies was proposed. The simplified techniques in the form of a nomograph and Waldram diagram were developed and described. The performance of the method was evaluated using scale-model and real building field measurements. The numerical method was then extended to DFave calculation. The techniques for calculating the two configuration parameters for the DFave determination in an unobstructed environment, namely; (a) light received directly from the sky above the horizon on the vertical building façade, and (b) light received directly from the ground below the horizon on the vertical building façade were established and described. The performance of the proposed method was assessed against the result obtained by computer simulation. In an obstructed environment, the light incident on the building façade is actually the sum of four components, namely; (a) sky component, (b) obstruction-reflected component, (c) ground-reflected component and (d) inter-reflected component. Computer simulation technique was employed to investigate the contribution of each component to the daylight available on the vertical façade. Simplified methods for calculating each component under different sky conditions were proposed. The findings of this study provide architects and engineers with a quick and reliable way to conduct daylighting analysis during the design, construction and operation stages.
- Computer programs, Daylighting, Measurement