Defining standard skies and indoor daylight prediction
Student thesis: Doctoral Thesis
Daylight is one of the natural resources, which creates a better working environment and reduces both the building lighting energy and cooling load if proper lighting controls are used. Traditional method of predicting indoor daylight illuminance is not flexible enough to assess daylighting performance. The indoor daylight illuminance actually depends on the luminance levels and patterns of the sky viewed from a window. Availability of reliable climatic information is vital for indicating the sky luminance distribution to estimate indoor daylight illuminance. The aims of this study are to identify a subset from the CIE standard general sky which could best represent the sky luminance distribution in Hong Kong, to systematically establish ranges of climatic parameters in 3 typical sky conditions, and to develop a simple design tool for the prediction of indoor daylight illuminance under non-overcast skies. The sky luminance model evaluation was based on the measured luminance data collected in Hong Kong from 1999 to 2001. Statistical methods were used to identify which subset of the CIE standard general skies was best fit to describe the daylight climate in subtropical Hong Kong. The general findings of outdoor illuminance and sky luminance distribution were presented by graphical methods. Before developing a simple design tool to predict indoor daylight illuminance under the CIE standard clear sky (sky no. 12) for different orientations and solar positions, computer technique was used to demonstrate the flexibility of daylight coefficient approach to estimate indoor daylight illuminance. The proposed simple design tool using this approach was further justified by being compared to other calculation approaches. These findings can be used to provide architects and building designers a reliable and simple alternative that incorporates the daylight coefficient approach to predict indoor daylight illuminance under non-overcast sky conditions.
- Light in architecture, Daylighting