Tropical daylighting : predicting sky types and interior illuminance in north-east Brazil
Daylight is present in tropical regions in a considerable intensity throughout the year. The sky characteristics are changeable and sunlight cannot be disregarded. Daylighting techniques are still wanted to answer particular tropical features. The main aim of this thesis is to present a daylighting analysis tool for the tropics developed out of existing procedures. It is structured in three parts. The first part provides a broad view of climatic aspects related to daylighting studies in a typical tropical city - Maceiö, Brazil. A brief climatic description of the city and a study relating climate and building are followed by a literature review of climatic fundamentals. A study is made of meteorological station measurements in relation to the city and a field investigation is described. These lead to a simplified method for sky type selection. It shows that a reasonable assumption about daylight climate can be made from very simple data and that new structure of CIE standard general sky could be applied everywhere. The second part investigates methods that could be appropriated for calculating daylighting in humid climates and concludes with a methodology based on an adaptation of existing techniques. The Monte Carlo and ray tracing techniques are reviewed, as well as the daylight coefficients concept. These are incorporated in prototype software, TropLux, written in MATLAB code. The development of the method in this thesis can be seen as an extension of the daylight factor concept to the CIE Standard General Sky and reflected sunlight. The software validation is done and results show that the level of prediction is comparable with those produced by Radiance and overall the results appear to be robust. Analysis indicates that it is not essential to have climate-specific calculation technique. Universal lighting software is viable, providing the local climate and architectural characteristics are taken into account. The last part applies TropLux to ground-reflected light. It is found that the influence of reflected sunlight on interior illuminance can be very large. Among shading devices analysed, overhang has shown the best performance. There is a key zone of ground outside window that provides the majority of the reflected light. A direct design implication can be the reduction of window size.