Browsing by Author "Ikuzwe, Alice"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Modelling, design, construction and installation of a daylighting system for classrooms in rural South Africa
    (Stellenbosch : Stellenbosch University, 2014-12) Ikuzwe, Alice; Sebitosi, A. B.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Use of natural daylight for interior illumination of schools doesn’t only contribute to the conservation of energy and the reduction of greenhouse gases emission but has also been found to enhance the performance of children in schools. In the case of most rural African schools the supply of electricity is totally absent and many classrooms operate with insufficient lighting levels especially during cloudy winter days. Many technologies have been suggested as ways to utilise natural daylight. The simplest and most commercially available is the passive zenithal light pipe (PZLP). The light at the end of an open pipe is characterised by sharp patches and shadows which result in uncomfortable and frustrating contrasts and glare for the user. In order to eliminate these imperfections the commercial tube is fitted with a diffuser. However this reduces the lux levels to very low values and renders the system unusable for high performance tasks such as reading and classroom illumination. Through the design and manufacture of a light collimator, the performance of the system has been improved from 178 lux distributed by a commercial diffuser to 370 lux distributed by a light collimator. This level is compliant with the South African Bureau of Standards regulation for reading. The next challenge however was the presence of glare patches of the order of 1000 lux. A range of reflector materials was tested but yielded similar disappointing results. Finally a breakthrough was achieved when a rough re-used aluminium cooking foil was discovered that totally eliminated these patches. The daylighting system (PZLP combined with a collimator) was installed in a classroom at Lynedoch, and its efficiency assessment has shown that the system is cost effective as it decreases up to 79 % of annual electricity consumption and has a payback period of ten years with a reduction of 1.6 tonnes of CO2 over the period. Furthermore, post installation tests and simulations were performed to test the stability of light levels for different altitudes of the sun and at different times of the year. It was found that the system provided acceptable levels between 9 a.m. and 5 p.m. even during cloudy winters with minimal drift from the geometrical centreline of the collimator.