Modelling, design, construction and installation of a daylighting system for classrooms in rural South Africa

[摘要] ENGLISH ABSTRACT: Use of natural daylight for interior illumination of schools doesn't only contributeto the conservation of energy and the reduction of greenhouse gasesemission but has also been found to enhance the performance of children inschools. In the case of most rural African schools the supply of electricity istotally absent and many classrooms operate with insufficient lighting levelsespecially during cloudy winter days. Many technologies have been suggestedas ways to utilise natural daylight. The simplest and most commercially availableis the passive zenithal light pipe (PZLP). The light at the end of an openpipe is characterised by sharp patches and shadows which result in uncomfortableand frustrating contrasts and glare for the user. In order to eliminatethese imperfections the commercial tube is fitted with a diffuser. Howeverthis reduces the lux levels to very low values and renders the system unusablefor high performance tasks such as reading and classroom illumination.Through the design and manufacture of a light collimator, the performanceof the system has been improved from 178 lux distributed by a commercialdiffuser to 370 lux distributed by a light collimator. This level is compliantwith the South African Bureau of Standards regulation for reading. The nextchallenge 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 aluminiumcooking foil was discovered that totally eliminated these patches. The daylightingsystem (PZLP combined with a collimator) was installed in a classroomat Lynedoch, and its efficiency assessment has shown that the system is costeffective as it decreases up to 79 % of annual electricity consumption and hasa payback period of ten years with a reduction of 1.6 tonnes of CO2 over theperiod. Furthermore, post installation tests and simulations were performedto 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 acceptablelevels between 9 a.m. and 5 p.m. even during cloudy winters with minimaldrift from the geometrical centreline of the collimator.

[发布机构] Stellenbosch University