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

Ikuzwe, Alice (2014-12)

Thesis (MEng)--Stellenbosch University, 2014.

Thesis

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.

AFRIKAANSE OPSOMMING: Die gebruik van natuurlike daglig vir die beligting van die binnekant van skole dra nie net by tot die bewaring van energie en die vermindering van kweekhuis gasse nie maar verbeter ook die prestasie van kinders in die skole. In die geval van die meeste plattelandse skole in Afrika is elekktriese krag onverkrygbaar. En is daar veral op bewolkte of wintersdae te min lig in die klaskamers. Daar is al baie voorstelle gemaak vir die gebruik van tegnologie vir optimum gebruik van daglig. Die passiewe zenital ligpyp (PZLP) is die eenvoudigste tegnologier en dit is ook geredelik kommersiaal beskikbaar. Die lig aan die einde van’ n oop pyp word gekenmerk deur skerp kolle, skaduwees, kontraste en fel lig wat vir die gebruiker ongerieflik en frusterend is. Om hierdie imperfeksies te elimineer word kommesiële pype vervaardig met ’n diffundeerder wat die lig versprei. Dit verminder egter die ligvlakke (lux levels) en veroorsaak dat die sisteem nie gebruik kan word in klaskamers waar daar gelees word nie. Die ontwerp en vervaardiging van die lig kollimator het die prestasie van die sisteem verbeter vanaf 178 lux wat deur ’n kommersiële diffundeerder versprei is tot 370 lux wat deur ’n lig kollimator versprei word. Hierdie vlak voldoen aan die Suid-Afrikaanse Buro van Standaarde se regulasies. Die volgende uitdaging was die teenwoordigheid van kolle helder lig (glare) van 1000 lux. ’n Hele aantal materiale wat kan weerkaats is getoets maar die resultate was teleurstellend. Daar was uiteindelik’n deurbraak toe daar op ’n rowwe gebruikte aluminium foelie afgekom is wat hierdie helder kolle totaal elimineer. Die daglig sisteem (PZLP gekombineer met ’n kollimator) is in ’n klaskamer by Lynedoch installeer waar gevind is dat die elektriese krag gebruik met 79% per jaar gesny is, dat dit ’n jaar lank in gebruik kan bly en datv dit die CO2 met 1.6 ton tydens die periode verminder). Verdere installasies en toetse is vir verskillende ligvlakke en verskillende sonshoogtes en seisoene is gedoen om sodoende die stabiliteirt van ligvlakke by die verskillende hoogtes van die son en die siesoene gedoen. Daar is gevind dat gebruik van die die sisteem lei tot aanvaarbare vlakke tussen 9 vm. en 5 nm. selfs op betrokke wintersdae, met ’n minimale skuif vanaf die geometriese middellyn van die kollimator.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95770
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