Murielle Martin1, Francois Garde1, Mathieu David1, Laetitia Adelard1, Michael Donn2

1LPBS. -Laboratoire de Physique du Batiment et des Systemes Universite de La Reunion. 40 avenue Soweto

97410 Saint-Pierre

2Centre for Building Performance Research Victoria University of Wellington, New Zealand

murielle. martin@univ-reunion. fr

Abstract

In the building sector in tropical climates, the quality of solar shading of windows is often preferred to a good natural lighting. Few design guides exist in the field of natural lighting/solar shading in tropical climates and

This paper deals with the taking into account of efficient solar protections coupled with an efficient natural lighting. We focused on overhang type solar shadings. First the lighting index of windows is determined for different size of overhangs then compared to the design values of PERENE -Building design guide for Reunion Island. Second, the daylight autonomy and the luminance level are calculated for different size of overhangs. The paper concludes that the PERENE design rules are too demanding in terms of solar factor to meet and that it is impossible to have an efficient solar shading of windows and an acceptable mean luminance level. It is thus proposed to reduce the luminance level to 250 lux and to set a minimum daylight autonomy percentage.

KEYWORDS : Daylighting, solar shading, tropical climate.

1. Introduction

The design of low energy buildings in tropical climate and in warm climate first concerns generally the quality of solar shading. Solar shading is a prevailing parameter to avoid the overheating inside the building and thus decrease the cooling capacity of air conditioning. The operating time of air conditioning systems can be reduced or avoided if solar shading is combined with an adequate architectural design such as cross natural ventilation.

As the reduction of the consumption in the building sector constitutes now a priority objective to achieve, the consideration of the natural lighting in study is essential as well. Few projects take into account the design of natural lighting. The solar impact of the protections on natural lighting is not much studied. In certain cases, it is even possible to use artificial lighting because of too efficient solar protections. This makes an overconsumption while one thought that the best had already been done with the solar protections to reduce air-conditioning. A compromise must also be found between effective solar protections and a suitable natural lighting. The combination of both objectives in terms of reducing the overall building consumption is not obvious.

This paper presents a preliminary works of the simultaneous taking into account of solar shading and natural lighting in a typical room. The studied room is a cross ventilated classroom with a porosity of 20 %. The solar protection studied is a overhang-type one. After a brief thinking about the index used in mainland France such as Daylight Factor, the first values of the glazing ligting index vs the overhang size will be presented.

Then, the classroom daylight autonomy according to the overhang size will be presented for two different azimuths.