Illuminance level and daylight autonomy for North and South oriented window

The available illuminance level and the daylight autonomy for the three defined strips have been determined. Only the results of the central zones is presented in Figure 6 and 7 because this zone is the most unfavourable one.

One notice that the available illuminance in a classroom with a 10 % porosity of glazing, is higher to the 300 lux value required for d/h ratio lower than 0.65. These values of overhang are incompatible with the requirements of PERENE in term of solar protection. The associated daylight autonomy is slightly above 88%.

For values of d/h above 0.75, the illuminance level is near 250 lux with a daylight autonomy of 87% for d/h = 1.5. One can see that it is difficult to have efficient solar shadings combined with an acceptable daylighting level.

It would be necessary to reconsider the minimum value of illuminance level in the middle of the room. Maybe it is possible to propose a minimum threshold of 200 lux and to fix a mimimum percentage of autonomy in natural lighting around 87%.

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Figure 6: Daylight autonomy and illuminance level in the middle strip for North-and South. oriented openings

4. Conclusion

This study is a first step in the combined taking into account of solar shadings and daylighting in buildings under tropical climates. The influence of solar shading on the daylight autonomy and the illuminance level of a room has been underlined. It is true that it is difficult to combine efficient solar shading with a good daylighting level.

The daylight autonomy in natural lie values of debordfor o ofbelow 0.,6ich are ncompatiwith the requirements of the PERENE standard in terms of solar protection. It would be necessary to reconsider the minimum value of illuminance level in the middle of the roomIt would be nblo of 250 luxd to fix a a percentage of daylight autonomy in natural libe an acceptable compromise. An acceptable

Furthermore, thanks to this study, we are capable of asserting that the PERENE requirement for solar shadings are too demanding to get an acceptable daylighting level. A proposal for reducing the solar factor values for windows is in progress. The results will allow the establishment of design rules for a future thermal standard for the French tropical island of La ReunionFuture studies will focus on other types of solar shadings and other typical rooms such as offices with the consideration of the glare risk as well.

References

[1] Garde F. et al (2005). Elaboration of Thermal Standards for French Tropical Islands : Presentation of The PERENE Project, Clima 2005, october, 2005, Lausanne.

[2] Adelard L. Garde F. (2008). Adaptation des cibles 04, 08 09 et 10 du referential HQE du CSTB au contexte des DOM. Actualisation Fevrier 2008. Convention ADEME/UR.

[3] Fontoymont. M, Tsangrassoulis. A, Synnefa. A (2004). Synthlight Handbook : chapter 2 : daylighting.

[4] INRS. (2005), Soudry C., aide memoire juridique TJ 13 : Eclairage des locaux de travail.

[5] Marchio, Abdessalam, Casari. (1998) Guide pratique pour le tertiaire : maitriser les apports par l’architecture (1998). Editeur : EDF

[6] OFEN., Morel N., Scartezzini J. L. (2003). Daylighting Buildings in the 21st century, IEA Solar task 31: rapport annuel 2003

[7] Sketchup, (2008). http://sketchup. google. com[8] Energy Plus, (2007). http://www. eere. energy. gov/buildings/energyplus/getting. html

[9] DaySim, (2007). http://irc. nrc-cnrc. gc. ca/ie/lighting/daylight/daysim_e. html

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