Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan - Dec 2014
3.4 THE INFLUENCE OF INTERIOR SURFACE REFLECTANCE
The internally reflected component plays an influential role on the performance of a daylighting strategy in that it increases the number of inter-reflections and aids the mitigation of light from the window aperture to deeper parts of the day lit zone. An obvious observation is that natural light rapidly reduces from the window aperture within the first 3 m from the façade (as illustrated in figure 8). The influence of reflectance can be seen to increase both the depth and amount of light penetrating the zone, consequently reducing the annual lighting load of the zone as can be seen in figures 20, 21 and 22 for a given glazing percentage. The case studies below were taken from a southerly orientation in Barcelona which exhibit’s the lowest annual mean lux levels. The walls, floors and ceilings were considered as perfectly diffuse sources acquiring reflectance’s outlined in table 4.
For the purposes of the worst and best case scenario figures 20, 21 and 22 represent zones that have ceiling and wall reflectance’s set at 2 levels as indicated in table 4. The process of reflection and interrefleaction is a complicated interaction to model, however, it is sufficient
to component.
Figure 20. Annual Lighting Loads at different glazing percentages and internal surface Zone)
reflectance’s (Cabin
assume the average internally reflected For this reason the floor reflectance was
considered with common obstructions such as beds carpets,
tables and desks, and assumed to reduce the
overall reflectance of the floor to the lowest level of the 2009 SLL suggestions. Illustrating the effects of this in figures 20, 21 and 22, identifies that regardless of low floor reflectance a reduction in annual lighting loads was observed for both, the cabin, lounge and dinning zone with a 30% glazed façade, saving an additional , 5.15%, 27.8% and 10.25% respectively, from the base case low level surface reflectance’s. It is also identified from these figures that the greatest reduction in annual lighting loads is experienced at 20% glazing, from which the gains seems to decrease and stabilize at 50%. The improvements to surface reflectance in accordance to the SLL guidance can help to improve lighting loads on average 4.37% for cabin zones, 22.8% for day/lounge zones and 8.4% for dining zones when considering a southerly orientation.
Overall the impact of reflectance has a significant importance on the daylighting strategy and is likely to also influence other psychological elements of the user’s experience. The importance of surface reflectance and colours is reflected in both the SLL codes [38] as well as design guides for architectural practitioners such as the BRE digest and the BS 8206-2:2008 [50]. Although identifying the annual impacts of surface reflectance it is necessary to conduct further work on the daily impacts on the user experience and visual comfort. Furthermore the specifics of interior design such as furnishings can have a significant impact on the ability of reflectance to support a natural daylighting scheme.
Figure 21. Annual lighting loads at different glazing percentages and internal surface reflectance's (day/lounge zone)
Figure 22. Annual lighting loads at different glazing percentages and internal reflectance’s (dining zone)
© 2014: The Royal Institution of Naval Architects
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