Ingineria Iluminatului - Journal of Lighting Engineering - Prof. Florin ...

1. Introduction
A STUDY ON INTEGRATING EFFICIENT SHADING DEVICES
IN OFFICE BUILDINGS
Katerina TSIKALOUDAKI
Laboratory of Building Construction and Physics,
Department of Civil Engineering, Aristotle University of Thessaloniki
The main objective of the proposed paper is the analysis of the relationship between
solar shading and daylighting. Moreover, the applicability of several types of
conventional sun shading devices in the Mediterranean climate is studied, with respect
to their potentiality to act both as sun protection and daylight elements. The study is
focused on the analysis of visual and thermal conditions, which prevail on the models of
a parametric study. The models share the same geometrical and optical characteristics,
but differ on the type and function of shading devices. Furthermore, they encompass the
typical characteristics of a contemporary office; the basis of this approach emerges
from the fact that the indoor environment in such spaces is almost always artificially
controlled, since the requirements for their use with regards to indoor temperature and
lighting are specific, leading thus to high energy consumption.
Transparent elements are considered as the most
sensitive component of the building envelope,
since they are often associated with excessive
thermal losses and direct heat gains, glare, poor
acoustical conditions, as well as feeling of
insecurity and loss of privacy. In Mediterranean
climates, problems of overheating dominate and
are often confronted by the implementation of
shading devices. However, the shading devices do
not only prevent the solar radiation from entering
the room, but also regularly lead to the reduction of
lighting levels indoors. In such cases, the demands
result in the increase of artificial lighting use,
which can also cause overheating during the
summer period. Therefore, the careful design of
sun-protective devices with respect to their impact
on daylighting is very important for the overall
function and the energy behaviour of the building.
Solar protective devices can be classified
according to their position with respect to the
opening: they can be applied externally (i.e.
overhangs or vertical fins), internally (i.e. louvers,
blinds, curtains), or they can be incorporated in the
fenestration (i.e. solar control glazing). The
decision upon their type and characteristics are
based on the geometry and orientation of the
opening. Typically, the integration of external solar
protection devices is more efficient, at least in
terms of thermal conditions, since they block the
solar radiation before entering the interior.
Conventional solar control glazing can reduce the
heat gains significantly, but its low light
transmittance may cause increased artificial
lighting demands and therefore indirect cooling
load. However, the use of reflective glazing is very
common for office buildings in Greece.
The impact of sun protective devices on the
quantitative assessment of indoor daylight levels
focuses mainly on the limitation of the visible patch
of sky, since the adequacy of daylight levels is
usually examined for the worst outdoor conditions,
i.e. under overcast skies. Furthermore, beam sunlight
is assumed to contribute to the formation of indoor
daylight conditions indirectly, through the
determination of the reflected component.
Additionally, the orientation of the façade does not
influence the levels of daylight factor, since under
overcast conditions the luminance of a sky patch
depends merely on its altitude on the sky dome.
INGINERIA ILUMINATULUI 15-2005 33 1