S o l a r – o p t i c a l P r o p e r t i e s o f V e n e t i a n B l i n d s
319
SOLAR-OPTICAL PROPERTIES OF VENETIAN BLINDS:
MODELLING, EXPERIMENTATION AND DESIGN OPTIMIZATION
Maria da Glória Gomes
1
, António Moret Rodrigues
1
, Daniel Aelenei
2
1
Department of Civil Engineering, Architecture and Georesources (DECivil/ICIST), Instituto Superior Técnico,
Technical University of Lisbon, Lisbon, Portugal
2
Department of Civil Engineering, Faculty of Science and Technology, Universidade Nova de Lisboa, Lisbon,
Portugal
Abstract
An important and fundamental strategy in sustainable building design is the use of solar
shading devices. Solar control by means of shading devices may help reducing the
cooling and heating demands of buildings and controlling daylight into the spaces. Solar
shading devices can be incorporated into building design on sun facing windows by
using a louvered design which rejects direct radiation and allows a better control of
diffuse radiation and glare.
Venetian blinds are one of the most commonly used louvered shading devices due to
their easy operation, effectiveness in rejecting direct sunlight, and relatively low price.
The operation of these devices is usually based on the rotation of movable slats, which
allows for a more flexible use than typical roller blinds but makes the modelling of their
optical behaviour much more complex.
The present study describes a numerical model, based on the net radiation method, for
calculating solar-optical properties (transmittance, absorptance and reflectance) of
venetian blinds. The model can be used for different venetian blind configurations and
control strategies and is suitable for integration into building energy simulation tools.
Results from in situ experiments on an outdoor venetian blind are also presented and
compared with numerical predictions. Finally it is shown that the knowledge of the
venetian blinds optical properties is crucial in identifying the most effective strategies to
improve the fenestration system performance, regarding building energy consumption
and indoor comfort issues.
Keywords:
shading devices; venetian blinds; solar-optical properties; in-situ
experiments; net-radiation method; shading control.
Introduction
Glass is today one of the key materials in modern architecture. The higher transparency
of modern commercial buildings with highly glazed facades leads, however, to frequent
overheating and glare problems. Shading devices are used to reflect direct sunlight,
reducing glare and preventing overheating. The use of this passive solar technique can
contribute to significantly reduce the buildings energy consumption, which represents in
Europe to almost 40% of the global energy demands. The use of venetian blinds is
particularly common due to their relatively low cost and high versatility. The operation of
these systems is usually based on the rotation of movable slats. By rotating the slats, the
occupants have the possibility of controlling solar heat gains through windows and
daylight into the spaces, while ensuring privacy and some view to outdoors. This allows
