Shading devices have long been used to control solar gain and daylighting t
hrough windows. The optimal design and use of such devices requires a detai
led knowledge of their optical and thermal properties, including their vari
ation with the angle of incidence of the solar radiation. We describe the e
xperimental methods used to characterise two types of double-glazing units
(DGU) incorporating Venetian blinds. The first consists of a DGU with an ad
justable blind located in the space between the panes. The second incorpora
tes a fixed blind element bended between two glass sheets. The spectral bi-
directional transmittance functions (BRTF) were measured for a range of inc
idence angles, using the Cardiff goniospectrometer. The thermal properties
were measured with an illuminated hot box. These measurements are laborious
, and it is desirable to develop simple models, that could be used for prod
uct development to estimate the effect of changing the properties of the bl
ind material and its design, without the need to make detailed measurements
on each variation. A model is described, that calculates the properties of
the DGU using as input the optical proper ties at normal incidence of the
component elements (glass and the blind's slats). The model is applied to t
he variable blind DGU, varying the angle of rotation of the blind. Despite
the simple nature of the model, it is shown to satisfactorily predict the p
roperties of the DGU. The model can easily be incorporated in building ener
gy simulation programs. (C) 2001 Elsevier Science B.V. All rights reserved.