Modelling the solar factor of glazing combined with indoor Venetian blinds

Windows and facade systems combining solar control glazing with indoor Venetian blinds can be a very effective strategy to provide thermal and visual comfort. The solar factor of such systems strongly depends on the blind tilt angle and on the relative angular positions of the Sun in respect to the window. In the present paper a modified version of Tilmann E. Kuhn model for the complete angular determination of the solar factor is presented and discussed. The new version was developed in order to avoid the need for measured angular glazing properties and of calorimetric measurements of the solar factor for the window system, which were data required in the original version. This implementation has been carried out by means of a suitable extension of Arne Roos glazing angular variation model and by using the J.L.J. Roosenfeld's approach for complex systems. Moreover a three spectral band reformulation in place of broadband formulation has been introduced to improve the a ccuracy of the new version. An experimental angular characterisation of the solar factor has been carried out on a case study adopting mirror finished blinds. The analysis of the results shows that: in the new fully predictive approach the accuracy improvement of adopting a three-band formulation can be significant; the implemented version still ensures a good agreement with measured values, at least for this case study, with no need of angular data as input.