A Simplified Method for Calculating the Effective Solar Optical Properties of a Venetian Blind Layer for Building Energy Simulation

The use of venetian blinds to control solar gain through windows is common in both residential and commercial buildings, and their potential for reduction in peak cooling load and energy consumption is recognized to be large. As such, there is a strong need for models that allow a venetian blind to be included in glazing system analysis. A simplified method of calculating the "effective" solar optical properties of a venetian blind is presented. The solar optical properties of the entire blind are determined based on slat geometry and the optical properties of the slat material, and on the direction and nature (beam or diffuse) of incident radiation. The slat material optical properties are assumed to be independent of the angle of incidence, and are assumed to transmit and reflect beam radiation diffusely. As a first approximation, the slats are assumed to be flat with negligible thickness. A correction is then developed and applied that accounts for the curvature of the slat. The results of the flat and curved slat models are compared with experimental data for commercially available venetian blinds. Both models demonstrate excellent agreement with experiments, except when the profile and slat angles are aligned. In that case, the flat slat model predicts blind transmissions that are too large. The models developed in this study provide useful input to multilayer glazing/shading models used for rating or for building energy simulations.