Experimental and numerical determination of the total solar energy transmittance of glazing with venetian blind shading

In response to the increased occurrence of overheating problems in glazed buildings in recent years, EMPA has focussed on the determination and modelling of the total solar energy transmittance (TSET) of multiple glazing combined with different shading systems. Measurements were performed in a calorimetric outdoor test facility near Zurich, Switzerland. In the first phase, average TSET-values related to the incident global solar radiation were identified for various Venetian blind configurations with a measurement period of a few days each. As expected the results strongly depend on the slat tilt angle as well as on the solar reflectance of the slat surface. The influence of the directional distribution of the incident radiation is demonstrated by comparison of results from different measuring periods with the identical shading–glazing configuration. An extended identification model accounting for the angle-selective transmittance is presented. The experimental results are also compared with weighted g-values from numerical modelling, which are based on a view factor method extended for curved slats in a louver type shading device. In general, the agreement between the measured and calculated results is satisfactory. Some deviation is explained by a significant non-diffuse albedo component in the hemispherical radiation field.