An important part of IEA 34/43 is concerning validation of building simulation models. Analytical andcomparative validation of multizone building simulation models are the object of Subtask B whileempirical validation of models dealing with the shading, day lighting and cooling load interaction istargeted by Subtask C.For the first approach, the Multizone Building Component of TRNSYS (Type 56) was tested in aseries of exercises ranging from analytical and simplified cases up to more complex situations wherespecial features like presence of site obstructions, internal windows are taken into account. The goodcapabilities of TRNSYS Type 56 as well as its limitations were pointed out by the exercise and theresults are discussed in the paper.In the second approach, a well-instrumented testing infrastructure (a test-cell) located at EMPA inZrich, Switzerland was used to check the performance of TRNSYS regarding the solar processingfeatures (calculation of diffuse radiation; repartition of solar radiation on vertical facades) as well asthe dynamic behavior of the Multizone Building model in different shading situations: no shading,internal shading, external shading. High quality measurements corresponding to periods of 600h weregenerated for each of these situations and the simulation model was tailored to represent as much aspossible the experimental conditions. In general, the behavior of TRNSYS was demonstrated verygood. The influence of some specific features of Type 56, for instance concerning the calculation ofthe infrared exchanges, is illustrated in the paper.