A small test room has been built which is five times smaller than the so called Annex-20-room. Different kinds of tracers have been used for visualizing of flow patterns. Velocities, concentrations and mass transfer coefficients have been measured. The measuring instrumentation is based on thermal anemometry (hot wire probes) and a special ammonia-mass transfer method, respectively, in order to estimate the heat flux coefficient at the walls. The values measured and the flow patterns have been applied in order to compare and to evaluate a computer code developed in Dresden to simulate three dimensional flows. This code is based on a finite-volume-discretization for the transportequations (Navier-Stokes- with k-e-model) solved with a new iteration technique including a multi grid solver.