Multizone building energy simulation programs become popular among building designers. They include a wide variety of techniques and advanced heat transfer models, yet require only limited computation time. Unfortunately, the use of correlations to predict the convective heat transfer undermines their reliability. The correlations actually apply only to specific cases. Meanwhile, convective heat transfer modelling is particularly important in mixed convection regimes with high ventilation rates. It is selfevident that researchers would investigate to what extent including more room/system design parameters is necessary to model mixed convection heat transfer. The authors of this study imitated sequences of typical mixed convection cooling regimes (a day regime possibly preceded by night cooling) in a modified PASLINK cell and varied the air supply/exhaust configuration and added to some cases a thermally massive floor. The analysis was based on airflow data and the convective heat flux. The results indicate that the air supply/exhaust configuration is important when high ventilation rates are combined with heterogeneously distributed thermal mass. Existing convection correlations cannot predict the convective heat flux accurately for the studied cases.