In the previous papers, the P. V. Method (Prescribed Velocity Method : P. V. Nielsen et al. : 1980) was applied to the coarse grid CFD simulations with the isothermal and non-isothermal airflow data obtained by the experiments. The simulated results showed good agreement with the experimental ones. If the effect of the buoyancy is smaller than that of the kinetic energy around the ceiling air diffuser, the airflow data obtained under isothermal condition can give the boundary condition for the coarse grid non-isothermal CFD using the simplified modeling method. The possibility of the application of the isothermal airflow data to the non-isothermal CFD simulation was examined in this paper. The eftect of the buoyancy in the vicinity of the ceiling air diffuser was compared to that of the kinetic energy by calculating local Archimedes number. When the virtual box around the air diffuser was small, the local Archimedes number at the box surface were much lower than 0.1 and the buoyancy effect was not significant. The CFD simulation using the P. V. method with the small virtual box based on the isothermal airflow data was carried out and compared to the experiment. The CFD can reproduce the distributions of the airflow and temperature obtained by the experiment. Therefore it was concluded in this paper that the isothermal airflow data can be applied to the non-isothermal CFD simulation under the certain conditions.