Numerical simulation of transient effects of window openings.

This work is centered on the transient analysis of natural ventilation provided by a single side opening when only indoor-outdoor temperature differences are present (no wind). Using both simplified "engineering" models and a CFD commercial code (2D), different cases have been examined by varying indoor-outdoor temperature difference, window size, and including or not a heating appliance in the room. The CFD results reproduce correctly the phenomenon, but the time-scale seems to be inconsistent with global mass and energy conservation principles, in spite of the fact that numerical convergence is always achieved. Re-scaling the time allowed the results of the simulation to substantially agree with zonal model results. Furthermore, they allowed to determine the values, varying with time, of ventilation efficiency when a window is opened. The air changes at steady-state are also expressed as a function of Grashof number