The lattice Boltzmann method (LBM) and large-eddy simulation (LES) are combined with a scalar subgrid-scale model to simulate the indoor air velocity field and harmful gas dispersion. The LBM-LES model is validated by comparing its results with published experimental and numerical simulation results. Taking a simplified chemical building as the scenario, the relative ventilation efficiency is evaluated based on the maximum harmful gas concentration, and configurations with centralized and distributed harmful gas sources with both mixing ventilation (MV) and displacement ventilation (DV) systems are considered. According to the results, if the density of the harmful gas is less than the air density, the DV system is more efficient than the MV system. The DV system is more stable than the MV system under fluctuating relative ventilation efficiency due to changes in the distance between the ventilation vents and in the distance between the centralized gas sources and the exhaust air vent.
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