Unsteady Rans Simulations Of Laboratory Ventilation With Chemical Spills And Gas Leakages - Toward Balanced Safety And Energy Effectiveness

Laboratories generally set high airflow rates, commonly measured by the number of air change per hour (ACH), to maintain safe ventilation environments in case of unintended chemical spills and gas leakages as well as to remove fugitive emissions. However, unnecessary high ACH results in wastage of energy and at times, even inefficient removal of pollutants. Due to the uncertain impact of ACH, the latest ventilation codes and standards provide laboratories the flexibility to establish performance-based minimum airflow rates instead of adopting standard criteria. As such, with high-performance computing resources, this study applies the Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations to explore the optimal ventilation strategies in a chemistry laboratory with high fume hood density, which is typical in National University of Singapore (NUS) but has not been studied. First, a chemical spill experiment was conducted to validate the simulation methods. Subsequently, transient variations of air contaminant concentration were simulated under chemical spills or gas leakages at 2 to 16 ACH with different fume hood operation during the unoccupied period of the laboratory. The simulation results show that when fume hoods are switched off, increasing ACH makes diminishing decreases of peak concentrations and clearance time of pollutants. In comparison, when fume hoods operate at a minimum airflow rate, mutual interference between room and fume hood exhausts are observed. In this case, increasing ACH becomes less effective for improving the laboratory ventilation. Based on the results, recommendations are given to optimize laboratory ventilation strategies during unoccupied period balancing occupational safety and energy conservation.