Laboratory Ventilation

The purpose of laboratory ventiliation systems is to minimize the risk of chemical exposure and fire hazard, as well as facilitate odor removal by reducing the contaminant concentration to safe level while simultaneously maintaining thermally acceptable environment for occupants. Often high airflow rates specified in terms of air change rates per hour (ACH) are perceived to minimize such risks. Although high airflow rates can reduce the overall concentration of contaminants, it may not ensure low levels of contaminant concentrations at all locations in a lab space, including the breathing zone of occupants which can potentially increase risk of chemical exposure. Our recent Computational Fluid Dynamics (CFD) analysis investigated the impact of supply airflow rates ranging from 4 to 12 ACH on the uniformity of contaminant concentration in a three dimensional lab space. This study indicates with increasing ACH the overall average concentration levels in the space decreases. However, the average concentration at breathing zone level was 26 percent higher than the expected diluted (target) concentrations at each ACH level whereas the maximum concentration was about 5 times higher than respective target concentrations. Furthermore, the flow path of the contaminants remains almost similar at all ACH levels, and thus, ACH has a little impact on the flow path of contaminants, which in turn affects the distribution of contaminants. For the case analyzed in this study the concentration levels at a breathing zone level were significantly reduced, even at low supply air flow rates, by modifying the location of air return from high ceiling level to a low level wall return. The flow path of contaminants and resulting distribution of contaminants in the lab space primarily depend on the HVAC configuration. Strategic design of HVAC configuration and optimization of the locations of air supply and return can be valuable in reducing the supply airflow rates and increasing ventilation effectiveness.