A theoretical study on gaseous pollutant flushing of natural ventilation driven by buoyancy forces in industrial buildings

The acceleration of industrialization worsening indoor environments of industrial buildings has drawn more attention in recent years. Natural ventilation can improve indoor air quality (IAQ) and reduce carbon emissions. To evaluate gaseous pollutant levels in industrial buildings for the development of buoyancy-driven natural ventilation, two theoretical models of pollutant flushing (Model I and Model II) are developed based on the existing thermal stratification theory in combination with the mixing characteristics of lower pollutant. The results show that indoor pollutant flushing is mainly dependent on the pollution source intensity and effective ventilation area. The mixing characteristics of lower pollutant has an important effect on pollutant stratification and evolution during ventilation, but it does not change the prediction results at steady state. When the dimensionless pollution source intensity is larger than 1, the pollution source should be cleaned up or other ventilation methods should be used instead to improve IAQ. In addition, the comparisons between Model I and Model II on instantaneous pollutant concentration are significantly influenced by the pollution source intensity, and the actual pollutant concentration is more likely to be between the predicted values of Model I and Model II. To reduce pollutant concentration to a required level, the pollution source intensity should be in a certain range. The theoretical models as well as the necessary conditions for ventilation effectiveness obtained can be used for the ventilation optimization design of industrial buildings.