Natural Ventilation Analysis
The purpose of natural ventilation analysis is to assure that ventilation rates in naturally ventilated hazardous areas fulfil applicable requirements for operation.
The CFD tool FLACS is used in these analyses, where a 3D model of the installation is made and ventilations simulations are run for relevant wind conditions. The simulation results, given as air changes per hour for a given area, are combined with probabilities of the wind conditions in order to evaluate fulfilment of requirements (e.g. minimum 12 air changes per hour for 95% of the time in a hazardous area). Further, it can be important to consider so-called “stagnant zones” in hazardous areas, where ventilation is very low and gas accumulation can therefore become significant even if very small leaks should occur.
Example of calculated air changes per hour for a hazardous area, given one wind speed for 12 different wind directions:
CFD simulation is a very effective and intuitive tool for proposing possible improvements for increasing natural ventilation.
Example of plot of velocities in an area: