CO concentration in car park ventilation

[Mohamed Elaqabawy]

Hello,

I need to simulate the CO concentration in the parking garage to evaluate the exhaust system capacity. I calculated the CO concentration in the parking garage based on the ASHRAE standard. then apply this concentration as a mass fraction in the INIT line, creating an initial condition for the parking garage as CO concentration distributed uniformly 

The question is, How to make the CO production with the same concentration over the simulation time without using supply vent, I need to inject the CO in the car park uniformly for the full domain not only at spot location?

I read the FDS manual Species section but I couldn't reach the way to do that   

Any one can help on that?

Regards

Mohamed

[dr_jfloyd]

It sounds like you are trying to apply a non-CFD approach with CFD modeling. A real parking garage does not have a uniform concentration of CO throughout it; there are discrete sources of CO from vehicle tail pipes, and the resulting concentration over time will depend on the effectiveness of the ventilation.  If you are just specifying a uniform source term of CO throughout the garage, you will not have a realistic assessment of the system performance. You should look into what are the assumptions in the ASHRAE standard and how can the be expressed as a reasonable input for a CFD model.

[Mohamed Elaqabawy]

I agree with your statement; however, the client asked me to do it this way. He thinks that this is the worst-case scenario for the CO concentration in the car park. But I understand now that the FDS doesn't have a feature to inject the gas from each cell homogeneously, and the only way to do it is through a vent defined as the supply surface. Am I understanding it correctly?

Appreciate your reply.  

[dr_jfloyd]

You can inject mass from a particle. See the isentropic verification cases for an example.

Just because a client requests a specific analysis approach doesn't mean that approach is appropriate. As the engineer performing the work, your local laws and customs may impose legal and ethical obligations on you to ensure an adequate design process. In a car park, CO is released by the vehicle exhaust system while the vehicle is running. In general this is along a path from the entry location, around the ramps until a parking spot is located at which point the vehicle is turned off or the reverse for a vehicle leaving. Distributing the source over the ramps would be a better approximation to reality than everywhere in the domain.