Help modeling a Scalar variable?

[Anonymous]

Hi, I've been working on a parking garage CO model with an initial CO value of 25 ppm and fresh air entering the system. I've noticed it runs smooth for a while with the scalar value in the convergence plot decreasing, however, after a while it starts rising. Now, I'm confused by this because there is no supply with CO entering the system.

For my model, I have scalar value 1 being pure CO, and scalar value 0 being pure air. There's only two inputs with 17500 CFM each and with a scalar value of 0 entering the parking garage. I have two exhaust fans pulling 21130 CFM out, so the scalar should be decreasing, right? I followed some of the other suggestions on these forums as well as watching older webinars, but I'm having some serious trouble figuring this out. 

I attached a picture below to show the convergence plot's scalar increasing. Thank-you.

[Jon.Wilde]

My first thoughts:

1. Are you pulling out more air than is entering?
2. Also, one of the inlet's or outlet (outlet is usually better) must have a P=0 assigned to it instead of a flow rate or the model will be over constrained
3. Extend all inlets and outlets too, so you have nice smooth flow entering and no recirculation over the outlets

I would guess that you have all three of these issues right now 🙂

Thanks,

Jon