Boundary condition in a closed domain
 

Dear all,

I want to do thermal comfort modeling in a closed big hall. The following are the properties of my system

a) Heat loads from wall, skylight, occupant
b) 28 supply grills
c) 60 extract grills
d) from ventilation drawings I have velocities of each supply and extract grill

I am confused about what boundary conditions should I use like I can define the mass flow inlet because I know the temp of supply air but I can't define the mass flow outlet because I don't know the temp at the outlet which will change due to heat loads within the domain
and my solution is not converging when I use mass flow inlet and velocity inlet at extract with a negative sign.

Can you please help what proper boundary conditions should I use at the inlet and extract grills for good convergence.

Thanks
Wali