HVAC Convergence not reached


I’m attempting to simulate a simple HVAC scenario in a small two story building. The goal of the simulation is to have the room reach a steady state temperature, and then shut off the inlets to see how the air flow behaves. I began by having the simulation run until a steady state temp is reached, but the simulation is not converging, regardless of how I change the boundary conditions. I’ve tried having a constant inlet flow rate and using a table input to turn the inlets off. The inlets and outlets appear to be the source of the problem judging from the convergence plots, along with the residuals being too high. Any tips on how I can improve the simulations?

Here is the Domain convergence plot

And here are the Residuals

Here is the link:
Two Story, Stairs, Two Inlets | SimScale



First, by your description, I think the correct approach would be a transient simulation, to take into account the time effects. Steady-state should be used for constant boundary and flow conditions, for it to properly converge.

But, keep in mind that a transient simulation is way more difficult to get to converge, you might have to ramp up the inlet flows in order to help the solver.

Second, before switching to a transient simulation, I would make sure that my mesh is good enough and that the steady-state simulation has good residuals. I think that the mesh is too coarse, and also there is this gap at the top of the stairs, which looks like a source for trouble:

Please try and implement this suggestions, and let us know of your results.

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