Hello, I am getting the same error as in the discussion I'm replying to. I have setup a simple enclosed room with two openings one for supply air and another for return. I have defined all materials for walls and inside air volume and defined the boundary conditions for the supply air of 95 deg and 500 CFM and 0 pressure for the return. I set meshing to autosize. Under Solve I set physics for heat transfer and made sure to set the gravity. Despite double and triple checking the solver fails to run. I get a "the analysis has stopped because solver had exited unexpectedly" error. I have attached the CFZ file for your review. Successfully running this simple scenario will allow me to try and run a more complex scenario for our project.
This all sounds sensible - although you might want to edit the air and change it to variable rather than fixed if you looking at gravitational effects (which will be zero unless you have heat loss/gain within the domain).
Feel free to share the model, we need a cfz file.