Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The conduction finite difference model has an inner loop, for each surface, and an outer loop for all the inside face surfaces (which can interact with each other by radiation).
If you are asking about the inner Gauss-Sidel loop, then the convergence criteria looks like this
sum( SurfaceFD( Surf ).TDT - SurfaceFD( Surf ).TDTLast ) / sum( SurfaceFD( Surf ).TDT ) ) < 0.00001
Which is looking at normalized temperature results for a surface from one GS iteration to the next for all the nodes in that surface.
The outer loop is controlled by the user input field called Inside Face Surface Temperature Convergence Criteria in the HeatBalanceSettings:ConductionFiniteDifference object, with a default of 0.002. This is looking at how the results change for the temperature right at the interface between zone air and the surface. It will recalculate all the surfaces until none change more than the criteria.
