[EnergyPlus_Support] Re: Easy question - Very thick massive external floor

["Jean marais" <jeannieboef@xxxxxxxxx>]

Hello Dr Li, sorry if I said the conductance changes with temperature. The conductivity or resistivity remains constant, but the heat transfer of coarse is temperature dependant. I have written a program when I was a student to model transient heat and mass transfer in a complete automobile exhaust system, so I understand the convergence difficalties as you described. My hand calculations where for a steady state case just to get a quick idea of what the magnitude of possible heat transfer could be. I did find however that the system is more responsive than I expected and that the consiqient propogation of increased temperature through the layers is faster than what I thought. I was hoping that the middle of the construction would stay at roughly the same temperature due to this big heat capacity effect, and that's why I wanted to run the simulation and report the inside temperature in the middle. As it turns out the system was indeed more responsive than I hoped which dismisses the otherside coeff approach. 

Which again got me thinking...if it is reacting faster than I thought, why is the convergence problem there. Turns out the tolerance for both temperature and load calculation convergence was set to 0.002. The model was failing to pass this very tight tolerance but still managed 0.05, which is actually still quite good. E+ default value is 0.4 for temp and 0.04 for loads. I've relaxed the tolerances and the severe errors are resolved. Finaly I just need to check how this effects the set point not met hours. 

In this case the relaxed tolerance will overall give the most accurate simulation results, bearing in mind that surface temperature errors are to the power of 4 for radiation exchange with dT in Kelvin.  



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