There are many reasons for a slow simulation speed. Especially at the beginning of 2D and 3D simulations the first time steps can take quite a long time, sometimes the simulations "in the middle" become very slow. If the simulation speed does not accelerate within some hours (simulation time) try these approaches:
the higher the number of discretized elements the slower the speed. Think about reducing the number e.g. by choosing a stretch factor of at least 1,6 (or higher) with the “Automatic Grid Generation”.
think about whether really every layer has to be modeled. Thin layers, especially foils, can be replaced by contact conditions what reduces the number of discretized elements significantly.
it should be avoided to assign boundary conditions associated with moisture on moisture dense materials, e. g. rain on steel or glass. There is no influcence anyway.
each material layer must consist of at least three layers in each direction.
at >> Simulation View >> Solver Options >> Relative Tolerance the precision of the results can be changed. Reasonable values are between 0,0001 and 1E-8. But a lower precision does not always lead to quicker simulations.
at >> Simulation View >> Performance Options >> Maximum Method Order instead of the predefined value 5 as well 2 or 1 can be used.
do NOT hook >> Simulation View >> Model Options >> Prevent overfilling. This can be especially helpful for simulations with air layers or very small elements of materials with very low moisture storage capacity.
The last three suggestions one can change during the simulation. Just cancel the simulation, change one or more simulation settings and click on “Continue simulation from last output time point”.