Convergence failed with explicit radiation balance

[WEI LI]

Hi there,

I am trying to simulate a simple roof strucutre.
First layer - metal deck
Second layer - 30 mm airlayer without additional moisture capacity
Third layer - 100 mm insulation Polyisocyanurate Board
Forth layer - metal deck.
All the material are from WUFI database.
I specified the weather of Dunedin from the database as the outdoor climate, 100 ACH ventilation from the outdoor on the airlayer.
Run the simulation for 168 hours.
The thing is when the explicit radiation balance was turned off, everything goes fine.
However, when it was turn on (keeping everything in the surface transfer coefficents as default), convergence failed. Adaptive time step does not help.
The water content is shown as below:

watercontent_explicit.png (46.23 KiB) Viewed 3220 times

Any helps will be appreciated.

[Christian Bludau]

Hi Wei Li,

please try to take in account the metal decks on both sides as sd-value in the boundary condition. This will lead to better convergence behavior.

Best regards
Christian

[WEI LI]

Hi Wei Li,

please try to take in account the metal decks on both sides as sd-value in the boundary condition. This will lead to better convergence behavior.

Best regards
Christian

Hi Chris,
Thanks for the reply.
Tried but didn't work.
I also tried to split the airlayer into two layers, one is 29 mm without moisture capacity, and one is 1 mm with moisture capacity.
It appears that the water content of the one without moisture capacity jumps up suddenly. Please see the figure down below.