University Wall Section

[C. Furtaw]

I am analyizing a new wall section and have two questions. The wall section is typical to the extent that is a brick veneer, densglass sheating, Tyvec, metal stud backup with insulation in the studs, gypsum board interior with an application of vynl wall covering that may be impervious. Also, the building is under negative air pressure.
How do I accomodate the vynl wall paper and negative air pressure?
Thanks,
C. Furtaw

[Thomas]

How do I accomodate the vynl wall paper and negative air pressure?

Dear Mr. Furtaw,

as to the vinyl wall paper, you can either take the "Vinyl Wallpaper" from the material database and insert it into the component assembly as an extra layer on the interior side of the gypsum board, or you can instead treat it as an extra diffusion resistance on the interior wall surface (it doesn't appear explicitly in the assembly then).
To do the latter, enter the appropriate permeance in the edit box "Permeance" for the "Interior Surface" in the dialog "Surface Transfer Coefficients". For example, the vinyl wall paper from the database has a permeability of 0.011 perm inch and a thickness of 0.00787 inch, which results in a permeance of 1.4 perm. That's the number to enter in the "Permeance" box. If you have a vinly wallpaper with a different specification or if you want to run numerical experiments on the effect of different permeances, just enter the appropriate number.

Differences in air pressure across the component cannot be taken into account by WUFI. If the component is leaking and air is streaming through the layers, any moisture or heat transport created by this convective flow cannot be computed with WUFI; it would be a more or less two-dimensional problem anyway (a future two-dimensional WUFI version currently under development will be able to treat these cases).
If the component is airtight, the slightly different ambient pressures in different parts of the construction will affect heat and moisture transport only on a negligible level and can thus be ignored.

Regards,
Thomas

[C. Furtaw]

Thomas,
Thanks for your reply.
CF