New User help

[pudding]

Hi all,

I'm trying out WUFI to investigate my barn conversion walls. There are 3 different wall sections, the original stone walls which will be internally insulated, new walls which will be clad in cedar cladding, and new walls clad in stone.

We're going to use Celotex PIR insualtion which is foil faced on both sides. I can't seem to find this exactly in any material database, so what I've used so far is the PIR insulation from the North American database, and then added a vapour retarder either side of it, with Sd=20, as the Celotex has a water vapour resistance of >=150MNs/g and I've read that multiplying this by 0.2 gives approxiamtely the Sd value, which then would be 30, hence using Sd of 20 should be conservative. Will this model the Celotex correctly, or should I do it differently?

Also, when modelling a stone wall, is there any way to model lime mortar pointing, or is it needed? Should I add a moisture source to model driving rain at the external surface?

Lastly, Ive been leaving the initial conditions as 80% RH throughout the wall. Is this realistic, or should I change the RH for each layer? In particular, the Celotex, as starting with 80% RH the moisture is basically trapped between the foil layers?

When analysing the results, I've basically been checking that total water content drops, and the RH in each layer never reaches 100%. Anything to check to see if there are any potential future problems with my walls?

Thankyou.

[Christian Bludau]

Hello pudding,
i think your way modeling the Celotex is right. But you should use the right sd-value for the foils. There are two ways: 1) edit material and adapt µ-value (thats not possible in WufiLight) or 2) adapt the thickness of the foil:
sd = µ * d, so at 1mm µ = 20000 for sd=20m and for 30m you have to change the thickness to 1,5mm

For your stone wall:
In Wufi 1D the only way to model the mortar joints is to use a material with effective values. in our database you can find for example a solid brick, for which the material data was measured brick and joint.
The rain source is only needed if you want to adapt some rain water in special places in the construction (eg behind the EIFS according to ASHRAE 160). If you have a material on the surface which can suck (contains coefficients for liquid water transport), the rain (if available, depending on adhering fraction and orientation, wind and rain model... and your climate file has to contain rain) is absorbed.

The 80% is usually higher than the equilibrium state of the construction, so you normally can see the behavior of the construction quite fast. If you have a material which is tightened and build in with a lower water content it may make sense to reduce the initial water content for the single layer.

For analyzing see "Handling of typical constructions" in our tutorial section to get some ideas:
http://www.wufi.de/frame_en_tutorials.html

Christian

[fostertom]

I've basically been checking that ... the RH in each layer never reaches 100%

AFAIK, you won't see RH reach 100% because in a porous solid some vapour liquidises at all RHs, and that ramps up exponentially as it approaches 97%. So 92% or thereabouts might be the RH limit to check.

[Peterbilt]

Below is a quote form an earlier post and I just wanted to double check that ALL material data on brick (including the North America database) includes the mortar, as stated below.

I have often heard that a problem with WUFI 1D is that modeling the brick tells little of the real "story" because the real "action" is through the mortar.

Should we be modeling the mortar or the brick with WUFI 1D?

Thanks - Peter

Hello pudding,

For your stone wall:
In Wufi 1D the only way to model the mortar joints is to use a material with effective values. in our database you can find for example a solid brick, for which the material data was measured brick and joint.
The rain source is only needed if you want to adapt some rain water in special places in the construction (eg behind the EIFS according to ASHRAE 160). If you have a material on the surface which can suck (contains coefficients for liquid water transport), the rain (if available, depending on adhering fraction and orientation, wind and rain model... and your climate file has to contain rain) is absorbed.


Christian

[Christian Bludau]

Hello Peter,
the mortr is only included if it is stated in the Info-Text of the material. Usually it is not included.
Regards,
Christian