dew point and temperature graph

serenewongsa · Post by **serenewongsa** » Thu Sep 13, 2007 9:38 am -1100

I ran WUFI for a wall section of brick, air layer, vapor retarder, gypsum sheathing, batt insulation, and interior sheathing. In the quick graphs, the temperature and dew point lines appear to be overlapping at several positions in the all of the layers. However, if I zoom in very closely, the lines are not exactly touching but are parallel. If the temp and dew point lines don't touch when zoomed all the way in, does that mean condensation did not actually occur?

Thanks.

Manfred Kehrer · Thu Sep 13, 2007 7:09 pm -1100

Yes this means that no condensation occurs and the RH is always below 100%. But an RH of about 95% for instance for a longer time can also be a problem for some material (wood, organic material, ...)

serenewongsa · Post by **serenewongsa** » Fri Sep 14, 2007 2:22 am -1100

Hi Manfred,

If there's no condensation, how does the water content in the material go up? How can I find out the paramenters of what's bad for materials like the 95% for wood, etc.? And how long does the 95% have to be sustained to be a problem?
Thanks.
Serene

Manfred Kehrer · Sun Sep 16, 2007 8:34 pm -1100

serenewongsa wrote:If there's no condensation, how does the water content in the material go up?

Please take a look at the moisture storage function of the materials. There is defined how much water content a material can store depending of the RH of the enviroment. The physical process is called capillary condensation and this means that in very small capillary's condensation can happen below 100 % R.H.

serenewongsa wrote:How can I find out the paramenters of what's bad for materials like the 95% for wood, etc.? And how long does the 95% have to be sustained to be a problem?

At this time there are less exactly defined rules.

The state of the art is
1) the water content of wooden material should be below 20 M.-%, if temperature is over 10°C
2) German standards say that water content at layer´s boundary should be below 0,5 kg/m²
3) RH of indoor surface should stay below 80% because of mould growth

Manfred

serenewongsa · Post by **serenewongsa** » Mon Sep 17, 2007 4:23 am -1100

thanks, manfred. I will take a look at the moisture storage function.

yalinu · Post by **yalinu** » Sat Jul 12, 2008 7:17 am -1100

Can similar criteria be applied to concrete?
For example to keep the moisture content below the storage capacity at RH=80%? Also to keep surface RH<80% for extended periods to prevent mold growth?
The storage capacity of the materials in the library is in units of kg/cu.m. The result graphs also show moisture content by %M.
How can I convert the moisture capacity from kg/cu.m to %M?
Is there a difference in assessing allowable moisture in materials using %M versus kg/cu.m?

Thanks,
Yalin

Manfred Kehrer · Sun Jul 13, 2008 7:46 pm -1100

yalinu wrote:Can similar criteria be applied to concrete?
For example to keep the moisture content below the storage capacity at RH=80%? Also to keep surface RH<80% for extended periods to prevent mold growth?
Yalin

Yes, but the growth of mould does also depend on the suface type (Aga-Aga, organic, or mineral)

yalinu wrote: The storage capacity of the materials in the library is in units of kg/cu.m. The result graphs also show moisture content by %M.
How can I convert the moisture capacity from kg/cu.m to %M?
Is there a difference in assessing allowable moisture in materials using %M versus kg/cu.m?

Thanks,
Yalin

to derive water content [mass %] percent, divide the water content [kg/m³] by the bulk density [kg/m³].

yalinu · Post by **yalinu** » Wed Jul 23, 2008 3:18 pm -1100

Thanks Manfred. Appreciate the prompt response.

Manfred Kehrer wrote: Yes, but the growth of mould does also depend on the suface type (Aga-Aga, organic, or mineral)

I understand that the material is a factor. But if the organic matter is available such as dust, dirt, etc., and the moisture level and temperature is right, growth may happen even on concrete. Is this not right?
It's common in damp basement walls with inadequate damproofing.

Best regards,
Yalin

Manfred Kehrer · Wed Jul 23, 2008 7:09 pm -1100

Yes, you are right!

StrawConstruction · Mon May 13, 2019 8:27 am -1100

Hello, I am interested in the same topic.
I am analyzing a wall construction with WUFI 2D. Is it possible to display the dew point and temperature graph with it? If yes, how?
Thank you in advance.
G.

Christian Bludau · Mon May 13, 2019 10:38 pm -1100

No, thats not directly possible in WUFI Graph.
But you could export temperature and RH as ascii and the calculate the dew point.
Christian

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dew point and temperature graph

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