Mineral wool - Condensation

[msteinwender]

Hello,

the moisture storage function of mineral wool says, that reaching a water content of 44,65 kg/m³ (100% r.h.) leads to condensation and therefore to a critical situation. But mineral wool does not "store" moisture, so you cannnot be sure why the water content varies in the range below the 44,65 kg/m³ (condensation?).
Question 1: From which point on (r.h. or w.c. (and over what period of time)) you would say a critical situation is reached?
Question 2: By investigating a mineral wool in a wall construction it turns out that (at a given position) a rel. humidity of 90-92% (relates to a water content of 6 kg/m³) is the most "critical" situation. Would you say that there is no risk of condensation in that construction?

Markus

[Christian Bludau]

Dear Markus,

for the mineral wool there is not really a critical situation, as it is not harmed by the water. Starting at 10 percent by volume water content the thermal conductivity will increase and starting with thicker layers of dew water, the water may run out of the construction. There are also tests that the stability of the mineral fiber may decrease with higher water content. But it is not destroyed by water.
Did you use the mineral fiber insulation with the light green generic moisture storage function? As in this material the moisture storage function is generic, the shown water contents are to high. That can not be taken by the mineral fiber in reality. For materials with generic msf it would be better to only access the relative humidity and not the water content.
Try to use a measured mineral wool, for example the ones from ISOVER. They have much lower capability of water. But the may cause problems in the convergence especially in WUFI 2D.

Maybe our presentation about dew water would be also interesting for you (unfortunately only available in German):
https://wufi.de/de/service/downloads/
-> Leitfaden zur Tauwasserauswertung

Christian

[JMarsh4087]

Christian,
I am also studying condensation within mineral wool.
I'm following the WUFI Powerpoint at viewtopic.php?f=8&t=1623 .

I split off 1mm of mineral wool material, but it still has a water content that is basically 0 although I know RH and temp are very often hitting a state of condensation.
In the Powerpoint study, how did their material hit such a high water content?

[Christian Bludau]

Hi JMarsch

are you sure, that you
- are on the right position
- did only mark the wanted area
- selected the right unit?

Please also note, that depending on the moisture storage function you will only get a notable water amount, if your RH is close to one.
If you are at 0.99 or something like that, no noticeable water content may appear.

Maybe try to plot the water content and the RH in one diagram to see what is happening.

Christian