Hi,
In the description of wood fibre-board in your database you mentioned that wood fibre tends to swell and shring during hygrothermal testing.
So you based your data on the present and past moisture contet. I am not sure what you actually means. Can you please explain how you dealt with the swlling problem in the absorption curve?
What data have you reported for the free water saturation and how did you take into account of swelling?
Thank you
Free saturation for wood fibre insulation
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Daniel
- WUFI SupportTeam IBP
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- Joined: Tue Jul 19, 2005 2:50 am -1100
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Re: Free saturation for wood fibre insulation
Dear Utente101,
yes - swelling and shrinking can be often observed. However, that cannot be directly considered in the simulation. Normally such materials have limits of max. around 18 % by mass or max. 97 % RH. Up to that range, the effects are mostly of little relevance - and higher moisture levels shouldn't be accepted due to the damage risk.
We provide the moisture content in kg/m³ or relate it to the dry mass of the material. Both values are independent on the swelling or shrinking effects.
Only when the free saturation exceeds the measured porosity of the dry material it can be necessary to slightly increase the porosity to provide enough space for the water. How to handle this in future is currently topic of discussion in several standards - no rules for that up to today.
If the swelling is a problem or not can be discussed with a structural engineer - normally in case of the insulation material it is not. But once more - such high moisture contents should normally not occur in swelling materials.
best regards
Daniel
yes - swelling and shrinking can be often observed. However, that cannot be directly considered in the simulation. Normally such materials have limits of max. around 18 % by mass or max. 97 % RH. Up to that range, the effects are mostly of little relevance - and higher moisture levels shouldn't be accepted due to the damage risk.
We provide the moisture content in kg/m³ or relate it to the dry mass of the material. Both values are independent on the swelling or shrinking effects.
Only when the free saturation exceeds the measured porosity of the dry material it can be necessary to slightly increase the porosity to provide enough space for the water. How to handle this in future is currently topic of discussion in several standards - no rules for that up to today.
If the swelling is a problem or not can be discussed with a structural engineer - normally in case of the insulation material it is not. But once more - such high moisture contents should normally not occur in swelling materials.
best regards
Daniel
Dr.-Ing. Daniel Zirkelbach, Deputy Head of Department Hygrothermics, IBP Holzkirchen