Hello,
We want to use a Multifonctions pannel Wodego (MFP) with moisture resistant glue.
We tried to obtain the material properties for hygrothermal calculation but it is very hard to find.
We want to use a MFP pannel with a density of 680 kg/m3 (22mm), a thermal conductivity of 0.13 W/m.K and a dry water vapor diffusion resistance factor of 100.
In a first time (waiting for manufacturer answers) we want to approach the material properties with a similar material from the Wufi database,
We choose to use the chipboard.
We changed this values :
ro bulk = 600 to 680
lambda = 0.11 to 0.13
mu = 70 to 100
We kept the same hygrothermal functions as for chipboard, we just increase by 43% each value of the curve mu = function (RH) to rich the value of 100 for RH=0
Indeed MFP panel contain moisture resistance glue, we made the assumption that the water resistance diffusion factor supplement due to glue is independant of RH.
If someone has something to say about this, it would be nice.
Thanking you by advance.
Greetings.
MFP Wodego
Re: MFP Wodego
Hi Raymond,Raymond wrote:We choose to use the chipboard.
We changed this values :
ro bulk = 600 to 680
lambda = 0.11 to 0.13
mu = 70 to 100
We kept the same hygrothermal functions as for chipboard, we just increase by 43% each value of the curve mu = function (RH) to rich the value of 100 for RH=0
Indeed MFP panel contain moisture resistance glue, we made the assumption that the water resistance diffusion factor supplement due to glue is independant of RH.
this sounds reasonable. The chipboard may be considered somewhat similar, as long as no facts contradicting this assumption are known.
You are using the bulk density and the thermal conductivity the manufacturer states in the product catalog (p. 22).
The specific heat capacity is given in mass-specific units and stays the same as long as only the density of the considered material changes.
The porosity may be somewhat different in the tighter-packed denser material, but in WUFI it only affects the maximum possible water content, so a calculation investigating normal hygric conditions will be more or less independent of this value. Furthermore, at least part of the higher density of the MFP may be due to a different glue, so it is not really clear how much the porosity is changed.
One might consider adjusting the moisture storage function for the higher density. In materials where the moisture is mainly taken up in micropores and the density is mainly determined by the size and frequency of macropores (such as in aerated concrete, but wood and wood-based materials as well), the mass-specific water content stays basically the same for product variants which have the same microstructure and differ only by their density. So it could be argued that the moisture storage function should be increased in the same ratio as the density has increased. But in the present case the difference is not very large anyway, and - as in the case of the porosity - it is not really known whether the higher density is indeed caused by denser packing or partly due to a different glue.
Concerning the mu-value, the manufacturer quotes a "dry" value of 100 and a "wet" value of 50. Please note that these values do not correspond to humidities of 0% and 100%, respectively. They usually refer to test conditions where the sample is exposed to a humidity of ~50% on one side and ~0% on the other side ("dry" case) or to ~50% on one side and ~95% on the other side ("wet" case).
The mu-values measured under these circumstances are representative for conditions where the mean humidities in the sample are about 25% and 75%, respectively. (In detail, the situation is more complicated, because the moisture profiles during the test are not necessarily linear, depending on the moisture-dependence of the mu-value; but for simplicity and for lack of detailed data, mean humidities of 25% and 75% are usually assumed).
So one might try to adjust the moisture-dependent mu-values in such a way that the curve passes through 100 at a humidity around 25% and through 50 at a humidity around 75%.
Kind regards,
Thomas