Hygric Extension properties

[Tomás]

Hi all,

Im a student investigating hygrothermal performance of a hydrophilic mineral wool insulation when retrofitting existing buildings with internal insulation. With the wall buildups I have, there are a few materials that are not present in the Wufi Material database and therefore I need to create new ones. I have obtained all the basic data properties required but I am wondering how do I get the hygric extensions. It was my understanding that Wufi calculates these on the basis of the basic properties but this hasn't happened. I know simulations can be done without these properties but giving that the the mineral wool insulation is hydrophilic, I thought additional data would be needed.

Any advice you may have would be greatly appreciated,
Kind Regards,
Tomás O'Hanlon

[Thomas]

I have obtained all the basic data properties required but I am wondering how do I get the hygric extensions. It was my understanding that Wufi calculates these on the basis of the basic properties but this hasn't happened. I know simulations can be done without these properties but giving that the the mineral wool insulation is hydrophilic, I thought additional data would be needed.

Hi Tomás,
in general, the hygric extension properties can not be determined from given basic properties.

Some extensions describe properties which may not be present in some materials but may be crucial in other materials. Other extensions simply describe refinements of basic properties such as a possible moisture-dependence of the thermal conductivity etc. It must be determined for each material which extension properties are needed.

In your case, the mineral wool certainly has no capillary transport, so the liquid transport coefficients for suction as well as redistribution can be set to zero. The water vapor diffusion resistance factor is probably not moisture-dependent, so there is no need to fill in that table. The mineral wool undergoes no phase changes, so its enthalpy-related properties are already fully described by the constant heat capacity which is given as one of the basic parameters.

Whether and to which degree the moisture-dependence or the temperature-dependence of the thermal conductivity need to be taken into account in your investigations is for you to decide. If you want to allow for them, you can model them after the mineral wool in the database.

Your hydrophilic mineral wool will exhibit some sorption moisture, so a moisture storage function must be defined.
For mathematical reasons, WUFI needs such a function for all materials and uses a pre-defined function for materials where the user has not defined such a function. This pre-defined function has been modelled after some dense and not very hydrophobic kind of mineral wool, so maybe this is already good enough for your purposes. This default moisture storage function is described in the references section in WUFI's online help. If this default function is not sufficient for your purposes, you have to provide and tabulate appropriate data.

Regards,
Thomas

[Tomás]

Hi Thomas,
Thanks for getting back to me. Since my last post, I have obtained the Liquid Water Transport coefficient (k) for the hydrophilic mineral wool insulation. I think this is an important property for this type of mineral wool insulation as I am trying to investigate the materials ability to quickly transport water. WUFI will automatically generate a table with estimated liquid transport coefficients once I input the following:

w Dws
[kg/m³] [m²/s]
__________________
0 0
w80 Dws(w80)
wf Dws(wf)

However, I'm not entirely sure what I'm exactly meant to be entering here. I know Wf is free water saturation, but what do I put in for it? For example, the liquid water transport figure I obtained (from studies compiled by the Czech Technical University) is 8.40e-6. How do I use this figure to get the DWS at different water contents?

Secondly, it was mentioned to perhaps calculate the moisture storage function of the material. I am a bit confused on how to calculate this.

Any help would be greatly appreciated, as i need to get these two properties in order to correctly analyse the performance of the insulation.

Kind Regards,
Tomás