'Porosity' and 'Optional data'

[RvS-AdB]

I have designed an historic small building and want to simulate it in Wufi®Plus with detailed information. It may looks like im doubting the specific information about 'porosity' and 'Optional data'. But the fact is i really want to make an simulation with real data, which i cannot find myself at the moment from suppliers. In Declaration Of Performance (DoP's) you would think to find a lot of data i lookt for, but that is not the case.

I need this information because:

Porosity is in percentages [%]. Based on the porosity, Wufi itself creates a fixed water storage function based on the porosity. When no furtermore 'optional data' is determined these data will be assumptions. It is an important parameter for the 'moisture-regulating' part i want to calculate. The fixed value cannot, be substantiated in an advice. Materials may fluctuate. So you have to accurately input how a material reacts in different conditions. So the question is up to Fraunhofer, is it true that for example 'Gutex Thermoroom' and all other materials that come from suppliers, are imported based on assumptions regarding Porosity? Or have substantiated data been used, derived from standards?

Under 'Optional data' you can enter more detailed information. You can see Gutex Thermoroom (which 'is' in the Wufi database), that it is elaborated in detail under the heading 'Moisture storage function'. Did you got this information from the supplier, because we can't find this detailled information.

What is this value based on? On the Wufi forum website, there is an topic viewtopic.php?f=3&t=139, I read that Thomas-Wufi adminstrator says: 'I don't know offhand how that value was determined, and right now I can't reach the colleague who collected those dates. But I would think that it's very likely just a guess.'

This relates to the following question 'About the cellular glass in the wufi materials database (Holzkirchen), I'm estonished about the value of the porosity : 0,25 : is it not high for a total porosity and very high for an open porosity ?'.

In our country this specific information under 'Optional data' is verry hard to find. For so far it is impossible. Can you give me a sourch where we can find this information regards to 'porosity' and everything under 'optional data'?

[Thomas]

So you have to accurately input how a material reacts in different conditions. So the question is up to Fraunhofer, is it true that for example 'Gutex Thermoroom' and all other materials that come from suppliers, are imported based on assumptions regarding Porosity? Or have substantiated data been used, derived from standards?

Hi RvS-AdB,

it is not true. If you look at the "Material Information" tab for that data set, the source of the data for the 'Gutex Thermoroom' is

"IBP laboratory test F067 (2011)".

The porosity is listed among the measured data. So the manufacturer sent us a sample, we measured the data listed in the "source" info in our own laboratory and then created a WUFI material dataset from the results. One would have to consult the full report to see which method was used to measure the porosity; it was probably helium pycnometry or mercury intrusion porosimetry.

You can see Gutex Thermoroom (which 'is' in the Wufi database), that it is elaborated in detail under the heading 'Moisture storage function'. Did you got this information from the supplier, because we can't find this detailled information.

According to the source information for this material, our laboratory measured the moisture storage function for the relative humidities 50%, 65%, 80%, 93%, 97% and for free saturation. The additional points between 97% and free saturation have been calculated with an interpolation formula.

Based on the porosity, Wufi itself creates a fixed water storage function based on the porosity. When no furtermore 'optional data' is determined these data will be assumptions.

Please note that it is only in rare cases that the moisture storage function of a material in WUFI's database has been derived from the porosity. For materials which are comparable to dense mineral wool, we sometimes use an empirical formula for the moisture storage function which is based on the porosity. For these materials, changing the porosity will also change the whole moisture storage function.

However, for the vast majority of materials there is a tabulated moisture storage function, giving definite values for moisture contents between the dry state and free saturation. These data are independent of the value of the porosity and independent of whether the porosity value has been measured precisely or just estimated.

The porosity does affect the moisture storage function above free saturation: WUFI assumes that the maximum saturation is given by the porosity multiplied by 1000 kg/m³, the density of water. However, even if only a crude estimate were used for the porosity, it would usually not affect your simulation results, because if you are simulating the building components under "normal" conditions, the materials will never exceed free saturation to such an extent that it makes a difference whether the material can maximally absorb 900 kg/m³ or just 800 kg/m³ of water. As mentioned, the tabulated part of the moisture storage function is completely independent of the value for the porosity.

In our country this specific information under 'Optional data' is verry hard to find. For so far it is impossible. Can you give me a sourch where we can find this information regards to 'porosity' and everything under 'optional data'?

This information is everywhere hard to find, this is why we are trying to provide WUFI users with a broad selection of materials in the database. Unfortunately, given the almost infinite variety of existing materials, we can only provide data for a small fraction of them.

While understandably users would like to use exactly the material they found on the architect's list, this will usually not be possible. It is then useful for the user to understand which properties of the material used in a given simulation are important and which ones are not. This may sound challenging, but test calculations with WUFI (with variations of some parameters) can show quickly which parameters are important in the specific simulated situation and must be known accurately, and which ones are not important and can be estimated.

Regarding this question, WUFI's help file gives a few hints
at the beginning of the topic: Reference - Material Data - How to Measure Material Data
and at the end of the topic: Appendix - Assessment Criteria.

The cellular glass in the database is a case in point. Cellular glass is basically an inert material which allows some thermal conduction, but which admits virtually no vapour diffusion and no liquid moisture transport. Accordingly, the "Cellular Glass" in the database is just some generic material which basically reflects this fact. The thermal conductivity may have been measured or taken as a typical value from some data sheet. All the rest, in particular the hygric properties, are probably just guesses or estimates. If you use it in one of your constructions for the kind of situations for which it is intended (as a hygrically inert thermal insulation) you will find the same simulation results even if you change the details of that material's porosity or moisture storage function. On the other hand, if you want to find out whether cellular glass as thermal insulation in a high-temperature water tank will have taken up some condensation moisture after fifty years of exposure, this generic material from the database is not adequate to answer that question and you will need data measured on the specific brand used in that case.

Kind regards,
Thomas