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.
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
Hygric Extensions of Hydrophilic Mineral Wool Insulation
Re: Hygric Extensions of Hydrophilic Mineral Wool Insulation
Hi Tomás,Tomás wrote: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.
I'm not sure whether any mineral wool can exhibit capillary transport, even if it is hydrophilic, but if you say so...
No. This is the table which WUFI estimates.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)
If you need to take liquid transport into account (that is, if the material is capillary-active), you have to find out what the liquid transport coefficients are at the various moisture levels. You enter these data in the table and you are done.
Since it is often difficult to obtain these coefficients, WUFI offers a way to estimate them. If you know the "water absorption coefficient" (or "A-value") which describes how much water the material absorbs in a water absorption experiment, you can check the option "generate" and enter the A-value in the appropriate "Approximation parameter" field. WUFI will then estimate the simplified table of liquid transport coefficients you cited above.
First of all, you should make sure what this number means precisely. Is it a liquid transport coefficient as defined in WUFI (there a various possible definitions in the literature)?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?
If so, do they mention that in this mineral wool liquid transport is more or less constant over the whole relevant moisture range? Then it is sufficient to enter just this number in the table.
Do they say, or can it be seen from their paper, that the measurements were done at only a single moisture level and the behavior at other moisture levels is unknown? Then this is a case of insufficient data. In these situations we often assume that the liquid transport coefficients at the highest and the lowest relevant moisture levels differ by a factor 1000, but this can only be a very rough estimate. You may do test calculations for different assumptions about the variability of the liquid transport coefficients and see whether different assumptions lead to unacceptable differences in the results. If so, you need to find better data.
If you have measured data concerning the moisture storage function (maybe from that Czech paper?), enter these data in the relevant table and you are done.Secondly, it was mentioned to perhaps calculate the moisture storage function of the material. I am a bit confused on how to calculate this.
On the other hand, WUFI uses a default moisture storage function for those materials where the user has not defined such a function (that is, where the relevant table has been left empty). This default function has been modelled after some dense and not very hydrophobic kind of mineral wool. Maybe this default function is sufficient for your purposes. If so, you may just leave the moisture storage table empty for your material, and WUFI will automatically use the default function.
To see whether the default function is good enough for you, you may look up its definition in WUFI's online help and compute a few values to compare them with what you know about the properties of your material.
Regards,
Thomas
Hi Thomas,
Thanks for getting back to me so quick. I think I have sorted this issue now.
I have two more questions though if you don't mind. When setting up the simulation, with regards to the initial conditions, I ran a simulation on the existing wall (before retrofitting with internal insulation) and then plugged this data into the initial conditions for the retrofit case. However, I also ran a simulation on the retrofit case without plugging in the initial conditions - I kept it constant across component' - just out of interest to see if it there was a major difference. I know plugging the existing wall data in is more accurate but there was a dramatic difference in both results even though it was the exact same wall.
The wall with the plugged in initial conditions resulted in a lowering of total water content from start of simulation to end whereas the wall with the initial conditions kept constant across component illustrated severe rising water content over the period of the simulation. Just out of interest, why do you think this is? Surely the initial conditions, although important, wouldn't have that big of an impact upon the performance, would they?
Also, as I previously mentioned, for my thesis I am looking at the performance of a hydrophilic and hydrophobic internal insulation systems. I am basing the hydrophilic insulation on research carried out by the Czech Technical University. I simulated their wall construction with the only difference being that I had 300mm concrete instead of 450mm brick. The wall failed. Initially I thought it was to do with the Dublin climate being different to the Prague climate, but after checking that, the wall still failed. I then changed the concrete to brick and the wall passed. Does anybody know why this would be? Is the concrete preventing any interior moisture which comes through the hydrophilic insulation from going through the concrete, whereas the brick, being more porous, would allow more, thus preventing moisture buildup behind the insulation.
Any advice would be greatly appreciated.
Thanks,
Tomás
Thanks for getting back to me so quick. I think I have sorted this issue now.
I have two more questions though if you don't mind. When setting up the simulation, with regards to the initial conditions, I ran a simulation on the existing wall (before retrofitting with internal insulation) and then plugged this data into the initial conditions for the retrofit case. However, I also ran a simulation on the retrofit case without plugging in the initial conditions - I kept it constant across component' - just out of interest to see if it there was a major difference. I know plugging the existing wall data in is more accurate but there was a dramatic difference in both results even though it was the exact same wall.
The wall with the plugged in initial conditions resulted in a lowering of total water content from start of simulation to end whereas the wall with the initial conditions kept constant across component illustrated severe rising water content over the period of the simulation. Just out of interest, why do you think this is? Surely the initial conditions, although important, wouldn't have that big of an impact upon the performance, would they?
Also, as I previously mentioned, for my thesis I am looking at the performance of a hydrophilic and hydrophobic internal insulation systems. I am basing the hydrophilic insulation on research carried out by the Czech Technical University. I simulated their wall construction with the only difference being that I had 300mm concrete instead of 450mm brick. The wall failed. Initially I thought it was to do with the Dublin climate being different to the Prague climate, but after checking that, the wall still failed. I then changed the concrete to brick and the wall passed. Does anybody know why this would be? Is the concrete preventing any interior moisture which comes through the hydrophilic insulation from going through the concrete, whereas the brick, being more porous, would allow more, thus preventing moisture buildup behind the insulation.
Any advice would be greatly appreciated.
Thanks,
Tomás