Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

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tommao
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Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by tommao » Tue Feb 14, 2017 2:07 am -1100

Hi, i am wondering if i am misstaken some of the parameters in WUFI 2D. I am trying to simulate the same results from a laboratory research project in WUFI 2D. It is a simple flat roof construction with homogenous layers. A wooden spruce board is saturated with an exact amount of water inside a plastic box with insulation, vapour open membrane and a plasterboard on the interior side.

The surface conditions are set correctly with indoor and outdoor climate on bottom and top. The rest is adiabatic.
I set the initial water content of the spruce board to about 100 kg/m3 and insulation and gypsum to 40% RH.

After the simulation is done with no errors, i see that in WUFI Graph it shows that the starting condition of the construction has a total of about 10 kg/m3. Everything seems to be correct apart from the decimal number on the y-axis. Seems like it is a tenth (10,0) lower number than what i am expecting.

Could anyone who knows, explain to me why this is?

Thanks in advance!

Christian Bludau
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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by Christian Bludau » Wed Feb 15, 2017 8:16 pm -1100

Hello tommao,

is it the preset diagram of the total water content you are looking at? Or did you generate a diagram only evaluating the water content in the spruce?

Christian

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by tommao » Thu Feb 16, 2017 12:54 am -1100

Hi Christian

It is the total water content of the construction.

Ive added a picture of the geometry, which is very simple.

Image

I have also encountered another issue. The box is supposed to be sealed, except for the bottom side with the membrane.
This is to simulate the moisture release through intelligent membranes.

I did a test with a PE-foil membrane with a constant water vapor diffusion resistance of 70 000, with bitumen surface on top and adiabatic surface conditions on each side.

For some reason there is still release of water through the construction. Also in the laboratory i experienced the RH to quickly rise to 100%. but in the simulation it only reaches about 95% during 5 months.

The climate is controlled and have a constant indoor climate with 23 *C and 50% RH.
The outside climate is shown in the picture below
Image

The initial moisture in the plywood is 105 kg/m3 and for insulation and plasterboard its 40% RH.

I have tried out different membranes with high Sd-values but never seem to reach 100% RH.

I also tested different thickness of the membrane, from actual size to 1mm which i saw was recommended for some situations. but i am still not getting results that match the grafs collected from the lab research, where RH reaches 100%.

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by Manfred Kehrer » Thu Feb 16, 2017 2:28 am -1100

Have you checked the heat transfer resistances to be > 0 ?
Manfred
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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by tommao » Thu Feb 16, 2017 2:39 am -1100

Heat transfer coefficients are 19 W/m2K for outside climate and 8 W/m2k for indoor climate.

The measurement sensors in the laboratory have some deviation of cause, so reaching 100% RH will not allways be precise.
But i am still unsure of the results for the total water content as mentioned in the topic and first post.
With this high amount of water in a sealed box, why does the result graph show a starting moisture content of just under 10 kg/m3?

Added a picture below to illustrate.
Image

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by Sebastian Boegl » Thu Feb 16, 2017 3:00 am -1100

Could you attach the graph of the spruce board's water content?

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by tommao » Thu Feb 16, 2017 3:16 am -1100

Here is a picture of the water content in the spruce board.
Image

For information, this simulation is done with a intelligent membrane with variating Sd-values.

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by Sebastian Boegl » Thu Feb 16, 2017 3:36 am -1100

According to your latest graph, the initial water content in the spruce board is 100 kg/m³.
In comparison to a material specific selection the total water content is a combined value for each grid element weighted by its volume.

Does this clarify your first question?

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Re: Issue with indexes in WUFI 2D initial moisture and WUFI Graph total water content?

Post by Christian Bludau » Thu Feb 16, 2017 8:06 pm -1100

Additional to the answer from Sebastian:
The total water content is a mean value of the water in the spruce and the insulation weighted by volume. So this course is starting at much lower values.
The water content in the spruce is what you are looking for.
Christian

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