Investigate to find boundary condition

[PierreC]

Hi

I would like to know if in your mind, Wufi 2d can be used to do a serie of simulations in order to finally find some values of interieur boundary condition.
I explain : i'm gonna have to study some slab system (with differents layers of materials) above crawl space.
I have exterior climatic conditions with my own file and the interior boundary conditions above the slab. However i don't have the hygrothermal behavior of crawl space on a entire year.

I have for the moment 2 ideas :

-Consider the space of the crawl space as a "air blade" in materials library and examine the relative humidity and temperature of this material after the processing. Though i cannot add an air exchange source in the crawl space with this way and i'm not sure the processing would correctly execute.

-Consider in a first time some approximate boundary conditions from the litterature and do some simulation in order to assess the difference of T° and RH in the crawl space, and repeat this operation until the stabilisation of the results. But i don't think Wufi gives the interior condition after simulation, isn't it ?

Here is a arbitrary modelisation to explain myself :

Photo forum wufi.png (5.61 KiB) Viewed 18964 times

Many thanks!

[mwinkler]

Hi PierreC,

WUFI 2D is not quite suitable to simulate the climatic conditions in the crawlspace, but you can use WUFI Plus (https://wufi.de/en/software/wufi-plus/) to do exactly this. What kind of assessments do you want to perform in detail? Do you need to do a 2D hygrothermal simulation?

You can also write me a PM if you have further questions.

Greetings
mwinkler

[Christian Bludau]

Dear Pierre,

we have developed a climate model for crawlspaces. Unfortunately that is only available in German. See our report of the climate project:
"Energieoptimiertes Bauen Klima- und Oberflächenübergangsbedingungen für die hygrothermische Bauteilsimulation"
https://wufi.de/literatur/Zirkelbach,%2 ... gungen.pdf

That can be used to set the climate in the crawlspace and use in your WUFI 2D calculation as boundary condition.

Christian

[Alberto Morales]

Hi,

Could you please send that climate for crawlspace in .wac to be add in WUFI2D?

Thanks

[Christian Bludau]

Hi Alberto,
the climate file has to be created based on the local climate or climate used in your calculation.
The climate in the crawlspace (German: Kriechkeller) is derived from the outdoor temperature and humidity (see report of climate project pp. 303).

The crawlspaces from the research were badly ventilated, we set up two models, one with for the case the ground is covered by a membrane (usually a cheap PE-foil), so the moisture from the ground can not get into the crawlspace and one model without covered ground.
To create the climate according to the model 72 hours floating mean values are used.

The temperature is derived according to the green regression line:

Temperature in crawlspace derived from outdoor temperature.

kriechkeller_temp.png (261.46 KiB) Viewed 14276 times

The x-axis is showing the outdoor temperature in [°C]
The y-axis is showing the temperature in the crawlspace in [°C]

For uncovered crawlspace floors the absolute humidity inside is related to the absolute humidity outside as follows (green line):

Absolute humidity in crawlspace derived from absolute humidity outside for uncovered crawlspace floors

kriechkeller_absF_ohneAbdeckung.png (126.51 KiB) Viewed 14276 times

The x-axis shows the absolute humidity outside in [g/m³]
The y-axis shows the absolute humidity in the crawlspace in [g/m³]

For crawlspaces with covered floors the absolute humidity inside is related to the absolute humidity outside as follows (green line):

Absolute humidity in crawlspace derived from absolute humidity outside for covered crawlspace floors

kriechkeller_absF_mitAbdeckung.png (187.34 KiB) Viewed 14276 times

The x-axis shows the absolute humidity outside in [g/m³]
The y-axis shows the absolute humidity in the crawlspace in [g/m³]

And that is how to create the crawlspace climate from your own climate. You can do that in excel or some other program.

1. Calculate the crawlspace temperature from the outdoor temperature according to pic 1.
2. Calculate the outdoor absolute humidity from your climate file
3. Add the humidity supplement according to pic 2 or 3
4. Calculate the relative humidity from the indoor absolute humidity using the indoor temperature
5. Create a wac-file out of that

Please remember to use floating 72 hours mean values for steps 1 and 2.

To create your own wac file, the CreateClimateFile.xlsm in the WUFI tools folder can be used, usually here:

Code: Select all

c:\Program Files (x86)\WUFI\Tools\CreateClimateFile.xlsm

Hope that helps.
Christian

[Alberto Morales]

thanks for your feedback, but I do not understand the explanation.

can you explain it in an easier way (more in detail) please?

what do you mean with "humidity supplement"?

how do you generate y-axis for temperature and absolute humidity in the crawlspace if you did not take measurments previously? because what I thought it is to measure the temperature and HR in the crawspace in different positions and to create mean values (put together all these measurements in the different positions) for each hour and with that to create your climate file for the crawlspace. but i am sure I am worng do please any advice?


what do you mean with "floating 72 hours mean values "? the wac file for crawlspace cannot have 8760 data because it is pointless to take measurement for such long time but the data in the winter and summer in the crawlspace will be different so... I do not understand to be honest

Regards

[Christian Bludau]

Hi Alberto,

what do you mean with "humidity supplement"?

You have to set the absolute humidity indoor for each hour corresponding to the humidity outside as shown in pic 2 or 3.
So for pic 2: If your absH outdoor is 0, set the indoor to 4, if it is 10, set the indoor to 12.

how do you generate y-axis for temperature and absolute humidity in the crawlspace if you did not take measurements previously? because what I thought it is to measure the temperature and HR in the crawlspace in different positions and to create mean values (put together all these measurements in the different positions) for each hour and with that to create your climate file for the crawlspace. but i am sure I am wrong do please any advice?

In our models the conditions of the crawlspace are based on the outdoor conditions from the climate file you use for calculation. You also could create eg. an sine curve based on measurements. These can set easily user-defined in WUFI climate GUI, so you would not need to create a climate file for that.

what do you mean with "floating 72 hours mean values "? the wac file for crawlspace cannot have 8760 data because it is pointless to take measurement for such long time but the data in the winter and summer in the crawlspace will be different so... I do not understand to be honest

In WUFI we usually use hourly climate data. If you calculate the crawlspace conditions based on the climate file, you will get 8760 values. As the crawlspace conditions behave somewhat lagged to the outside climate, we use here a 72h average value.

If you plan to create a climate for WUFI with less than hourly values, please keep in mind, that WUFI is not interpolating here, but uses always the time from the last step available. So if you use 24 hours time steps, hour 1-23 will be used with the first value and so on.

Christian

[Alberto Morales]

thanks again for your answer but

"In our models the conditions of the crawlspace are based on the outdoor conditions from the climate file you use for calculation. You also could create eg. an sine curve based on measurements. These can set easily user-defined in WUFI climate GUI, so you would not need to create a climate file for that."

How do you generate the the y-axis of each pic that shows the temperature/humidity in the crawlspace from the outdoor conditions from the climate file?

because you said:

1-Calculate the crawlspace temperature from the outdoor temperature according to pic 1

but the crawlspace temperature (y-axis) is unknown.

I missed something,

Regards

[Christian Bludau]

1-Calculate the crawlspace temperature from the outdoor temperature according to pic 1
but the crawlspace temperature (y-axis) is unknown.
I missed something,

Nope, the crawlspace temperature is derived from the first picture. Picture 1 shows which temperature your crawlspace has at which outdoor temperature. So open your climate file in excel or some other program and for each hour derive a crawlspace temperature from the outdoor temperature according to pic 1.

For example if your climate file shows an air temperature of 25°C, the temperature in your crawlspace is at 20°C.

Christian

[Alberto Morales]

apologise if I explain my question badly but , how do you generate that crwalspace temperature from the scratch? do you use a model from outdoor temperature? which model is and how do you define depending on the location?

i hope you understand me now

thanks in advance

[Christian Bludau]

Dear Alberto,

the three pics ARE the model we created. They show the relation between outdoor climate and indoor climate measured for different objects (colored lines) and the regression line we derived from the measurements is the green line.
So you just have to transfer your outdoor climate into a crawlspace climate using the green lines, as it is described step by step below the three pics above:
viewtopic.php?p=5878#p5849

Christian