WUFI

Hi,

I'm a researcher looking into modeling the drying of flooded walls using WUFI with the relative humidity of the materials set to 100%. I was wondering whether WUFI 2D is suitable for modeling this kind of scenario, and what the pros and cons of using it would be. Are you aware of any work that has been done in this area before?

Cheers,

Jonathon

Hi Jonathon,

i see no problem in simulating the dry out process of walls. This is a typical application of WUFI.

Why do you want to use WUFI 2D? In case of stud walls the free saturation with 100 % may be not enough - especially fibre insulations will be super saturated...

What type of walls do you deal with?

regards
Daniel

Hi Daniel,

My intention is to simulate many different types of walls that can be found in the current building stock, as well as current popular wall types. The work is to do with flood resilience.

To be honest, I started using WUFI 2D because I thought it could do gravity. I was wrong... But, I have found it handy to do things like stud walls. I am also interested in the intersection of walls and floors, so I have continued to use it.

I have done things so far in two steps. Firstly, I have simulated absorption of water into the wall by having a weather file with 1000kg kg water/m3, and having a rain absorption factor of 1. I basically followed the instructions in the forum topic about submerging an object in water.

Then, I have simulated drying using natural and forced drying techniques, using custom weather files again, and a reduced rain absorption factor.

For cavity walls, both insulated and uninsulated, I have thought about maybe adding a moisture source inside to simulate the slow draining of the cavity. Not sure, though. What kind of saturation do you think I should use in insulation? Are you aware of anyone else doing this?

Thanks again,

Jon

Hi Jonathan,

The dry-out process caused by gravity should be finishes within a short time after the flooding. So it shouldn't play an important role...

Enclosed cavities (for example the cavieties in a rendered brick wall) shouldn't get filled with water. Only during a very long flooding the cavities could be filled due to the hydrostatic pressure through small cracks...

So in fact the intitial moisture content of 100 % is maybe the best idea.

I would only simulate the dry out process and start with complete wet walls.

What is the aim of your work - to determine the duration of dry out?

best regards
Daniel

Hi Daniel,

That's right, I'm looking at the length of time taken to dry out walls - or, more realistically, the relative differences between walls.

Do you really think gravity and depth won't play a significant role? I thought it might.

Can you tell me how the different climate files work? I've been generating WAC and KLI files for this work, but they appear be uploaded so that short-term fluctuations are averaged out. Is there any way to change this?

Thanks again.

Dear Jonathan,

regarding the Climate Files:

If you can use hourly data, use the WAC format otherwise use the KLI format.

Hi Jonathon,

did you solve the climate file problem? I didn't understand well your question...

If you have water in an "open" construction the water will runoff due to gravity very fast after the flooding. I think there is an influence only for the first hours or maybe days. Compared do a drying perios of a few weeks or even months I think it is negligible... don't you think so?

best regards
Daniel

Hi,

I think my problem with the climate file was that I was trying to do too much with one simulation. I would have a flood scenario for 12 hours, and then normal weather (with no driving rain) for 2 years, with hourly data. It is much simpler to do the flooding and drying in two seperate simulations.

One problem I do sometimes have, though, is with some more complex assemblies that have supersaturated insulation. The simulation takes a very short time, and the results don't make sense. When you watch the video generated, it switches after a second to the previous project I was working on.

I regards to gravity... I don't know. I think the capillary size and the liquid water transport coefficient will have a big impact on the gravitational drying of the material, as it is the capilalry force that will resist gravity. So, perhaps there will be a big gravitational difference between materials?

Thanks for your help with this - I am new to hygrothermal modelling.

Jon

Supersaturation can cause numerical problems in the program from time to time - maybe this is the case in your calculation. Please have a look on the iteration information in the calculation window if you have zeros as results - then the equations couldn't be solved.

Concernign capillarity and gravitiation I agree with you that they are contrary forces - but the pores must be very wide, that gravity get's any influence. This is the case for example for fibre insulations. But if the water runs off due to gravity - this process will already be finished within a few hours... and then there is no more important impact.

Daniel