Wufi Bio: Mould Growth

manexi · Post by **manexi** » Tue May 24, 2011 3:28 am -1100

Hello.

First, I'd like to thank you all for helping me understand how WUFI works, you're great

!

Now, a little question has come to my mind while analysing mould growth with WUFI: How do you define mould growth?

Let me explain: As you know, WUFI Bio can use 2 scales in order to assess mould: Mould Growth (in mm) and Mould Index (from 1 to 6). If I assume my tolerance goes as far as MouldIndex = 3 ("some growth detected visually, thin hyphae found under microscope"), then the equivalent mould growth should be ~250mm.

However, I believe that a 250mm mould would be fairly big (and easy to detect with naked eyes, no need for a microscope), so the question is how do you define this "growth".

At first I assumed it was a linear growth along the thickness of the wall... but it wouldn't make sense for thin walls... then I assumed it was a linear growth alongside the largest growth direction in the wall surface... but still, it doesn't make sense with the "Index to Growth" equivalence.

So this is the dilema. I believe it would be easier to assess the growth by the surface (or even the volume) rather than a linear parameter wich I'm having trouble to understand (but I know it's not your fault since this data was made before WUFI, I just want to understand)

Any ideas on this?
Thanks!

veitner · Post by **veitner** » Wed May 25, 2011 7:52 pm -1100

Hi Manexi,

WUFIBio solves the equation for humidity inside a model spore (in one dimension). It is assumed that the heat capacity of the spore is small and the temperature inside the model spore is held constant at boundary conditions.

Using the isoplethe-system WUFI-Bio calculates a "critical water content". Each time the water content of the model spore exceeds the critical water content (germination occured) the algea can grow. The amount of growth is calculated out of a second isoplethe system together with a relationship growth/RH.

You will find more details in:

http://www.wufi.de/ibp/publikationen/di ... tion_e.pdf

Because the calculated growth is a somewhat abstract number we introduced the relationship mould index - growth (valid for a single year only).

Also search our website (http://www.ibp.fraunhofer.de/publikatio ... schriften/) for the author "Krus" to find more information.

Regards
Veit

manexi · Post by **manexi** » Wed May 25, 2011 10:47 pm -1100

Thank you Veitner!

I had read some articles about the biohygrothermal model, but I hadn't been able to find specifics about this "growth measure". Yours however was trully enlightening

.

As you said

...the calculated growth is a somewhat abstract number ...

I just managed to find the relationship between the calculated "virtual growth" and the growth rates:

The indication in mm/d comes from biological examinations where a Petri dish with complete medium is inoculated with fungus spores in the centre and a circular growth appears. So one can interpret 1 mm/d in a way that the diameter of a fungoid growth increases by 1 mm per day

The problem being that for long periods, this "growth" is not real anymore. Moreover, "1mm/day" doesn't have the same meaning depending on the value of the previous surface.

The growth rates usually indicated in mm/d or corresponding area occupancies (e.g. 70 % of a petri dish) can be used to evaluate the growth on building components only in the figurative sense in a way that the values are analyzed comparatively

Thank you for your help. I think I'll switch my cases to the Viitanen model scale so as to be able to easily explain the results to other people.

veitner · Post by **veitner** » Wed May 25, 2011 11:16 pm -1100

Hi Manexi,

Thank you for your help. I think I'll switch my cases to the Viitanen model scale so as to be able to easily explain the results to other people.

There is a little problem in the current WUFIBio: The mould growth is additive but the transformed mould index is not. This means the mould index is valid for a one year period only. Currently I'm working on an update which should be ready for download by the end of next week.

Regards

manexi · Post by **manexi** » Thu May 26, 2011 1:24 am -1100

Hi Veitner

I see your point.

What I did was to take the Limit Values From the "Mould Growth - Mould Index" Table corresponding to a certain level in the Viitanen Model (Index 3 --> 250mm), and then I just had to make sure I didn't have more than 250mm in the normal growth scale at any point.

I had already thought about the time range of the model (1 year) since it doesn't take into account the possibility for the mould to disappear. This can lead to an infinity amount of mould if we run simulations for several years, but I realized the "traffic light" algorithm only takes into account the mould "production" over one year only, so I assumed it was safe enough to consider only the mould production over 1 year

Still, my main concern was this "measure of mould growth" which can be misleading, since in real life, even a 10mm mould should be seen with the naked eye.

Regards,
Manexi