Moisture source issue

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Moderatoren: ghorwin, fechner, ruisinger

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xfaure
Beiträge: 4
Registriert: 31 Jan 2022, 16:56

Moisture source issue

Beitrag von xfaure »

Hi to all,
I am trying to model a moisture leak effect inside a three layer wall.
I read a lot about source term to model the condensation effect of a moisture leak (with defining a specific location for expected condensation) and wanted to implement this in my Delphin case but I'm confuse on how to make it depending on the local vapor pressure. Indeed, the source/sink definition seem pretty obvious in Delphin. we can link it to an external file as well, but how does it take into account the local vapor pressure to compute the mass flow rate of condensation/evaporation) ? The condensation/evaporation rate is a function on the vapor pressure gradient between the incoming air and the local one (the average vapor pressure along the several meshes selected for expecting condensation), thus the former one can be embedded an external file (linked to the boundary conditions), including the air mass flow rate, but how the local one is considered ? (I have this formulae : m = q(PvBC- Pvi) with q airflow; PvBC vapor pressure from boundary Condition, and Pvi the average vapor pressure along the selected meshes (should be computed by Delphin)).
Thanks for your help,
New Delphin user
fechner
Beiträge: 90
Registriert: 19 Dez 2018, 09:32

Re: Moisture source issue

Beitrag von fechner »

Hello,

May you can explain me more in detail what do you want to simulate? Which kind of construction, where is the source, what is the reason for the source?

A simple moisture source only create or remove liquid water from the assigned location based on the given climate data.
The other sources (air change, WTA convection) are a bit more special.
xfaure
Beiträge: 4
Registriert: 31 Jan 2022, 16:56

Re: Moisture source issue

Beitrag von xfaure »

Thanks for your reply,
I would like to simulate (still in 1D) the experiment conducted in : [https://web.ornl.gov/sci/buildings/conf ... _Desta.pdf]
I already made the model without the air convection (all materials being airtight), works perfectly and results are in the expected range. but now I'd like to add the 10 Pa difference and thus compute the extra amount of moisture advected inside the different layers (and that accumulates in the fibrewood layer especially.
I went through [https://www.sciencedirect.com/science/a ... 2312001990] that uses Delphin with a 2D model and made comparison with other cases but not the previously mentioned one (even though the first graph present is part of it).
I understood that these kind of phenomenon could be also modeled using a source term as in WUFI or EnergyPlus [https://www.osti.gov/servlets/purl/1560500]. But I haven't seen any with Delphin. The inputs being the amount of advected air and the vapor pressure as well as a specific (averaged) location for which the amount of liquid water is computed (dynamically).
does that make it clearer ?
thanks in advance for your help
fechner
Beiträge: 90
Registriert: 19 Dez 2018, 09:32

Re: Moisture source issue

Beitrag von fechner »

As far as I understood you would like to model a air flow through specific material which can accumulate condensation inside the structure.
You will do it for a 1D simulation by using a source model. Right?
You can try the air change source model. This is actually for airspaces. Delphin will show a warning if this model is assigned to a material that is not air. But it will still calculate.
xfaure
Beiträge: 4
Registriert: 31 Jan 2022, 16:56

Re: Moisture source issue

Beitrag von xfaure »

thank you very much for the tip.
There are two models that could fit then : "air change with ambient air for a given air change rate" and "Moisture source due to air flow through leakages WTA 6.2"
I therefore have 2 questions :
1. which one would best fit (or what are the differences between each)
2. for both I am encountering convergence issue unless I drastically lower down the air flow rate (per Pa or not depending on each model's input). what would be the trick and tips for convergence issue (I played a bit with tolerance and performances option with no success from now...).
Thanks again for your help
fechner
Beiträge: 90
Registriert: 19 Dez 2018, 09:32

Re: Moisture source issue

Beitrag von fechner »

Hello,

I would prefer the air change model. The other one is a simplification for calculating condensation due to air flow through a structure. I will send you some presentation slides with further explanations by email.
May you can send me your project (as project package) so I can have a own look on it?
xfaure
Beiträge: 4
Registriert: 31 Jan 2022, 16:56

Re: Moisture source issue

Beitrag von xfaure »

Thanks a lot, I have replied to the mail with the cases as attached compressed file.
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