Different air exchange source than indoor/outdoor air?

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Sami Roikonen
Posts: 13
Joined: Thu Jul 04, 2013 3:05 am -1100
Location: Finland

Different air exchange source than indoor/outdoor air?

Post by Sami Roikonen » Tue Apr 23, 2019 12:57 am -1100


Is it possible to simulate a model with a ventilated air layer that isn't outdoor air or indoor air?

In my model there is a cooler room element (-24 celcius) complete with insulated floors, walls and roof, basically a panel-sandwich-construction. The cooler room element is inside a room on the floor and I'm interested in the interaction between the cooler element and the floor structure. The floor structure is a simple concrete slab which is insulated from the bottom, and under that there is grovel and soil.

It's clear that the moisture from the ground will rise up through the floor and stop as it reaches the cooler element's vinyl covering. But if the cooler element is installed on top of pads or some other platform that will allow air to flow under the cooler, the moisture might just harmlessly evaporate. In order to simulate the cooler element with platform, I would need to have an air exchange source that is neither to indoor temperature (inside cooler element -24 celcius, 50 RH%) or outdoor air (beneath floor structure estimated +5 celcius, 95 +-5 RH%) The room in which the cooler room element is located has normal room temperature of 21 celcius and estimated 10...60 % RH. Is there any way I can have the room that contains the cooler room element as air exchange source, while I have the indoor air assigned to cooler room element's inside and outdoor air assigned to soil under the floor structure.

I have enclosed a screenshot of my current model.

Sami Roikonen

EDIT: I had the wrong ambient temp for the storage room...
EDIT2: Is it possible to to circumvent the air exchange and simulate the storage room's ventilation by adding a thermal source of some sort and a negative moisture source?
EDIT3: Perhaps it's not so bad an idea to have the air layer simulated with the cooler room's indoor air (-24 celcius). The moisture capacity of the air layer is by default the same as +20 celcius air (~17,2 g/m3), regardless of it's actual temperature. The only remaining difference is the air temperature, which affects the temperature and moisture transfer rate of the concrete slab. I'm just thinking out loud hoping that someone replies with an interesting take on the subject.
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Christian Bludau
WUFI SupportTeam IBP
WUFI SupportTeam IBP
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Re: Different air exchange source than indoor/outdoor air?

Post by Christian Bludau » Sun Apr 28, 2019 9:39 pm -1100

Dear Sami,

in WUFI Pro it is not possible to use another climate for source than inside or outside. You can try to work with sources from file, but you will probably meet some borders.
You can set the temperature OR the moisture from file, also as a sink, as you wrote), but not both together. This way you could steer the ventilation depending on time. See WUFI help on how to set up the source file.

Referring to your EDIT3: If you can assess the conditions of the air gap, maybe by doing a thermal approach, you could try to simulate without the cooler wall. Maybe you can set the outside surface of the cooler as boundary conditions.

Another idea: With WUFI 2D it would be possible to use a third climate for your source, if you just assign it somewhere it has no influence on the rest of your construction.


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