Air water content

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WEI LI
WUFI User
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Posts: 3
Joined: Thu Oct 29, 2020 1:02 pm -1100

Air water content

Post by WEI LI » Mon Jan 04, 2021 10:41 am -1100

Hi there,

I am simulating a ventilated roof and I set the air change rate of the air layer as 50/h.
The output relative humidity seems reasonable, which is between 95% to 95%.
However, when it turns to the water content of the air layer, the result is unrealistically high, which is between 0 to 3 kg/m3.
I have used the "without additional moisture capacity" air layer.
I have read the topic "Water Content of an Air Layer" in FAQ, and I understand WUFI calculates the water content according to the RH through the moisture storage function.
The moisture storage function shows that the max water content of the "without additional moisture capacity" air layer is around 0.025 kg/m3.
How could the water content possible to be around 3kg/m3 in my simulation output.
It confuses me a lot, please help.
Thanks!

Thomas
WUFI Administrator
WUFI Administrator
Posts: 311
Joined: Sun Jun 19, 2005 10:33 pm -1100

Re: Air water content

Post by Thomas » Thu Jan 07, 2021 2:18 am -1100

Hi WEI LI,

I'm not sure where the number 0.025 kg/m3 comes from because the air layers "without additional moisture capacity" have a free saturation of 0.017 kg/m3.

But the free saturation can always be exceeded if there is condensation. Maybe there are condensation conditions on one side of your air layer so that some condensate accumulates there. If you are looking at grid elements in this region, or even if you are looking at the average water content in a region in part of which much condensate is deposited, you may well see average water contents exceeding 0.017 (or 0.025) kg/m3.

Kind regards,
Thomas

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