IBP Air Infiltration Model

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Bonilauri
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IBP Air Infiltration Model

Post by Bonilauri » Thu Aug 10, 2017 3:15 am -1100

Hello,
I'm using WUFI Pro 6.1 to analyze assemblies in hot, humid climates such as Florida and Queensland (Australia).

We are working with assemblies where the airtight layer is a breathable external membrane (sd = 0.5m).

The internal environment is provided with cooling and dehumidification, so the vapor flow is from the outside in.

I'm trying to set up the WUFI model to include possible condensation due to air infiltration from the outside, to condensate against the internal gypsum board. I set up the IBP Air Infiltration Model to Class C, in the internal gypsum board. However, even if I set the internal temperature at 5˚C (not the design temperature, I was just testing!), I see no condensation happening due to air leak.

Is the IBP Air Infiltration Model set up to only consider condensation through convection of internal air?

Thank you!

Enrico

Manfred Kehrer
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Re: IBP Air Infiltration Model

Post by Manfred Kehrer » Thu Aug 10, 2017 3:24 am -1100

Hello Enrico,
the IBP infiltration model should be renamed to "IBP exfiltration model" as this considers only indoor moisture convection to the outside of the insulation in cold climate zones.
If you want to model vapor from the outside convecting to and condensing on the inner side of the insulation, you should probably use an air exchange rate.
Manfred
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Enjoy WUFI® :) .... It is easy and complex.

Bonilauri
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Re: IBP Air Infiltration Model

Post by Bonilauri » Thu Aug 10, 2017 9:21 am -1100

Hello Manfred,
Thank you for the advice!

I'm going to test it, and see what happens.

Cheers,

Enrico

Bonilauri
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Re: IBP Air Infiltration Model

Post by Bonilauri » Thu Aug 10, 2017 9:32 am -1100

If I wanted to simulate the equivalent infiltration of outside air of a Class A assembly (q50 = 1 m3/m2h), but using the air exchange rate, how would that translated into a 1/h value?

Thank you

Manfred Kehrer
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Re: IBP Air Infiltration Model

Post by Manfred Kehrer » Thu Aug 10, 2017 9:58 am -1100

First you would need to specify what typical pressure difference to assume from outside to inside for your building enclosure. Next thing is to reduce your q50 to that pressure. Be reminded that this is typical not a linear relationship, but as you probably don't have an flow exponent, you might assume a linear relationship. Then you can calculate the ACH according to:
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Manfred
Wiss, Janney, Elstner Associates, Inc.
Official WUFI® Collaboration Partner for USA/Canada
Enjoy WUFI® :) .... It is easy and complex.

Bonilauri
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Re: IBP Air Infiltration Model

Post by Bonilauri » Fri Aug 11, 2017 4:02 am -1100

Thank you!

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