Explicit radiation balance - solid wall IWI

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EsTresidder
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Explicit radiation balance - solid wall IWI

Post by EsTresidder » Sun Jan 22, 2023 12:34 am -1100

Hi there. I'm modelling a sandstone external wall with woodfibre internal wall insulation in a wet and windy part of the world (Glasgow). I understood from the WUFI training that explicit radiation balance is only normally used for roofs, not walls, but out of curiosity I turned it on for the walls too. This made the moisture risk at the outer 5mm of woodfibre insulation much higher. This left me wondering, is it more accurate, but usually unnecessary, to do explicit radiation balance for walls, or is it more accurate to omit the explicit radiation balance?

Thanks in advance!

Es

EsTresidder
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Re: Explicit radiation balance - solid wall IWI

Post by EsTresidder » Sun Jan 29, 2023 10:45 pm -1100

Nobody got any input on this?

Daniel
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Re: Explicit radiation balance - solid wall IWI

Post by Daniel » Tue Jan 31, 2023 5:55 am -1100

Dear Es,

the explicit radiation balance considers the long wave radiation exchange with the atmosphere - in case of roofs or flat roofs this is rather trivial, because the field of view to the sky is normally not shaded and rather complete.

In case of walls WUFI assumes 50 % atmosphere and 50 % terrestric ambience in the field of view. This represents a building on the coast or in the desert (no plants, no other buildings) without any roof overhang. For most real situations this is far to extreme. Often the atmospheric part is only 20-30 % or even less. Thus switching on the explicit radiation balance leads in most cases to an unrealistic worst case. However, as you cannot influence the percentages at the moment, we normally recommend to leave it away for walls, as the result is much closer to reality.

best regards
Daniel
Dr.-Ing. Daniel Zirkelbach, Deputy Head of Department Hygrothermics, IBP Holzkirchen

EsTresidder
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Re: Explicit radiation balance - solid wall IWI

Post by EsTresidder » Tue Jan 31, 2023 11:25 pm -1100

Hi Daniel,

That's really helpful, many thanks for taking the time to reply.

Kind regards, Es

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