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Psi value calculation

Miha Nahtigal
Advocate
I am trying to simulate thermal bridge similar to certified slab-wall connection by passive.de

I've attached the detail mentioned above with Psi=-0.2 W/mK

I cannot come close to the certified Psi value using Ecodesigner as thermal bridge simulator. I've tripple checked every value I use and still get weird results from Ecodesigner.

What am I doing wrong here?

Passiv.jpg
6 REPLIES 6

Miha Nahtigal
Advocate
Ecodesigner's result - Psi=0,36 W/mK
EcoD.jpg

Miha Nahtigal
Advocate
I am attaching my source file to clarify things a bit:
https://dl.dropboxusercontent.com/u/3128804/PsiCoefficient.pln


Could somebody verify my detail and Psi calculation?
Where might be the problem?

Psi value should definitely be negative in this case. Is there a problem with ground that should be calculated as infinite element?

Anonymous
Not applicable
I think Psi in Ecodesigner doesn't mean Psi but I don't know what does it mean:D If I move border of detail, I'll get the another Psi value and this is not possible. Can this explain anybody from Graphisoft? I thought It could be thermal transmittance of the whole detail, but it isn't too.

Anonymous
Not applicable
May I ask here about an error?
Why does it happen?

Anonymous
Not applicable
martyl wrote:
I think Psi in Ecodesigner doesn't mean Psi but I don't know what does it mean:D If I move border of detail, I'll get the another Psi value and this is not possible. Can this explain anybody from Graphisoft? I thought It could be thermal transmittance of the whole detail, but it isn't too.
Follow the standards which describe how thermal bridge conductivity is calculated. In case of wall/wall for example you must take 3x thickness of construction as its length in the detail. In case of the floor on ground it is 4 meters or a half of building (the bigger value).

furtonb
Expert
Vahur wrote:
Follow the standards which describe how thermal bridge conductivity is calculated. In case of wall/wall for example you must take 3x thickness of construction as its length in the detail. In case of the floor on ground it is 4 meters or a half of building (the bigger value).


Hi Vahur,

Could you elaborate a bit more on the standard calculation?
I'm a student of architecture, and I don't have access to standards, and they are a bit pricey for my budget.

I've started looking for reference online, but no luck so far.

According to this post:
https://emu.systems/2015/11/09/thermal-bridges-the-psi-value/

The PSI value accounts for the difference between the simplified 1D heat loss and the simulated 2D loss, if I understand correctly. The PSI value given by ARCHICAD is the L2D in the following equation in the case of a L corner detail:

PSI = L2D - (U1 * L1 + U2 * L2)

And L1 and L2 would be a standardized length?
So the Psi,e and Psi,i values could be calculated with the simulated Psi from ARCHICAD.

Is there an official documentation on this from GRAPHISOFT?
The HelpCenter guide is a bit shallow in this sense.

Anyone to point me in the good direction to put the pieces together?

Thanks!
odv.hu | actively using: AC25-26 INT | Rhino7-WIP | macOS @ apple silicon / win10 x64

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