Custom material with only U-value input

Hello,

I would like to create a generic opaque material for which I just want to input the U-value.

From what I understand, thickness and conductivity are impacting the resulting U-value on the right of this Grasshopper script, but I can’t find the right way to achieve what I would like to do: input only 1 value (the U-value) for the material.

Is there a way to achieve this? I found a topic with the same question, but the file with a solution is no longer available.

Thank you,

Hi @av

You could use the HB opaque no mass material. Accumulation will be none.

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Thank you @Erikbeeren

I tried it but I get this:

The resulting U-value is way below the input, even if the R-value is correct.
I saw that the U-factors include the resistance of air films on either side of the construction, but isn’t 3.125 to 2.067 quite a big difference?

I think there is something I don’t understand here.

The input is the U value, the output is the U factor which in includes the thermal resistances of the indoor and outdoor bounding air layrers

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Thank you, so is it better to simulate my model with HB opaque no mass materials with my U-values, or to create a material that has a final U-factor that matches my original value?

I don’t quite understand the difference between U-value and U-factor, and explanations I find are mixing the two notions as the same thing.


Rsi and Rse are added to the heat resistance of the total construction

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Ok thanks a lot, this is much clearer.
It’s crazy how these values are impacting my initial value of 3.13 to a final 2.06 W/m².K, I definitely need to learn more about this.

The better the insulation the less influence this factor has,

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Thanks a lot for taking the time to explain this clearly!