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Design forum

## Surface Heat Transfer

Contributor

Hi! Can someone explain this parameter to me? I am not sure how to determine these coefficients and what they are used for in the Energy Evaluation tool. Aren't the specific U-values for the materials used when running an energy simulation?

I have read the explanation in the Archicad manual, but I am still confused as to how to calculate these or look for a local alternative.

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Champion

@Balint Kezer Regarding our earlier exchange I believe @SidselVincents has posed a question that no one here will answer. Can you or someone else at GS help so we can all learn?

Apple iMac macOS Monterey / AC26UKI (most recent builds)
Solution
Graphisoft

Yes, the U values for the materials are used when running the simulation. The Surface Heat Transfer values (under Environment Settings) are locked and should not be changed unless the local standards tell you to do so.

The Surface Heat Transfer coefficients (under Environment Settings) are not alternatives to the U values but to the external and internal heat transfer coefficients that are defined for each structure (vertical walls, horizontal flat roofs, tilted roofs, basement floors, etc.):

The external and internal heat transfer coefficients are defined by the country’s standards or building codes. These values should be entered in Archicad. An example:

When the U values are calculated, three physical processes are included:

• The heat conduction within the solid structure (within all its layers or skins)
• The heat convection between the structure and the air on the internal and the external surfaces of the structure
• The heat exchange by radiation between the structure and other “objects”

The external and internal heat transfer coefficients are pre-calculated in the local standards and they consider both the convection and the radiation happening on the internal and external surfaces.

It is possible that the default way of calculation (leaving the two boxes for Surface Heat Transfer locked) will provide you correct results according to local standards. As you most probably know calculation in EcoDesigner STAR is done according to the ASHRAE 90.1 standard, so if your local standard is based on this, that most probably you do not need to look for a local alternative.

Balint Kezer
GRAPHISOFT Product Manager
Champion

@Balint Kezer Thank you for the explanation that is most useful and correlates with my recent findings.

Apple iMac macOS Monterey / AC26UKI (most recent builds)
Contributor

Thank you so much for the clarification 🙂

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