The convective heat transfer coefficient

Is there a component in the HB component that changes the convective heat transfer coefficient on the exterior surface of the building ?

If I understand correctly, convective heat transfer coefficients (both inside and outside) are being automatically calculated when EP runs (based on the air speed and roughness of the surface?):

I don’t really understand what the reference means here:

However, if you need to match pre-existing convection coefficients (from another program) or are trying to match a test suite of results, you may wish to use the “override” convection coefficients in the following object. This object allows for a single surface to be given specific convection coefficients.

Which object does it refer to? The SurfaceConvectionAlgorithm:Outside object set to “Simple convection” applies heat transfer coefficients based on roughness and airspeed, according to its documentation. I’m lost.

My guess would be that you could add the necessary object using the Additional Strings feature of the Model To OSM component (I don’t know which version of HB you are using, my screenshot is from 1.1.0):

I wouldn’t know what to set in EP, so my guess ends here.:frowning:

(I don’t know about any HB component that does this easily…)

Yes, @furtonb . E+ automatically calculates convective heat transfer coefficients based on the indoor/outdoor air speed, surface roughness, and surface orientation.

There are some boundary condition objects that allow you to override this autocalculated value with a fixed value, which we eventually plan to expose in the Ladybug Tools SDK if not also on Ladybug Tools Grasshopper components.

However, this conversation may be far off base from @fish0920 's question since we don’t even know if they want to change the coefficient for an energy simulation or for a THERM simulation. Or if they are using the legacy plugin or LBT plugin.


Hi @chris ,

Since energyplus has different methods for calculating convective heat transfer, such as TARP, MoWiTT, DOE-2, etc. May I know which one ladybug tools used?
Or is there an option to choose which one in the ladybug component?

Thank you

Hi @ricardo ,

We pretty much always use the EnergyPlus/OpenStudio default when it comes to comes to global settings like this. From what I can tell from this section of the E+ Input/Output Reference, the default seems to be TARP for the inside convective heat transfer and DOE-2 for the outside.

No, not on a Ladybug Component. But you can always do this by manually editing the OSM or IDF output by Honeybee and use the Run OSM or Run IDF component to run the simulation. Or you could write an OpenStudio Measure that changes the convection algorithm or make a Custom Python component to edit the OSM like you see here if you want more of an automated solution to this.

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Thank you @chris for clarifying this!

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