Custom convection coefficients

ladybug-tools
1

Hi all,

I’m trying to use custom outside convection coefficients in my honeybee energy model in order to compare results to another tool. I have a list of coefficients corresponding to all my surfaces. Can someone give me an example of how to do this?

Thanks,
Joe

2

Hi @jroberts ,

Outside convection coefficients typically change a lot with outdoor wind speed so they are typically autocalculated by EnergyPlus using the wind speed and direction in the EPW file (as it relates to the orientation of each Building Surface).

However, if you’re studying conditions under constant temperature and wind speed, then the HB Other Side Temperature component should give you what you need.

3

Hi @chris

Interestingly enough I did try to change the terrain input from the city default to open country to see the effect of wind speed, but this didn’t appear to make any difference to the convection coefficients. Is that to be expected?

I’m not using a constant outdoor condition, but comparing results with a tool which uses equations from CIBSE, and open country terrain in my particular case.

Joe

4

How did you check what the coefficients calculated by E+ were? Did you find an E+ output related to the coefficients in the HB Read Result Dictionary?

Generally speaking, the effect that changing the terrain has on coefficients is pretty subtle. You will see a bigger effect if you significantly change the wind speeds in the EPW file you are using, for example.

5

Hi Chris,

Sorry for the late reply! Yes, I used the output Surface Outside Face Convection Heat Transfer Coefficient. I’ve played with the wind speed and now my coefficient is in the same ball park as the other tool. Thanks for the suggestion!

Best,

Joe

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