Discrepancy between the generated .wea file and DAYSIM values

Dear @mostapha and @chris,

How does HB+ generate .wea from .epw file ? Does it use direct normal or direct horizontal radiation?

But, even either of them, diffuse horizontal radiation should remain the same between epw and wea file which I found significant discrepancy here in case of Melbourne climate. In the upper image shows direct normal and diffuse solar radiation from epw file, while the lower image shows the generated .wea file. If you compare the first hours you see they are not the same, in which they have to be the same. Both time steps are for one hour.




Do you have any clue on this issue? I thought maybe you might have an idea.


Hi @AMIRTABADKANI , can you share the EPW file? The output from HB[+], or rather LB[+], should be the same as epw2wea in Daysim.

How did you generate the wea file? The output of honeybee[+] should be in half an hour timesteps. I also did a quick check and the values are the same:

epw_vs_wea.gh (27.3 KB)

Thank you @mostapha and @sarith for your replies,

I noticed my question was not clear at all after reading it again, I apologize for that.

I have created the .wea through DAYSIM 3 itself for 20 minutes time intervals, in which the values for direct and diffuse radiation are different from the ones that HB+ is creating.

The upper image is the one from DAYSIM and the lower one is the same code @mostapha used. It seems HB+ creates it based on linear interpolation which is not the case for DAYSIM.

I have attached both epw and wea files. The attached .wea file was generated by DAYSIM using the same epw file.

Am I missing sth here?


Mel.zip (377.7 KB)

Now I see what you meant. That is intentional. See this issue on GitHub. Daysim approach randomizes the numbers based on algorithm which I didn’t feel comfortable using for a file that supposed to show a typical weather for a location.

Thanks a lot for clarification @mostapha

You were saying “If one wants to use Daysim approach they can generate the wea file from Daysim and then use WEA.from_file method to create a WEA object.”,

Now the question is; which is the component to import .wea from a file?


We do not have a component but you can create one from a GHPython component. Here is the classmethod: https://www.ladybug.tools/ladybug/docs/ladybug.wea.html#ladybug.wea.Wea.from_file

from ladybug.wea import Wea

# timestep 3 for every 20 minutes
wea = Wea.from_file('path_to_file', timestep=3)
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Thanks a lot @mostapha