Sky matrix containing horizontal irradiation

Hi Nills,

Please find attached file.

-Devang (377 KB)

Hi Devang,

thanks for the fast response. It worked like a charm.

There’s only one question I’d like to ask: When I sum the values of the sky dome and compare it to the annual sum of the epw weather file, they match only for direct normal radiation:

            global horizontal     direct                     diffuse horizontal

epw 1183.5 911.9 (normal) 628.7

skymtrx 2172.7 911.9 (horizontal?) 1260.7

Should it not be the other way around, i.e. matching values for global and diffuse horizontal and not for the direct part. Am I confusing something?


Hi Nils,

Apology for not writing your name right the first time.

As the hint on directNormalRadiation says, it is the radiation received on a surface perpendicular to the sun ray coming from the skydome. Therefore, only direct normal radiation should match, as you pointed out.

globalHorizontalRadiation and diffuseHorizontalRadiation are radiation on a horizontal surface, so they will differ. Attached image should give you a clue. You can test this using Ladybug.

Take the total of globalHorizontalRadiation. From that deduct the total of diffuseHorizontalRadiation. That number will be less than the total of directNormalRadiation.


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Hi Devang,

no worries for the name spelling:)

Now it became clear to me. My mistake was to assume that the sky matrices produced by the model you sent me, were already containing the horizontal values. Didn’t think about verifying it with the elevation angles… sorry.

Thank you again for your help and explanations!


Hi Nils is it possible to get the definition. I ran into this problem where I need to get DiffHorzRad and DirecHorzRad. And I cannot get them easily. The link seems to be broken

Thank you in advance

No worries I got it from the old forum


Found it. Thanks!!!