I guess ladybug calculate direct radiation instead of diffuse radiation and conversely

#1

hi all

For any specific day during 24 hour, it is not possible that on a horizontal surface direct radiation be less than diffuse radiation. Especially when we have 270 sunny days in a year. I talked with two professor about these results. both of them said results are wrong.
in the 6th july sky is so sunny but diffuse radiation on a horizontal surface is more than direct, this is impossible and so wrong unfortunately.
one time, i set “true” (remove diffuse) and i sum values and gained total direct
another times, i set “true” (remove direct) and i sum values and gained total diffuse
and finally i compared them.
i guess ladybug calculate direct radiation instead of diffuse radiation and conversely

SkyMetrix (1).gh (378.2 KB)

#2

There are few things worth look into here:

  • You are using very outdated ladybug components. There could be bugs which are fixed in newer versions. Try updating it and see if the strange behaviour remains.
  • Secondly, before thinking certainly that there is a bug, I’d question the weather data. Could you upload the *.epw file so we can check it out as well?
  • I don’t see the connection between your grasshopper and excel screenshots, one shows the value of sky patches and what about the other?

V

#3

there a few answer here:

  1. in new updated version … no different… i tested yesterday.

  2. IRN_FA_Shiraz.Intl.AP.408480_ITMY.zip (305.6 KB)

  3. i copied results and then pasted in Excel.

#4

I had a quick look at the horizontal radiation extracted from weather file, it seems that only in December there is high direct solar radiation, most of the year you’d have mainly diffuse solar radiation.
Cloud coverage aside, it could be from other reason like dust and pollution in the air. Whether this matches with real world condition, I’m not sure as I’m not as familiar with the climate.

The question lies in the data rather than the tool itself as ladybug only interprets it in this case.

Note that the values you copied from SkyDome component is values for 3 sky domes: total, diffused, direct so you need to be careful when summing them up.

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#5

dear admin
thank you for attached picture.
this picture shows diffuse radiation is more than direct, and unfortunately
these results are wrong. ( my results are like your attached pic too.)
i consulted with two university professors about these results, they didn’t confirm results.
however i tested for other cities, like London and Boston unfortunately results were wrong.

i guess, programmer had fault between diffuse and direct values, total radiation may be correct but maybe programmer applied diffuse instead of direct.

if you compare diffuse radiation with others study you find results are wrong, however i guess total radiation is correct, note i’m talking about diffuse values.

do you know where is @mostapha ?
Mostapha can help maybe.

#6

@ahad,

Read what @vhoang said again:

Ladybug does not correct your data. It uses the input weather data to calculate the radiation results. If your input data is wrong the output will be also wrong or as they say it: Rubbish in, Rubbish out!

What does wrong mean? As I suggested before in a different discussion I would use Radiation Rose to quickly compare direct and diffuse radiation values from a weather file. If you input a weather file with a higher values for diffuse irradiance then you will get a higher diffuse radiation values from Ladybug - This is how it is supposed to be.

#7

Related:

#8

dear @mostapha
you right.
i changed my epw and new results are more reliable.
however i’m thinking why, epw that i downloaded from energyplus site gave me wrong results. new epw was built by meteonorm.

you are best and thank you so much for your help and et all

#9

Hi @ahad,

Great that you found an alternative weather file. Was your weather file from the energyplus website or onebuilding. If it is the second one we can let them know and there is a good chance that they will get it fixed for us.

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