Min max values of GHI, DHI etc

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MySchizoBuddy
Topic Author

05 Sep 2015 12:07 #3681 by MySchizoBuddy

Min max values of GHI, DHI etc was created by MySchizoBuddy

In EnergyPlus epw data files there are some large values for GHI, DHI and DNI. which cast a doubt on the accuracy of the data.
For eg for file CHN_Jiangsu.Huaiyang-Qingjiang.581440_CSWD.epw it has a max GHI of 2267 Wh/m2. For EGY_Al.Minya.623870_ETMY.epw it has max DNI of 2540 Wh/m2. There are others like these.

I understand the GHI values can indeed be higher than a solar constant because of cloud enhancement. But these values are crazy high. Also DNI isn't influenced by cloud enhancement, then why are they so high.

So based on experience what could be the possible max values of GHI, DHI and DNI for any location so I can clamp them to these max values. Should they be clamped to a fixed value of ETRN of 1415 Wh/m2 for DNI and ETR for GHI.

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Janine Keith

23 Sep 2015 16:45 #3682 by Janine Keith

Replied by Janine Keith on topic Min max values of GHI, DHI etc

I've sometimes used a value of about 1500 W/m^2 as a flag for unreasonable data. This has a little bit of wiggle room from the solar constant, but at least draws your eye to the data that you may need to verify. It's a tough call whether to modify those values in the weather file, or maybe just exclude those timestamps from the analysis completely.
If one of your irradiance components is unreasonable at a given timestamp but the other two seem correct, you can always use the reasonable two to calculate the third using:
GHI = DHI + DNI * cos (Z)
where Z = zenith angle (you can use the zenith angle output from SAM if needed). More info on that equation can be found in the definition from the NREL RREDC Glossary of Solar Resource Terms .  Hope that helps!

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