Direct sw radiation in atmosphere

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Jay
Posts: 4
Joined: Sat Feb 20, 2021 1:05 pm

Direct sw radiation in atmosphere

Post by Jay »

Hi ENVI-met Staff
I'm using the epw file to simulate the neighborhood PET distribution, and the radiation condition is also forced. But when checking the radiation information I found a confusing problem, the Direct shortwave radiation value in 'surface' folder is reasonable, but the Direct sw radiation in 'atmosphere' is extreme large before sunset, even larger than 1367W/m2. I have already check the latitude, longitude and reference time zone. Is that normal?

Jay
2021.2.21
Attachments
extreme large radiation.png

Tim
Posts: 2224
Joined: Mon May 15, 2017 3:46 pm

Re: Direct sw radiation in atmosphere

Post by Tim »

Hi Jay,

No, that is definitely not normal. Did you check the radiation values coming from the EPW file in the Forcing Manager?
Which version do you use?

Best regards,
Tim

Jay
Posts: 4
Joined: Sat Feb 20, 2021 1:05 pm

Re: Direct sw radiation in atmosphere

Post by Jay »

Tim wrote: Mon Feb 22, 2021 7:18 am Hi Jay,

No, that is definitely not normal. Did you check the radiation values coming from the EPW file in the Forcing Manager?
Which version do you use?

Best regards,
Tim
Hi Tim,
We used ENVI-met version 4.4.5 and the geometry was modeled in grasshopper plugin. I checked the normal direct solar radiation at 17:00 of the simulation time, the value is 402W/m2.
I found this phenomenon is most obvious in winter condition.

Best regards,
Jay
Attachments
location.PNG
grasshopper.PNG

Tim
Posts: 2224
Joined: Mon May 15, 2017 3:46 pm

Re: Direct sw radiation in atmosphere

Post by Tim »

Hi Jay,

Could you attach SIMX, INX, and FOX here as zip?

Best regards,
Tim

Jay
Posts: 4
Joined: Sat Feb 20, 2021 1:05 pm

Re: Direct sw radiation in atmosphere

Post by Jay »

Tim wrote: Tue Feb 23, 2021 11:28 am Hi Jay,

Could you attach SIMX, INX, and FOX here as zip?

Best regards,
Tim
Hi Tim,

The attachment is the setting file and epw file, the simulation date is December 8th, and the format is auto produced by dragonfly plugin in grasshopper.

Best regards,
Jay
Attachments
INX&simx_file.rar
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Tim
Posts: 2224
Joined: Mon May 15, 2017 3:46 pm

Re: Direct sw radiation in atmosphere

Post by Tim »

Hi Jay,

The values get that high because they are recalculated according to sun height angle. The issue however is not the calculation method but the raw data. The radiation values of the EPW file show that the maximum values (e.g. at the 8th of December) are at 15:00h instead of around noon (12:30h). This shift leads to high radiation values at the evening hours where the sun height angle is pretty low. The recalculation thus gives extremely high (and invalid) values. Sun angle and radiation values don't fit to each other. We also checked other Chinese EPW files, they all seem to be corrupted that way. You may search for an EPW file modifier and correct the time shift or create an own CSV file to force your simulation. That would make sense since precipitation is also very high and wind speed is not correct during nighttimes at 8th December as well (jumps down to 0 m/s for several nighttime hours). Check the Forcing Manager to see those incorrect values.

Furthermore, there are building cells in your model area that feature 9999 m. That also caused large simulation issues and should be corrected (probably to the 99 m high buildings of the surrounding buildings).

Best regards,
Tim

Jay
Posts: 4
Joined: Sat Feb 20, 2021 1:05 pm

Re: Direct sw radiation in atmosphere

Post by Jay »

Tim wrote: Tue Feb 23, 2021 5:44 pm Hi Jay,

The values get that high because they are recalculated according to sun height angle. The issue however is not the calculation method but the raw data. The radiation values of the EPW file show that the maximum values (e.g. at the 8th of December) are at 15:00h instead of around noon (12:30h). This shift leads to high radiation values at the evening hours where the sun height angle is pretty low. The recalculation thus gives extremely high (and invalid) values. Sun angle and radiation values don't fit to each other. We also checked other Chinese EPW files, they all seem to be corrupted that way. You may search for an EPW file modifier and correct the time shift or create an own CSV file to force your simulation. That would make sense since precipitation is also very high and wind speed is not correct during nighttimes at 8th December as well (jumps down to 0 m/s for several nighttime hours). Check the Forcing Manager to see those incorrect values.

Furthermore, there are building cells in your model area that feature 9999 m. That also caused large simulation issues and should be corrected (probably to the 99 m high buildings of the surrounding buildings).

Best regards,
Tim
Hi Tim,

Thank you very much for checking the setting. The building height was corrected before I start the simulation. So the key is that the epw file cannot be imported directly when making the forcing file, the radiation model will recalculate the time series of solar distribution rather than allocate the epw file value to each time spot. I'll also share this point with my colleague.

Best regards,
Jay

Tim
Posts: 2224
Joined: Mon May 15, 2017 3:46 pm

Re: Direct sw radiation in atmosphere

Post by Tim »

Hi Jay,

Yes, exactly. However, in our understanding EPW files should already include the correct diurnal cycles and time spots. Your file also includes the tag that it is provided for UTC+8. However, the values do not match this time zone.

Best regards,
Tim

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