I agree it probably has something to do with my sensor recording a pre-dawn or twilight solar input when in fact the sun was not up. That would spike the direct
beam and not simply assign the input reading to a global solar. Since I was inputing 10 minute weather data, I saw it more often�
Ned Lyon, P.E. (MA, WV)
Staff Consultant
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Wednesday, November 02, 2016 2:20 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Perez direct/diffuse spliting model
Ned,
Your mention of "odd calculations around dawn and sunset at times" may be related to my observation in 2013 that the sun position calculated by the WeatherConverter was off an hour compared to another source (see plots from Nov 13 2013 e-mail sent to the
EnergyPlus Team. Base data was ASHRAE IWEC weather file for London, WC2 is recalculated Dir Nor using the same Global Horizontal. Notice that the source GHI and DNI are symetrical, while the WC2 DNI is not and more spiky.
If the sun position is inconsistent with the recorded data, you will tend to see spikes at sunrise and sunset hours, as the model tries to adjust for an abnormally high or low amount of solar for the amount of time the sun is above the horizon at those hours.
Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
http://weather.whiteboxtechnologies.com for simulation-ready weather data
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On 11/2/2016 8:45 AM, 'Edward G. Lyon'
eglyon@xxxxxxx [EnergyPlus_Support] wrote:
Read the documentation about defining a custom input file. You can read a text file using a definition array and the converter will do a split using whatever additional information you give it. Note that you should review the file generated. I have had some odd calculations around dawn and sunset at times, but then I worked with sub hourly data as well. Pasting into an existing .epw file format will not give you the conversions.
Ned Lyon, P.E. (MA, WV)
Staff ConsultantSIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
Send FilesFrom: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Wednesday, November 02, 2016 10:58 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Perez direct/diffuse spliting model
Thank you Linda for the repply. I used the Weather Converter utility. Actually I modified an existing epw file by inserting my own values for global radiation and inserted zero values for the direct/diffuse components. When I converted the file I found out that energyPlus replaced the zero values with the value 999. Any help with this?
Regards,
Kostas
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Posted by: "Edward G. Lyon" <EGLyon@xxxxxxx>
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