Ned,
I beg to differ. The little bit of solar that you record should not affect the Perez Model in any appreciable way. I would think the spikes are due to the calculation of the sun position, which is used to calculate the extraterrestrial radiation that in turn is compared to the total solar to derive the amount of direct normal radiation.
If the sun position is inconsistent with what's actually happening, this messes up the ratio of extraterrestrial to measured total and creates spikes at sunrise and sunset. For example, if the calculated sun is setting too early, this will cause the Perez Model to produce a spike at sunset, and if the calculated sun is rising too late, this will produce a spike at sunrise.
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 (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
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 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 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 HuangWhite Box Technologies, Inc.346 Rheem Blvd., Suite 205AMoraga CA 94556yjhuang@xxxxxxxxxxxxxxxxxxxxxxxxhttp://weather.whiteboxtechnologies.com for simulation-ready weather data(o) (925)388-0265(c) (510)928-2683"building energy simulations at your fingertips"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
__._,_.___
Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>
EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The EnergyPlus web site is found at:
http://www.energyplus.net/
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
__,_._,___