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Re: [EnergyPlus_Support] Re: custom weather file with multiple years with the converter tool



Incidentally,  it has also occurred to me that an even simpler and perhaps less confusing way to account for the  sun position in -0:30-0:30 solar data is to NOT move the building Longitude by 7.5 degrees, but just to add 0.5 to the Time Zone!

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"
On 2/10/2016 8:49 PM, Joe Huang wrote:
I've been quiet on this thread because I decided the situation is so confusing the only way to verify the right direction is to look at some weather files compiled with the solar data as -0:30-0:30.  So, I went on the EnergyPlus Weather site to look for European weather data compiled by Europeans (NOT the IWEC which were done by ASHRAE and hence follow the -1:00-0:00 convention) and could only find one set - the IGDG data for Italy.  I had hoped that comparing the hours of sunrise and sunset would reveal the direction of the shift.  However, I was surprised to find the comparison to be inconclusive, because there were days when the IGDG has sunrise in an earlier hour and sunset in a later hour than on the IWEC2!  This tells me there was a difference in how the "equation of time" has been calculated.

Therefore, I ask those  with European-compiled weather files, esp. Lukas and Jean, to send me a few sample files to test out my hypothesis.

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"
On 2/8/2016 11:56 PM, lukas.rokka@xxxxxxxxx [EnergyPlus_Support] wrote:
 

Jim,


Your example is correct, but what is your conclusion: move the building to the east or west?


East is the right answer. I'm attaching a radiation rose by WUFI that expects solar data in the same convention as E+. The data is imported as .epw file with the solar data as -0:30-0:30, for Greenwich, London (lat=51.5, long=0). Left figure is shifted east, middle no shift and right shifted west.


You can test it in E+ as well by meassuring the yearly amount of solar radiation recivied by a west and an east oriented walls, these sums should match.


Regards,

Lukas


Ha ha... If you guys are confused, us plebs feel like we're in a roman administration house. For the record, the last time Joe was on this topic with me, he said to move the building location eastwards +7.5 deg :-). I have to agree.

On 7 Feb 2016 6:21 pm, "lukas.rokka@... [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
 

Joe,


Sorry but I've to argue you there. Having data of -0:30-0:30 convention in Energyplus means that your data is half an hour ahead in time. You have to give that information to EP, this is done by adding 7.5 degrees (going eastwards).


E.g. at time stamp 6:00 EP would normally do sun position calculation using the 5:30 time stamp, because of the TimeHourOffset=-0.5 setting. But with data in -0:30-0:30 format we want it to make the sun position calculation with the 6:00 time stamp instead, right? Adding 7.5 degrees takes out the TimeHourOffset=-0.5 parameter (+7.5 degrees longitudes equals +0.5 hour on the clock => 7.5 degrees + -0.5 hours = 0), thus the sun position calculation is correctly done at the 6:00 time stamp.


I agree it is confusing though.


Regards,

Lukas




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Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>


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