Re: [EnergyPlus_Support] Weather Converter Direct Solar Radiation Spikes

[Joe Huang <YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx>]

Jean,

Glad that you asked. From my experience on several international projects, all the weather data I've seen from Europe, Australia, maybe East Asia as well, follow the second convention that I mentioned, i.e., all parameters are meant to be the average or total around the time stamp. For solar, that would mean it's the total from -0:30 to +0:30 (on an hourly file...) .
I first discovered this difference back in the early 90's when I tried to convert weather files from the UK and France and got the same wierd spikes at the sunset hours that Maxim mentioned.

Therefore, when I convert such weather files, as I had to do last year for 100+ Australian locations, I add a simple awk script to shift the solar by 30 minutes. The script is extremely simple, with the only complication for what to do at the sunrise and sunset hours.  I would suggest that you do the same, UNLESS EnergyPlus allows an input for an OFFSET of 30-minute. I've heard of such a keyword, but only in the context of the WeatherConverter, not in EnergyPlus itself.

When I compared a few IWEC2s to the European weather files for the same locations on the EnergyPlus weather web site, I could clearly see the 30-minute shift in the solar radiation.  Thus, I have a deep suspicion that many of the international weather data on that web site have this 30-minute shift.  Now, that's not the end of the world, but it could lead to wierd
effects at sunrise and sunset hours on some days.  I brought this to the attention of those maintaining the web site  last year, but they said they didn't want to mess around with other people's data, which I can understand.  For a while, I thought of turning my awk script into a simple free program, and might still do that if I have time.

Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
<a class="moz-txt-link-abbreviated" href="mailto:yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx";>yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx</a>
<a class="moz-txt-link-freetext" href="http://weather.whiteboxtechnologies.com";>http://weather.whiteboxtechnologies.com</a> for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 4/8/2014 2:33 PM, Jean Marais wrote:
>  
Joe, on that note...do you know how zi Germans do this? I've converted several (hourly) TRY2010 weather data, and the concern of the radiation data being valid from the timestamp until before the next timestamp, has been raised.
> 
> 
> 2014-04-08 23:07 GMT+02:00 Joe Huang <<mailto:YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx>YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx>:
>>  
 I've encountered the same difficulty multiple times in calculating direct normal from measured total horizontal radiation data, all of which were due to a mismatch between the measured horizontal solar and the time stamp.  The fact that all these warnings appear on hour 19 on consecutive days indicates that the EnergyPlus weather converter is calculating the sun as having set earlier than what's indicated by your data.  Therefore, when it's deriving a direct normal radiation that's far in excess of the maximum available based on the amount of time the sun is above the horizon  (footnote:  it seems that the weather converter does not do a similar reality check on the total horizontal, or else that would have also been flagged).
>> 
>> In EnergyPlus, as well as other US building energy simulation programs, the solar radiation is assumed for the preceeding time step, rather than around the time step, as assumed in most non-US building simulation programs. Therefore, you should make sure that the time stamp for your measured solar is that at the end of the time step, rather than the beginning.  In the files that I've worked on, this just meant I had to shift up the solar radiation by one time step.
>> 
>> If that doesn't solve your problem, then get back in touch with me.
>> 
>> Joe
>> 
>> Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
<a moz-do-not-send="true" href="mailto:yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx"; target="_blank">yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx</a>
<a moz-do-not-send="true" href="http://weather.whiteboxtechnologies.com"; target="_blank">http://weather.whiteboxtechnologies.com</a> for simulation-ready weather data
(o) <a moz-do-not-send="true" href="tel:%28925%29388-0265" value="+19253880265" target="_blank">(925)388-0265</a>
(c) <a moz-do-not-send="true" href="tel:%28510%29928-2683" value="+15109282683" target="_blank">(510)928-2683</a>
"building energy simulations at your fingertips"
>> 
>> On 4/8/2014 1:33 PM, Sankey, Maxim L wrote:
>>>  
Hi,
>>> 
>>> I'm using the Weather Converter program to create an custom epw file. I've input global horizontal radiation data and allow the converter to create direct normal solar radiation data. The converter works well for the first month, but the direct normal radiation values spike several times for the rest of the data. I went through and checked that the global horizontal radiation data has no spikes. I'm using 15 minute intervals. Below is a readout of the audit file:
>>> 
>>> There were 26 warnings, all interestingly at hour 19.
>>> 
>>> Warning ** DirectNormalRadiation 1910.5 > max theoretical= 6.3 Wh/m² on date= 3/27 at hour=19
>>> Warning ** Direct Normal Radiation= 1910.5 Wh/m² on date= 3/27 at hour=19
>>> Warning ** DirectNormalRadiation 593.5 > max theoretical= 347.6 Wh/m² on date= 3/30 at hour=19
>>> Warning ** DirectNormalRadiation 1736.2 > max theoretical= 186.5 Wh/m² on date= 3/30 at hour=19
>>> Warning ** Direct Normal Radiation= 1736.2 Wh/m² on date= 3/30 at hour=19
>>> Warning ** DirectNormalRadiation 1913.5 > max theoretical= 191.0 Wh/m² on date= 3/31 at hour=19
>>> Warning ** Direct Normal Radiation= 1913.5 Wh/m² on date= 3/31 at hour=19
>>> Warning ** DirectNormalRadiation 1602.2 > max theoretical= 195.7 Wh/m² on date= 4/ 1 at hour=19
>>> Warning ** Direct Normal Radiation= 1602.2 Wh/m² on date= 4/ 1 at hour=19
>>> Warning ** DirectNormalRadiation 1100.3 > max theoretical= 200.4 Wh/m² on date= 4/ 2 at hour=19
>>> Warning ** Direct Normal Radiation= 1100.3 Wh/m² on date= 4/ 2 at hour=19
>>> Warning ** DirectNormalRadiation 1080.5 > max theoretical= 205.2 Wh/m² on date= 4/ 3 at hour=19
>>> Warning ** DirectNormalRadiation > max theoretical 26 times
>>> 
>>> Any insight would be helpful.
>>> 
>>> Thanks,
>>> 
>>> Max
>>> 
>>> 
> 



__._,_.___

Primary EnergyPlus support is found at:
<http://energyplus.helpserve.com>http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The primary EnergyPlus web site is found at:
<http://www.energyplus.gov>http://www.energyplus.gov

The group web site is:
<http://groups.yahoo.com/group/EnergyPlus_Support/>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.


<http://geo.yahoo.com/serv?s=97476590/grpId=3387488/grpspId=1705007389/msgId=31672/stime=1396995506>

<https://groups.yahoo.com/neo/groups/EnergyPlus_Support/info;_ylc=X3oDMTJldXRmc2JsBF9TAzk3MzU5NzE0BGdycElkAzMzODc0ODgEZ3Jwc3BJZAMxNzA1MDA3Mzg5BHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTM5Njk5NTUwNg-->Visit Your Group
* <https://groups.yahoo.com/neo/groups/EnergyPlus_Support/members/all;_ylc=X3oDMTJmOTJwcWk1BF9TAzk3MzU5NzE0BGdycElkAzMzODc0ODgEZ3Jwc3BJZAMxNzA1MDA3Mzg5BHNlYwN2dGwEc2xrA3ZtYnJzBHN0aW1lAzEzOTY5OTU1MDY->New Members 6
<https://groups.yahoo.com/neo;_ylc=X3oDMTJkaGEycHZnBF9TAzk3NDc2NTkwBGdycElkAzMzODc0ODgEZ3Jwc3BJZAMxNzA1MDA3Mzg5BHNlYwNmdHIEc2xrA2dmcARzdGltZQMxMzk2OTk1NTA2><http://l.yimg.com/ru/static/images/yg/img/email/new_logo/logo-groups-137x15.png>
� <https://info.yahoo.com/privacy/us/yahoo/groups/details.html>Privacy � <mailto:EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx?subject=Unsubscribe>Unsubscribe � <https://info.yahoo.com/legal/us/yahoo/utos/terms/>Terms of Use
__,_._,___