Re: [EnergyPlus_Support] Weather Converter Direct Solar Radiation Spikes

Please note that the time offset only helps if you're using the WeatherConverter to calculate the Direct Normal Radiation, but not for weather files that supply both Total Horizontal and Direct Normal, in which case you're stuck with the "offset" as decided by those who created the weather file. Furthermore, using the time offset would get the calculated direct normal in sync with the total horizontal radiation, but now both would differ from what is expected by EnergyPlus, unless EnergyPlus itself also allows for a time offset in the simulation. Could someone let me know if EnergyPlus allows for an time offset input?

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
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 4/8/2014 3:09 PM, Linda Lawrie wrote:

Everyone should make sure they are using the latest Weather Converter.
There is also a "time offset" value that can be input for those of you
whose data appears to be "off".

On 2014-04-08 16:03, jeannieboef@xxxxxxxxx wrote:
> I feel stupid. But thanks anyhow. ;-)
>
> On 08.04.2014, at 23:41, <dru.crawley@xxxxxxxxxxx> wrote:
>
>> Best way to check is to look at the solar patterns (DView or
>> spreadsheet). Do the peaks occur around noon? If not, then the data
>> may be shifted an hour.
>>
>> FROM: EnergyPlus_Support@xxxxxxxxxxxxxxx
>> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] ON BEHALF OF Jean Marais
>> SENT: Tuesday, April 08, 2014 5:34 PM
>> TO: EnergyPlus_Support@xxxxxxxxxxxxxxx
>> CC: Sankey, Maxim L
>> SUBJECT: Re: [EnergyPlus_Support] Weather Converter Direct Solar
>> Radiation Spikes
>>
>> 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
>> <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
>>
>> yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
>>
>> http://weather.whiteboxtechnologies.com [1] for simulation-ready
>> weather data
>>
>> (o) (925)388-0265 [2]
>>
>> (c) (510)928-2683 [3]
>>
>> "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/mÂ² on date= 3/27 at hour=19
>> Warning ** Direct Normal Radiation= 1910.5 Wh/mÂ² on date= 3/27 at
>> hour=19
>> Warning ** DirectNormalRadiation 593.5 > max theoretical= 347.6
>> Wh/mÂ² on date= 3/30 at hour=19
>> Warning ** DirectNormalRadiation 1736.2 > max theoretical= 186.5
>> Wh/mÂ² on date= 3/30 at hour=19
>> Warning ** Direct Normal Radiation= 1736.2 Wh/mÂ² on date= 3/30 at
>> hour=19
>> Warning ** DirectNormalRadiation 1913.5 > max theoretical= 191.0
>> Wh/mÂ² on date= 3/31 at hour=19
>> Warning ** Direct Normal Radiation= 1913.5 Wh/mÂ² on date= 3/31 at
>> hour=19
>> Warning ** DirectNormalRadiation 1602.2 > max theoretical= 195.7
>> Wh/mÂ² on date= 4/ 1 at hour=19
>> Warning ** Direct Normal Radiation= 1602.2 Wh/mÂ² on date= 4/ 1 at
>> hour=19
>> Warning ** DirectNormalRadiation 1100.3 > max theoretical= 200.4
>> Wh/mÂ² on date= 4/ 2 at hour=19
>> Warning ** Direct Normal Radiation= 1100.3 Wh/mÂ² on date= 4/ 2 at
>> hour=19
>> Warning ** DirectNormalRadiation 1080.5 > max theoretical= 205.2
>> Wh/mÂ² on date= 4/ 3 at hour=19
>> Warning ** DirectNormalRadiation > max theoretical 26 times
>>
>> Any insight would be helpful.
>>
>> Thanks,
>>
>> Max
>
>
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