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/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