Not so fast Linda, it turns out that you have been programming in the dark ;)
First let me apologize for the Frankenstein weather data file I sent to you. The first couple of weeks were standard time, then the server switched to daylight
savings, back to standard time on 4 Nov, crash in late Nov, back to daylight savings in Mar 2013. I set my servers to standard time only when logging data, but this station had a bad hard disk crash and then got unplugged by mistake for a while. Unfortunately
for me, I will have to repair this file to complete my study of a renovated building. It is also unfortunate that it obscured the real problems with the converter. I’ll send you a set of “good” files from 4 different locations to play with as you wish next
week.
First issue: the input file must start with data for the first time step of the day, not the last step of the previous day or anywhere else. Everything you
initially developed the program for starts at hour 1:00. When one starts at the odd 0.05, 0.10, 0.15, 0.20, 0.30, the program issues a torrent of warnings, but it keeps chugging along and stays in sync with the input data. Perhaps that should be a little
clearer in the docs. I initially thought the program actually understood where it was from the initial date and time, but that is not true. I’ll just work that into my preprocessor since I have to fix compass directions and check data integrity in the file
anywhy.
The calculation works fine (I’m not judging what it calculates, just that it is happy) if it is generating solar data by itself with no solar component data
input from the user. A limitation of the program is that it does not calculate predawn or post sunset diffuse solar radiation. I happen to be using Davis Vantage 2 weather stations on my sites, so I am collecting global solar radiation data (ok, so it is
not super calibrated, thousands of dollars device). Now the converter is working to fill in the blanks based on some input. There are two faults in the current program for this task.
Second issue: when there is predawn or post sunset global horizontal radiation input, the internal solar calc has nothing to work with, so it does nothing with
the input. What it should do is recognize that there is no direct solar radiation at this time so the input global horizontal radiation must be all diffuse solar radiation. (ok throw a warning if you want…this isn’t the big problem)
Third issue and bigger problem: when it is critical sunrise or sunset event in the time step, something completely blows up in the calculation , and a small
to an extremely large and bogus direct normal solar is calculated. The program recognizes a simple error that it has calculated something larger than it thinks possible, so it throws an error flag. If that error routine were a little smarter, it could correct
any error when the direct normal is calculated as zero or some very small value that indicates a sunrise or sunset event, but still pass the error along when the sun is a little higher in the sky and maybe the Global Solar is in error..
With a 10 minute time step, I see errors for almost every day of the conversion in my files. I think I have a workaround for the moment. If I calculate a
.csv using my solar input that generates errors and a second .csv using the converter calculation alone, I can write a quick routine to compare the files an fix the bogus direct normal calculations and repair the skipped predawn and after sunset data.
…time for an Easter egg….
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of Linda Lawrie
Sent: Friday, March 29, 2013 2:36 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Weather converter issues
That wasn't the problem.
It was bad data on input. Missing intervals, etc that were overlooked in quality control by the user.
At 12:31 PM 3/29/2013, Joe Huang wrote:
I would be interested to find out how this problem gets resolved. In my work developing the IWEC2 weather files for ASHRAE, I encountered problems applying the Perez model to get the direct/diffuse split, and ended up switching to a simpler Gompertz Function model.
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