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Re: Type 16a
- Date: Wed, 26 May 2004 12:06:53 -0500
- From: Michaël Kummert <kummert@xxxxxxxxxxxxx>
- Subject: Re: Type 16a
Pietro,
I wanted to see the type 16a output compared to weather data input. So
with iisibat I made a simple model with a type 9d data reader, the rad
sol processor type 16a and the common output types (see the iisibat file
attached).
The weather data I used contains mean monthly hour values, so in a
month each day has the same value of radiation at the same hour.
Tilted surface mode is =2
shift in solar time = 7.5
latitude = 44.5
orientation = 90° (poiting west)
Site: Milan
from my graf, along every month I see the Tot and the Beam Rad on
Surface 1 to vary while the radiation input is constant...It actually
makes sense since weather data are mean values but I don't understand
their trends:
referring to the 2nd part of thy year, Tot and Beam Rad grows along
every month when acutally daylight is decreesing, so I would expect
higher values at the beginning of every month, not at the end! I found a
similar trend (but opposite, of course) in the first part of the year (I
didn't include it in the file attached) even though in a less evident way...
Another thing concerning my simulation: as you can see in the months of
september and october Tot and Beam Radiations are higher than their
input at the end of the month!! how is it possible??? (At least this
doesn't occur in the first part of the year)
Sorry for my belated answer.
You seem to have a timing problem between your data file and the way you
configure Type16. The most obvious sign of that is the computed beam
radiation, which is always 0 in the morning.
One possible reason is the shift angle. If your data file is in local
standard time (which I couldn't check), it seems to me that:
LST = -15 (standard meridian for UTC+1, 15° East i.e. -15°)
LLoc = -9 (longitude... Approximatively) 9° East, i.e. -9° West
SHIFT = LST - LLoc = -15 -(-9) = -6
You have +7.5 (again if your data file uses another time convention it
may be OK)
Another reason might be the fact that you don't start the simulation at
hour 1. Sometimes the data reader gets confused and does not skip the
appropriate number of lines, especially if you have header lines that
you did not specify.
In both cases, I always recommend to plot the extraterrestrial radiation
computed by Type16 and the global horizontal directly from the data
file. When you take a look at those two plots, you will immediately see
if there is a time shift problem (e.g. calculated sunrise later/earlier
than the one in the data file, etc.)
I hope this helps,
Michaël Kummert
--
_________________________________________________________
Michaël Kummert
Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706
Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@xxxxxxxxxxxxx
SEL Web Site: http://sel.me.wisc.edu
TRNSYS Web Site: http://sel.me.wisc.edu/trnsys