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Re: [EnergyPlus_Support] Weather files and Pyranometer measurements
Jeb:
I have some info for you about custom weather files for EnergyPlus.
It will answer some of your questions, but probably not all of them.
If you still need to know more, please ask, and I'll try to dig up
answers. Again, I apologize for the delay in responding to this
request.
Mike
-------------------------------------------
Indeed, it is necessary to somehow split the measured global solar
into direct and diffuse components on the measurement file--EPlus
won't do that for you.
Not having separate measurement of the beam solar is a fairly serious
limitation, especially for partly cloudy conditions, because sky models
are not very accurate.
The question of one minute time steps on the data file is another
unknown for me. Fred says that only Linda could answer whether EPlus
can handle such a file correctly, but in any case it would probably mean
that EPlus would use a one minute time step, which is "not advised".
I would recommend that the one-minute data be averaged to produce data
periods of at least ten minutes, and these put onto the weather file.
The time entered for the average should be the center of the averaging
period (i.e., the average of the times at which the measurements were
made), since this will be the time that drives the simulation, and
EnergPlus assumes that the values on the weather file are instantaneous
values at the given time.
When I was making my weather file the documentation on which fields in
the data record are necessary and which aren't was pretty spotty. Maybe
it has improved since then. Clearly it depends on what you are trying
to simulate; my experience was that not including a data field (i.e.,
entering -999) that turned out to be necessary produced a program crash
that Linda had to sort out. (Maybe the documentation now covers this
and has, or could have compiled, a table listing "for simulating
this...these fields are requred") I proceeded by thinking through what
information was physically necessary to produce the information I wanted
to simulate. With the exception of the problem noted above (I entered
-999 for dewpoint), this worked pretty well. For a required field for
which one does not have measurement data it is necessary to enter some
plausible calculation, guess, or whatever, and to interpret the effect
of this on the resulting simulation.
I found that I was able to get away without entering data in the
following fields:
Extraterrestrial solar: Horiz & direct normal
Horizontal sky IR
Site Illuminance--Horiz Total, Direct Normal, Horiz Diffuse
Zenith Luminance
Total Sky Cover
Opaque Sky Cover
Visibility
Ceiling Height
Present Weather Observation
Present Weathe Codes
Precip. Water
Aerosol Optical Depth
Snow Depth
Days since Last snowfall
------------------------------------------------------
On 28 Mar 2002, at 19:21, jebitsy wrote:
> Hello,
>
> I am trying to build a local weather data file for a test site in
> Wyoming. I started with a TMY2 file for the closest location I could
> find and am "adjusting" it for locally measured conditions. One of
> my measurements is a LI-COR LI-200SZ pyranometer sensor that "records
> radiation received from the whole hemisphere." My understanding is
> that this is equivalent to the global horizontal radiation with sky
> cover (total and opaque?) taken into account. The measurement is
> recorede in W/m^2.
>
> Do I have to try to back out which part of this is direct normal
> radiation and which part is diffuse horizontal radiation, or can I
> get the software to do this for me? Is there another/better/easier
> way to use this measurement? (e.g. a multiplier on some weather file
> entries)
>
> This radiation measurement is recorded every minute. If I build the
> weather file with minute resolution, what units should I use for
> radiation values? The software is looking for Wh/m^2. If I were to
> build a weather file with one hour resolution, I assume I would add
> up the previous 60 1-minute values and use that. I do not know what
> to do for a 1 minute resolution file.
>
> I used the following web site with detailed definitions for the
> weather file.
> http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html
>
> Thanks in advance for your help.
> Jeb Blakeley
>
>
>
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