The Zhang-Huang Model, developed by Dr. ZHANG Qingyuan of Tsukuba University in Japan and yours truly, is a multi-linear regression model that estimates the solar as a function of cloud cover, temperature change over the past three hours, wind speed, and relative humidity, bounded by what someone earlier called a "sanity check" of no more than 0.8 * extraterrestrial solar.
1) Although other researchers and I have found that the Z-H Model produces a good match to measured data on an aggregate basis, such as annual or monthly totals, while working on the IWEC2 files, I found that the Z-H Model often produced uneven hourly profiles when the data would suggest otherwise, such as for a clear day with no clouds. To overcome this problem, I now use the new ASHRAE Clear Sky Model afterwards to adjust the hourly solar profiles coming out of the Z-H Model. This procedure was incorporated for the IWEC2 files, but I am still not finished working on it.
2) Make sure that the raw weather data contains cloud cover (or opaque cover) information. If not, using Z-H will produce a weather file as if there were never any clouds.
3) Because of first caveat, I would not recommend using the Zhang-Huang Model as a Clear Sky Model. The new ASHRAE Clear Sky Model (2009), simplified from a detailed model by Chris Gueymard, is far superior, although getting the inputs might present problems if the location is not among the stations in the ASHRAE HOF.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 108D Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx www.whiteboxtechnologies.com (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
On 11/8/2012 7:13 AM, Linda Lawrie wrote:
If global radiation is provided, the weather converter uses the Perez split model for direct and diffuse calculations. If no global is provided then it uses the Zhang-Huang model to come up with Global and then Perez model to split.
I believe all this is described in the Auxiliary Programs document.
For design days, there are several solar models available -- ASHRAE Clear Sky, ASHRAE Taub (2009 clear sky) and Zhang-Huang. Along with you being able to put in your actual beam and diffuse values, if desired. The methods are described in the Input Output Reference and the Engineering Reference.
At 08:04 AM 11/8/2012, rokkas80 wrote:
Ok. Based on cloud information from the weather files, or?
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Dru Crawley <dbcrawley@...> wrote:
>
> The EnergyPlus WeatherConverter now does calculate direct/diffuse solar
> radiation if it's missing.
>
>
> On Thu, Nov 8, 2012 at 9:47 AM, rokkas80 <lukas.rokka@...> wrote:
>
> > **
> >
> >
> > E+ don't model the solar radiation by it self. You need to have weather
> > files with measured or/and modeled values. But E+ may have some simple
> > "sanity check" (like that there shouldn't be any solar radiation during
> > night time and min/max limits).
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@>
> > wrote:
> > >
> > > no. i mean from latidute and longitude and the equation of time, etc.
> > together with some assumptions about atmospheric conditions, the direct and
> > diffuse radiation can be calculated. It does not have to be measured, or?
> > If there was no weather data for this, or incorrect weather data...I was
> > under the impression that e+ runs a "sanity check" to see if the radiation
> > from weather files is okay. And if not, it uses it's calculated results?
> > I've made a excel spreadsheet once to do this as a check...and the results
> > are okay.
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "rokkas80" <lukas.rokka@>
> > wrote:
> > > >
> > > > I don't understand what you are asking for, could you please clarify?
> > > > Do you mean that e+ calculates the direct normal solar from global and
> > diffuse solar? Well, the Weather Converter program can calculate the direct
> > normal from global and diffuse solar according to the documentation.
> > > >
> > > >
> > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@>
> > wrote:
> > > > >
> > > > > "Even though the solar data from STR�NG varies in quality it's
> > still better, for most sites, than that provided in the ASHREAE IWEC files"
> > > > >
> > > > > Doesn't e+ calculate the direct solar?
> > > > >
> > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "rokkas80" <lukas.rokka@>
> > wrote:
> > > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > I've updated my tool for creating Actual Meteorological Year (AMY)
> > files for North Europe. The tool can be downloaded at
> > http://rtwc.blob.core.windows.net/clickonce/publish.htm.
> > > > > >
> > > > > > News for this version, Real-Time Weather Converter 2.0:
> > > > > > - All data from ISD is available, also data marked as
> > "Additional". If you tried the tool before but didn't get any data for your
> > station, you should now be able to get usable data for most locations.
> > > > > > - A new server that maps data from the SMHI server. Now retrieval
> > time are just a few seconds for one year of solar data. A AMY-files can now
> > be made in under a minute.
> > > > > > - Missing data points are visualized graphically.
> > > > > >
> > > > > > The tool was made as part of my MSc degree project at
> > M�lardalens University, Sweden. It uses observed actual weather data from
> > the Integrated Surface Database (ISD),
> > http://www.ncdc.noaa.gov/oa/climate/isd, and modeled solar radiation data
> > from STR�NG, http://strang.smhi.se.
> > > > > >
> > > > > > Roughly, the tool covers most of Europe excluding south Europe.
> > Long-term coverage is from 1 of January 1999 to up to date for the
> > northernmost area, the southern area is covered from 1 of June 2006 (see
> > website for map).
> > > > > >
> > > > > > The quality of the solar radiation data from STR�NG varies in
> > the geographical dimension. Roughly the model gives good result for Sweden
> > and Central Europe, but underestimates for ocean coast near areas like UK,
> > Norway etc. The model do underestimate as well for the Baltics, northern
> > Finland and some high altitude sites. There's a validation figure (for
> > Google Earth) at the tools homepage in the help section. Even though the
> > solar data from STR�NG varies in quality it's still better, for most
> > sites, than that provided in the ASHREAE IWEC files (which underestimate
> > direct solar radiation in the range of 20 to 40 % for the area in
> > question). For model calibration these data are very useful.
> > > > > >
> > > > > > You are free to use the modeled solar radiation data from
> > STR�NG. Weather data from ISD may however have restrictions regarding
> > commercial usage, depending on country and what data is being used. Some
> > countries (UK, Norway, Netherlands, Slovenia and Sweden from next year(?))
> > have free weather data, other countries some restrictions and some
> > countries have most of their weather data restricted. There is a method in
> > the tool that excludes data marked as "Additional" by WMO, this should make
> > commercial use of resulting weather files possible for most countries (my
> > personal interpretation of WMO resolution 40 Annex I). But it's up to the
> > end user of the tool to read and interpret the WMO resolution 40 and check
> > with their National Weather Service for their data policy. If intentions
> > are non-commercial the data accessed and created by this tool can be used
> > freely for all countries in question.
> > > > > >
> > > > > > The ISD lack recent data for many of the German weather stations.
> > Observed weather data can still be acquired from other sources (i.e.
> > EnergyPlus real-time weather service, Wunderground) and by using copy/paste
> > inserted into the tool. The tool has methods for re-sampling, interpolating
> > and filling data gaps.
> > > > > >
> > > > > > This tool was developed to make AMY-files to be used for model
> > calibration. But it would be possible to use a similar approach to create
> > Typical Metrological Year (TMY) files as well, at least for the geographic
> > area where there soon exist 13 years of free solar radiation data available
> > free via STR�NG. Let me know if you think there's a demand for this kind
> > of weather files or if you know of any available tools or algorithms that
> > can make this kind of files.
> > > > > >
> > > > > > Best regards,
> > > > > > Lukas Lundstr�m
> > > > > > https://sites.google.com/site/weatherconverter
> > > > > >
> > > > >
> > > >
> > >
> >
> >
> >
>
------------------------------------
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