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Re: [EnergyPlus_Support] Re: AMY-weather files for North Europe

David, Chris,

I'm rather surprised that people are still using the Z-H Model with the single set of coefficients that were developed in 2000 from measured solar for two locations in China, but that seems understandable since the ASHRAE paper describing the new coefficients is still under review and will not be publicly available for at least six months.

I have to check with ASHRAE on the rules on public distribution of final reports from ASHRAE projects, so for the interim, in the interests of promoting better usage of the Z-H Model (:-)), I have attached the ten pages of the final report related to the solar modeling. Page 19 shows a world map of Koeppen climate classifications; page 23 shows the regional solar coefficients for the Z-H Model.  Also please note that the model formulation has changed slightly from the description in the 2001 paper (see equation on page 17).

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 11/9/2012 3:01 PM, David Reddy wrote:
I've played around a bit with using the ZH model to generate solar for custom annual weather files. 

The approach I used was to develop "site specific" ZH model coefficients from the observations listed in TMY3 files.  You can't let all the coefficients vary (at least using the least-squares solver I used), but developing new coefficients for 2-3 of the more influential variables helped quite a bit in fitting the model to the data (as might be expected, CC was most important, have to look back a notes to remember the others I settled on).   Up until this thread, I was not aware of the Koeppen Climate Classification coeffs, but would like to look at those now to see how they might apply to my location (Pacific NW).

One of the biggest issues with this approach was hourly cloud cover data in the TMY3 files didn't always appear to jive with the solar radiation data (ex. CC = 8-10 when the GHorz was close to expected clear sky value).  Haven't had enough time to investigate further, and I assume there maybe a serious flaw in this approach if the TMY3 data values aren't expected to jive with eachother, but in any case, this was just my first pass at trying to use the model for my application.  Now, that custom weather files are readily available from a few vendors, it has been hard for me to justify spending a lot of time on it...

- David

On 11/9/2012 1:35 PM, Joe Huang wrote:


Not sure how far to follow this thread on EnergyPlus_Support, but I have a question on your tests of the Z-H Model. Did you use the single set of coefficients developed in 2000 (and described in my 2001 ASHRAE paper), or the 23 sets of coefficients assigned by a location's Koeppen Climate Classification developed in 2010 for the IWEC2 project (and described in the Final Report for RP-1477)?  I'll send you the link to the Final Report in a separate e-mail.


Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

On 11/9/2012 11:27 AM, cgueymard wrote:

Like Joe, I feel flattered too because of how things are connected: STRANG calculates the clear-sky irradiance with my SMARTS spectral radiative transfer code, which formed the basis of the REST2 broadband model, itself at the root of the new ASHRAE parameterized model. The latter made its debut with the 2009 HOF, as Joe mentioned. Note, however, that the 2009 model has now been updated and improved in anticipation of the 2013 HOF, which will also have more world stations than in 2009.

My own tests with the Z-H model showed it was not accurate (and sometimes unreliable) in climatic areas away from its intended "comfort zone" (i.e., parts of Asia). This is most probably because it is purely empirical. Based on that experience, I can confirm Joe's comments.

Outside of ASHRAE's weather stations and linked irradiance information, it is still possible to obtain hourly clear-sky irradiances with the REST2 model. Its input atmospheric data are gridded, and available globally over the world.


Chris A. Gueymard, PhD
Solar Consulting Services
P.O. Box 392
Colebrook, NH 03576, USA
Florida's Office:
Tel. (386) 402-8949

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Joe Huang <YJHuang@...> wrote:
> Although I feel flattered by the mention of the Zhang-Huang Model, I need to add three
> caveats to its use.
> 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


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