Ke, others,
Historical weather data are now increasingly available on the Web. The National Climatic Data
Center, which is the archival arm of the National Weather Service, two months ago changed their policy
to make the ISH (Integrated Surface Hourly) data base going back to 1980 for 6,000-16,000 stations
around the world publicly accessible to anyone on the Web
(See http://www.ncdc.noaa.gov/oa/climate/isd/index.php for data access, info, etc.)
The ISH is the original source for NREL's Real-Time Weather Data, the TMY3 weather files, as well as
ASHRAE's IWEC2 weather files for 3,012 international locations for which I was the contractor. From my review,
the ISH contains close to 7,000 stations worldwide (2,000 in the US, 600+ in Canada) of sufficient
quality to produce hourly weather files.
(see the map on my web site www.whiteboxtechnologies.com/weather_data.html
for the stations for which I've already produced weather files for 2010).
Another source for historical weather data is the Weather Underground (www.wunderground.com).
I'm impressed by the sheer number of stations available, which must be upwards of 10,000 for the US alone.
The biggest problem with all these weather data is, of course, the absence of solar radiation data.
It's just a fact of life that, outside of a very few number of research stations, solar radiation is not
recorded. A major, perhaps the major, task in the creation of "typical year" weather files
like the TMY, TMY2, IWEC, IWEC2, etc., is to derive the solar radiation (total global and direct normal)
utilizing other climatic indicators, esp. cloud cover, temperature rise, etc. There have been dozens
of models and techniques developed around the world, e.g., NREL uses the Metstat Model, IWEC
used the Kasten Model, and I combined several models (Zhang-Huang, Gompertz, ASHRAE Clear
Sky) for the IWEC2. The bottom line is that you can expect to get within 5-10% on the yearly totals
(especially if there's measured data to calibrate the models), but don't expect great agreement on an hourly basis.
In the last few years, another avenue has opened with deriving solar radiation from satellite observations.
For US locations, Clean Power Research has a Web site ( www.solaranywhere.com/Public/SelectData.aspx )
that allows you to download hourly solar data for free on a 10 km grid from 1998 through 2009, but data for later
years requires a hefty license fee. I did a study in June 2011 comparing satellite-derived solar to high-quality
ground measurements and found them to be very close, particularly at the daily level.
So, the data are all out there, but putting them together would take some time and effort, especially if
you haven't dealt with this before. Another option is to get in touch with me, since over the past five
years I've built up all the software and techniques that I could create either a historical year weather file
from the ISH in almost no time at all, and at a cost much lower than the time you would have spent in
working this out.
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 4/10/2012 11:48 AM, Ke Xu wrote:
Linda,
I recalled this question today, and looked into the E+ AuxiliaryPrograms document, it is stated that
"Real-Time weather data is available from the EnergyPlus web site. From the web site:
"Hourly weather data from stations across the world is continuously collected and stored into
a local database. The data is available through this web interface. Most stations have
information for dry bulb temperature, wet bulb temperature, wind speed/direction,
atmospheric pressure, visibility, cloud conditions, and precipitation type. Data may not be
available for all stations and may not be contiguous for time period selected." The data is
available in two output formats: CSV and IWEC. Note that their CSV is not the same as
EnergyPlus CSV format. If you wish to get weather data from the real time sources, it may be
easier to use the IWEC format with the EnergyPlus WeatherConverter program; HOWEVER,
they do not collect solar data and, currently, the WeatherConverter cannot generate solar
data for these data files."
And I also checked the document "Real-Time Weather Data Access Guide" downloaded from http://apps1.eere.energy.gov/buildings/energyplus/pdfs/weatherdata_guide_34303.pdf
It indicated that the IWEC format file contains the following variables:
Entry Units/Notes
Local Date and Time YYYYMMDDHH
Dry Bulb Temperature Tenths of Degree Celsius
Dew Point Temperature Tenths of Degree Celsius
Wind Direction Degrees (0º = North)
Wind Speed Tenths of Meter Per Second
Altimeter Hundreds of Pascals
Visibility Tenths of Kilometers
Therefore, I think that the original data sets-either .IWC or .CSV doesn't contain solar radiation as a variable, is WeatherConverter adding the solar information somehow during the translation?
Thanks.
Ke
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Linda Lawrie <linda@...> wrote:
>
> I believe the real time weather site includes "global horizontal"
> solar. If you put that through the EnergyPlus Weather Converter it
> will use an algorithm to split the global into direct and diffuse
> that EnergyPlus needs.
>
> At 08:04 PM 9/25/2011, Ke Xu wrote:
> >Hello,everyone,
> >
> >To my understanding, the real-time weather file only includes
> >outside air dry bulb temp, dew point temp, wind direction and speed,
> >etc., but there is no solar radiation information. My question is,
> >without the solar radiation information, how does E+ calculate the
> >hourly cooling load and if it is necessary to incorporate the solar
> >radiation data, is there any public resources that I can reach? and
> >how can I incorporate that into EPW file?
>
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