The rain and snow flags are still available in the raw weather
station data, but haven't been included in the processed weather
files since the 1990's because everyone in this hemisphere at
least have adopted the TMY2/TMY3 formats, in content if not the
literal file format, developed by NREL, which does not include
these two flags. I was also under the impression that none of the
simulation programs, such as DOE-2, do not use these two flags
anyway. If these flags are of use, it would make sense to
include them, which would not require a change in the DOE-2 *.BINM
format, but would require a change to the EnergyPlus *.epw format.
Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
I have a
question � what happened to the rain and snow flags
that were in the old CWEC file but are missing in the
latest versions. Many snow melting systems have a
snow/rain sensor in the slab used to trigger the
system on.
Christopher R. Jones, P.Eng.
Technical Specialist
Sustainability & Energy
![](txt1d2roaXN15.txt)
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Nick,
This is an interesting topic that has evolved in an
unexpected way. Now that NREL has mastered the
technology of satellite-derived solar radiation, they
have regarded weather station data as an impediment,
since there's no way to get such measured data to match
the 5-kilometer grid of the satellite-derived solar.
Therefore, they have abandoned the weather station data
(which was was used in all the TMYs to date) and gone
instead to Reanalysis Data from NOAA's MERRA, which is
running a climate forecasting model in retrospective
mode. I don't have time now to discuss reanalysis,
except to say that from what I've seen the results are
decidedly "iffy". Almost two years ago, I managed to
get a Work Statement through ASHRAE for someone to take
a good look at reanalysis data.
So, what does this mean for your question? NREL's
National Solar Radiation Data Base (NSRDB) can now get
you the hourly time series or a TMY for more than a
million grid points over the US, all with
satellite-derived solar radiation but MERRA results for
the other climate parameters. I've told NREL several
years ago that for the building simulation industry it
would be much better to merge the satellite-derived
solar with actual station data that give good accurate
coverage of urban areas where buildings are located.
NREL's response was that they'd be happy to do this, but
someone has to pay them for the work.
In response to your hypothesis below, I think you're
being too disparaging of the previous modeling efforts
while raising too high your expectations of satellite
solar. It's not that the previous models failed to
account for local climate conditions, but that they
lacked good data to drive them. For example, all models
included terms for cloud cover and clearness, or for the
more detailed physical models arcane parameters like
aerosol optical depth, preciptable moisture, etc., but
how available are the input data and how reliable are
they? The advantages of satellite-derived solar are
that they provide a comprehensive and objective view of
the cloud conditions, which combined with satellite
measurements of the atmospheric conditions and improved
modeling, results in accuracies that previous modeling
efforts can not attain. As far as discerning localized
effects of smog and dust in urban areas, that would
still depend on whether there's sufficient monitoring at
that spatial and time scale to detect the differences.
What I mean is that it's one thing to observe that in
general urban locations have more smog and particulates
than rural locations, but it's something else to
quantify the resultant differences in solar radiation
over time and distance.
I'd like to take the opportunity here to step back and
comment on the status of weather data for the building
energy community, My interactions with NREL has brought
the realization that we have been piggy-backing on the
efforts of others outside our community for our weather
data. I don't intend to pick on the NREL Solar Program,
several of whom I consider friends and colleagues, but
their target client is the solar power industry. Since
solar power arrays can be installed anywhere, preferably
in rural uninhabited locations, it makes sense to go to
satellite-derived solar. It's also clear that to serve
that industry, NREL would focus its efforts on getting
the best solar values, while all the other climatic
parameters, like temperature, humidity, wind speed,
etc., are secondary, which may be why getting them from
MERRA is a satisfactory choice. The focus on solar is
also evident in the weighting used by NREL to develop
the TMYs, with 50% weight placed on the 2 solar and 50%
on the remaining 8 non-solar parameters.
For the building energy community, or priorities are
somewhat different. Since 99% of buildings are located
in urban locations, we should focus much more on climate
in urban areas. Luckily, that's also where the great
majority of existing weather are located, which is why
I'm resistant to throwing out measured weather data and
replacing them with synthetic data, no matter how much
they've been "seeded" with real data. As for the
weighting of climate parameters in selecting the typical
months, why not use building energy simulations and
weight them by the distribution of heating and cooling
loads?
Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 1/2/2018 9:30 AM, Nicholas Caton
wrote:
Hi
Joe,
From
your perspective, are NREL or any other
government/professional bodies making
moves/indications to update/refresh the current TMY3
sets to utilize satellite-derived solar radiation?
Seems like a no-brainer for our industry, but is
there a counter-argument? It seems likely, but has
there been rigorous comparisons of satellite-derived
solar radiation against measured values and/or our
“present-day” solar models used to derive solar
radiation information for building energy
simulation?
Also,
I’m trying to understand and correctly characterize
the impact of this development in simple terms my
brain can follow. Is it fair to say:
The
solar models used in developing weather files for
building energy simulations to-date in our industry
(including all/most industry-standard TMY weather
sets), because they have been using solar radiation
derived from (evolving) solar models, have not
accounted for the likes of local climate cloud cover
/ smog / dust? Seattle (~47°N) has perhaps been
seeing as much sunlight through the winter as Paris
(~48°N)?
Does
satellite-derived solar radiation address some or
all of these local climate issues (cloud cover,
smog, dust) affecting direct/indirect solar
radiation?
Thanks
sincerely for all your teaching Joe,
~Nick
![](txthXFsf5laGd.txt)
Nick
Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric
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E nicholas.caton@xxxxxxxxxxxxxxxxxxxxxx
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![](txtQRQfJqBBhK.txt)
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It is with joy and some trepidation to report that
White Box Technologies (WBT) is updating all its
historical weather files with satellite-derived solar
radiation. Joy because this overcomes what has been
the most significant question mark with weather files;
trepidation because of the amount of work needed to
carry out and maintain this effort. To show that this
is more than marketing hype, I need to give a rather
long explanation about this development.
The bane of weather data over the past three decades
has been the solar radiation (global horizontal and
direct normal) which are not measured parameters, but
derived using various solar and sky models. All the
familiar "typical year" sets, i.e., TMY, WYEC, IWEC,
etc., let alone the historical weather files, have
modeled solar radiation. Although a lot of
work has gone into such models (see M. Iqbal,"An
Introduction to Solar Radiation", Academic Press,
1983), there remain an almost intractible problem of
the lack of good measured solar to tune any of these
models. For example, in the ASHRAE IWEC2 weather
files, my team was able to find one or two years'
measured data for less than 50 locations,
from which were derived 28 sets of regression
coefficients then used for all 3,012 IWEC2 locations.
For the past decade and a half, researchers around the
world have been working to derive solar radiation from
weather satellite imagery, driven largely by the needs
of the solar power industry for the siting of solar
power plants and getting "bankable" solar estimates
for their arrays. Our little building energy
simulation sector can of course benefit by hanging on
the coattails of the solar power industry, but the
downside has been to be totally priced out, since the
commercial cost for one year's solar data for one
location (grid cell) typically runs around $1,000.
A welcome development over the last five years is that
various government offices or affiliated consortia are
now beginning to also providing access to
satellite-derived solar radiation at minimal or more
acceptable costs under various conditions. Over the
past three years, WBT has obtained access to such data
and permission for its use in WBT weather files.
WBT is now either replacing the solar radiation on its
historical weather files, or using satellite-derived
radiation to develop custom solar coefficients for
each location to extend the satellite-derived solar to
time periods outside the available time window. With
the exception of polar locations above or below 60/66
degrees, island nations in the Pacific and Indian
Ocean, and a few unfortunate "blind spots", the entire
land mass is being covered with at least 10 years up
to 18 years of hourly solar records.
Starting in 2018, WBT historical weather files in the
following areas will all have satellite-derived solar
radiation for the following time periods: Europe,
Africa, South America east of 66 West, i.e., Brazil
and Uruguay (2004 to date), Australia (1999 to date),
and East Asia (2007 to date, access pending). WBT
historical weather files in the following areas will
have satellite-derived solar radiation for the
indicated time periods - North America and
Central/South American down to 20 South (1998-2015),
South Asia (2000-2014), with modeled solar radiation
from 2016 on that has been individually tuned to the
past satellite-derived solar.
Another benefit to the satellite-derived solar is to
increases the number of available weather stations,
which in many places has been limited by the lack of
cloud cover data needed to model the solar radiation.
For reasons that are not immediately identifiable,
several English-speaking Commonwealth countries has
seen a marked drop in the number of available stations
due to the decreases in the reporting of cloud cover
(see plot, ZAF = South Africa). For example, the
number of stations in the UK has dropped by almost
2/3s between 2001 and 2017 (174 to 64), but with
satellite-derived solar, it will go back up to over
180, while in Australia and South Africa the
comparable numbers are from 175 to well over 500, and
from 37 to over 100, respectively.
![](txtp5BEIxqAdD.txt)
If interested, customers who have purchased a
historical weather files from WBT over the past five
years can get an updated weather file at no cost.
Lastly, although it will take at least a month to
update all 10,000 2017 files, it's very quick to do
for any specific location or even 50 or so locations.
Therefore, if you have an urgent request please e-mail
me and I will put that at the beginning of the queue
for that day.
--
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
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