The 9-digit Present Weather Code (PW) was used only in North
America before the turn of the century an long since replaced by a
METAR 2-digit PW code now used in weather reports around the
world. So, if the epw format leaves space for this old coding,
it's functionally dead space and probably filled with 999999999 in
all files except the old TMY2s and CWECs. The Liquid Precipitation
(LP) is very different because it gives the amount of
precipitation and time over which it occurred, typically in
multiples of 6 up to 24 hours, not whether or not there is rain
during that hour. This makes LP reports basically unusable in
simulations, which is why I spent several weeks back in 2015 to
convert the LP in the TMY3s to hourly records. So, if EnergyPlus
is relying on the LP field to detect the presence of rain, make
sure that the LP has undergone such a data transformation. And
what about snow flag, which seems to be of greater interest ?
In my opinion, if the rain and snow flags are useful, we should
take them from the current 2-digit METAR PWC. I've already doing
that starting with the IWEC2 weather files, where I added an
extra field for PW to the end of the TMY3 format, although I
never made a big fuss about the format change. PW appears on all
the weather files that I produce in the *.FIN4 format, but it's
lost in the conversion to epw nor have I bothered to use them to
set the ISNOW and IRAIN flags in the DOE-2 bin files. To do so
is very easy, since in the METAR PWC all instances of rain have
the same initial digit, as do all instances of snow.
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 1/9/2018 4:32 AM, Linda Lawrie
wrote:
Actually, EnergyPlus (and the epw format) uses coded flags in the 9 digit "Present Weather Codes" to determine and set Rain/Snow. Now that some stations include precipitation (albeit liquid) EnergyPlus sets the rain flag when there is adequate precipitation currently.
I believe the updated TMY3 format went away from the 9 digit present weather codes, so EnergyPlus would rely on the "preciitation" field in the epw file.
It would not be impossible to bring those back to the CWEC data; however, probably not as individual flags.
Linda
At 04:44 PM 1/8/2018, Joe Huang via Bldg-sim wrote:
Content-Type: multipart/alternative;
boundary="------------E16429D68ABA1BA04C74DF5C"
Content-Language: en-US
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"On 1/8/2018 12:15 PM, 'Jones, Christopher' christopher.r.jones@xxxxxxx [EnergyPlus_Support] wrote:
Â
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.
Â
Â
Christopher R. Jones, P.Eng.
Technical Specialist
Sustainability & Energy
Â
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T +1 416-644-0252
Â
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4 Canada
wsp.com
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Please consider the environment before printing...
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From: Equest-users [ mailto:equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Joe Huang via Equest-users
Sent: Tuesday, January 02, 2018 10:15 PM
To: Nicholas Caton <Nicholas.Caton@xxxxxxxxxxxxxxxxxxxxxx>; BLDG-SIM <bldg-sim@xxxxxxxxxxxxxxxxxxxxx>; EnergyPlus_Support <EnergyPlus_Support@xxxxxxxxxxxxxxx>; equest-users@xxxxxxxxxxxxxxx
Cc: Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Equest-users] White Box Technologies brings simulation weather data to the satellite age
Â
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:
Â
- Hi Joe,
- Â
- 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?
- Â
- 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:
- Â
- 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)?
- Â
- Does satellite-derived solar radiation address some or all of these local climate issues (cloud cover, smog, dust) affecting direct/indirect solar radiation?
- Â
- Thanks sincerely for all your teaching Joe,
- Â
- ~Nick
- Â
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- Nick Caton, P.E., BEMP
- Â Senior Energy Engineer
- Â Regional Energy Engineering Manager
- Â Energy and Sustainability Services
- Â Schneider Electric
- DÂ Â 913.564.6361
- MÂ Â 785.410.3317
- FÂ Â 913.564.6380
- EÂ Â nicholas.caton@xxxxxxxxxxxxxxxxxxxxxx
- 15200 Santa Fe Trail Drive
- Suite 204
- Lenexa, KS 66219
- United States
![[]](txtvl6BlH75TU.txt)
- Â
- Â
- From: Equest-users [ mailto:equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Joe Huang via Equest-users
- Sent: Thursday, December 14, 2017 8:13 PM
- To: BLDG-SIM <bldg-sim@xxxxxxxxxxxxxxxxxxxxx>; EnergyPlus_Support <EnergyPlus_Support@xxxxxxxxxxxxxxx>; equest-users@xxxxxxxxxxxxxxxxxxxxx
- Subject: [Equest-users] White Box Technologies brings simulation weather data to the satellite age
- Â
- 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.
![[]](txtj7NIRAybcJ.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.
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