[Bldg-sim] Revised TMY3 Weather Files now available on the Web

Nathan Kegel nathan.kegel at iesve.com
Tue Feb 10 22:51:33 PST 2015


Hi Kapil,

Several people have emailed me off the list to express a similar sentiment.  I’ll let them remain anonymous unless they choose to chime in.

Two parts to this email: further exploration of the problems in part 1 and some ideas for solutions in part 2.

Part 1.

I’ve presented on this topic at ASHRAE conferences as well as whenever I do a training on doing LEED or code compliance energy simulation.  I’ve done my own sensitivity analysis of many of the free Minneapolis area climate files and found I can vary the EUI of an office building with a VAV system by 14% just by selecting a different climate file that’s 12 miles away.  Even more interesting (at least to me) was that I could change which design decision was best by changing the climate file.  For example, the MSP climate file resulted in glazing X being the lowest EUI while selecting the Eden Prairie file (12 miles away) resulted in glazing Y being the best.  There’s no micro climates involved and both of these files “bin out” to CZ6.  However, neither of them are particularly “representative”.  Eden Prairie has -12 F hours in May while the MSP file has 92 F degree hours in April.  A quick check of the historical records show that -12F has never happened in recorded history in May in the Minneapolis area.  Anyone who lives in Minneapolis can tell you that 90+ in April isn’t common.  Even 70+ in April isn’t that common.  A quick check of the historical record shows one time in nearly 200 years of records where above 90 was recorded before April 15.  The third file, Crystal, was documented as having sub-freezing temps in the summer months in my previous reply to this thread.  So that’s not representative, either.  If there were no other options (which there are), I’d go with MSP as the best of a bad hand of climate files.

Appendix G only requires in G2.3 (90.1-2010): “The simulation program shall perform the simulation using hourly values of climatic data, such as temperature and humidity from representative climatic data, for the site in which the proposed design is to be located.  For cities or urban regions with several climatic data entries, and for locations where weather data are not available, the designer shall select available weather data that best represent the climate at the construction site.  The selected weather data shall be approved by the rating authority.”

The way this is written, I can literally pick any weather file – even if it is known to be filled with errors – and use it for LEED compliance and/or code as long as its nearby my proposed building.  It’s up to the rating authority to question it.

I’ve gotten many LEED review and code review comments in doing simulation.  I’ve never once been asked about the quality of the climate data that was used in the simulation.  Yet it impacts everything in the simulation: envelope, equipment performance (as many equipment performance curves are dependent on ambient conditions), and glazing selection just to name a few.

The mentality of “plug and chug”, or worse, not even bothering to know which climate file your simulation program is actually using when it spits out results, is a very dangerous game if you’re at all concerned about a reliable result – and by extension – providing your customers with sound recommendations on how to spend their money.

While nothing is perfect, I’ve had good experiences with using www.weatheranalytics.com<http://www.weatheranalytics.com> as a source for both TMY and AMY files.  If there’s a problem with a file they create, they’ve been really good about making it right quickly.

Another big problem with the free TMY3 files is they aren’t very up to date (2005 was ten years ago).  Which is another reason why I like weatheranalytics.com – I can get more up-to-date weather data to help make a more informed decision.

Part 2.

In my opinion, Appendix G needs a new section for compliance: Pre-simulation Climate Analysis (call it Table G3.09).


1.       Perform analysis on at least 1 TMY and 3 AMY (within the last 10 years) climate files near your site.  If three aren’t available, document where you looked and what process was done to select the climate file used in simulation.  (Although with services like Weather Analytics now available, this shouldn’t really be a problem for pretty much any project anywhere).  Submit plots of dry-bulb temperatures and provide a narrative describing the process used in selecting the climate file used in the simulation.  Include metrics like climate zone, bin analysis, and numerical justifications as well as local knowledge from trusted data sets in either the public or private domain.

2.       Document both the ASHRAE defined climate zone from 90.1/169 and perform your own BIN analysis in accordance with ASHRAE methodology for non-defined locations.  Submit both the defined climate zone and the derived climate zone.  If they are different, advise as to which climate zone is being used in the simulation for baseline building generation.

·       Fun facts (using TMY3 data sets): Dallas is defined at CZ 3A, it bins out to 2A.  Nashville is defined as CZ 4A, it bins out to 3A.  Toronto is defined as 6A, it bins out to 4A.  All these are listed in 90.1-2010 which is the referenced standard in LEED v4 as well as an approved compliance path in IECC 2012.  This is another potential design quandary: to get code approval and/or LEED points, I use a defined list in a table.  However, the building is being built and will never actually see the weather that was used to define the climate zone.

Better yet – get rid of defined climate zones altogether when taking a performance path.  Require professionals who do simulation to understand how to open and analyze a climate file and derive the climate zone.  Require review of that process by the AHJ and agreement that the analysis is valid and the CZ selected makes sense for the project.

[cid:image004.png at 01D04589.45775930]<http://www.iesve.com/>

Nathan Kegel
Business Development Manager

O:

  763.276.9981

M:

  415.420.9314

http://www.iesve.com<http://www.iesve.com/>


Integrated Environmental Solutions Limited. Registered in Scotland No. SC151456
Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP

Email Disclaimer<http://www.iesve.com/disclaimer.html>



From: Kapil Upadhyaya [mailto:KapilU at kirksey.com]
Sent: Tuesday, February 10, 2015 5:59 PM
To: Nathan Kegel; West, Scott P; 'RobertWichert'; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Revised TMY3 Weather Files now available on the Web

Nathan,
After you pointed this out, we started exploring this issue and did find significant differences in current weather files and 30 year average/EPW files.
As IBPSA members, we should take this issue up on a national level to come up with a resolution.

Regards,

Kapil Upadhyaya, ASHRAE BEMP, LEED AP
Senior Associate
Kirksey | Architecture
6909 Portwest Drive  |  Houston Texas 77024  |  www.kirksey.com<http://www.kirksey.com>
o  713 426 7508  |  f  713 850 7308  |  kapilu at kirksey.com<mailto:kapilu at kirksey.com>

From: Nathan Kegel [mailto:nathan.kegel at iesve.com]
Sent: Monday, February 09, 2015 10:37 PM
To: West, Scott P; 'RobertWichert'; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Revised TMY3 Weather Files now available on the Web

To add to the list of tools that already does this for you:

IES VE does this for you in the Vista application.  Whether you’ve run an annual simulation or not, you can plot multiple variables overlaid on one another:

[cid:image005.jpg at 01D04589.45775930]

[cid:image008.jpg at 01D04589.45775930]

3D graphs:

[cid:image010.jpg at 01D04589.45775930]

“Heat Maps”:

[cid:image011.jpg at 01D04589.45775930]

You can also create your own custom variables in the VE (so you could create an enthalpy variable from the other variables and plot it on a graph or export to a spreadsheet, etc.):

[cid:image012.png at 01D04589.45775930]

This is a .EPW file format from: http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/region=4_north_and_central_america_wmo_region_4/country=1_usa/cname=USA
For those of you still tuned in – a bit of a digression:

Note the values that are errors in June and August (the DB is well below freezing 10 F) – that’s never happened in the recorded history of the area – let alone in the timeframe that TMY3 files are comprised of).  The coldest value EVER for the entire state in the month of August is 21 F.  That occurred in Kelliher which is more than 200 miles north of this location.

I’d suggest opening any of the climate files you get and ensuring they aren’t full of invalid data points.  I’ve found far too many of them to be too error-filled to be useful for simulation.  Eden Prairie, MN (still spelled incorrectly on the DOE website – “Edin”) is also rife with sub-zero temperatures in May (also never happened in recorded history).  The Portland, OR TMY3 has 114 F days in late October (ditto).  I think you get the idea.

[cid:image004.png at 01D04589.45775930]<http://www.iesve.com/>

Nathan Kegel
Business Development Manager

O:

  763.276.9981

M:

  415.420.9314

http://www.iesve.com<http://www.iesve.com/>


Integrated Environmental Solutions Limited. Registered in Scotland No. SC151456
Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP

Email Disclaimer<http://www.iesve.com/disclaimer.html>



From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of West, Scott P
Sent: Monday, February 9, 2015 6:47 PM
To: 'RobertWichert'; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Revised TMY3 Weather Files now available on the Web

Robert,
Once you get two psychrometric data points of moist air, you should be able to derive the other properties that you desire.  A lot of the hourly weather files just happen to provide humidity in DP.  Obviously if you have more than a few data points to evaluate (like a full TMY3 file), looking them up on a psych chart isn’t very practical.  Unless you’re particularly interested in evaluating partial pressure equations, I would recommend using readily available software as a data filtering tool.  I recommend ClimateConsultant which is a free software produced by UCLA:
http://www.energy-design-tools.aud.ucla.edu/climate-consultant/request-climate-consultant.php

The software can be used for visualizing weather data and evaluating heating and cooling strategies.  It’s great for that, but I often simply use it to filter raw weather files and then export to Excel.  The whole process takes 5 minutes once you have the software installed.  You simply find the appropriate EPW weather file (EnergyPlus format) from the web (link provided in the software) and import it into ClimateConsultant.  You can then export to csv.  I like how the software will automatically convert from SI to IP units.  You can choose other ways of representing humidity like RH and WB.  You can also use it to quickly construct daily or monthly averages if desired.

[cid:image013.png at 01D04589.45775930]

Anyway, that’s my plug for ClimateConsultant for those of us that can’t program good data filters (or are too lazy).  I hope it’s helpful.

Scott P. West, P.E., LEED AP BD+C, BEAP, BEMP | JACOBS | Mechanical Engineer | Energy & Power Solutions | 817.222.8512 office | 817.897.1882 cell | scott.west at jacobs.com <mailto:scott.west at jacobs.com> | www.jacobs.com<http://www.jacobs.com/> | www.jacobs.com/energyportfolio<http://www.jacobs.com/energyportfolio>

From: RobertWichert [mailto:robert at wichert.org]
Sent: Monday, February 09, 2015 2:34 PM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Revised TMY3 Weather Files now available on the Web

These weather files are great, thanks for the info, but I am trying to get wet bulb temperature too, and they do not seem to give wet bulb temperatures.

Any ideas on that, perhaps?

--

Robert P. Wichert P.Eng.  LEED AP

CEPE  CEA  HERS I/II BPI BA

+1 916 966 9060

FAX +1 916 966 9068


========================================
On 1/30/2015 9:10 PM, Joe Huang wrote:
White Box Technologies (WBT), in collaboration with the National Renewable Energy Laboratory (NREL), has revised the TMY3 weather files to correct inconsistencies in units for illuminances, improve the reporting of Liquid Precipitation, replace all missing records with interpolated or filled values (chiefly for visibility, ceiling height, aerosol optical depth, and albedo), and add a new variable for Present Weather.

Since their release in 2005, the TMY3 weather files covering 1,020 locations in the US and dependencies has become the standard set of weather files for use in computer simulations of solar energy conversion systems and buildings. The intent of this revision is not to redo the fundamental analysis, but correct some known errors and make modest improvements in the reporting of subsidiary climate variables.

The only impact from these corrections and changes are for daylighting simulations that use the illuminance values, and for building simulations that use the liquid precipitation to model green roofs or moisture transport through the building envelope. The added Present Weather variable is not directly used in any simulation program, but allows the DOE-2 BINM files to have correct IRAIN and ISNOW flags, although these two variables are not being used in DOE-2.  Filling in missing data for Visibility, Ceiling Height, etc., should have no impact on the use of the TMY3s, but improves their overall record-keeping.

The revised TMY3 files in their native CSV format have been provided back to NREL and are available here:    http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3

The revised TMY3 files in EPW and BINM formats are available for free download on the White Box Technologies web site at  http://weather.whiteboxtechnologies.com/wd-TMY3 or by selecting File Type as "TMY3" at http:/weather.whiteboxtechnologies.com/search<http://weather.whiteboxtechnologies.com/search> to search using GoogleEarth. The zip file names are unchanged, but the underlying EPW and DDY files will have the *TYA designation to distinguish them from the previous TMY3 versions.

For a more detailed description and full documentation of the revision,  please see the attached memorandum.

Joe
--
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com<mailto:yjhuang at whiteboxtechnologies.com>
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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