Wet-bulb is not generally measured in weather stations, but can be derived from other
measured climatic variables, such as dry-bulb temperature, dew-point temperature, and
atmospheric pressure. Unfortunately, the derivation requires several equations and
trial-and-error iteration (see Chapter 1 of the ASHRAE Handbook of Fundamentals). If you
don't relish writing a script or program to do this, you can look at the unpacked DOE-2
format (*.FMT or *.FMTM) of the weather file, which does contain the calculated wet-bulb
temperatures in the first data column (see attached sample snippet). However, you will
need a utility Fortran program wthfmt2.f or wthfmt3.f to convert the packed (*.BIN or
*.BINM) DOE-2 file to a humanly -readable text *.FMT or *.FMTM file.

E-mail me for details.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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"

Forgot to attach the snippet, but it seems like others have mentioned various tools that
can calculate the Wetbulb.

(have to look at this with a nonpropotional font for the columns to line up)
TRY CHICAGO 0 41.80 87.75 6 3 < - loc,year,lat,long,time-zone, solar flag
0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.98 0.98 < - monthly
clearness numbers
500.0 497.0 499.0 504.0 511.0 518.0 524.0 526.0 524.0 519.0 512.0 505.0 < - monthly
ground temps in R
1 1 1 20. 20. 29.3 10. 1 0 14 0.0019 0.081 7.0 0.0 0.0 2 17.
1 1 2 18. 18. 29.4 10. 1 0 14 0.0017 0.081 6.0 0.0 0.0 2 18.
1 1 3 17. 17. 29.4 10. 0 0 14 0.0016 0.082 6.0 0.0 0.0 2 16.
1 1 4 15. 16. 29.4 10. 0 0 14 0.0015 0.082 5.5 0.0 0.0 2 16.
1 1 5 15. 15. 29.4 10. 0 0 14 0.0015 0.082 5.0 0.0 0.0 2 15.
1 1 6 14. 14. 29.5 7. 1 0 14 0.0014 0.082 5.0 0.0 0.0 2 16.
1 1 7 13. 13. 29.5 9. 0 0 14 0.0012 0.083 4.5 0.0 0.0 2 16.
1 1 8 10. 11. 29.5 2. 0 0 14 0.0010 0.083 3.5 0.0 0.0 2 12.
1 1 9 9. 10. 29.5 0. 0 0 14 0.0009 0.083 3.5 0.0 0.0 2 11.
1 110 9. 10. 29.5 3. 0 0 13 0.0009 0.083 3.5 0.0 0.0 2 14.
1 111 10. 10. 29.6 7. 0 0 13 0.0010 0.083 3.5 0.0 0.0 2 12.
1 112 11. 12. 29.6 8. 0 0 14 0.0011 0.083 4.0 0.0 0.0 2 12.
1 113 12. 13. 29.5 7. 0 0 13 0.0011 0.083 4.5 0.0 0.0 2 13.
1 114 12. 13. 29.5 8. 0 0 13 0.0009 0.083 4.0 0.0 0.0 2 14.
1 115 12. 13. 29.5 7. 0 0 12 0.0010 0.083 4.0 0.0 0.0 2 16.
1 116 10. 12. 29.6 5. 0 0 12 0.0008 0.083 3.5 0.0 0.0 2 10.
1 117 9. 10. 29.6 5. 0 0 12 0.0008 0.083 3.0 0.0 0.0 2 11.
1 118 8. 9. 29.6 10. 0 0 12 0.0008 0.084 3.0 0.0 0.0 2 12.
1 119 9. 10. 29.6 10. 0 0 12 0.0009 0.083 3.5 0.0 0.0 2 11.
1 120 8. 9. 29.6 10. 0 0 11 0.0008 0.084 3.0 0.0 0.0 2 11.
1 121 8. 9. 29.6 10. 0 0 11 0.0008 0.084 3.0 0.0 0.0 2 13.
1 122 9. 10. 29.6 10. 0 0 11 0.0009 0.083 3.5 0.0 0.0 2 12.
1 123 10. 11. 29.6 10. 0 0 10 0.0009 0.083 3.5 0.0 0.0 2 10.
1 124 10. 11. 29.6 9. 0 0 12 0.0010 0.083 3.5 0.0 0.0 2 12.
^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
| | | | | | | | | | | | | | | | |
Mon| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
Day | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | |
Hour | | | | | | | | | | | | | |
| | | | | | | | | | | | | |
Wet Dry Atmos Cloud | | Wind Hum. Atmos Enth- Total Direct | Wind
Bulb Bulb Press Amount| | Dir Rat. Dens. alpy Solar Normal | Speed
(F) (F) (inHg) (0-10)| |(0-15) (lb/cf)(btu/lb) Rad. Solar | (knots)
| | (Btu/hr-sf) |
Rain Snow Cloud
(0,1)(0,1) Type
(0-2)

Note: Snow, rain, and wind direction are not needed; either total and direct
solar OR cloud type are required.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
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"

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:image002.jpg at 01D044B8.F4201980]

[cid:image003.jpg at 01D044B8.F4201980]

3D graphs:

[cid:image006.jpg at 01D044B8.F4201980]

?Heat Maps?:

[cid:image008.jpg at 01D044B8.F4201980]

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 01D044B6.3B232500]

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 01D044B4.AE2CFB90]

Nathan Kegel
Business Development Manager

O:

763.276.9981

M:

415.420.9314

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

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 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]

Nathan Kegel
Business Development Manager

O:

763.276.9981

M:

415.420.9314

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

?Kapil,

Speaking on behalf of the Chicago Chapter of IBPSA-USA, we are planning a webinar for later this year on weather data for energy modeling. We will make an announcement on the BLDG-SIM and IBPSA-USA listservs, as well as our LinkedIn group page: https://www.linkedin.com/groups?gid=5130922&trk=nmp_rec_act_group_photo

And a tip of the hat to Nathan Kegel--he got me thinking about this topic when he spoke to our group last summer and mentioned inconsistencies in weather data files.

Best regards,

Matt Huffman, LEED AP

Manager, Energy Services

Murphy & Miller, Inc.

www.murphymiller.com ?

To amplify Dru's recommendation to get involved with ASHRAE -- an
additional route would be to develop a weather file quality standard via
the ASHRAE consensus process. This would specify algorithmic tests applied
to a file. Then any simulation-based compliance method could specify
"shall use a weather file that conforms to ASHRAE Std XXX."

Many software developers, including me, have developed weather file QC
checkers (half-baked at best in my case). Getting everyone around one
table and agreeing on exactly what is "good enough" would be very helpful
to the industry.

The standard could be an addendum to Std 169 perhaps (with a suitable
extension of Scope) or a new Standard. TC 4.2 is the cognizant TC for Std.
169.

Chip Barnaby

Hi Bill,

You missed the Eden Prairie file which is the one that causes the most variation in EUI as it?s the most extreme. Below is a graph showing 3 different climate files for a 120,000 SF office in Minneapolis with loads of glass (it?s a LEED Gold building FWIW).

[cid:image002.jpg at 01D045F6.1A42C840]

Since there?s a lot of glass on this project, you can also see the impact of changing glass type as well. Similar colors use the same glass and vary the climate file. The TMY7 file is one that was purchased from Weather Analytics and contains the most reasonable climate data I could find at the time. I used IES VE for this analysis for a variety of reasons including system type, details of the solar model, and ability to plot data from the climate files to ensure it wasn?t going to be GIGO.

Your note on unmet hours would have a varying impact in providing insight into this depending how the systems are sized in the tool you?re using. My guess is the baseline would have unmet hours in it but the proposed would not given that most proposed buildings are sized with more extreme values than in the climate files and we input the actual equipment sizes into the proposed building as opposed to the baseline building.

[cid:image001.png at 01D045F4.6B1E77C0]

Nathan Kegel
Business Development Manager

O:

763.276.9981

M:

415.420.9314

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

I just opened up a couple of the CSV files of the TMY3 data sets and found exactly what I suspected: the TMY3 data reports the incorrect values. So the errors aren?t in the conversions from TMY3 to EPW. It?s a problem with the raw data.

[cid:image001.png at 01D0463D.EAE6AD80]

Nathan Kegel
Business Development Manager

O:

763.276.9981

M:

415.420.9314

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

Hi Bill,

I?m referencing .EPW file formats ? so perhaps the error is in there (although I doubt it ? more on that in a bit). Have you investigated the dry bulb temperatures and other psychrometrics in the files you?re using to ensure they show the same things appear in the .EPW files I?m using (at least for the files that are common between the formats)? I know there?s a significant difference in the solar models in the VE and eQuest and since solar data is something that?s used from the climate files, this also likely plays a role (like I said, the climate file affects everything). Based on the randomness and frequency of the errors, I think the raw TMY3 data was the source of the data problems ? but perhaps it?s a conversion error (or maybe even some combination of the two). I?ve looked at hundreds of these climate files doing training for projects all over the world and there?s lots of errors in them. Anyone can plot the dry bulbs from these files and see them for themselves. And the errors aren?t consistently occurring in the same time or place in the climate files ? they appear to be random. Plus, it?s not one or two files. So I assumed the raw data set was the trouble rather than some conversion. Since we?re using two different file sets in different formats, this may well be why I show a large discrepancy in EUI while your simulations show a smaller discrepancy. Which reinforces my point about ?plugging and chugging? being a dangerous game.

I had to re-size the graph so it?s hard to read ? but the results show a small flip of which glazing has the lowest EUI between climate files. My hunch is that if I were to reduce the EUI further for this building the flip would become more pronounced. Based on the responses to this thread, seems like I?m going to have to do that and make it a research paper.

Other questions I have about the work I?ve done to this point:

Is this flip ?real?? In other words, does using old data from over a decade ago actually help me understand how this building might perform in the future given the climate is rapidly changing? Is data that is that old even useful for compliance for projects in the future? If so, how far back is the data valuable to include? If not, what other options are there that might be better? Which of these climate files is the right one to use when considering future climate impacts that this building will see that will never be captured in TMY data sets? Is TMY really that valuable or are we better off using multiple AMY data sets to develop trends for use in simulation? I?m also recalling conversations about Bayesian calibration from the last couple ASHRAE conferences and wondering if there might be an application of that to creating climate files.

The larger point of the presentation (which is available through ASHRAE) was that using only EUI or weighting EUI as ?most important? to evaluate design decisions is often insufficient. For example, the results of ASHRAE 55 comfort simulations in this same building along with peak load calculations using ASHRAE Heat Balance Method showed that the lowest EUI glazing was a poor choice for satisfying occupant comfort as well as requiring the owner to purchase larger equipment than if they went with a slightly higher EUI number.

No, I wouldn?t recommend the lowest EUI glass in this particular instance even if the climate files didn?t present such a problem. I would recommend an option that balanced EUI with occupant comfort and peak loads among other considerations. ?Best choice? from an EUI perspective would have been a disaster from the perspective of first cost and thermal comfort ? not to mention visual comfort (daylight and glare). Every project is different ? but it seems that the industry trend lately has been to make decisions on simulation with EUI as the comparison metric and largely not consider other equally important metrics in building simulation.

You also noted that a more energy efficient building seems less sensitive to climate variation. Perhaps, but there are at least three things that need further exploration before we can safely arrive at that conclusion (two of which you mentioned directly already and the third you alluded to):

1. Is there a ?tipping point? of an EUI where a super-low EUI building becomes more sensitive than a merely ?average? low-energy building? Think about a more passive building ? one with natural ventilation or hybrid ventilation. I?d expect that building to be more sensitive to climate than one that?s focused solely on HVAC systems to provide comfort.

2. The sample size of comparing one building in Minneapolis to another that is in upstate NY is a sum of two.

3. Building type. If your office became a school, lab, or hospital, what happens then?

I?m on the fence about adding more standards. In theory, they make things similar for valid comparisons. In practice, they often restrict reasonable people with sound knowledge from doing things that would be good because the standard easily becomes too restrictive. It?s extremely difficult (if not impossible) to write a standard that allows for adequate flexibility while making things similar enough to be valid comparisons. To put it another way, a standard is as much of a floor as it is a ceiling.

Kind regards,

Nathan

[cid:image001.png at 01D04610.80AC4920]

Nathan Kegel
Business Development Manager

O:

763.276.9981

M:

415.420.9314

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