[Equest-users] Tightening up the nomenclature for weather files (semi-serious rant!)

Joe Huang via Equest-users equest-users at lists.onebuilding.org
Wed Sep 21 12:26:19 PDT 2016

I've been getting numerous requests for AMY weather files that I've finally decided to 
post this rant that I composed a couple of years back suggesting that we tighten up our 
nomenclature for weather data.  Don't worry - I'm not rabid about this, but I do wish 
people would see the point I'm trying to make.


Adrian's post got me thinking about the imprecision with which weather data are often 
 From my point of view, AMY is not a very useful label, and TMY an often misused one. All 
weather data have to be "actual", so it seems a little silly to categorize them as such. 
Adding the
acronym AMY bring no new information and leads to the immediate question, "which year?", 
but once the year is
given the acronym AMY becomes superfluous. From what I can tell, AMY was coined by a 
vendor several years
back as a branding exercise to contrast to TMY,  i.e, data for a specific year, rather 
than a typical year.

But these days when giant climate models are routinely run for forecasting, backcasting 
(reanalysis), etc.,
it would be easy to generate historical time series for the past as well as future years. 
Would those then
also be considered AMY, even though they might have very little actual weather data 
(reanalysis) or
none at all (forecasting)?

The use of the term TMY suffers from different but equally bothersome problems. To me, TMY 
to either the typical year weather files (TMY, TMY2, TMY3) developed by NREL for US 
locations, or
the format of those files. However, many people have misused the term as the generic label for
a "typical year" weather file. Not only is it unfair to all the other sets of "typical 
year" files,
such as TRY, WYEC, WYEC2, IWEC, IWEC2, CWEC, CWEC2, and that's just for North America, but
it's also very confusing. Whenever someone asks for a TMY file, I have to ask, "do you mean a
TMY file from NREL, a file in the TMY format,or a "typical year" file in whatever format? 
(95% of
the time they mean the last, so why not just say a "typical year" file?)

In hopes of clarifying the situation, I propose the following strawman for labeling 
weather files
developed in the course of ASHRAE 1477-RP that produced the IWEC2 weather files:

(Country or state code)_(Station name)_(data source)_(data type).(data format)

1 Country or state code:
     ISO-3166-1 3-letter country code for international locations, 2-letter state codes 
for US/Canadian locations
2. Station name:
     At the discretion of the file creator; for official weather stations, use the ISD 
Station List;
     for others, use the location name as provided in the raw data, for synthetic model 
data, use grid coordinates.
3. Data source:
     For official stations, use WMO#; for Weather Underground, use station call name; for 
synthetic data,
     use name of computer program
4. Data type:
     For historical data, use last two digits of year; for typical year data, use typical 
year acronym.
5. Data format:
     Use commonly recognized file extension, e.g., CSV, TXT, BINM, CSV, etc.

As examples,

for a 2013 weather file for the official NSW station at Sea-Tac Airport in the (TMY3) CSV 
for a 2013 weather file for a Weather Underground station in Lynwood in the DOE-2 BINM format:
for the TMY3 typical year weather file  for Sea-Tac Airport in EPW format:
for a synthetic 2013 weather file from reanalysis data for Seattle in the EPW format 
(hypothetical example):
     WA_4735N-12225W_REANAYSIS_13.epw  or WA_4735N-12225W(SEATTLE)_REANALYSIS_13.epw

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"

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