Weather file types

This page summarizes different data sets and file formats of weather data. Representation and storage of short-term weather data have evolved along with the computer and information revolution of the last 40 years.[1]

Data included in weather files

Weather files include hourly values of numerous weather metrics in the following categories:

• Temperature data
• Humidity data
• Wind data
• Solar data
• Cloud cover data
• Precipitation data

The specific values included in the file vary depending on the file format (see below). A list of included variables by file format can be found here in the EnergyPlus documentation.

Data set sources

The table below lists typical year weather data available on the internet. Most data sets can be downloaded from DOE2.com.

Data Set	Full Name	Derived from	Covered Locations
CTMY	Canadian TMY	Canadian Government data	12 Canadian locations
CTMY2	Canadian TMY 2	Canadian Government data	40 Canadian locations
CTZ2	California Thermal Zones 2	Supplied by the California Energy Commission in 1992	16 California zones
GBRI[5]	GRIdded Binary	Standardized by the World Meteorological Organization to store historical and forecast weather data
TMY	Typical Meteorological Year	US NOAA NCDC data sets	238 US locations
TMY2	Typical Meteorological Year 2	US DOE NREL data sets	238 US locations
TMY3	Typical Meteorological Year 3	US DOE NREL datasets	1,200 US locations
TRY	Test Reference Years	US NOAA NCDC data sets	60 US locations
IWEC[2]	International Weather for Energy Calculations	US NOAA NCDC data sets	227 locations outside the USA and Canada
WYEC	ASHRAE Weather Year for Energy Calculations	US NOAA NCDC data sets	51 US locations
WYEC2	ASHRAE Weather Year for Energy Calculations	US NOAA NCDC data sets	51 US locations

Typical Meteorological Year (TMY) weather data

A Typical meteorological year (TMY) is a collation of selected weather data for a specific location, generated from a data bank much longer than a year in duration. It is specially selected so that it presents the range of weather phenomena for the location in question, while still giving annual averages that are consistent with the long-term averages for the location in question. The latest TMY weather data sets, TMY3, are data sets of hourly values of solar radiation and meteorological elements for a 1-year period. Their intended use is for computer simulations of solar energy conversion systems and building systems to facilitate performance comparisons of different system types, configurations, and locations in the United States and its territories. Because they represent typical rather than extreme conditions, they are not suited for designing systems to meet the worst-case conditions occurring at a location. The source data are available for download from the National Solar Radiation Data Base.

File formats

Early automated data formats of weather data replicated punched card layouts formerly used for data entry by weather services. To save transcription cost, often data from only every third hour were made available. High cost, inconvenient formats, and omitted data made for difficult application to simulation. Until recently, sources files of weather data typically consist of 8,760 fixed format records (values located in specific columns of each data line). Current formats, such as TMY3 and EPW, are now more compatible with desktop spreadsheet tools. They are comma-separated and include metadata (such as site location) and column headings that make them somewhat self-documenting.

Format	Description	Applications	Download
.EPW	EnergyPlus weather files	EnergyPlus, ESP-r	EnergyPlus
.DDY	ASHRAE Design Conditions Design Day Data file		EnergyPlus
.BIN	Binary data	eQUEST, DOE-2	DOE2.com Whitebox
.STAT	Summary report	Directly read from Notepad	EnergyPlus
.CSV	Spreadsheet data for TMY3 files	Spreadsheet-based and home-coded tools	NREL
.TMY2	TMY2 data in ASCII format	TRNSYS	NREL

The actual weather variables included vary between the different formats. The EnergyPlus auxiliary programs documentation provides a detailed comparison of which variables are included in the different file formats.

Weather file format conversion

• EnergyPlus Weather Statistics and Conversions: A utility in the EnergyPlus installation package
• TMY3toTMY2: A utility developed by NREL
• eQ_WthProc: Convert EnergyPlus EPW Files into eQUEST and DOE-2 BIN Files
• DOEWth: Convert NOAA/NCDC and Other Common Format Files into eQUEST and DOE-2 BIN Files
• .xls to .bin

References

[1] C. S. Barnaby and D. B. Crawley, "Weather data for building performance simulation," in Building Performance Simulation for Design and Operation, J. L. M. Hensen and R. Lamberts, Eds., ed Oxford: Spon Press, 2011.

[2] IWEC, Building Energy Software Tools Directory, available at: http://apps1.eere.energy.gov/buildings/tools_directory/software.cfm/ID=369/pagename=alpha_list

[3] Weather Data & Weather Data Processing Utility Programs, DOE2.com, available at: http://doe2.com/index_wth.html

[4] National Solar Radiation Data Base, 1991- 2005 Update: Typical Meteorological Year 3, available at: http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/

[5] World Meteorological Organization, A GUIDE TO THE CODE FORM FM 92-IX Ext. GRIB, available at: http://www.wmo.int/pages/prog/www/WDM/Guides/Guide-binary-2.html