IWEC logo.

Contains "typical" weather data in ASCII format files, suitable for use with building energy simulation programs, for 227 locations outside the USA and Canada. The International Weather for Energy Calculation (IWEC) files are derived from up to 18 years of DATSAV3 hourly weather data originally archived at the National Climatic Data Center. The weather data is supplemented by solar radiations estimated on an hourly basis from earth-sun geometry and hourly weather elements, particularly cloud amount information.

The IWEC files contain hourly weather observations such as dry bulb temperature, dew point temperature, wind speed, and wind direction, which are derived from the DATSAV3 database of surface observations developed by the National Climatic Data Center, Asheville, NC; and hourly solar radiation and illuminance data that is calculated from earth-sun geometry and cloud cover. The development of the IWEC files followed a two step process. First, up to 18 years (1982-1999) of DATSAV3 weather data were processed. Small gaps in the data were filled, and solar radiation was computed from cloud cover and earth-sun geometry. In a second step, twelve Typical Meteorological Months were selected from the long-term time series and assembled into an IWEC file. Screen Shots


international weather, weather data, climate data, energy calculations



Expertise Required

Student or engineer of HVAC system design or building energy analysis. Low level of computer literacy required.


Worldwide distribution and use.


: International and US/Canadian engineers that provide engineering services outside North America.


Select weather data file by location name or six digit WMO#.


ASCII file. The IWEC files contain a header and 8760 hourly records. The size of the IWEC files is calculated as follows:

  • Header: 76 characters + 2 termination characters
  • Data records: 150 characters + 2 termination characters
  • Total: 1,331,598 bytes.

Computer Platform

CD-ROM is ISO-9660 compliant and should be readable in any standard CD-ROM drive.

Programming Language



Includes 227 international locations. The IWEC files are well suited to the following uses:

  • Input to building energy hourly simulation software (such as DOE-2, BLAST or EnergyPlus) to estimate the typical annual energy consumption of buildings.
  • Input to simulation software for the hourly simulation of solar energy systems.


The IWEC files are not suited to the following uses:

  • Simulation of wind energy or other renewable energy systems. The weights used for the selection of typical months (see section 1.1) are heavily biased toward dry bulb temperature and solar radiation. There is no guarantee that wind speed or other variables are typical of the conditions experienced at the site.
  • Derivation of bin data or monthly averages. These should be derived from the long-term data series (up to 18 years) from which the IWEC files were assembled, not from the IWEC files themselves. The typical month selection process guarantees that the month chosen is the 'most representative' overall, but not necessarily that monthly averages will match those calculated from longterm time series.
  • Sizing of systems. The IWEC files are 'typical years' that normally stay away from extreme conditions. Sizing of HVAC systems that require the consideration of extreme conditions cannot be done with the IWEC files.





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ASHRAE's International Weather for Energy Calculations is available for $230 ($190 for members of ASHRAE). Order on the web at www.ashrae.org/bookstore/bookstore.html. Order by phone by calling ASHRAE Customer Service at 1-800-527-4723 in the U.S. and Canada, or at (404) 636-8400 worldwide. Fax your order to (404) 321-5478. Questions about this or other ASHRAE products should be e-mailed to orders@ashrae.org.