Weather Year for Energy Calculations 2

Weather Year for Energy Calculations 2 logo.

Contains typical year hourly weather data for 77 locations in the United States and Canada. The Weather Year for Energy Calculations 2 (WYEC2) format updates and replaces the earlier WYEC format weather data files and was developed specifically for use with building energy simulation programs. A manual for the WYEC2 weather files and the software toolkit for manipulating and viewing the data is provided. Create multiple reports using a software toolkit on the CD-ROM.

WYEC2 weather files consist of 8760 or 8784 identical fixed format records, one for each hour of a 365 or 366 day year. Each record is 116 characters in length.

The WYEC2 format is derived from the NOAA TD 9734 Typical Meteorological Year (TMY) format in that WYEC2 uses the same field encoding and units as TMY. However, it should be noted that all WYEC2 values are for Local Standard Time. Screen Shots


weather data, energy calculations, simulation data



Expertise Required

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

WYEC2 Software Toolkit: Targeted at users with at least moderate programming experience.


Worldwide distribution. Useful data for U.S. and Canada locations.


Researchers, Students, Engineers, and Energy Software Developers


The programs interactively access the WYEC2 data sets and have the capability of producing three types of customized output upon user's input request: (a) time series, (b) bin data and (c) summary tables.

a. Time series: A customized hourly time series may be produced by selecting one or more weather data quantities and by selecting the desired site and the beginning and end of the time series.

b. Bin Data: These consist of tables reporting the number of hourly occurrences of a selected quantity within selected bins (i.e. quantity ranges). User-configured bin data tables have two axes: the rows consist of the bins per se, the columns may be, upon user selection, either time of day or time of year. The bin table may be configured using default settings or by selecting:

  1. considered site (no default)
  2. quantity of interest (i.e. any of the 24 WYEC2 file parameters)
  3. considered time period (e.g. June 1 to July 17)
  4. number and size of the bins
  5. table's time axis (time of day/month of year)

c. Summary Tables: These tables report statistical summaries (i.e. mean, extremes and standard deviation) of user specified quantities. These tables have two axes, which sort the statistical summaries as a function of time of day and time of year. As above, the user will interactively select:

  1. considered site
  2. quantity of interest
  3. time period of interest
  4. statistics to be reported
  5. table's rows and columns


Two kinds of software "tools" are provided for output. The first is a set of executable computer programs, which have been designed to read, manipulate, and analyze WYEC2 data. These are called MOD and POLYMOD. The MOD program is a menu driven, mouse compatible user interface which creates ASCII driver files which the POLYMOD program uses to perform the actual manipulations and analyses. POLYMOD can also be driven by DOS batch files for more labor intensive operations. These two executable programs are intended to allow the novice user the ability to directly and immediately access WYEC2 data for most common purposes. The user may specify either SI or IP units for each selected quantity. Both MOD and POLYMOD may be used to produce a user-specified output product.

The output product (i.e., a time series or a table) is stored in an ASCII file. The file may then be viewed, printed, imported in a spreadsheet program, or used as input to another program. Note that, depending upon the file's intended use, its format may be customized.

The output quantities include all the meteorological, solar radiation and daylight availability data available in the WYEC2 data sets plus the following modeled quantities:

  1. Global, direct and/or diffuse irradiance impinging at normal incidence or on any tilted, unobstructed surface. The user selects the surface's azimuth and orientation as well as the ground's albedo (reflectiveness) with and without snow on the ground.
  2. Global, direct and/or diffuse illuminance at normal incidence or on any tilted surface, as above
  3. Sky luminance originating from any portion of the sky dome using the ASRC CIE model. The user selects the azimuth and zenith angle (slope) of the considered point.
  4. Relative humidity and wet bulb temperature.

MOD is a comprehensive program that invokes POLYMOD via a simple interface that lets the user interactively describe the desired output product. In fact, the MOD interface produces a product description file that may be stored for later use or executed on the spot.

The occasional or beginning user will use MOD while experienced users, becoming familiar with the coded description language, may prefer to use POLYMOD by directly typing or editing task description files. In addition POLYMOD, unlike MOD is well suited for batch processing, where a series of potentially time consuming tasks may be executed without user intervention.

The second set of software "tools" are intended specifically for energy software developers. The WYEC2 Software Toolkit is a package of functions for accessing WYEC2 weather files. These functions are written in the C programming language and are provided in source language form. Engineers and software developers who wish to retrieve WYEC2 data in their programs can take immediate advantage of the subroutine package or may use it as the starting point for enhanced capabilities of their own devising. The techniques allow correct use of WYEC2 data with a minimum of development time. They consist of computer source code written to perform selected operations with WYEC2 format files. These include source code elements to:

  1. READ WYEC2 file data into memory.
  2. Perform psychometric calculations.
  3. Perform calculations to derive the direct normal, diffuse, and total broadband irradiance falling on a surface of any orientation from WYEC2 data.
  4. Perform illuminance calculations using the latest accepted algorithms.
  5. Produce statistical summaries of WYEC2 data.

Computer Platform

Designed to run in DOS 3 or later environment on PC compatible computers. MOD will work on any 8088-or-higher-based PC with 512 kilobytes of main memory.

Programming Language



Hourly weather data has become increasingly important in HVAC practice. With the proliferation of low cost, powerful computers, full year hourly modeling of building energy use has become an extremely powerful tool for estimating and analyzing the long term average energy consumption and operating cost effect of design alternatives. The need for reliable and representative weather data for this purpose should be apparent, and has been the specific focus of WYEC2 hourly weather file development.


The use of "typical year" hourly weather files for building energy calculations is a compromise between accuracy and expedience. Running a computer model of building energy consumption against a full 20 to 40 year set of recorded hourly weather data would simply require 20 to 40 times the computer resources of running the same model against a single "representative" year of hourly data. If the single, "typical" year is properly devised, the shorter, single year calculation should yield close to the same results as averaging the longer calculation. This is the basic assumption underlying development of the WYEC2 data base, and its predecessor data files, TMY and WYEC1. Also, the use of a standard, "typical year" data set allows meaningful "average annual energy use" comparisons of building energy system designs.

Use of WYEC2 data for equipment sizing should be avoided, since the WYEC2 data set and its predecessor data sets were not specifically intended for this purpose.





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ASHRAE's Weather Year for Energy Calculations 2 is available for $230 ($190 for members of ASHRAE). Order on the web at 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