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ABSTRACT
ASHRAE Technical Committee 4.2, Weather Information, commissioned the development of a second generation of hourly weather files for energy calculations. Called the Weather Year for Energy Calculations Version 2, or "WYEC2, " these files and their revised format represent a significant improvement over the original set of WYEC files first developed a quarter century ago.
This paper describes both the process and rationale for WYEC2 development and also describes a companion WYEC2 User's Manual and Software Toolkit, which was also commissioned by TC 4.2 to aid the ASHRAE membership in the use and application of the WYEC2 hourly weather files.
The WYEC2 hourly weather files and User's Manual and Software Toolkit are available now from ASHRAE.
BACKGROUND From 1969 through 1983, ASHRAE Technical Committee 4.2 sponsored development of hourly weather files called "Weather Year for Energy Calculations" (WYEC) for 51 U.S. and Canadian locations. These files were intended for use in the computer simulation of energy use in buildings. The original 51 WYEC files were developed by Loren Crow under ASHRAE Research Projects 100, 239, and 324 in 1970,1980, and 1983, respectively.
In 1988, TC 4.2 initiated a major revision of the WYEC files. This included the addition of the 26 Typical Meteorological Year (TMY) hourly weather files developed by the U.S. Department of Energy (DOE) to the original 51-city WYEC database and a number of significant improvements and enhancements including:
Use of a single, consistent, time convention for all records, based on the use of local standard time, and the definition of midnight as hour 24.
Correction of instances where, near sunrise or sunset, the global horizontal irradiance appearing in the TMY or WYEC Version 1 file exceeds a physically possible value based on a calculation of the corresponding extraterrestrial irradiance for that point in time. Use of improved models for estimating direct irradiance from global horizontal irradiance. Addition of 12 new fields (compared to the original WYEC format) in each record to accommodate data useful for daylighting calculations and data source identification.
Adoption of a new file format.
The work of revising and improving the WYEC database was performed at the Solar Radiation Resource Assessment Program (SRRAP) at the National Renewable Energy Laboratory (NREL), formerly the Solar Energy Research Laboratory...