International Weather or Energy Calculations (IWEC) weather files were developed under ASHRAE research project RP-1015. These files can be used as input to building energy simulation software and are available for 227 locations outside the United States and Canada. DATSAV3 data from the National Climatic Data Center (NCDC) were used as the basis of the files; a large part of the project was devoted to calculating solar radiation from cloud cover, using a model calibrated on a station-by-station basis with measured solar radiation data archived at the World Radiation Data Center (WRDC). This paper details the algorithms used to develop the files: the model used to calculate solar radiation from cloud cover, the interpolation procedures used to fill gaps in the data, and the methods used to select representative months. A companion paper (Part II:Production)deals with issues related to model optimization, site selection, evaluation of model performance, and comparison of solar radiation in the files with published long-term averages.

Units: SI