Any energy use calculations for planned commercial (non-residential) buildings require some set of weather data which can be considered as representative for the location of that building. For several years the Energy Calculations Committee of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has recommended the use of a full set of 8760 hours which contains real weather sequences that truly represent the long term climatic means of the several semiindependent weather parameters.

Research Project 239 covers the development of hourly data sets for 21 stations which are each identified as a "Weather Year for Energy Calculations (WYEC)". Each set includes hourly solar radiation data representing the long term mean for such observations. The locations of these 21 stations are shown in Fig. 1. A 22nd representative set of hourly weather data for Chicago, Illinois, which included solar data measured at the Argonne National Laboratories, was prepared by this same author in 1969-70 under ASHRAE Research Project RP 100.