Energy standards and codes, including ASHRAE/IESStandard 90.1 and ASHRAE Standard 90.2, have used coolingdegree day (CDD) and heating degree day (HDD) values andrepresentative weather files in the development and specificationof criteria. Since the selection of the previous CDD andHDD values and representative weather files in 2002, climatedata have become available for a more recent period of recordand for a more extensive set of U.S., Canadian, and other internationallocations. The CDD and HDD values for individuallocations, and the representative weather files for those locations,have changed, in some cases markedly. Consequently, itwas necessary to update the CDD and HDD values and therepresentative weather files being used for the developmentand specification of criteria. This first paper in a two-paperseries explains how the CDD and HDD baseline values wereupdated, including the use of population to inform the determinationof the CDD and HDD baseline values. This paperprovides those values for the various climate zones, includingClimate Zone 0, newly established in ASHRAE Standard 169-2013. The second paper explains the process used to selectrepresentative weather files for the various climate zones andlists those weather files.