This paper provides an overview of recent refinements tothe radiant time series method (RTSM) as part of ASHRAEResearch Project RP-1616. These refinements include replacingthe ASHRAE three-parameter (A, B, C) clear-sky modelwith anewglobally applicable model, introducingnewdesigndaytemperature profiles, updating the weather data, andimproving the treatment of interior shading in the fenestrationmodel. In addition, the sensitivity of the calculated coolingloads to the weather-related refinements is investigated with aparametric study.