By developing a novel vehicle thermal comfort model, Delphi Harrison Thermal Systems has been able to evaluate the performance of many more heating / ventilation / air conditioning (HVAC) system designs than was ever possible in the past. By using this model a more thorough investigation of the design parameters space brings the final design closer to optimum. Traditionally, HVAC design alternatives have been evaluated by testing prototypes in wind tunnels, a very time-consuming and expensive process. Though automotive OEMs and suppliers have developed many cabin climate prediction models over the last several years, Delphi’s new virtual thermal comfort engineering model goes considerably farther than it’s predecessors by integrating a 16-zone human physiology model that predicts human comfort by calculating skin temperatures. The model uses computational fluid dynamics (CFD) to predict local thermal comfort as a function of air temperature, surrounding surface temperatures, air velocity, humidity, direct solar flux, as well as the level of activity and clothing type of each individual. This technology is currently being used to design and optimize HVAC systems and in the future its use is to be extended for the development of control algorithms and the calibration of electronic controls.