Determining optimal local thermal environment for a vehicle passenger using thermal comfort model

Vehicle HVAC systems consume substantial energy to ensure passenger thermal comfort under summer and winter. Predicting passenger thermal comfort can contribute to optimizing the heating and cooling energy use. This study proposed local heat loss for passengers under summer and winter conditions using a thermophysiological model and comfort model. Local heat loss and thermal comfort were conducted under steady thermal environments by independently varying the air temperature, mean radiant temperature, and air velocity for each body segment. The conditions corresponding to neutral thermal sensation and maximum comfort sensation were defined as optimal heat loss and were represented by the equivalent temperature. Local optimal equivalent temperatures were compared with the Nilsson comfort zones defined in ISO 14505-2, showing that most temperatures were largely within the comfort zones, while local segment and seasonal deviations were observed. The results indicated that the required optimal heat loss differed among local body segments, with the chest and thigh able to satisfy thermal neutrality and optimal comfort under relatively large heat loss conditions. The proposed local optimal heat loss may serve as basic reference for HVAC system design, contributing to improved passenger comfort and reduced energy consumption.