Improvement of Thermal Comfort in a Passenger Car by Localized Air Distribution

The thermal environment and air quality in a passenger car can affect driver's and passengers' health, performance and comfort. Due to spatial and temporal variation of state variables and boundary conditions in the vehicle cab, the heating, ventilating and air-conditioning (HVAC) does not have to be designed to provide a uniform environment, especially because of individual differences regarding to physiological and psychological response, clothing insulation, activity, air temperature and air movement preference, etc. Therefore the system should be able to generate preferred local environmental conditions, even on individual body part level. Comfortable thermal conditions in the vehicle are easier to achieve in cold conditions than in warm conditions, therefore this paper focuses on human thermal sensation in warm ambient. Vehicle HVAC system delivers conditioned air into the cab space, and human body is cooled by convection and sweat evaporation. The heat loss from the body will mainly depend on air velocity and temperature over the individual body part. The resulting distribution of skin temperature over the body surface will dictate human thermal sensation and thermal comfort. The aim of this paper is to provide an overview of local microclimate parameters which HVAC system should achieve in vehicle cab in warm ambient, regarding thermal sensitivity of individual parts of human body obtained from empirical data. Required conditions are prerequisite for air distribution design that would have optimized performance from the point of view of thermal comfort as well as energy consumption, in comparison with the conventional approach.