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Automotive Thermal Comfort Assessment

The figure shows an automotive simulation example (summer load case), where the sun heats up a car body with 1000W/m2. The fast increase of interior temperatures is mainly driven by short wave transmission through the wind screen. Natural convection processes on the dashboard then heat up the cabin air to 70°C after about 50 minutes. Until that point in time the simulation runs without a manikin.

Then the manikin enters the cabin. Therefore the simulation first stops and then restarts with a manikin FIALA-FE that has been added to the empty cabin. Initial temperatures of the manikin are those from thermal neutrality. All other temperatures now start in step 2 with the final values of the passive heating. The contact closes between manikin and seat, and the mean skin temperature rises from 34.4 to 35.4°C. This sudden slope makes the DTS index rise up to his maximum value of +3 which represents "hot". The PMV index takes into account the actual boundary condition parameters inside the cabin and shows a quite similar behaviour to the DTS. Finally (after 90 minutes) both indices reach neutral conditions. The mean skin temperature finally arrives at its initial value of 34.4°C again.

On the one hand the global indices show comfortable thermal conditions at the end of simulation, while on the other hand a local comfort model (here based on EN ISO 14505-2) leads to a completely different assessment. Different thermal boundary conditions applied to different regions of the human body seem to be uncomfortable in some regions. Whereas in the global comfort model too hot and too cold region neglect each other in the overall energy balance.