Approach for the Transient Thermal Modeling of a Vehicle Cabin

In the thermal system of a vehicle cabin, the heat transfer modes of convection, conduction and radiation all have a large impact on the thermal behavior. When trying to develop a model with reduced complexity compared to 3D CFD, it becomes essential to represent not only the physics of the solid parts (conduction), but also heat sources on surfaces (radiation) and effects resulting from the fluid flow inside the cabin (convection). The latter are summed up in the presented approach in the parameters ‘Heat Transfer Coefficients’ (HTC) on the inside surfaces, ‘weighting factors’ for the energy distribution into zones which allow a zonal resolution of air temperatures and the ‘average cabin air temperature’. With a load case specific transient modeling of these parameters a fast calculating cabin model is provided, which considers all the temperature relevant flow phenomena without resolving the fluid dynamics explicitly. From the results of transient thermal 3D CFD simulations of the load case ‘Cooldown’ a model for the respective parameters is derived by means of a Linear Time-Invariant System (LTI) approach. These parameters then serve as transient boundary conditions in an independently running, predictive thermal cabin model. The quality of the presented model is evaluated by comparison of the predicted temperatures of the model (i.e. surface and air temperatures) with the corresponding values from a transient 3D CFD test case.