A Study of an Integrated HVAC-Vehicle Model for Automotive Vehicles

The objective of this work is to develop an integrated HVAC-VEHICLE model for climate control studies. A published lumped parameter based HVAC model has been used as the framework for the HVAC modeling with some modifications to realize the climate control and to improve the robustness of the model. R134a (1,1,2,2-Tetrafluoroethane) has been used as the refrigerant fluid in this study. The stand-alone HVAC model has been compared qualitatively with the experimental works available in the literature. The experimental trends of the thermodynamic and performance related parameters of HVAC are reasonably well captured by the HVAC model. In particular, Coefficient of Performance (CoP) was found to decrease with increase in compressor speed and increase in ambient temperature but increase with increase in evaporator blower mass flow rate. On the other hand, compressor power was found to increase with increase in the compressor speed and increase in the ambient temperature but decrease with increase in the evaporator blower mass flow rate. The employed HVAC model was found to be insensitive to refrigerant mass and condenser fan mass flow rate variations. A simplified vehicle model of the rectilinear motion of the vehicle has been built and integrated with the HVAC model. The entire model was built using MATLAB/SIMULINK. The integrated model is capable of computing the fuel economy with and without HVAC. Parametric studies of the integrated model are performed. For the parameters used, the vehicle was found to be consuming nearly 25% more fuel when HVAC was operating. Finally, conclusions and recommendations for further studies are presented.