Energy Efficient HVAC System with Spot Cooling in an Automobile - Design and CFD Analysis

Spot, or distributed, cooling and heating is an energy efficient way of delivering comfort to an occupant in the car. This paper describes an approach to distributed cooling in the vehicle. A two passenger CFD model of an SUV cabin was developed to obtain the solar and convective thermal loads on the vehicle, characterize the interior thermal environment and accurately evaluate the fluid-thermal environment around the occupants. The present paper focuses on the design and CFD analysis of the energy efficient HVAC system with spot cooling. The CFD model was validated with wind tunnel data for its overall accuracy. A baseline system with conventional HVAC air was first analyzed at mid and high ambient conditions. The airflow and cooling delivered to the driver and the passenger was calculated. Subsequently, spot cooling was analyzed in conjunction with a much lower conventional HVAC airflow. Spot cooling was achieved by strategically placing multiple nozzles in the vehicle directed at specific body parts. Nozzle design and nozzle locations were paramount to the success of comfort delivery and achieving energy efficiency through spot cooling. CFD analysis was mostly done in steady state mode for designing the spot cooling system. Based on the results of CFD simulation and heat transfer analysis, spot cooling airflow quantities and temperatures were recommended for implementation in the vehicle and testing in the wind tunnel. Lower cooling requirement on the conventional HVAC system due to spot cooling is the primary basis for energy savings achieved in AC mode. On a pure heat transfer basis, significant improvement in cooling delivery to the occupant was achieved through a quad combination strategy of spot cooling at significantly lower airflow and cooling assist from the conventional HVAC system.