Parametric Modelling and Performance Analysis of HVAC Defroster Duct Using Robust Optimization Methodology

Thermal comfort and safety of automotive passengers are the most important factors in the development of the automotive HVAC system. HVAC system is responsible for the demisting and defrosting of the vehicle’s windows and for creating/maintaining a pleasant environment inside the cabin by controlling airflow and temperature. Fog or ice which forms on the windshield is the main reason for invisibility and leads to major safety issue to the customers while driving. It has been shown that proper clear visibility for the windshield could be obtained with a better flow pattern and uniform flow distribution in the defrost mode of the HVAC system and defrost duct. Defroster performance has received significant attention from OEMs to meet the specific global performance standards of FMVSS103 and SAE J902. Therefore, defroster performance is seriously taken into consideration during the design of HVAC system and defroster duct. The HVAC unit provides hot air to the defroster duct which is blowing high velocity air to the windscreen to clear the frosting. Currently as a traditional defrost duct design process, multiple flow simulation needs to be carried out for various design configurations of defrost duct through CFD analysis until the performance targets are achieved during the design cycle and it is very time consuming. In this paper, the focus is to develop defrost duct modelling using parametrization technique and optimize the defrost duct system to meet the performance requirements through robust optimization Design for Six Sigma (DFSS) methodology to reduce the design time, cost, size and weight of the system. Parametric modelling technique is used for designing the defrost duct through design software to reduce the design time for simulation. A 3-dimensional model of a car cabin with full HVAC system was developed using Star-CCM+ to predict the performance of the system in the windshield. DFSS is a systematic process and a disciplined proactive approach to achieve robust design. Parametric modelling of defrost duct remarkably aids in reducing the manual design time for simulation by 70% and DFSS methodology helps in finding out the optimized design factors of defrost duct to meet the performance targets such as pressure drop, airflow and velocity at windshield aim points simultaneously. The optimized defrost duct design results were compared with the baseline defrost duct design results and the improvement in performance results is more than 60%. This DFSS methodology helps to achieve lower cost, smaller duct design considerably reducing the weight of the product and improving packaging space within Instrument Panel. This optimization approach can be used during early design stages of the program resulting in robust duct design and better customer satisfaction. Successful validation of the model has led to the application of this methodology in the pre-production stage of new programs during the design phase and it helps to reduce the physical testing iterations during system development and validation.