Characterization of HVAC Noise and its Dynamic Interplay within the Vehicle's Environment

Vehicle HVAC noise performance is an important vehicle design validation criterion since it significantly links the brand image of a vehicle. It affects the customer’s buying decision and the business of selling vehicles because it directly affects driving comfort. Customers expect continuous improvement in HVAC noise without compromising cooling performance.The process of cascading vehicle-level acoustic performance to subsystem and component levels becomes an important factor in the vehicle NVH development process. It was found that the component-level HVAC unit without duct performance of an HVAC system measured in an anechoic chamber was at par when compared to targets, whereas the subsystem-level performance HVAC unit with duct and dashboard was on the higher side of the targets. Advanced NVH tools were used to identify the source of noise at the subsystem level. It helped to locate the source and its transfer path. A design modification done at the transfer path location gives a good improvement in HVAC noise at the subsystem level. However, when the same HVAC system was tested at the vehicle level, it showed an increase in noise as compared to the subsystem level. A detailed study was conducted to understand the acoustic behaviour of the vehicle environment. HVAC systems tested in an anechoic chamber and in a car are in a free-field and diffuse-field environment, respectively. In free-field sound propagation, there are no reflections, whereas in diffuse-field sound, it is reflected in many times that it travels in all directions with equal magnitude.Additionally, this paper encompasses a methodology aimed at attaining a less diffused field and fostering a more open environment within the vehicle, ensuring that HVAC performance measured at the subsystem level aligns with integration within the car.