Comparative Study of HVAC Noise Sources Using Acoustical Duct Method and Near Field Method

As the automotive industry is transitioning from conventional engine driven to electric battery driven, many of the vehicle aggregates are getting re-engineered and changing accordingly. Being air-conditioning manufacturer one of the aggregates that needs attention and focused effort is the Heating Ventilation and Air Conditioning system (HVAC). Acoustic comfort of electric vehicle gets impacted due to the HVAC noise in absence of engine and hence other noise sources becomes prominent which were earlier masked by the engine noise. It is important to understand the HVAC noise sources for implementing right countermeasures for masking the noise. There are three methods of noise source identification namely acoustical duct method, cocooning or lead covering method and near field method. Out of these method, acoustical duct method and near field methods are used for minor and major noise identification in this study.

The present paper describes the comparative study of HVAC noise source identification using acoustical duct method and near field method. Significant amount of works has been done in past with these two methods as these are quick and easy methods to identify the sources of noise. An automotive HVAC was used for the study and was kept in a semi-anechoic chamber with input voltage of 12.5V DC being supplied. Noise measurement was carried out from these sources namely blower motor, fresh/recirculation opening, face and defrost air outlet. A comparative study was carried out to understand the difference and to evaluate the right method to figure out these noise sources and to identify the limitations of both methods. The study shows a good trend between near field method and acoustical duct method in order to understand the prominent noise sources and take appropriate countermeasures. Hence the study is quite useful in early design stage for better taking the right design alternatives.