On the Reduction of the HVAC Noise Using Active and Passive Noise Control Technologies

Abstract

Abstract In this study, an attempt to reduce the flow-induced noise generated by heating, ventilation, and air-conditioning (HVAC) systems for commercial electric vehicles using feedback active noise control with real-time filter update in frequency domain was conducted to improve the quietness of a running vehicle. In active noise control (ANC), the frequency-domain gradient descent algorithms (FDGD) to adapt the noises were studied. In the experiment, air conditioner noise was measured using a microphone placed at the driver’s left ear and referenced by a microphone at a map lamp for ANC. Results shows that in the 1/3-octave band, the sound pressure level in driver’s left ear was 7.2 dB smaller at maximum when the control was operated. The effective frequency bands were between 50 and 150 Hz. Its reduction was 4.7 dB on average. In passive noise control (PNC), the focus was on porous materials inspired by the properties of bird feathers with a closed structure, which have high sound permeability but low fluid permeability. The overall value of noise reduction at the ear position of the driver was approximately 5 dB; this was achieved by attaching this porous material to a part of the HVAC system of a commercial electric vehicle and ventilating it. Furthermore, the noise reduction measured from the velocity fields at the airflow exit of the HVAC system was caused by the change in the magnitude of the velocity fluctuation in the flow field.