Comparison between wave theory and energy method in acoustic prediction of HVAC duct networks

Sound predictions based on the wave theory were carried out on HVAC duct networks. This requires the driving wave pressure amplitude and the characteristic reflection factor for every port of every component, and the complex coherence of the driving wave pressure and the characteristic transmission factor between every two of the ports of every component. Determination techniques of these acoustic properties in the presence of airflow, and an acoustical assembly procedure of the component acoustic properties in a large-scale duct network are newly developed. Their effectiveness was confirmed by an experiment on a small-scale duct network. Predictions by the energy base method used widely in the area were compared with those by the wave theory on HVAC duct networks for several office buildings. Consequently, it has been found that the energy base prediction easily gives about 10dB under-estimation in terms of outlet 1/3 octave band PWL.