Experimental Acoustic Testing Of Alternative Ventilation Ducts

Ducts of alternative materials to galvanised steel, are widely employed in residential buildings' mechanical ventilation systems in a bid to comply with the conservation of energy regulations in circumstances that prevent the use of natural ventilation. The noise transfer predictions of systems with alternative ducts are still being based on data for galvanised steel due to the lack of the acoustic performance data of alternative ventilation ducts tested in controlled conditions. To close this knowledge gap, alternative ventilation ducts and associated 90º bend samples were acoustically tested in controlled laboratory conditions utilising the substitution principle as outlined in BS EN ISO 7235 (2009) as well as applying a novel "zero substitution" approach. Static and dynamic tests were undertaken and sound attenuation (per meter) as a function of frequency was obtained. Preliminary results revealed the different acoustic characteristics of alternative ventilation ducts when compared to published galvanised steel ducts. The "zero substitution" approach showed good agreement with results obtained from the standardised substitution method when tested in straight duct sections. It is expected that the new acoustics knowledge on alternative ventilation ducts will influence the current design approaches and enhance confidence in noise transfer predictions resulting in cost and energy savings.