UBC Theses and Dissertations
Investigation of the acoustical and airflow performance of interior natural ventilation openings Bibby, Chris
Natural ventilation is being adopted in building design to reduce building operational energy usage and increasing building occupant comfort. Unfortunately, ventilation openings in interior partitions of naturally ventilated buildings also reduce the noise isolation across the partition, resulting in a poor acoustical environment – for example, insufficient privacy and excessive annoyance. This work moves toward an understanding of, and design methodology for, interior natural ventilation opening silencers which will allow design optimization for both airflow and noise isolation. An optimization parameter is defined in terms of both airflow and acoustical transmission performance. Using a simple diffuse-field model, factors that affect acoustical privacy between two spaces separated by a partition are investigated, showing the relationship between ventilation opening acoustical performance and acoustical privacy. In order to maintain the privacy provided by a partition it is shown that the sound energy transmitted through the ventilation opening should not exceed 10% of that transmitted through the remainder of the partition. Ventilation openings and ventilation opening silencers in naturally ventilated buildings are studied experimentally to gain an understanding of current design practices. Airflow and acoustical performance of 19 ventilation opening and ventilation opening silencer types were measured in a purpose-built lab facility. Cross talk silencers are shown to have the highest performance of all silencer types tested. Lining the ceiling above a slot ventilation opening was measured to increase the transmission loss by 3 to 6 dB. A novel “acoustical baffle” silencer type is proposed for application when the silencer length is limited; measured performance is superior to that of an acoustical louver. Numerical acoustical and airflow modeling techniques are developed for ventilation opening silencer performance optimization and analysis work. Airflow modeling indicates that the errors associated with using a high-Reynolds number discharge coefficient are not of practical concern. By way of result synthesis, best-practice guidelines for silencer design in the context of speech privacy are provided. Select conclusions for cross talk silencers are: flow-path shape does not affect acoustical performance; straight sections before the silencer termination increase airflow performance by up to 30%; elbows in the silencer flow path reduce overall silencer performance.
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