High acoustic insertion loss facade devices that allows natural ventilation in a densely populated high-rise built environment

Abstract

Rapid population growth and economic development have led to serious noise pollution in densely populated cities. As the noise level keeps on increasing, opening windows for natural ventilation has become nearly not possible, especially in urbanized residential areas. Mechanical ventilation can be used but this may increase the energy consumption of the city. This thesis deals with the design of a facade devices of high acoustical insertion loss which can yet allow certain degree of natural ventilation across it. The study begins with an investigation of a facade device that has been believed to be an effective self-protecting building form under the exposure of traffic noise. It consists of a window and a balcony. Unfortunately, this device does not provide significant protection to the facade compared with the conventional opened window. Thus, investigation on an alternative facade device, which is modified from a partially opened double glazing window system formed by staggering the inlet and outlet window openings, named as plenum window, is then conducted. The acoustical protection, in term of insertion loss, of this facade device is investigated both experimentally and theoretically. Laboratory measurements have been carried out to evaluate the effectiveness of the device in reducing sound transmission. Further analysis has been made to examine the effects of noise source directions on the acoustical protection of the device. The results reveal that the acoustical insertion loss of the device is more sensitive to the change in device configuration when the facade device is located at "favourable" propagation condition. A series of on-site measurements have also been conducted to address the effectiveness of this device when it is applied to the real noisy built environment. An empirical formula for the prediction of the acoustical insertion loss of the facade devices has also been proposed. It is hoped that this study can provide a useful baseline on the recent status of acoustical protection of plenum window which can be applied as a noise-blocking facade device for the dwellings located close to noisy traffic roads, without forfeiting the chance of natural ventilation.