An innovative approach for facades with optimised noise protection and natural ventilation
Starting point / motivation
The main aim of this research was to advance the state of the art in the engineering double-leaf building facades that facilitate natural ventilation while providing sufficient sound insulation. Building envelopes that would allow natural ventilation without compromising the acoustical performance would be highly critical in view of energy efficiency of buildings located in urban settings and noise-affected locations.
Realization of natural (window) ventilation is in some instances difficult not only due to climatic factors but primarily because of noise issues (especially traffic noise). The proposed research focused on the latter impediment.
Noise from outside of a building (particularly traffic noise) travels unhindered through open windows and can interfere with occupants' requirements (e.g. sleep and regeneration in residential habitat, concentration and communication in office spaces). One must thus address acoustical issues, while pursuing the - as such desirable - natural ventilation solutions for buildings.
Contents and goals
Based on previous research and prior experiences in building acoustics, a set of candidate variables of a generic double-leaf construction were considered that would affect the sound insulation performance of double-leaf building elements with openings for natural ventilation. These included the size - and to a certain extent, the shape - of the openings in each layer, the relative positions of the openings (expressed, for instance, in terms of displacement or view factors), and the presence of acoustical absorption in the interstitial cavity between the two layers of the construction.
To experimentally assess the influence of these variables under reliably controlled conditions, a modular and flexible model instance of a double-leaf construction was designed, assembled, and installed between two adjacent reverberant chambers of our acoustics laboratory.
The constitutive elements of both layers of this modular construction can be removed to emulate facade openings. A comprehensive sequence of parametric configurations of these openings was constructed.
These configurations were subjected to systematic sound transmission measurements. Thereby, various values of the aforementioned candidate variables could be realized and examined. The results of the comprehensive measurements was structured in terms of both frequency-dependent and weighted sound transmission indices.
The results were analyzed towards developing empirically-based statistical models for the prediction of the sound insulation properties of double-leaf constructions with openings for natural ventilation. Likewise, the empirical results were deployed to examine the applicability of computational room acoustic applications for acoustical modeling of such double-leaf elements.
Department of Building Physics and Building Ecology
TU-Vienna, Univ. Prof. Dr. A. Mahdavi