NOISE TRANSMISSION & CONTROL

Noise Transmission & Control

Noise Transmission & Control

1. Introduction

Natural ventilation systems in buildings need to have inherently low airflow resistances so that the small pressure differentials utilized to drive them can achieve adequate ventilation rates. Low airflow resistance can be achieved by opening large areas of the building facade but this will have the associated problem of significantly decreasing the noise insulation of the building fabric. Attempts to treat inlet and outlet openings using conventional noise control treatments will generally cause significant increases in the airflow resistance and as such will often prove untenable. Thus natural ventilation systems, while generating minimal self- noise, will offer little resistance to the ingress of externally generated noise. For these reasons the option of natural ventilation will often be restricted to buildings in areas of low ambient noise concentration. However, with an increasing trend to exploit natural ventilation it is pertinent to look at measures which will render it a viable option in a wider range of areas including those of higher noise concentration such as urban sites.

There are examples of workable natural ventilation strategies for buildings located in areas of relatively high noise concentration. These have generally developed as a result of substantial innovation on behalf of the consulting engineer [1 and 2]. However, dedicated research into noise control treatments at natural ventilation inlets and outlets has been fairly limited, although some examples exist [3, 4, 5, 6, 7, 8, 9 and 10]. Further to this to the authors' knowledge no combined parametric study of noise control and airflow characteristics has ever been undertaken for natural ventilation system components.

This paper concentrates on existing and future techniques to reduce noise ingress into naturally ventilated buildings while minimizing airflow path resistance. The work is aimed at large non-domestic buildings of open plan design as small domestic buildings tend to be closed plan causing difficulties with airflow paths. The acoustical and airflow characteristics of simple apertures are identified and then used to devise a method of relating the acoustical and airflow performance of a ventilation aperture in a wall. Subsequently, a number of noise control strategies which might be applied to reduce the ingress of externally generated noise are reviewed and their potential performance systematically examined.

2. Advantages of natural ventilation

With a view to sustainability and economy of use it will, in many cases, be pertinent to look to renewable energy sources to provide the ventilation for new and existing buildings. Economy of use, exemplified in case study references [1, 2 and 11], becomes more important as high levels of thermal insulation in new buildings shift the major energy loads on to the running of the ventilation and air-conditioning system. Further advantages of employing a natural ventilation strategy cited in the CIBSE Applications Guide [12] include reduced construction costs, simpler and more user-manageable environmental control, reduced use of mechanical refrigeration and reduced requirement of space for services [13]. Research also suggests that use of natural ventilation has health benefits for building occupants [14, 15 and ...