The prime aim for sound attenuation in HVAC systems and equipment is to ensure that the acoustical environment in a given confined space is maintained. Sound is created by a source, transmitted along one or more paths, and eventually reaches a receiver. Treatments and modifications can be applied to some or all of these elements to achieve an acceptable acoustical ambiance, although it is usually the most effective and least expensive method to attenuate noise at the source.
In HVAC systems, the source of sound is mainly associated with the building, mechanical and electrical equipment. Sound sources are the components that either intrinsically generate noise as in electric motors, or when air passes through them, like dampers or diffusers. Sound receivers are generally the occupants of the building. The noise control engineers are most often constrained to modify the sound transmission paths as a means of achieving the desired sound levels in those areas of a building which are inhibited. As a preliminary approach to control noise it is well worth to examine the source of noise, the sound transmissions path and the receivers.
The noise control is achieved by means of selective sound absorbing material by absorption course. Silencers or attenuators used in HVAC installation are for treating air borne noise. For better attenuations in mid and high frequency range (0.5 kHz – 8 kHz) sound attenuators are to be in absorptive type design. The acoustic energy propagating through the silencer is effectively absorbed by the fibrous absorption material and converted into heat energy.
The selection shall be on the basis of maximum allowable pressure drop at rated flow and the silencing
criteria. Flow area throughout a silencer must be sufficient to accommodate the air flow without imposing excessive restriction. Efforts to controls noise and vibration in a wide range of mechanism and devices inevitably require the use of passive acoustical materials. It not only requires the right choice of materials but also understanding the properties of the how acoustical materials work, their installation procedure and most appropriate location to install them which in turn is vital to achieve the greatest performance.