Condenser Fan Attenuation
Condensing units, chillers, and air conditioning units all have fans located on the top of the unit. The condenser fan pulls air over the coils that provide the cooling function for the unit. Because the fans are at a lower frequency in the sound spectrum, the noise created by these fans travels and is the predominate sound source at distance. The most effective noise control for this application is an acoustical silencer. Acoustical silencers are an assembly of solid steel outer skin and an absorption filled inner skin engineered per the airflow (cfm) and available pressure loss (w.g.) of the subject fan. The silencers are tuned to reduce the specific sound frequency of the fan and its function. Silencers offer very high sound reduction with low back pressure or pressure loss so they do not affect the functioning of the unit or system.
Typical reduction can be as high as 35 dB depending on the frequency. Per the design shown above, the attenuation will come from the 60″ centerline baffles. The overall height is 72″ due to an included 12″ transition on the inlet end of the silencer. The 12″ transition provides clearance from the fans and the bird screen covering.
Usually the condensing unit casing is not designed to support the weight of the silencers, so an attenuator support must be supplied or constructed. This structure will be designed to support the silencers over the condensing unit fans as to not damage the unit.
Condensing Unit with (6) fans – 40,000 cfm total airflow/6 = 6,670 cfm per fan
Flow Volume (cfm): 6,670
Pressure Drop (wg): 0.03
Fan Baffles are silencers or a part of an acoustical silencer. Fan Baffles are the interior section of the silencer. The silencer is typically constructed to connect to a fan or ductwork and has a solid steel exterior shell and a perforated interior shell that is filled with acoustical absorbent material. As air passes through a silencer the sound waves contact the absorbent material and the sound levels are reduced. Many times in the inside of the silencers there are absorbent filled perforated structures shaped like partitions or bullets that add addition sound reduction. These structures are called Fan Baffles.
The most effective method to reduce fan noise is with an acoustical silencer. Silencers are designed specifically for noise control and are engineered for the subject fans airflow in CFM and the fans available pressure loss in the system, so as to not restrict its airflow. Constructed of solid and perforated steel and made to be outdoors in the weather. Silencers offer potentially the highest noise reduction of any noise control equipment. Because of their construction, Silencers are typically heavy and many times require additional structural steel to support its weight when attaching to the equipment. Silencers can be custom made to almost any size and length to fit the application.
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