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Glass &Windows Selection

Fan Noise & Isolation

Fan noise is a function of the fan design, volume flow rate Q, total pressure pt, and efficiency ht . After a decision has been made regarding the proper type of fan for a given application (keeping in mind the system effects), the best size selection of that fan must be based on efficiency, because the most efficient operating range for a specific line of fans is normally the quietest. Low outlet velocity does not necessarily ensure quiet operation, so selections made on this basis alone are not appropriate. Also, noise comparisons of different types of fans, or fans offered by different manufacturers,
made on the basis of rotational or tip speed are not valid. The only valid basis for comparison are the actual sound power levels generated by the different types of fans when they are all producing the required volume flow rate and total pressure.

The data are reported by fan manufacturers as sound power levels in eight octave bands. These levels are determined by using a reverberant room for the test facility and comparing the noise generated by the fan to the noise generated by a noise source of known sound power. The measuring technique is described in AMCA Standard 300, Reverberant Room Method for Sound Testing of Fans. ASHRAE Standard 68/AMCA Standard 330, Laboratory Method of Testing In-Duct Sound Power Measurement Procedure for Fans, describes an alternate test method to determine the sound power a duct fan radiates into a supply and/or return duct terminated by an anechoic chamber. These standards do not fully evaluate the pure tones generated by some fans; these tones can be quite objectionable when they are radiated into occupied spaces. On critical installations, special allowance should be made by providing extra sound attenuation in the octave band containing the tone.


Direction of rotation is determined from the drive side of the fan.
On single-inlet centrifugal fans, the drive side is usually considered
the side opposite the fan inlet. AMCA has published standard
nomenclature to define positions.

Fan Isolation

In air-conditioning systems, ducts should be connected to fan outlets and inlets with unpainted canvas or other flexible material. Access should be provided in the connections for periodic removal of any accumulations tending to unbalance the rotor. When operating against high resistance or when noise level requirements are low, it is preferable to locate the fan in a room removed from occupied areas or in a room acoustically treated to prevent sound transmission. The lighter building construction that is common today makes it desirable to mount fans and driving motors on resilient bases designed to prevent transmission of vibration through floors to the building structure. Conduits, pipes, and other rigid members should not be attached to fans. Noise that results from obstructions, abrupt turns, grilles, and other items not connected with the fan may be present.

Fan Control




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