Fans
(A) Noise Problems
Air-borne Noise
• The noise problem associated with fans may cause noise disturbance to nearby residents (see Figure 13). It mainly comes from the interaction of flow turbulence and solid surface of fan blades, and blade / fan vibration. The noise is transmitted upstream and downstream in the connecting ducts or to the atmosphere through the fan case.
Structure-borne Noise
• Vibration from an operating fan may be transmitted to the interior of the building through building structure when the fan is directly mounted on a supporting structure without proper isolation (see Figure 14). The vibration transmitted may activate the building structure to generate noise which causes noise disturbance to residents inside the building.
(B) Practical Remedies
Air-borne Noise
• Reduce the speed of fans at non-rushed hours.
• Divert duct openings away from receivers (see Figure 15).
(Noise Reduction up to 5 dB(A))
• Install a silencer at air discharge point of a fan (see Figure 16) so as to absorb noise generated from the fan.
• Fabricate a complete enclosure (see Figure 16) to contain and absorb the noise energy radiated by the source.
(Noise Reduction up to 30 dB(A))
Structure-borne Noise
• Provide an inertia block to support the fan (see Figure 17) so as to add rigidity and stability to the ventilation system, and provide vibration isolators to support the inertia block (see Figure 17), thereby isolating it from the building structure.
• Provide flexible connectors between the fan and associated ducts (see Figure 17), thereby isolating it from the ductwork.
(Noise Reduction up to 20 dB(A))
