The laboratory ventilation system is one of the most essential systems in laboratory renovation, which is closely related to the overall safety of the laboratory. Fans inevitably produce a certain level of noise during operation, which may even interfere with the work of laboratory staff. The following introduces effective methods to reduce the noise of laboratory ventilation devices.
I. Noise Reduction via Transmission Paths
Install silencers on the inlet and exhaust pipelines of centrifugal fans
When glass fiber reinforced plastic centrifugal fans are adopted for roof exhaust, a silencer shall be installed at the air suction inlet of the fan. The silencer is a noise reduction device designed to lower the noise level of laboratory exhaust emission systems. It features rainproof and anti-corrosion performance. The overall shell is made of white PP plate, and sound-absorbing materials are used inside.
Vibration damping design
(1) Large centrifugal fans generate intense vibration during operation. To prevent such vibration from affecting the surrounding environment, vibration damping measures must be implemented for the fans. The fan base shall adopt a concrete foundation, and damping spring vibration isolators shall be installed between the fan base and the concrete foundation. For economic consideration, rubber vibration damping pads can be used for small centrifugal fans for vibration reduction.
(2) Install flexible connectors at the air inlet of the fan, which can prevent the noise and vibration generated by fan operation from transmitting to laboratories on each floor through air ducts.
(3) Conduct sound insulation treatment for ventilation fans
Install sound insulation enclosures for ventilation fans; lay sound-absorbing materials on the inner lining of fan casings; arrange ventilation fans in dedicated fan rooms equipped with sound insulation doors and sound insulation windows or other sound-absorbing facilities. A separate duty room can also be set up inside the fan room as required.
II. Noise Reduction at the Sound Source of Ventilation Fans
Select appropriate fan models reasonably
For occasions with high noise control requirements, low-noise ventilation fans shall be selected. Under the same air volume and air pressure conditions, centrifugal fans with airfoil blades produce lower noise, while those with forward-curved plate blades generate higher noise.
Keep the fan operating point close to the maximum efficiency point
For fans of the same model, higher operating efficiency corresponds to lower noise. To maintain the operating condition point of the fan within the high-efficiency range, avoid adjusting the operating condition by means of valves as much as possible. If a valve has to be installed at the fan discharge end, the optimal installation position is 1 meter away from the fan outlet, which can reduce noise below 2000 Hz. The airflow at the fan inlet shall be kept uniform and stable.
Reduce the fan speed appropriately where conditions permit
The rotational noise of a fan is proportional to the 10th power of the impeller circumferential speed, and the eddy current noise is proportional to the 5th or 6th power of the impeller circumferential speed. Therefore, lowering the rotational speed can effectively reduce noise.
The noise level at the fan inlet and outlet increases with the rise of air volume and air pressure. Therefore, in the design of ventilation systems, system pressure loss shall be minimized. When the total air volume and pressure loss of the ventilation system are relatively large, the system can be divided into several independent small systems.
The airflow velocity inside pipelines should not be excessively high, so as to avoid generating regenerated noise. The airflow velocity in pipelines shall be determined in accordance with relevant specifications based on actual application requirements.
Pay attention to the transmission mode between the ventilation fan and the motor
Fans with direct connection transmission produce the lowest noise, followed by those with coupling transmission, and seamless V-belt transmission comes next. Ventilation fans shall be equipped with low-noise supporting motors.
