The impact of central air conditioning system noise on the environment and occupied spaces cannot be overlooked, making noise reduction, isolation, absorption, and vibration control critical. In engineering design and installation, these measures are essential to ensure that noise levels in occupied spaces and surrounding areas meet regulatory standards, thus providing a comfortable environment.

 

1. Sources of Noise in Central Air Conditioning Systems

 

Primary noise sources in central air conditioning systems include:

 

1. Noise and vibration from the refrigeration units, cooling towers, and auxiliary equipment like pumps and water treatment systems;

 

2. Air noise generated by airflow from supply outlets;

 

3. Noise caused by air friction and vibration as it moves within ducts;

 

4. Water flow noise within chilled water pipes and vibration-induced noise from piping;

 

5. Mechanical noise generated by equipment such as air conditioning units and fan coils due to operation and vibration;

 

6. Resonance from external noise sources interacting with the system;

 

7. Noise from ventilation and air conditioning systems, particularly from the ductwork and mechanical equipment.

 

2. Noise Control Methods for Central Air Conditioning

 

Noise control in air conditioning systems involves suppression, isolation, absorption, and vibration isolation. Noise transmission occurs through both air and solid structures. Structural noise propagation mainly involves vibrations from compressors, cooling towers, air conditioners, fan coils, and piping, while airborne noise transmission includes duct noise propagation and direct noise radiation from system terminals.

 

Key noise control strategies include:

 

- **Selecting low-noise equipment** to reduce noise from the source;

 

- **Reducing air and water flow noise** by maintaining chilled water flow rates at approximately 1.5 m/s, with branch air duct flow rates ≤ 3.5 m/s and main duct flow rates ≤ 4 m/s;

 

- **Choosing advanced, low-noise equipment**, such as low-vibration compressors for chillers, low-speed pumps (≤ 450 rpm), and high-quality, low-noise fresh air fans and fan coils, especially in public, office, or rest areas where noise can directly impact occupants.

 

3. Noise Suppression in Air Conditioning Systems

 

A silencer is a duct with sound-absorbing linings or specialized structural designs that effectively reduces noise while allowing smooth airflow. Silencers are typically installed within ventilation ducts to decrease sound pressure levels, and they are crucial in controlling noise transmission from air conditioning units to service areas. They are widely used for sound suppression in air conditioning and exhaust systems, including intake and exhaust ducts in air conditioning rooms, boiler rooms, and chiller rooms.

 

 4. Vibration Isolation Measures for Air Conditioning Equipment

 

Reducing vibration involves eliminating rigid connections between noise sources and receivers. To control equipment noise in air conditioning systems, it is essential to mitigate solid-borne noise from vibrating units and ventilation duct fan noise. Achieving the designated noise control standards in HVAC spaces depends on reducing both vibration and airborne noise, thereby ensuring compliance with established noise control guidelines.