A silencer is an airflow duct with a sound-absorbing lining or a special structure that can effectively reduce noise. It can not only effectively reduce noise, but also allow airflow to pass smoothly. It is usually necessary to install a silencer in the ventilation duct to reduce the noise sound pressure level.

 

It is mainly to control the noise of air-conditioning equipment such as air-conditioning units from being transmitted to the air-conditioning service area and the airflow noise in the air duct through the ventilation duct. In noise control technology, silencers are the most widely used noise reduction equipment, such as silencers for the return air ducts of air-conditioning systems and silencers for the inlet and outlet of cooling towers. It is used for silencers for the inlet and outlet of equipment rooms such as air-conditioning rooms, boiler rooms, and refrigeration rooms.

 

4.Vibration isolation measures for air conditioning equipment

 

The way to attenuate vibration is to eliminate the rigid connection between the vibration source and the receiver. To control the noise of air-conditioning system equipment, it is necessary to control the solid sound transmitted by the vibration of air-conditioning units and refrigeration equipment, and at the same time reduce the fan noise transmitted by the ventilation duct and the equipment noise through the enclosure structure. Only in this way can the air-conditioned room meet the predetermined allowable noise control standards.

 

Equipment vibration isolation can be controlled in two ways: one is to reduce the vibration transmission efficiency, and the other is to reduce the vibration of the vibration source. Controlling vibration at the vibration source is the most effective way, but this method is often not possible in real engineering because it requires redesigning or modifying the vibration source equipment to control vibration on the vibration propagation path.

 

Common methods include: increasing the damping of the vibration propagation path, such as adding vibration isolation hoses. Its main purpose is to absorb the energy of vibration propagation (converted into heat); adding spring vibration isolators or rubber pads. Currently, commonly used vibration isolation hoses include various rubber soft connections and stainless steel corrugated hoses.

 

Rubber hoses have good vibration isolation and noise reduction effects, but their disadvantages are that their use is limited by the temperature and pressure of the medium, and their corrosion resistance is poor.

 

Stainless steel bellows are widely used because they can withstand high temperature, high pressure and corrosive media, are durable and have good vibration isolation effects. However, they are expensive. In the vibration isolation control of air-conditioning pipes, various rubber hoses can be used for low-temperature and low-pressure water pipes, while stainless steel bellows are required for refrigerators, air compressors and high-pressure water pumps.

 

5.Sound insulation of air conditioning equipment

 

Refrigeration main units, chilled water pumps, cooling water pumps and other noisy refrigeration main units and cooling water pumps should be installed in the basement as much as possible to reduce the impact on the rooms on the ground. The walls of the machine room and the underground floor should be used to isolate the sound waves. If it can only be installed on the ground, an equipment room and soundproof walls should be set up.

 

① Combined wall sound insulation. Combined walls can improve the sound insulation by leaving an air layer in the middle. When sound waves are incident on the first layer of wall panels, the wall panels vibrate. The air layer can be regarded as a "spring" connecting the wall panels. This vibration is transmitted to the second layer of wall panels through the air layer.

 

② Single-layer homogeneous solid wall sound insulation. The larger the unit area mass of the wall, the better the sound insulation effect. In the main sound frequency range, the sound insulation performance of a single-layer homogeneous solid wall is mainly controlled by quality. For every 1 doubling of the unit area mass, the sound insulation increases by 6dB. Therefore, the choice of walls should be as thick as possible to improve the sound insulation of the wall.