The impact of high-precision constant temperature and humidity air conditioning system noise on the environment and the room in which it is used cannot be ignored. How to silence, soundproof, absorb and damp the air conditioning system, so that the noise in the room and the surrounding area of ​​the building can meet the standard requirements in the actual engineering planning and construction process, and meet everyone's requirements for environmental comfort.
1 Sources of noise in high-precision constant temperature and humidity air conditioning system
The main noise sources are as follows:
① Noise and vibration of the refrigeration unit, noise and vibration of the cooling tower, in addition to its auxiliary equipment water pump, water treatment, etc.;
② Air is ejected from the air outlet to form wind sound;
③ Noise generated by the movement of air in the air duct and the vibration
of the air; ④ Noise generated by the movement of refrigerated water in the refrigerated water pipe to generate water flow sound and water pipe vibration;
⑤ Mechanical noise generated by the operation of equipment such as air conditioners and fan coils and equipment vibration;
⑥ Resonance sound that may be generated by other external noise sources and the above noise sources, etc.
The noise of the air conditioning system mainly comes from the ventilation and air conditioning system.
2 High-precision constant temperature and humidity air conditioning noise control method
    Air conditioning system noise control involves silencer, sound insulation, sound absorption and vibration isolation. The transmission modes of air conditioning noise include air transmission and solid transmission. Solid sound transmission mainly includes the transmission of vibration of equipment such as refrigeration units, cooling towers, air conditioners, fan coils, and pipelines. Air sound transmission includes the noise transmission of air ducts and the direct radiation of terminal noise.
2.1 Select appropriate low-noise equipment to control noise from the sound source ① Use reasonable air conditioning methods to reduce noise; ② In order to reduce wind noise and water flow noise, the chilled water flow rate is controlled at about 1.5m/s, the branch pipe wind speed should be ≤3.5m/s, and the main air duct wind speed should be ≤4m/s. Choose appropriate wind speed and chilled water flow rate; ③ Use high-quality low-noise equipment. For the refrigeration host, a compressor with relatively small vibration should be selected. For the water pump, a low-speed pump with a speed of ≤450rpm should be selected as much as possible. The new fan equipment and fan coil are located in public areas or work areas and rest areas. Therefore, it is necessary to use products with good quality and low noise, and the noise can be directly transmitted to the crowd.
2.2 Air conditioning system silencer 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. The main purpose is to control the noise of air-conditioning equipment such as air-conditioning units transmitted through the ventilation duct to the air-conditioning service area and the air flow noise in the air duct. In noise control technology, the silencer is the most widely used noise reduction device, such as the silencer of the return air duct of the air-conditioning system, and the silencer of the inlet and outlet of the cooling tower. It is used for the silencer of the inlet and outlet of equipment rooms such as air-conditioning rooms, boiler rooms, and refrigeration rooms.
2.3 Air conditioning equipment vibration isolation method The method of attenuating 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 the air-conditioning unit 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 reach the predetermined permitted noise control standard. Equipment vibration isolation can be controlled in two ways: one is to reduce the vibration transmission power, and the other is to reduce the vibration of the vibration source. Controlling vibration at the vibration source is the most effective method, but this method is usually not possible in actual engineering because it requires redesign or modification of the vibration source equipment. Controlling vibration on the vibration transmission path. Common methods include: adding damping to the vibration transmission path, such as adding vibration isolation hoses. Its main purpose is to absorb the energy transmitted by vibration (converted into heat); adding spring isolators or rubber pads. Commonly used vibration isolation hoses include various rubber soft connections and stainless steel corrugated hoses. Rubber hoses have excellent vibration isolation and noise reduction effects, but the disadvantage is 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, it is 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.
2.4 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 operating rooms on the ground. The walls of the machine room and the underground floor should block 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. The combined wall can improve the sound insulation by leaving an air layer in the middle. When the sound wave is incident on the first layer of wall panels, the wall panels will 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 the single-layer homogeneous solid wall is mainly controlled by the mass. For every 1 doubling of the unit area mass, the sound insulation increases by 6dB. Therefore, the wall should be selected as thick as possible to improve the wall sound insulation.
2.5 Air conditioning noise control and building noise prevention plan The cooperation between building plan, air conditioning plan and noise control mainly involves the noise prevention plan in the building, the allocation of building space and building structure. From the perspective of noise control, the machine room of air conditioning equipment should be far away from the air-conditioned rooms and rooms with high noise control requirements, so as to increase the natural attenuation of noise and reduce the impact of air conditioning noise on the air-conditioned rooms. In order to reduce the airflow noise of the air duct, the construction planner should reserve as much space as possible for the air conditioning system, including the shaft and ceiling space. In the planning of air-conditioned rooms, rooms with high noise control requirements should be concentrated in the inner area of ​​the building, and auxiliary rooms or working rooms with low noise control requirements should be used as sound insulation barriers to isolate the interference of external noise. In terms of building structure, for rooms that generate noise and rooms that need to be quiet, their enclosure structures need to have sufficient sound insulation, and are usually made into thick and dense structures. If it is not handled well in the construction planning stage, it may cost a lot to compensate for it during noise control.
2.6 Reasonable construction methods The main method to reduce noise
① In order to better control the air supply noise of the fan coil, the outlet area should be increased and the wind speed should be reduced.
② Installation of the main bracket of the chilled water pipe: In order to effectively eliminate noise and vibration, a spring damper should be added to the rigid bracket. This method is often used for chilled water main pipes with large pipe diameters and slight vibrations, so that the noise of the spring damper between the floor and the rigid bracket can be effectively controlled.
③ Duct installation: The manufacture and installation of ducts must strictly comply with national standards for construction. The air harmonic and fresh air silencers are the same as the static pressure box. Excellent sound-absorbing materials are pasted inside, and excellent thermal insulation materials are used for insulation outside. Silencers are set at the elbows of the ducts, and silencers are set at the appropriate parts of the ducts. The manufacture and installation of ducts must strictly comply with national standards for construction. Silence shutters are used for the fresh air inlet, and impedance silencers are installed at the inlet and outlet of the fan. For ducts with larger cross-sectional areas, rubber vibration-damping pads should be used for duct hangers as much as possible to ensure that the ducts do not generate vibration noise. If the duct installation strength and overall rigidity are insufficient, friction and vibration noise will occur.
④ Water pipe installation: Water pipe installation must strictly comply with national standards. The hanger cannot be fixed on the floor slab, but should be fixed on the beam as much as possible. Spring vibration-damping hangers should be used for chilled water trunk pipes and cooling water pipe hangers. Casings must be used for water pipes passing through floors or walls, and they must be sealed with non-combustible materials.
⑤ Equipment installation: Fresh air and air conditioners are installed with damping spring vibration dampers, fan coils are installed with spring hooks, fan coils are connected to water pipes with hoses, fans are connected to air ducts with soft connections, and fresh air fans are connected to water pipes with soft joints. Sound-absorbing treatment is carried out in the air-conditioning room to prevent the transmission of equipment noise. For example, sound-insulating materials are used to make the enclosure structure in the air-conditioning room. In order to enhance the sound absorption effect, concave and convex three-dimensional sound-absorbing panels can also be used as the walls or ceiling panels of the room. Sound-absorbing materials are pasted in the room. The room should also reduce the number of doors and windows as much as possible to minimize the transmission of equipment noise. The doors and windows used should also be sound-absorbing windows or sound-absorbing blinds.