Knowledge!Central air conditioning system noise effective control methods

Central air-conditioning system noise on the environment and the use of the room can not be ignored, how the air-conditioning system for anechoic, acoustic insulation, sound absorption, vibration damping, in the actual engineering design and construction process, so that the use of the room and the building around the noise to meet the specification requirements to meet the requirements of people on the environmental comfort.

1. central air conditioning system noise sources
The main sources of noise are as follows:
① the noise and vibration of the refrigeration unit, cooling tower noise and vibration, in addition to its auxiliary equipment pumps, water treatment and so on;
② air from the air supply outlet to form the wind sound;
③ air in the duct flow friction vibration noise;
(4) Noise generated by the flow of chilled water in the chilled water pipe and the vibration of the water pipe;
(5) Mechanical noise generated by the operation of air conditioners and fan coils and other equipment and vibration of the equipment;
(6) The resonance sound that may be produced by other external noise sources and the above mentioned noise sources, etc..
The noise of air-conditioning system mainly comes from the ventilation and air-conditioning system.
2.central air conditioning noise control methods
Air conditioning system noise control involves muffling, sound insulation, sound absorption and vibration isolation. The propagation of air conditioning noise includes airborne sound transmission and solid sound transmission.
Solid sound propagation mainly includes refrigeration units, cooling towers, air conditioners, fan coils, piping and other equipment vibration propagation, airborne sound propagation, including air duct noise propagation and end noise direct radiation.
Choose suitable low-noise equipment to control noise from the sound source
1.The use of reasonable air-conditioning form to reduce noise;
2. To reduce wind and water noise, chilled water flow rate control at about 1.5m / s, branch duct wind speed should be ≤ 3.5m / s, the main duct wind speed should be ≤ 4m / s, the use of appropriate wind speed and chilled water flow rate;
3.The selection of advanced quality low-noise equipment, for refrigeration host should choose relatively small vibration compressor, for the pump should try to choose ≤ 450rpm speed of the low-speed pumps, fresh air equipment, fan coiler set up in the public field or office area, rest area, so it must be selected from the good quality, low-noise products, and its noise can be directly transmitted to the crowd.
2. Air conditioning system muffler
Muffler is a kind of airflow pipe with sound-absorbing lining or special structural form that can effectively reduce the noise, it can effectively reduce the noise, but also can make the airflow pass through smoothly, usually need to install muffler in the ventilation duct to reduce the noise sound pressure level.
Mainly to control the air conditioning unit and other air conditioning equipment noise through the ventilation pipe to the air conditioning service area and the airflow noise in the duct, in the noise control technology, muffler is the most widely used noise reduction equipment, air conditioning system supply and return air duct muffling, as well as cooling tower inlet and outlet muffling, etc., which is used in air conditioning room, boiler room, refrigeration plant room and other equipment room inlet and outlet muffling.
3. air-conditioning equipment vibration isolation measures
The method of attenuating vibration is to eliminate the rigid connection between the vibration source and the receiver. Control of air-conditioning system equipment noise, must control the air-conditioning unit, refrigeration equipment vibration propagation of solid sound, while reducing the fan noise propagated by the ventilation ducts and through the enclosure structure of the equipment noise. Only in this way can the air-conditioned room meet the predetermined permissible noise control standards.
Equipment vibration isolation can be controlled in two ways:
One is to reduce the vibration transfer efficiency, the second is to reduce the vibration of the vibration source, vibration control at the vibration source is the most effective way, but this method is often not possible to realize in the real project, because it requires the vibration source equipment redesign or renovation, in the vibration propagation pathway to control vibration.

Commonly used approaches include:

Increase the damping of the vibration propagation path, such as increasing the vibration isolation hose. Its purpose is mainly to absorb the vibration propagation of energy (converted to heat); increase the spring vibration isolator or rubber pads.

Currently commonly used vibration isolation hose has a variety of rubber soft connection and stainless steel corrugated hose. Rubber hose has a good vibration isolation and noise reduction effect, the disadvantage is that its use by the medium temperature, pressure limitations, while poor corrosion resistance.

Stainless steel bellows due to high temperature, high pressure and corrosive media, durable and has a good vibration isolation effect, so it is more widely used.

But it is more expensive, in the air conditioning pipeline vibration control, for low-temperature, low-pressure water pipe can be used in a variety of rubber hose, while the freezer, air compressor and high-pressure pumps need to use stainless steel bellows.

4. air-conditioning equipment sound insulation

Refrigeration host, chilled water pumps, cooling pumps and other noisy refrigeration host, cooling pumps should be set in the basement as much as possible, thus reducing the impact on the use of rooms on the ground, by the walls of the room, the underground floor of the acoustic isolation; if you can only be set up on the ground, it should be set up to the equipment room, soundproof wall.

① combined wall sound insulation

Combined wall can be left in the middle of the air layer to improve sound insulation. Sound waves incident on the first layer of wallboard, wallboard vibration, air layer can be seen as a connection between the wallboard “spring”, the vibration through the air layer to the second layer of wallboard.

② single-layer homogeneous solid wall sound insulation

The greater the mass per unit area of the wall, the better the sound insulation effect, in the main sound frequency range, single-layer homogeneous solid wall sound insulation performance is mainly controlled by the quality of the mass per unit area of each increase in mass by a factor of 6dB increase in sound insulation.

Therefore, the selection of the wall should try to choose thick, in order to improve the wall sound insulation.
5. air conditioning noise control and building noise design planning

Architectural design, air conditioning design and noise control collaboration mainly involves noise prevention planning in the building, the allocation of building space and building construction, etc. From the point of view of noise control, air conditioning equipment room should be away from the air conditioning room and the high noise control requirements of the room, so that you can increase the natural attenuation of the noise to reduce the impact of air conditioning noise on the air conditioning room.

In order to reduce the airflow noise of the air duct, the building designer should reserve as much space as possible for the air-conditioning system, including the shaft and ceiling space. In the layout of the air-conditioning rooms, the rooms with high requirements for noise control should be centrally located in the inner area of the building, and the auxiliary or office rooms with low requirements for noise control should be used as the sound insulation barrier to isolate the external noise interference.

In the building construction, for the noise room and need to quiet room, their enclosure structure need to have enough sound insulation, generally should be made into a thick and dense structure. If in the building design time is not dealt with, then in the noise control may need to spend a very high price to make up.
6.  reasonable construction methods to reduce the noise of the main measures
① in order to make the fan coiler air supply noise is better controlled, to increase the outlet area, reduce wind speed.
② chilled water main pipe stent installation: in order to make noise and vibration is effectively eliminated, should be added to the rigid stent spring damper, a large diameter and a slight vibration of the chilled water main pipeline is often used in this way, in order to make the noise in the floor and the rigid stent between the spring damper to get effective control.
③ duct installation: duct production and installation to strictly enforce the national norms for construction, air conditioning and fresh air muffler with the same static pressure box, inside the paste of high-quality sound-absorbing materials, the external use of high-quality thermal insulation material insulation, duct elbow parts set muffling elbow, the appropriate part of the duct muffler, duct production and installation should be strictly enforced to the national norms for the construction of the fresh air inlet muffling louvres in the imports and exports of fans to install impedance Muffler, for the cross-sectional area of large duct, duct hanger as far as possible using rubber damping pads, to ensure that the duct does not produce vibration noise, if the duct installation strength and overall rigidity is not enough, it will produce friction and vibration noise.
④ water pipe installation: water pipe installation should be strictly enforced national standards, hangers can not be fixed on the floor, should be fixed on the beam as far as possible, chilled water trunk pipe and cooling water pipe hangers should be used spring damping hangers, water pipe through the floor or wall must be used in the casing, and should be filled with non-combustible materials.
⑤ equipment installation: new air, air conditioning unit using damping spring damper installation, fan coiler using spring hook, fan coiler and water pipe connection using hose, fan and air duct connection using soft connection, new air machine and water pipe connection using soft joints.
Acoustic treatment in the air-conditioning plant room to prevent the outward transmission of equipment noise, such as the air-conditioning plant room using acoustic materials made of enclosure structure, in order to enhance the acoustic effect, you can also use the concave-convex shape three-dimensional acoustic panels, to do the wall or ceiling panels of the plant room, acoustic materials are pasted inside the plant room, the plant room also try to reduce the doors and windows, in order to minimize the equipment noise of the outward transmission of the use of the windows and doors should be used to absorb the acoustic windows or sound absorbing shutters.

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