Noise treatment of central air conditioning end equipment

Analysis of the mechanism of air handler noise generation
1. The mechanical noise of the air conditioning fan
Generally speaking, most of the air conditioner fans adopt double inlet type, and the shaft of the fan and the impeller and other parts on the shaft are heavier, and the manufacturers have gone through more strict balance (static balance and dynamic balance) test before putting them into use. But the fan speed is generally high, after a period of operation, will produce a variety of mechanical noise.
(1) The impeller wears unevenly or the wind pressure causes the deformation of the parts, so that the whole rotor is not balanced and the noise.
(2) The noise generated by the bearings after operation due to wear and tear, and shaft mutual.
(3) Noise due to poor installation or loose connection of each part.
(4) The impeller rotates at high speed to produce vibration, resulting in the noise generated by the resonance of a part of the body.
2. Motor noise
In the entire ventilation system of air conditioning, the motor is one of the important components, but the general manufacturers of fans are used by the motor manufacturers to provide the motor, fan manufacturers generally do not make the motor internal processing, but the motor noise of a wide range, briefly described below.
(1) the bearing itself is not accurate enough and the bearing noise;
(2) electromagnetic noise excited by radial alternating electromagnetic force;
(3) commutator rectifier carbon brush friction noise generated by the conductive ring.
(4) Strike noise of the rectifier;
(5) due to the vibration of some parts to make their own inherent frequency and excitation frequency resonance, the formation of a very strong narrow band noise;
(6) axial crosstalk noise generated by rotor imbalance or axial component of electromagnetic force;
(7) aerodynamic noise generated by the cooling fan of the motor.[/vc_column_text]

The control of fan noise
1. Control of mechanical noise
Normal operation of the air conditioning unit in the fan system, mechanical noise relative to gas dynamic noise and motor noise, relatively small, in the mixed noise, mechanical noise can be negligible.
2 motor noise control
In the design and manufacture or selection of motor to focus on reducing motor noise; in the use of motor to focus on the control of motor noise.
(1) blade sound and flute sound control, blade unbalance or blade and guide wind circle gap is too small, just correct or adjust; If the blade and duct ditch resonance flute sound, must change the number of blades, the blade is best to use the prime number of pieces.
(2) appropriate to reduce the diameter of the fan, a reasonable choice of fan size parameters, can reduce the fan vortex noise.
(3) electromagnetic noise in the low frequency band and motor stiffness, high frequency band and slot with the relevant. If the grid frequency of low-frequency electromagnetic sound, the motor stator eccentricity, air gap is not uniform, should be repaired and improved; if the load appears twice the slip frequency noise, the rotor has defects, should be updated or repaired.
(4) the use of anechoic isolation measures to anechoic mainly used in small motors, mainly to isolate the sound commonly used in large motors. One should pay attention to the heat dissipation of the motor, the second should pay attention to the vibration isolation and vibration damping of the anechoic enclosure.
Third, the air handling unit noise control path
1. Reduce the resistance of the air system
The size of the air system resistance directly affects the air volume of the fan, which is easy to be ignored in the design of the air conditioner, because the air volume of the fan is not only related to the characteristic curve of the fan, but also with the characteristic curve of the air duct, if the air duct resistance becomes large, the air pressure of the fan is also increased, but the air volume is then decreased. So reduce the resistance of each section of the air conditioner air path, to improve the air volume, reduce noise is very necessary.
2. Other methods of reducing noise
① Improve the dynamic balance accuracy of the fan and spindle.
② Cover the air duct system with a layer of sound insulation material.
③ Increase the cross-sectional area of air inlet to reduce the wind speed.
④ Installing a silenced static pressure box on the inlet and outlet air ducts of the unit, etc.

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