Research On Optimization Of Vibration And Noise Reduction For Typical Components Of Ceiling Mounted Cassette AC Units

Ceiling mounted cassette air conditioning(AC)units are the main models of central air conditioning.Because of the structure and installation characteristics,the noise level is generally high,and often accompanied by high level vibration.The rate of user complaints is also high.After analysis,the noise of the ceiling mounted cassette AC units is due to a variety of sources.The main noise sources are as following: the first is the aerodynamic noise of the centrifugal fan wheels and the air duct structure,including the rotating noise and the eddy current noise,and The second is the vibration and noise of the structures,mainly due to the vibration of the motor,the rotation of the fan blade,and The third is the cooling medium in the evaporator and other pipelines.The pulsating noise generated by high speed fluid.In view of the problems existing in the ceiling mounted cassette AC units,the author analyzed the source of the noise,together with the control scheme of vibration and noise reduction around the various parts of the Ceiling mounted cassette AC units.(1)By reducing the vibration displacement of the whole machine and adjusting the structure of the anti vibration damping rubber of the pump,the noise of the pump may be reduced by about 9dB(A)and the system noise is eliminated.(2)The oblique inserting process is adopted to improve the uniformity and performance of the evaporator.The noise the air flow produced by the cold medium throttle may be reduced by 0.5 to 3dB(A)by using a thick,large size damping rubber and a galvanized sheet box which is attached to the inside of the felt.The noise may then be eliminated.(3)Through the simulation analysis and test verification,the suitable centrifugal fan wheel is selected and the air volume is optimised for the same motor.The noise may be reduced by 1 to 3dB(A)of the fan wheel.(4)Using the combined method of computational fluid dynamics simulation and experimental verification,the model of the air channel flow field of the smallbox machine is established,and the noise may be effectively reduced by 3 ~ 7dB(A).The experiment of making the prototype by using the above scheme shows that the noise is reduced more than 5dB(A)as a whole,and the cold medium is eliminated effectively,and the purpose of reducing vibration and noise is achieved,and the rationality of the numerical model is also proved.The above research shows that by optimizing the fixed mode of motor and water pump,using damping rubber and sound absorbing cotton,the numerical analysis and experimental research on the flow field of centrifugal fan wheel and air duct,optimizing the comprehensive measures such as the suitable centrifugal fan and optimizing the air duct flow,have significant effect on eliminating vibration,cold medium noise and the noise of the whole machine.The results provide a theoretical reference for structural optimization and vibration reduction and noise reduction of similar products.