Recent developments in air-conditioning systems are leading to increased compactness and higher energy efficiency. These requirements impose more stringent operating loads on the system components, which inevitably result in an increase in the level of noise radiation. With this increased noise, control procedures are essential in the design and development stages to satisfy the customer's expectation for quiet air-conditioners. This paper reports an investigation of the noise problem encountered during the development stage of a commercial air-conditioning system. The system is of water-cooled packaged air-conditioning (PAC) type and is used in such large rooms as restaurants or canteens. High noise at 500 Hz one-third-octave band arises from the change of a more efficient compressor. Laboratory analysis has been performed to identify the sources and mechanism of the elevated noise. A simple but efficient noise control measure has been devised and tested. As a result, the level of the high noise band was significantly reduced by 6 dB(A).
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