Experimental Investigation of Water-Cooled Centrifugal Chiller Sound Radiation

Noise and vibration were measured on a 1600-ton capacity water-cooled industrial chiller that is comprised of a centrifugal compressor mounted on top of an evaporator in a side-by-side condenser/evaporator system. The broadband noise is shaped by the radiation features of the large cylindrical condenser shell. There are tones that track with the dominant compressor induced vane passing frequencies. An evaluation of the chiller components with an acoustic camera indicates that the dominant radiation mechanism of these tones results from the coupling of the compressor-induced tones with the low order shell modes of the compressor discharge pipe, which is comprised of a horizontal section attached to the compressor discharge, a 90-degree elbow, and a vertical section connected to the condenser. The structural modes of interest are above the 1.1 kHz and 1.3 kHz coincidence frequencies of the condenser shell and compressor discharge pipe structures, respectively, resulting in efficient sound radiation. Drive mobilities and surface-to-acoustic intensity transfer functions reveal the most efficient resonant modes that couple with the compressor induced blade rate tones. Many distinct discharge pipe resonances exist within the frequency range of compressor induced vane passing tones and different sections of the discharge pipe are excited depending on the speed of the compressor and chiller operating conditions. Surface-to-acoustic intensity transfer functions are used to identify the structural components and modes responsible for radiating the most energy in critical frequency bands. The intensity transfer function of the condenser shell is shaped by its ring coincidence frequencies, while the discharge pipe resonances dominate within the compressor induced vane passing tone frequency ranges. These transfer functions agree well with those generated using infinite structure theory showing that simplified models may be used to estimate chiller noise.