Heat Pumps Today

Info www.getzner.com/en www.acrjournal.uk/heat-pumps 27 T E C H N I C A L Figure 4: The measurements showed that the airborne noise levels are significantly increased at certain frequencies. Considerable improvements were achieved in the three frequency ranges examined by installing Isotop MSN-DAMP Figure 5: The one-third octave band analysis showed that a significant improvement can be achieved in the low-frequency range with Isotop MSN-DAMP measurements were taken (see Figure 3 for measurement setup). It was necessary to check to what extent the (primary) airborne noise could be improved through the introduction of an optimised vibration isolation solution for the compressor. In several trials, the airborne noise level in the area surrounding the system was first determined in relation to the rotational speed of the compressor. For this purpose, the frequency converter was used to increase the frequency continuously at 10 Hz/min steps over the entire setting range from 30 Hz to 70 Hz, and airborne noise levels as well as the accelerations and vibration velocities of the housing and floor covering were measured (see figure 4). The areas of extremely high sound radiation are marked in orange. Rubber- metal bearings were converted into elastic bearings with Isotop MSN-DAMP after all the measurements had been taken. The new measurement of the sound level at a low rotational speed resulted in considerable potential for improvement of roughly 8 db(A). But an improvement can also be seen in all areas with high sound radiation. The cause of the extremely large di‘erences at low rotational speeds of the compressor lies in the fact that the isolating e‘ect of the PU bearing with a low natural frequency of 10.8 Hz comes into e‘ect considerably earlier than that of the rubber bearings. Low-frequency sources of disturbance eciently isolated In urban areas, low-frequency noise is extremely disturbing. This can only be shielded very poorly with conventional measures and is perceived by people as extremely disruptive. Using a one-third octave band analysis, it can be shown that a significant improvement in the critical low- frequency range is achieved with Isotop MSN- DAMP. At low rotational compressor speeds of 30 Hz, there is a significant reduction in sound radiation over the entire frequency spectrum; at higher rotational speeds there is a drastic improvement, especially in low- frequency ranges (see Figure 5). Quieter equipment thanks to eective vibration isolation The results presented here show that a significant reduction in primary airborne noise is possible by optimising the elastic bearings used for compressor mounting. Due to the increasingly widespread technology of load-dependent modulation of the compressor rotational speed (inverter technology), minimising the dynamic forces on the housing excited by the compressor at di‘erent rotational speeds is decisive on sound radiation. This is achieved by selecting a suitable bearing that is specially designed for the respective application. Polyurethane materials have been proven to be ideal for this purpose, providing e•cient vibration isolation and a quieter device.