Heat Pumps Today

25 "It's loud. There's a buzzing noise and I can't sleep." E cient vibration isolation reduces airborne noise by approximately 8 dB(A) Manufacturers, installers, planners or end customers of HVAC devices, are familiar with this problem. People are becoming increasingly aware of noise as a disruptive factor, but despite this, we do not want to lose out on the convenience that modern building technology has to o er. Measures that prevent vibrations in devices and therefore significantly reduce noise levels are growing in importance. Finely tuned elastic bearings with polyurethane (PU) elements make this possible and reduce noise levels by up to 8 dB(A). In HVAC equipment with a built-in compressor, the compressor plays a crucial role as a source of vibrations. The latest inverter technologies are increasing the e… ciency of devices, but they are also presenting us with new challenges when it comes to noise. Variable rotation and excitation frequencies lead to an unpleasant, low-frequency "buzzing" T E C H N I C A L www.acrjournal.uk/heat-pumps By, Dirk Wehowsky, Product Development Industry Division, Getzner Werkstoffe GmbH and Siegfried Mühlbachler, Getzner Werkstoffe GmbH (recently retired) – responsible for measurements together with Dirk Wehowsky Innovative solutions for quieter devices noise, in particular, within the partial load range. E… cient vibration isolation counteracts this by preventing the transfer of vibrations to adjacent parts of the building and thus prevents the formation of structure-borne noise. If the compressor is mounted on an elastic bearing, the excitation of housing parts is reduced, cutting the primary airborne noise. When incorporating vibration isolation components into rotating machinery it is important to carefully control the damping characteristics. Low damping can lead to resonance e ects with high vibration amplitudes and therefor may reduce the service life of the machinery. Principles of vibration isolation In practice, a slight imbalance in the compression process on components with rotating parts (such as fans or compressors) cause the device to vibrate, thereby generating primary airborne noise. These vibrations spread inside and outside the device, leading to the excitation of additional surfaces that emit noise again (secondary airborne noise). ! = 1 2 ∙ ( The speed-controlled compressors frequently used in modern air-conditioni vibrations with different excitation frequencies fe depending on the rotatio effect of an elastic bearing depends on the ratio of excitation frequency to Figure 1: From a physical point of view, the machine and elastic bearing form an oscillatory system known as a single-mass oscillator > An elastic bearing decouples a vibrating mass from its environment and thus prevents the transfer of vibrations to adjacent structures. This isolation e ect is best explained based on the single- mass oscillator model (see Figure 1). If you consider a vibrating system component with mass m, which is bedded on elastic bearings with dynamic sti ness c, this is known as an ‘oscillatory system’. This system has a natural frequency f0 at which it would vibrate briefly if excited by an impulse, such as if it was hit by a rubber hammer. This natural frequency is a very important parameter for the isolation e ect of the system and can be calculated as follows: The speed-controlled compressors frequently used in modern air-conditioning units generate vibrations with di erent excitation frequencies fe depending on Dirk Wehowsky, Product Development Industry Division, Getzner Werkstoffe GmbH Siegfried Mühlbachler, Getzner Werkstoffe GmbH (recently retired)