Heat Pumps Today

26 February | March 2023 T E C H N I C A L the rotational speed. The isolation e ect of an elastic bearing depends on the ratio of excitation frequency to natural frequency: ! = 1 2 ∙ ( pressors frequently used in modern air-conditioning units generate excitation frequencies fe depending on the rotational speed. The isolation g depends on the ratio of excitation frequency to natural frequency: h = " ! y matches the natural frequency, this leads to resonance (see Figure 2). ided at all costs, as this will likely also cause damage to the device due to udes. An isolation effect, i.e., a reduction in the forces transmitted, is to be cy ratio of �=�2. In practice, it should be ensured that the natural frequency ates to only roughly 1/3 to 1/5 of the dominant excitation frequency of the eal degree of elasticity the vibration of surfaces and the emission of secondary airborne noise is ecast models have also gained a foothold in corresponding standards. t a reduction in vibrations in the device also leads to a reduction in emission. Elastic components made from polyurethane are ideal for ing demand for the reduction of vibration-induced sound radiation. Their ties are advantageous compared to rubber-metal elements. nts are particularly long-lasting and resistant to hydrolysis. For example, uperstructures where consistent material behaviour is required over loads and changing environmental conditions. PU materials gain the y from their microcellular foam structure. This means that their volume is tion of pressure, and they require neither softeners nor complex geometric timum degree of elasticity for vibration isolation. Polyurethane materials of d depending on the weight class. stic bearing is dimensioned in such a way that the natural frequency of the pressor and bearing is ideally at roughly 10 Hz, so that degrees of isolation verter frequencies of just 20 Hz. This is a major advantage if the sound ed at night, in particular, during partial-load operation. e <Insert Figure 3 plus caption - Figure 3: Measurement setup for noise level> l statements, measurements were taken (see Figure 3 for measurement o check to what extent the (primary) airborne noise could be improved of an optimised vibration isolation solution for the compressor. In several level in the area surrounding the system was first determined in relation to e compressor. For this purpose, the frequency converter was used to ntinuously at 10 Hz/min steps over the entire setting range from 30 Hz to levels as well as the accelerations and vibration velocities of the housing If the excitation frequency matches the natural frequency, this leads to resonance (see Figure 2). This situation is to be avoided at all costs, as this will l kely also caus damage to th device due to the high vibration amplitudes. An isolation e ect, i.e., a reduction in the forces transmitted, is to be expected from a frequency ratio of η =√2. In practice, it should be ensured that the natural frequency of the bearing always equates to only roughly 1/3 to 1/5 of the dominant excitation frequency of the device. PU elements have the ideal degree of elasticity The relationship between the vibration of surfaces and the emission of secondary irbor e noise is frequently noted and forecast models have also gained a foothold in corresponding standards. Measurements show that a reduction in vibrations in the device also leads to a reduction in (primary) airborne no se emiss on. Elastic comp ents made from polyurethane are ideal for meeting the ever-increasing demand for the reduction of vibration-induced sound radiation. Their excellent dynamic properties are advantageo s compared to rubber-metal elements. Polyurethane (PU) elements are particularly long-lasting and resistant to hydrolysis. For example, they are used in railway superstructures where consistent material behaviour is required over decades, even under high loads and changing environmental conditions. PU materials gain the majo ty of their elasticity from their microcellular foam structure. This means that their volume is reduced with the application of pressure, and they require neither softeners nor complex geometric shapes to achieve the optimum degree of elasticity for vibration isolation. Polyurethane materials of varying densities are used depending on the weight class. On HVAC devices, the elastic bearing is dimensioned in such a way that the natural frequency of the system consisting of compressor and bearing is ideally at roughly 10 Hz, so that degrees of isolation of ~60% are possible at inverter frequencies of just 20 Hz. This is a major advantage if the sound radiation is to be minimised at night, in particular, during partial-load operation. To confirm the theoretical statements, Figure 2: The isolating effect occurs if the ratio of excitation frequency to natural frequency is greater than √2 Figure 3: Measur ment setup for determining the airborne noise level