Page 34 - Climate Control News Magazine July 2021
P. 34

                 Product Focus
  Good vibrations:
How to install elastic bearings
  GETZNER WERKSTOFFE GMBH PRODUCT MANAGER, THOMAS MARTE, EXPLAINS HOW ELASTIC BEARINGS CAN RECTIFY VIBRATION PROBLEMS CAUSED BY HVAC UNITS.
Advances in the development of HVAC sys- tems result in ever lower primary airborne noise and in near-silent systems. Manufacturers al- ways refer to these values which are obtained un- der standard conditions (e.g. as per Eurovent 8/1) and in an ideal installation scenario without the use of any elastic decoupling. However, the ef- fects of the installation site on its surroundings cannot be ascertained that way.
The transmission of oscillations and vibra- tions and the emission of secondary airborne noise can be problematic.
VIBRATION ISOLATION
Installing elastic elements between the HVAC system and the foundation underneath will stop the transmission of vibrations. This is the only way to prevent the generation of unwelcome sec- ondary airborne noise.
In addition, elastic elements inside HVAC sys- tems decouple the actual excitation sources of the vibration from the rest of the machine. Adopt- ing such measures enables both the primary and the secondary airborne noise levels to be reduced.
The elastic installation elements and the
 THE VIBRATIONS CAUSED by HVAC units, especially when they are installed on a roof or inside a building, can have an adverse effect on the living and working environment in other parts of the building. Elastic bearings can rectify this problem. The use of polyurethane elements has proved to be particularly effective.
HVAC systems consist of many components that can cause unwanted vibrations. In addition to fans and pumps, the compressors in the refrig- erant circuit are the main source of vibrations in AC units.
The cause is not primarily the imbalance aris- ing from the operation of rotating compressors, as the units are generally adequately balanced by the manufacturer. Vibrations are introduced into the HVAC unit because of pressure pulsa-
tions during the compression process. Most compression principles work on the basis of one compression every rotation, which means the ex- citation often corresponds to the rotation fre- quency of the compressor.
If a HVAC unit is not decoupled, the operation- al vibrations are transmitted into the foundation via the generally rigid installation elements and connecting pipework (structure-borne noise ex- citation). Other oscillatory systems, such as ceil- ings, may generate natural vibrations, leading directly to the radiation of secondary airborne noise (Figure 1).
The resulting noise and vibrations are usually perceived as intrusive. If these noise emissions are above the legally permitted limits, commis- sioning of the air conditioning unit may not be permitted without adequate countermeasures.
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