Vibration isolation for HVAC appliancesGetzner Werkstoffe

Elastic bearings with Isotop® for an efficient solution

When installing technical building equipment (TBE), which includes HVAC equipment, various standardised regulations for sound control must be observed. This applies to both primary and secondary airborne noise. The latter occurs when vibrations are introduced into the building structure and cause ceilings or walls to vibrate. To inhibit this effectively, TBE devices must be fitted with an elastic bearing. The use of our Isotop® elements, which combine metal and polyurethane, has proved particularly successful in this respect.

Secondary airborne noise

Noise caused by vibrations

A wide variety of devices, consisting of many components that can cause unwanted vibrations, are used in technical building equipment. Studies have shown that in addition to fans and pumps, compressor assemblies are the main source of unwanted vibrations. As a result of pressure pulsations from the compaction process, vibrations are introduced into the device and transmitted into the foundation via rigid installation elements and connecting pipework. These vibrations then become audible as secondary airborne noise.

Unwanted vibrations are not transmitted

The simplest way to effectively minimise the propagation of vibrations into the building structure is to use elastic installation elements, such as our Isotop® products. Installing them between technical building equipment systems and the installation foundation prevents the transmission of vibrations. The generation of unwelcome secondary airborne noise can therefore be prevented. In addition, elastic elements inside the equipment decouple the actual excitation sources of the vibration from the rest of the machine. As a result, their housings and other components do not vibrate and both primary and secondary airborne noise are reduced. Neither are disruptive vibrations propagated. This is particularly important when constructing research facilities that will house highly sensitive equipment.

Case Study

Elastic bearing of building services systems at ETH Zurich in Basel

Discover why not only the recoolers and the technical centre on the roof of the Department of Biosystems Science and Engineering were fitted with elastic bearings. The building services systems inside and the sensitive devices themselves were also decoupled.

Find out more

This is important to note in the case of elastic bearings

Polyurethane (PU) as first choice

Polyurethane-based products promise the best possible quality in the field of vibration isolation. Due to their molecular structure, they are much more suitable for vibration isolation than other elastomers. Furthermore, they contain no plasticisers, so their elastic properties remain constant for decades. With regard to the use of elastic materials at temperatures below 0°C, which occur in our latitudes in winter, the PU materials display no tendency to temperature-related stiffening.

They can be used across a temperature range from -30°C to 70°C, with short-team peaks of 90°C permitted. Under dynamic loads, PU tends to stiffen much less than other elastomers and is therefore more effective at isolating vibrations when used underneath BSE systems. In combination with metal elements, PU becomes an easy-to-install machine bearing that allow devices to be set up quickly and easily.

Vibration isolation at a glance

Physically, a device with an elastic bearing is described as a "single-mass oscillator". The dynamic stiffness c of the elastic bearing and the mass of the system m determine the natural frequency f₀:

The exciting force – for example the compressor of the refrigerant circuit – causes the system to vibrate. In order to achieve the best possible vibration isolation, the ratio of the excitation frequency to the natural frequency should be 1.41 or higher. Vibration isolation is achieved at this level. This demonstrates that precise knowledge of the natural frequency of the elastic bearing is very important if unpleasant surprises during operation of the system are to be avoided. Ideally, suppliers of elastic bearing elements will provide corresponding diagrams in product catalogues or even online selection tools.

Clearly regulated limit values for noise emissions

If noise emissions lie above the legally permitted limits, commissioning of the building services equipment may not even be permitted until adequate countermeasures are introduced. Such regulations, some of which also specifically require structure-borne sound insulation, exist at national level for individual system types. For example, ÖNORM H 5190 stipulates appropriate structure-borne noise protection for heating systems. Limit values for airborne noise are also clearly defined in other national noise protection standards: DIN 4109, ÖNORM B 8115, SIA 181 are examples for Germany, Austria, and Switzerland. There are also specifications/regulations from trade associations, of which VDI 4100, DEGA Recommendation 103 and OIB Guideline 5 are examples.