Design quieter heat pumps

Minimize vibrations. Reduce noise.

"It's loud. It's humming. I cannot sleep." A situation probably all of us have been through - as a manufacturer, installer or end customer. This low frequency "rumbling" noise drives you crazy. And it's no surprise as we are getting more and more aware of noise and the impact on our daily lives.

"A major portion of the sound that reaches our ears - be it a chord from a guitar, the squeal from brakes or a lively discussion at the neighbours - originates from or is transmitted through vibration solid structures."

Cremer, Heckl, Petersson "Structure Borne Sound - Structural Vibrations and Sound Radiation at Audio frequencies" - Third Edition, 2005.

Different concepts of vibration isolation for quieter heat pumps

You can either decouple the entire heat pump externally, focus on the isolation of internal components (compressor) only or do both. While external decoupling reduces structure-borne noise by preventing vibrations from being transmitted into the building structure, the internal decoupling of the compressor has an additional positive effect on primary airborne noise.

External isolation reduces primarily structure-borne noise.

Isotop® spring mounts with damper core

Isotop® spring mounts with damper core

Isotop® sandwich vibration damping pads

Isotop® machine anti vibration mounts

Isotop® pressure-tension elements

Isotop® vibration damper

Internal isolation of the compressor reduces airborne and structure-borne noise.

Isotop® spring mounts with damper core

Isotop® vibration damper

Isotop® pressure-tension elements

Isotop® vibration damper

Compressor as source of noise

Compressors are the heart of every heat pump. Often "Silent Heat Pump Modes" are promoted and given sound values. The given sound values typically refer to primary airborne noise. In many cases, this "whisper quiet" mode is achieved by using inverter compressor technology. This means motor speed of the compressor is regulated according to the actual need. A wonderfully efficient way to make the most of your heat pump. Ironically, by reducing the motor speed you als change and reduce the excitation frequency of the compressor - creating even more of these unwanted, low frequency "rumbling" noises.

Five hints for quieter heat pumps

Get engineering support and input as early as possible in the product development process.
Try to get as close as possible to the main source of vibration (i.e. compressor isolation).
Select a vibration isolator that gets softer under dynamic use - not stiffer.
Choose a vibration isolator with a low natural freuency in order to efficiently decouple compressors under partial load.
Choose vibration isolators with consistent long-term performance. In other words, try to avoid materials with softeners.

Why you need Getzner's solutions for quieter heat pums

Keyword: Decarbonization

Decarbonization is a huge topic. Governments encourage the installation of heat pumps to promote efficient heating methods. This will certainly increase the number of heat pumps around us and lead to problem areas. We are all moving closer together. Several studies have shown that noise and noise reduction will become even more important in future.

This means we should take a closer look at the source of noise originating from a heat pump. Not only focusing on primary but also bringing attention to structure-borne noise in your product design and installation considerations. Therefore, protection against the generation and transmission of structure-borne noise plays an important role. In short, we need to talk about vibration isolation.

Learn more about vibration isolation

The elastic installation elements and the mounted equipment create, from a physcial point of view, an oscillatory system. This is described using the single mass oscillator model and possesses a resonance or natural frequency. The characteristic natural frequency of the system is derived from the decoupled mass m and the dynamic stiffness c of the elastic bearing.

The oscillatory system is excited by an external stimulus and starts to vibrate. The model refers to this as the exciting force. When assessing the isolating effect of a single mass oscillator, the frequency ratio between the excitation frequency of the external stimulus (f_e) and the natural frequency of the vibrating system (f₀) has to be considered.

An isolation effect only occurs in the frequency range f_e/f₀ > root 2.

In the resonancy range f_e/f₀< root 2 there is an amplification of the mechanical vibration in all cases, independent of the dampening.

PUR as best choice

Polyurethane (PUR) materials are the industry standard for high performance elastic vibration isolation of components. Compared to conventional rubber, PUR contains no plasticisers, so their elastic properties remain constant for decades. Even more important for the vibration isolation performance is the dynamic stiffness, that describes the material response under load. Machine bearings on a polyurethane basis show a significantly lower level of dynamic stiffness compared to conventional rubber. This softness results in lower natural frequencies and in an increased effectiveness of vibration isolation.

At a glance

Knowing the excitation frequency of your equipment is important to find the most suitable vibration isolation.
Using materials with exactly defined characteristics (e.g. polyurethane PUR) makes calculation easy.
PUR gets softer under dynamic use which results in a better vibration isolation.

Minimized vibrations. Reduced noise. Quieter heat pumps!

That is how to make your heat pump quieter

"Either by decoupling the entire heat pump from the outside - or even better - by isolating the compresor inside. Polyurethane materials from Getzner will provide you with the premium vibration isolation required."

Find measurement results and useful information about heat pump bearing in our whitepaper 'Make your heat pump quieter. Why it is important to focus more on the copressor vibrations and the transfer of structure-borne noise.'

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