The noise of a heat pump

The sound of heat pumps.jpgThe world’s climate is changing. Summers will be hotter and the future might hold more extreme weather. This means regulation of the temperature in our houses and workplaces is of increasing importance. The heat pump is one of the solutions for this, since it can cool in summers and heat in winters, and thus more sustainable than natural-gas-based central heating.

Unfortunately, the heat pump is less pleasant for the ear as it contains moving parts which cause vibrations. This means that heat pumps typically produce noise. If everybody would install a heat pump, the collective noise from all these installations would cause considerable noise pollution.

Noise pollution is not only annoying, but also dangerous. Research by the World Health Organizations shows that noise pollution is actually number two on the list of hazardous environmental factors in Europe, second only to air pollution. Exposure to noise pollution causes sleep problems and increased stress levels. Eventually, this can lead to serious conditions such as tinnitus (‘ringing in the ears’) or heart diseases. This means that noise pollution is actually a silent killer.

Noise regulations

Fortunately, the Dutch government is aware of these dangers. In April 2021, new regulations regarding noise levels of heat pumps have been effectuated. The maximum noise level, measured at the property boundary, is now limited to 40 dB(A). This noise level is comparable to chirping birds at dawn or soft office sounds.

For heat pump manufacturers, these regulations pose a real challenge. Especially when the distance to the property boundary is small, for example in terraced housing or in an apartment building. Currently most devices on the market produce about 50 dB(A) which is comparable with a washing machine during the washing cycle.

Noise control solutions in the form of sound-proofing enclosures are available, but those enclosures take up much space and can negatively impact performance of the heat pump: some models obstruct the air flow around the heat pump. Wouldn’t it be more beneficial to silence the noise at the source?

Make the noise insightful

To be able to do so, the noise must first be made insightful: which of the moving parts is the source, and via which paths does the noise travel outside? For this, we did a measurement with our acoustic camera Sorama CAM 64.

Heat pump soundsurface - where does the sound come from.jpg

Two sound images (using beamforming) for an installation consisting of two heat pumps. In each image, only one of the two heat pumps (which have different specifications) is turned on at maximum power. For the left heat pump, noise from the compressor is dominant, while for the right heat pump, the noise from the fan is dominant. Overall, the left heat pump is slightly quieter.

After identifying the behavior of the sound, it is possible to focus on the solution such as: a different compressor which produces less vibrations, rubber springs between the heat pump and the wall to prevent coupling of the vibrations into the building, improved fan controller electronics to make the timbre of the fan more pleasing, or even the use of Helmholtz resonators or meta-materials (‘acoustic crystals’) that absorb the sound at specific frequencies.

What can installation companies do?

It is very important to decouple the heat pump from the wall or roof it is mounted on. The use of good quality mounting materials, such as rubber springs and mounting beams could prevent years of noise disturbance. A small acoustic camera can be used to verify the effectivity of these components, and also to check whether the final installation meets the new noise regulations.

What can manufacturers do?

Awareness of sound design during the development cycle is vital. This ranges from selection of the components and anti-vibration design of the enclosure to post-production validation of acoustic performance. However, once the noise behavior of a product has been identified, for example using an acoustic camera, it is often easy and cost effective to achieve the first improvements. In turn, this allows for the opportunity to make quiet operation of the heat pump a unique selling point, in addition to the benefits for the living environment of the customers.

Let’s work together on creating quieter heat pumps.
Get in touch