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HEAT PUMP GUIDE
Vibration problems and solutions for heat pumps
Without the correct guidance and mitigation strategies, heat pumps have the potential to lead to acoustic and vibration problems. Adam Fox, director at vibration isolation specialist Mason UK, highlights the potential problems and solutions that lie ahead
A
heat pump is a device that is powered by electricity and absorbs heat from the air, ground or water around a building. It works a bit like a fridge in reverse. Heat pumps are roughly three times as energy efficient as gas
boilers, so the benefits of replacing the latter are clear from a decarbonisation point of view. In 2018 there were just 27,000 heat pumps installed in the UK. For comparison,
there were 1.7 million gas boilers installed in the same time period. The government has therefore mandated that all new heating systems installed in UK homes from 2035 must be low-carbon technologies, like heat pumps or hydrogen- ready boilers. Grants are available to incentivise their uptake. There’s no doubting that heat pumps could play a massive part in helping us reach
Net Zero and that we should move toward increasing installations as soon as possible. However, one thing that is being overlooked in the discussion so far is the noise and vibration problems these devices will cause if not installed or isolated correctly.
Heat pumps and vibration
Like all mechanical plant equipment, heat pumps generate vibration and noise. Vibration is generated by the rotating or reciprocating components, compressors and fans. If transmitted into a building’s structure, this can manifest as noise disturbance. Manufacturers are improving the technology and making it quieter, but vibration remains a problem. The physics of vibration are fixed, if the nature of the rotating components and the supporting structure are not considered in the isolator selection, vibration energy will not be correctly absorbed. As a minimum, it is essential to know the floor plate span and equipment rotating speeds. Most heat pumps come with a basic isolator, like a rubber mat, to limit the impact
of vibration. If you have a heat pump in your garden next to your house, you are unlikely to be troubled by vibration. However, depending on factors such as the location of the heat pump and the structure of the building, the standard approach from the original equipment manufacturer (OEM) might not be enough. You might need a bespoke approach. It is therefore good to be aware of the potential space requirements of vibration mitigation measures before installing equipment. Instances where this might be required include situations where the heat pump is
located on the rooftop of a building. Take a look at Google Street View in London and you will see the roofs crammed full of plant equipment. This is a practical location for plant equipment and works fine from an architectural point of view, but it’s not so great for the person in the apartment below who will have to endure the vibration problems that inevitably result. In general, vibration problems are likely to result in any scenario where the fan
is located directly on top of a slab or a suspended floor system. However, no two situations are the same. Modern buildings, with their lighter weight concrete or timber structure, are more problematic than more robust buildings.
Where to get help
As each situation is different, it’s not possible to say which type of isolator is needed at an abstract level. However, there might be situations where it is necessary to mount the heat pump on high deflection rubber or spring isolators, as this can provide enough deflection to guarantee a high level of acoustic performance when isolating mechanical equipment. Excessive noise is a common symptom of incorrect choice of mounts or faulty installation of mounts. It is worth making sure you have accurate data from the manufacturer about the noise the heat pump is likely to generate. Not everything will be included in the standard datasheets provided by the manufacture, so don’t be afraid of making further enquiries. For example, a heat pump’s defrost cycle can be noisier, but the acoustic data provided by a manufacturer will likely not include noise generated by the fan ‘blow down’ after a defrost cycle. The Chartered Institution of Building Services has a detailed guidance document (CIBSE B4) that deals with vibration caused by plant equipment, which is available to download through its Knowledge Portal. If you are trying to assess how to isolate a heat pump correctly, this document is a key resource. Additional resources include CIBSE Guide AM16, which provides guidance on heat pump installation in multi-residential buildings. CIBSE Guide AM17, which was published this year, covers heat pump installation for large non-domestic buildings and has a specific section on acoustics. Air source heat pumps are becoming more commonplace, particularly on
rooftops of residential buildings. This might be welcome from an environmental point of view, but we need to raise awareness of the acoustic problems that this might cause. Thankfully, most mitigative solutions are quite straight forward, provided the appropriate guidance is consulted. For more complex cases, a vibration control specialist like Mason UK can provide advice and offer a bespoke engineered solution.
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