The Acoustic Challenges of Air Source Heat Pumps
Air source heat pumps (ASHPs) have become a key part of the decarbonisation toolkit in the response to climate change. However, while their green credentials are second to none, senior acoustic consultant Jamie Large says that without proper consideration for the acoustics, ASHPs can be a particularly noisy elephant in the room.
Businesses and organisations are acutely aware of the climate challenge we are all facing and the ambitious targets set by the UK government to reach net zero by 2050.
Heating infrastructure can be a significant contributor to a building’s overall emissions, so comprehensive low carbon energy strategies need to balance the heating network’s functionality with its carbon footprint.
Gas boilers and diesel combined heat and power (CHP) installations have traditionally done a lot of the heavy lifting when heating buildings, particularly those of a larger scale. However, with energy centres that can reach the footprint of a small school, we often find there is a real drive from clients to move away from these incredibly carbon-intensive heating methods, and towards more sustainable approaches.
We were recently appointed to deliver an extensive MEP survey of a major university’s entire estate – which included a range of structures from new builds to centuries-old Grade I and II listed properties that have wide-ranging thermal performances – and produce a decarbonisation plan.
Following our passive design approach, we highlighted the need to substantially reduce heating demand and incorporate lower carbon emission supply alternatives – with a significant drive toward ASHPs.
Making a noise
On the surface, ASHPs seem like a simple solution to the carbon problem. They can operate from renewable energy sources, or the increasingly green national grid supply, and have a significantly lower carbon footprint than traditional methods.
However, while the positives outweigh the negatives for ASHPs in most circumstances, there needs to be careful consideration around one of their biggest perceived pitfalls – noise.
ASHPs primarily generate noise through two parts – aerodynamic noise across the fans and refrigerant pump noise. The reality is that any new noise source has the potential to cause disturbance to both internal and external receptors, so tackling this challenge with a robust acoustics strategy is critical.
Not only do you risk falling foul of the local authority’s noise control teams, but also a plethora of other building design documents and standards, from general certifications such as BREEAM, to industry-specific ones from the British Council for Offices Guidance or the Building Bulletin 93 Acoustic Performance Standards for Schools.
This was particularly true for our client given their local authority had a particularly stringent noise policy. Due to the proximity of residential dwellings, a detailed assessment was required to establish project viability and determine suitable noise control strategies.
We first undertook a detailed survey to establish the existing noise environment and an initial review of the proposed air source heat pump plant and its location. This included the principles of assessing noise emissions from the proposed plant, in the context of the highly residential location, and developing a range of control measures.
Lower the volume
Our proposals for the client utilised a combination of acoustic screening and ‘off the shelf’ noise attenuation packages from the plant supplier.
The acoustic screening includes an enhanced design, which wraps around ASHPs and is comprised of a solid, dense material such as sheet metal or timber, backed with an absorbent material like polyethylene foam that is UV stable and water resistant. This solid portion of the screen provides protection from the loud fans, which are typically located on top of the ASHPs.
The lower section of the screen would comprise an acoustic louvre – which avoids a ‘cold well’ within the acoustic enclosure – and is able to attenuate sound as air passes through it. This allows greater noise screening without compromising the air flow to the ASHPs.
Mind the pitfalls
When developing a noise strategy, collaboration is crucial between the project team, client, plant suppliers and local authority. It is important to balance the decarbonisation of energy sources with suitable noise control tactics that mitigate unwanted sound without watering down the scale of the proposals.
As a result of the initial review work and collaborative feedback, we were able to advise on viability of the proposed rooftop location and steer the plant selection toward a lower noise strategy, which comprises of an increased number of ASHPs but with a reduction in output heating capacity and noise emission per unit.
More detailed assessments are currently being undertaken with the client to develop a range of potential noise control options for consideration, which will further limit noise emission to achieve the local authority’s requirements and take the project to the next stage.
By engaging with an acoustics team at an early stage, design teams can incorporate these valuable noise control measures from the start of a project, ensuring local authority requirements are met and avoiding the need to redesign for acoustics at a later stage, which can be costly as well as time-consuming. By doing this in-house and combining the skills and expertise of not just the acoustics team but also those on the engineering side, consultancies can develop solutions that work both on a practical level, and a carbon emission one while aligning with environmental noise targets.
For more examples of our acoustics work, go to our acoustics page.
If you have your own acoustic challenge, contact us to find a solution.