Personal insights: acoustic design for air source heat pumps

Who am I?

In 2019, I first became aware of the field of acoustics; although it was a small module as part of the Music Technology degree I was studying, it rapidly took my interest. Before I knew it, it became the topic of my dissertation, and I moved on to study the field for my master's degree. What intrigued me was how software could be used to simulate acoustics in 3D scenarios, and how this data can be presented in a way that anyone could understand, regardless of how much they would know about the discipline.

Fast forward to the present day, and the importance of acoustics and design, and what the implications can be when it is badly designed, have become more apparent to me.

Why are acoustics important?

Speaking broadly, as I could write a dissertation on any of the fields within the discipline, acoustics is crucial in design. Having worked in both the Birmingham and London offices at Cundall, I have gained experience in a wide variety of projects across different sectors. Whether I am helping design the acoustics of classrooms to ensure clear communication or advising on glazing requirements for new residential buildings to protect residents from environmental noise, there are numerous examples of the importance of good acoustic design. This plays into the personal aspects of why I enjoy my job; the work I carry out helps improve people’s audible experiences of the world.

The adverse health impacts of noise pollution are also well-documented by The World Health Organization. Working in acoustics involves addressing various challenges and finding suitable solutions. There are often multiple approaches to the same issue, which can be contentious within the field. However, these challenges are less significant when acoustic design is integrated at an early stage in the project’s timeline. A common challenge I have encountered is implementing effective acoustic design for air source heat pumps (ASHPs).

Acoustics and air source heat pumps

ASHPs are known for their energy efficiency and environmental benefits, making them increasingly prevalent on rooftops and back gardens in central London and its suburbs. However, they also tend to generate a substantial amount of noise. Given the high density of London, where noise-sensitive receptors are common, numerous potential issues must be considered.

The primary objective when introducing new plant items such as ASHPs, is to avoid disrupting the existing noise climate. Potential problems could arise from any of the following:

• noise produced from components within the unit itself such as the fans, compressors and refrigerant pumps
• hours of operation
• location of the plant
• defrost cycles
• maintenance
• space around the plant to allow for any necessary attenuation.

When brought in at an early stage of the design, acousticians can have more influence over the above points. For example, we could identify if proposed ASHPs are too noisy from the offset, or if the location of the units is too close to nearby noise sensitive receptors. These fundamental factors are easier to discuss when the design is more flexible to change.

When brought into the process at a later stage, it might be that many other factors have now been designed around an ASHP which are fixed and therefore much harder to create solutions for.

Consider the following scenario: at RIBA Stage 4 (detailed design) of a project, the location of an ASHP has been finalised based on its integration with the initial design of the project. However, it is subsequently discovered that the ASHP generates significant noise and is located near to a residential development where existing background noise levels are very low. In this situation, the influence of an acoustician is significantly diminished. If there are no viable mitigation options to sufficiently reduce the noise from the ASHP, then the challenging discussion regarding redesigns must take place. This scenario ultimately incurs greater time and financial costs. Additionally, designs at this stage often become ‘romanticised’ and much more difficult to alter after substantial time and effort have been invested.

The graphic below illustrates the benefit of bringing an acoustician in early to a project - they have more influence to positively steer the design towards a more efficient plant noise mitigation strategy, reducing the risk of costly mitigation or even significant changes to the overall mechanical and electrical strategy.

Personal reflection

Over the first three years of my career, I've seen firsthand the impact of effective acoustic design, as well as the fallout when such design has not been accounted for at an appropriate stage of a project's lifespan.

Where I had previously had an appreciation for acoustics generally as a subject, I now have a newfound appreciation for the impact of good acoustic design, as well as the benefits it can bring. Working as a consultant has given me insight into the crucial value which acoustics can bring to a project.