Heat pump mythbusters commentary - part 3: Can heat pumps be installed in older properties?
The acoustics of air source heat pumps - part 1: Why noise matters
This is the first part of a series of posts about air source heat pumps from my perspective as one of the Acoustics team here at Max Fordham.
In this first post, I’ll be starting at the very beginning, and talking about why this is something we spend so much of our time thinking about in the first place. In Part 2, I’ll go over some of the details about what makes heat pump noise more complicated than it first appears, and what questions we still have about it. Then, in Part 3, I’ll be reporting back on what we did to try and answer some of those questions, and hopefully, how we’ll be able to apply what we learnt going forward.
Heat pumps: The way to net zero
As previous posts on this topic by my MEP colleagues have made clear, air source heat pumps are our best bet for decarbonising heating and hot water in this country. Without wide-scale adoption of this technology, we have very little hope of hitting our net zero goals.
As the global average temperature for the year looks set to exceed 1.5°C above the pre-industrial baseline, and as international politics looks like it will become even more hostile towards efforts to do anything about it, it is more important than ever to remove as many of the barriers holding back our progress towards decarbonisation as we can.
When it comes to the roll out of heat pumps, one of the barriers that is currently holding us back is noise. As an acoustician, I spend a good deal of time working with MEP engineers to help make sure that the heat pumps that we need don’t end up producing noise that upsets the neighbours.
Going by the information provided by manufacturers, the sound power (a measure of how much sound energy something puts out, rather than how loud it might sound at a particular distance from it) of a typical domestic heat pump tends to be somewhere between 50-70dBA. As a very rough comparison, this is about the range you might get from a domestic cooker hood, from somewhere around 50dBA at the lowest speed up to somewhere around 70dBA at the highest speed. As I’ll show in Part 2 of this series though, that’s far from the full picture.
Considering the clear benefits of installing as many heat pumps as we can, it would be easy to say that a bit of noise is a small price to pay, and that we shouldn’t let it stop us. It’s probably no surprise that, as an acoustician, I don’t share this view.
The impact of noise
Noise isn’t just something that can be a bit annoying, it is a matter of public health. High levels of noise exposure have been shown by the World Health Organisation to lead to a wide range of health impacts, including increased risk of heart disease and mental illness, reduced cognitive performance in children, and a whole range of effects related to disturbed sleep.
High noise levels also change your behaviour. You might avoid opening a window even when you’re too hot because you don’t want to let the noise in. You might not spend as much time outside because you can’t relax. You might not have a conversation with your neighbour because it’s not worth trying to make yourself heard.
Freedom from the adverse effects of noise must not be seen as a luxury that is only available to people with a greater ability to choose where they live. They aren’t always perfect, but the laws and planning policies around noise are there to protect everyone, and are based on the principle that we all have a responsibility to avoid subjecting those around us to levels of noise that are likely to significantly impact their lives.
In the case of most new heat pumps, it is necessary to demonstrate that the noise produced from the unit will satisfy a given target level at the nearest noise-sensitive position, either as part of a planning application, or an alternative route, such as MCS. Assessing whether this level is likely to be met, and helping to make sure it is, makes up a part of our job on the Acoustics Team.
Adoption of heat pumps in the UK
While it is still a long way off where we need it to be, the number of heat pumps being installed in the UK is growing, and the technology is becoming more mainstream. However, many of these installations are in areas where people live primarily in detached or semi-detached houses with private gardens and a reasonable distance between them and their neighbours.
If we are going to decarbonise the heating of our homes to the extent that we need to, we need to find a way to spread this roll-out more evenly and make heat pumps available to people living in high-density urban housing like flats and terraced houses. And we are going to need to do it without subjecting people to excessive levels of noise.
In these situations, there are fewer options for where someone can put their heat pump, and it will almost always end up being closer to the neighbours than it would be in a place with less dense housing. The closer the neighbours are to your heat pump, the more likely they are to be affected by the noise it produces, and the quieter your unit will have to be to hit a given level.
This makes it even more important that we get as good an understanding of the noise that heat pumps produce as we can, so that we can accurately predict where noise is and is not likely to cause any problems, and so that we can give advice on how to minimise the noise while still delivering the right amount of heat as efficiently as possible.
The problem is that there are a number of nuances around air source heat pump noise that can make this difficult. Compared to most other types of MEP equipment, the technology is still relatively new, and it is evolving quickly.
In my next blog post, I will go through some of the challenges we’re facing in our quest to learn everything we can about heat pump noise, as well as what we’re going to do about it.