One factor that may be a concern to property owners is the replacement of a relatively quiet gas boiler with external equipment that is potentially noisier. NBS has teamed up with its partner, Quiet Mark, to provide ‘sound’ advice on the specification of heat pumps.
Specification
It is important to establish that there are different types of heat pumps. Ground source heat pumps (GSHPs) have a considerable proportion of their installation below ground, which normally makes their noise impact minimal. Air source heat pumps (ASHPs) contain a fan, which is often the main source of noise from the unit. Airborne and vibration-based noise can emanate from the unit. Although heat pumps may be installed internally or externally, they are more commonly seen as an externally located unit.
Noise levels generated by heat pumps can vary significantly from product to product. Initially, specifiers are advised to scrutinize sound data provided by the manufacturer; ideally, this should be information that has been verified by a third-party assessor. Quiet Mark has a list of certified heat pump models that meet acceptable noise criteria, and this can be a great initial reference for all specifiers concerned about sound levels. Quiet Mark certifications are based on the basic unit, without additional attenuation measures such as acoustic lining or screening.
Specifiers using NBS Chorus can use its partner platform, NBS Source, to find essential acoustic data and compare the performance of a range of heat pump products at the point of specification.
Expert guidance
Heat pumps are not new technology, and there is a variety of technical guidance regarding noise. CIBSE Guide B4 Noise and vibration control for building services systems provides in-depth technical guidance for designers. BESA TR30 Guide to good practice – heat pumps provides technical and practical guidance from an installation perspective. For the specifier, NBS Chorus provides the necessary clause structure and essential guidance to allow informed specification of ASHP systems of all applications and sizes. For specifiers requiring more general information around heat pump technology, expert guidance on domestic heat pumps is provided by the GOV.UK article Heat pumps explained: experts answer your questions. This article features a useful Q&A section on heat pumps, as well as guidance on the Boiler upgrade scheme.
Location, location, location
The location of the unit is perhaps an obvious – but key – consideration for designers. Designers familiar with split and variable refrigerant flow air conditioning systems can apply a similar logic in their approach to locating heat pumps. Where possible, a common-sense approach should be applied; for example, ensuring that heat pumps are positioned far enough away from structures to allow sufficient airflow. Good practice also involves locating heat pumps away from ‘sensory receptors’, such as openable windows, or locating a unit on an alternative elevation away from neighbouring buildings. A location that provides a natural break, such as a wall or fence, will automatically provide additional sound protection.
Permitted development rights for domestic properties in England state that heat pumps must be located at least one metre from the boundary line (three metres in Wales), although this is subject to review, in line with the UK Government’s plan for increased heat pump installations as part of net zero targets.
Installation
Vibration from the moving parts of a heat pump may be transferred to connected components, such as pipework or nearby structures. A good installation will negate vibration by reducing its transfer. The use of anti-vibration mounts or acoustic matting are sensible options when fixing heat pump equipment. Dissociating the vibration transfer onto pipework can be achieved using flexible connections and appropriate bracketry that is suitably spaced. Success is achieved by good workmanship.
While some manufacturers can recommend approved installers for their products, the Microgeneration Certification Scheme (MCS) operates a contractor certification scheme for quality-approved installers of heat pumps and other renewable technologies.
Further measures, such as acoustic screens and compressor jackets, can be added to the installation to reduce the noise levels of ASHPs in operation. Some manufacturers use a psychological approach by concealing the rotating fan on the heat pump, following the rationale that ‘if you can’t see it then you can’t hear it.’
Assessment
An installed heat pump could generate a higher sound level during operation than listed on the manufacturer’s data sheet due to a variety of factors. For domestic installations, the MCS 020 noise-based assessment is available for heat pumps to help verify sound levels and may be required as a part of an assessment to meet permitted development rights.
The MCS 020 assessment aims to verify that installations comply with established noise criteria and factors in an existing noise assessment, prior to the installation taking place. Additionally, MCS 020 assessments consider the noise levels produced by heat pumps under different operating conditions, such as heating or cooling modes, and different fan speeds and load capacities. Measured results are compared against established noise criteria and are certified under the scheme (where compliance with these criteria has been verified by a third-party certifier). In cases where noise levels exceed the specified criteria, MCS assessments may include recommendations for noise mitigation measures. These might include a combination of installation adjustments and additional acoustic treatment to the heat pump itself. It is recommended that sound levels from installed heat pumps be monitored regularly, during their annual maintenance, to ensure that noise levels remain within acceptable limits over time.
Summary
Decarbonization is now a key agenda for the UK and, as a result, the number of heat pumps is going to significantly increase. Although recent Government research has found that the number of complaints involving heat pumps’ noise levels is relatively small – compared to the number currently operating in the UK – noise is certainly a factor that can impact people’s quality of life.
As heat pump installations increase in number, many people may find themselves living with, or next to one, soon. It is therefore incumbent upon property owners and designers to carefully consider the noise levels resulting from heat pump installations and refer to the trusted guidance available to them.
Specifiers can find a range of Quiet Mark-certified heat pumps on NBS Source. Here are some examples:
CS5800i AW Heat Pump Outdoor Unit - Air to Water Heat Pump | Bosch Thermotechnology Ltd | NBS Source
Download the tables
The current status of the classification tables is listed below. (See also: change log)
