Reducing air source heat pump noise: an aeroacoustic testing case study
Client: internal research
Sector: domestic heating
ISVR Consulting developed a test rig to assess the aeroacoustic noise associated with air source heat pumps and the effect of aerodynamic drag on the fan load and noise levels. Additional significant noise sources were also identified during the testing. The tests also have implications for the use of heat pump acoustic enclosures for heat pump noise reduction.
Talk to us to discuss how we can use methods such as aeroacoustic testing and CFD noise analysis to assess the acoustic characteristics of your product and offer design solutions to reduce noise levels without affecting performance.
The challenge: identifying sources of air source heat pump noise and mitigating them without adversely affecting thermal performance
Air source heat pump noise control is a big issue, with concerns regularly in the news – noisy heat pumps can affect people’s quality of life, cause neighbour disputes and ultimately affect uptake of this more environmentally friendly form of heating. To mitigate noise issues, manufacturers need to continue to invest in designing quieter technologies, but more insights are needed to help tackle causes and mitigations. As well as mechanical noise, understanding aeroacoustics will contribute to improved design.
Our solution: advanced aeroacoustic testing and CFD noise analysis
The air source heat pump test rig
ISVR Consulting’s experts carried out research to assess the dominant factors affecting aeroacoustic noise from an air source heat pump caused by air being drawn through the heating core and out over the exit grille.
The test rig showed that flow resistance through the core and grille resulted in the requirement for the fan to operate at higher speeds in order to maintain the same air flow through the air source heat pump, resulting in increased electrical load on the fan, and higher heat pump fan noise levels. Testing also uncovered high levels of tonal noise associated with the electrical drive of the fan.
CFD modelling of the refrigerant pipes
The design of the inlet and outlet components of the air source heat pump takes little account of the flow speed and direction through the machine, with unnecessarily high levels of aerodynamic drag associated with both the core and grille. CFD acoustic simulation of the refrigerant pipes in the core illustrated the potential benefit of aligning the pipes which provide very little of the heat transfer surface within the core.
Modifications to the shaping of the electrical speed controller may be used for fan component tonal noise reduction, reducing both the sound power of the air source heat pump and the likelihood of annoyance.
The outcome: identifying tonal noise and aerodynamic drag
Tonal noise characteristics, and the influence of drag on mid-frequency noise levels
Although the test rig was designed to address aeroacoustic noise issues, the testing uncovered significant tonal noise characteristics which may be addressed by modifications to the speed controller design.
The testing also showed the correlation between aerodynamic drag and noise. Aerodynamic drag analysis using CFD modelling indicated the potential to significantly reduce the drag through the air source heat pump, which would allow the fan to run at lower speed, using less power and producing less noise. The air flow through an air source heat pump is quite complex, presenting a number of opportunities to refine the air flow management through the machine.
The findings of this work also have implications for the use of acoustic enclosures to reduce air source heat pump noise. Most enclosures exhibit significant aerodynamic drag which may adversely affect the acoustic benefit of the enclosure and the operating efficiency of the air source heat pump.
Critical insight: heat pump acoustic enclosures
The design of an air source heat pump acoustic enclosure can significantly increase the fan load required to maintaining proper airflow and should take account of the insertion effect of placing the air source heat pump within an enclosure. These effects can have an adverse impact on the assumed performance of an acoustic enclosure. As our research shows, ISVR Consulting’s experts can identify issues with aerodynamic drag analysis to inform improved heat pump acoustic enclosure performance for efficiency.
Contact our aeroacoustics team to optimise your product’s noise performance.
Our aeroacoustics, testing and modelling experts
Dr Erika Quaranta: aeroacoustics and numerical modelling of noise and fluid dynamics
Dr Christos Karatsovis: building vibration, including modelling, testing and designing low-vibration buildings
Andy Varley: architectural and environmental acoustics, sound insulation testing and noise assessments, and product development
Malcolm Smith: acoustics, dynamics and low noise design, specialising in all sources of aerodynamic noise
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