Industrial Noise & Vibration Centre

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OEM air-source heat pump noise reduction

air-source heat pump noise reduction

The manufacturer of air-source heat pumps approached us to use our diagnostic skills and technology help them to reduce the noise from their units without recourse to expensive, efficiency-sapping enclosures and silencers. The objective was to design-in low-cost engineering noise control features to make the units inherently quieter - without compromising efficiency.

Heat pump noise diagnosis

The diagnostic analysis showed that there were 4 major noise sources, all of which would need to be reduced in order to achieve the desired noise reduction. The sources identified were:-

  • fan: tones at 70Hz + harmonic - cannot be reduced using silencers or barriers
  • mains hum: 100Hz tone
  • compressor: several tones
  • air noise: broadband sound
air source heat pump noise reduction 70Hz

Previous resources had been focused on reducing the overall dB(A). However, the low-frequency tones were the dominant noise complaint issue despite only contributing <0.5dB to the overall dB(A). These would not have been reduced by the conventional methods under consideration.

Noise-reducing modifications

These involved the following:-

  • fan tones: aerodynamic modifications
  • mains hum + compressor: high-performance damping of key components + local tuned acoustic absorbent
  • broadband air noise: once the low-frequency components had been cut, a simple small carefully designed screen was very effective

The combined effect was to reduce the 70Hz fan tone by 97% (15dB) and the overall noise by 90% (10dB(A)) without affecting the efficiency of the heat pump as demonstrated by the above analysis and the sound file.

View a more detailed guide to heat pump noise reduction covering both air-source and ground-source noise control.