Human response to air source heat pump noise: influence of background noise, operating conditions and acoustic characteristics

Air Source Heat Pumps (ASHPs) are key to reducing carbon emissions from heating requirements of buildings, especially in colder regions like Europe. However, installation rates remain below targets, with noise emissions posing a major barrier to wider adoption in residential areas. This study examines human response to ASHP noise under simulated conditions, focusing on Annoyance, Arousal, and Valence under varying source distances, background noise levels, and operating conditions, emphasising changes in the acoustic characteristics of the heat pump. A two-part listening experiment was conducted with 50 participants. Part One evaluated responses to continuous ASHP noise using 20-second recordings. Part Two focused on transient operating conditions, utilising 60-second recordings where the heat pump transitioned between operating modes. Recordings combined ASHP noise at three distinct source distances with two ambient background noise levels, simulating rural day- and nighttime scenarios. A contextual framing condition regarding ASHP ownership was also included. Results show that higher A-weighted Sound Pressure Level (SPL), Loudness, Roughness, and Tonality are associated with increased Annoyance and Arousal and decreased Valence. Correlation analysis revealed that conventional metrics (SPL) and psychoacoustic parameters (particularly Loudness and Roughness) show similar strength associations with subjective responses, with their relative importance varying across different experimental conditions. These results suggest that while conventional A-weighted sound level measurements remain important, ASHP noise regulations might benefit from additionally considering psychoacoustic characteristics. Simulated background noise suggests ASHP noise perception interacts with ambient conditions, but field studies with realistic background noise are needed to guide regulation.