Higher-fidelity analysis of air source heat pump noise via scanning intensity measurement

The need to shift to reduce carbon emissions to hit Net Zero is currently driving plans for large scale rollouts of Air Source Heat Pumps (ASHPs), due to their increased thermal efficiency and lack of direct carbon emissions. Concern exists, however, over the potential environmental noise impact that these units could generate. The noise generated by ASHPs is measured according to BS EN 12102-2:2019. This allows a choice of several laboratory test procedures for the acoustic part, but in each of these methods only overall sound power is measured. Such measurements are crucial, but they cannot give insight into the directivity of the noise from the unit - as is required for accurate acoustic propagation modelling - and they cannot give diagnostic information that would aid improvements to designs, e.g., by showing which parts of an ASHP radiate the most noise. This paper explores the benefits offered by scanning intensity measurement, here using a Microflown Scan and Paint 3D system. This can provide a map of active and reactive intensity around the unit - in addition to pressure and particle velocity - allowing noise from components and directivity to be estimated. Advantages and challenges are discussed.