HVAC and building services acoustic measurement covers a range of related problems: determining noise levels radiated from plant rooms and mechanical equipment rooms, measuring the insertion loss of ductwork attenuation systems, characterising fan and air handling unit noise in supply and return air ducting, and verifying compliance of occupied spaces with NR or NC design criteria. These measurements are performed during design verification, commissioning, and occupant complaint investigation.
Measurement in HVAC applications must account for the low-frequency dominated spectrum of fan noise — octave band measurements down to 31.5 Hz or 63 Hz are often required. For compliance verification in occupied spaces, the measurement procedure should capture time-varying HVAC operation modes and worst-case conditions. A 1/2-inch free-field Class 1 measurement microphone with sufficient dynamic range is appropriate for most HVAC measurement positions.
For duct insertion loss measurement to ISO 5136, the in-duct measurement requires pressure-field microphones and a suitable microphone probe assembly. PLACID Class 1 pressure-field capsules are used in this application. Contact PLACID for guidance on in-duct measurement setup and appropriate sensor selection for your specific duct geometry and frequency range.
Building services acoustic reports submitted for planning approval or tenant complaint resolution must state the instrumentation used and provide evidence of calibration. For HVAC noise compliance demonstrations in noise-sensitive buildings — offices, hospitals, schools — the measurement uncertainty should be accounted for in the assessment: if the measured level is within one uncertainty interval of the design criterion, it cannot be stated definitively that the criterion is met or exceeded. PLACID ISO/IEC 17025 accredited calibration certificates with stated expanded uncertainty provide the evidence needed to quantify this assessment margin.