Acoustic Attenuation Performance of Casing Stiffness Relative to Insulation Thickness in Compact Air Handling Units

The current global context, characterized by climate change and increased indoor occupancy, has necessitated prolonged daily operating hours for ventilation systems. Coupled with rising living standards, these factors have elevated occupants’ expectations for Indoor Environmental Quality (IEQ), driving a demand for quieter equipment which is a significant challenge for HVAC engineering. This study evaluates the acoustic attenuation performance of various casing constructions to quantify the impact of sheet metal stiffness compared to insulation thickness. Experimental measurements of the Radiated Sound Power Level (LwA) were conducted on a heat recovery unit across octave bands from 63 Hz to 16,000 Hz, ensuring a measurement uncertainty within ±0.5 dB as per ISO 3741 precision requirements. The methodology involved testing multiple enclosed configurations against a reference open-top unit, varying mineral wool insulation thickness from 40 mm to 100 mm (with optional 25 mm linings) and inner sheet metal thickness between 0.8 mm and 2.0 mm. The results indicate that enclosing the unit significantly reduced radiated sound power levels compared to the exposed reference. While the standard configuration with 50 mm insulation yielded 49.8 dBA, modifying the casing structure generated superior attenuation. Notably, a configuration utilizing a 2.0 mm inner sheet resulted in a radiated sound power level of 46.9 dBA, a result found to be statistically significant (p < 0.05) when compared to the baseline. This performance is statistically comparable to the 46.7 dBA recorded for the maximum insulation assembly, confirming the validity of structural stiffening as an equivalent alternative to bulk insulation. Consequently, the increased panel stiffness achieved approximately 94% of the attenuation efficiency provided by the thickest insulation option. The data demonstrates that increasing panel stiffness effectively reduces transmission, offering performance levels comparable to significantly thicker insulation layers. The study concludes that optimizing casing stiffness represents a superior strategy for noise control in high-density residential applications, as it decouples acoustic performance from the unit’s external dimensions, offering a high-attenuation solution that preserves a compact spatial footprint.