AHU noise control needs both internal absorption and external transmission loss; the panel and lining decide how quiet the unit runs.
Two Mechanisms
Internal absorption lines the casing with acoustic material so the sound generated by the fan and airflow is damped before it leaves through the openings, reducing the breakout into the airstream that would otherwise carry noise into the served rooms.
An air handling unit is both a source and a path for noise, and acoustic treatment decides whether the plant room stays quiet and whether sound travels into occupied spaces through the casing. The work splits into stopping sound leaving the box and absorbing sound inside it.
Breakout is sound radiating through the panel; a single-skin sheet transmits far more than a double-skin panel with insulated, damped skins, because the cavity and the mass break the path. Where the unit sits next to offices the panel construction is chosen for transmission loss, not just for thermal performance, and the figure is part of the specification.
Internal lining absorbs the sound the fan and the airstream generate before it reaches the openings. A lined mixing box or a short attenuator section drops the break-in and break-out levels, and the lining must be of a type that resists fibre release into the air stream where the air quality is sensitive, balancing acoustics against hygiene.
Vibration is a separate path: even a quiet unit shakes the structure through its base and ducts, so the acoustic plan includes flexible connections and isolated supports so the casing treatment is not undone by a rigid bridge. The fan selection itself, a slower wheel at lower tip speed, is the first and cheapest noise control.
The company's 80,000 m² production site builds AHUs under ISO 9001:2015 with CCC certification, and its engineers respond to selection enquiries within 24 hours to advise panel, lining, and isolation choices that meet the room rating the project's acoustic spec requires.
Treatment extends to the duct: a break-in attenuator section and external lagging on a noisy supply run stop sound travelling along the path the casing work missed, because noise follows the stiff duct as readily as the air. The lagging is a mass-loaded, absorbent wrap that breaks the radiation path, and it is specified where the run passes above a quiet room so the acoustic plan covers the whole route from fan to diffuser, not just the unit.
External transmission loss is the casing's ability to stop sound escaping through the walls to the plant room or occupied space; a stiff, heavy, well-sealed double skin performs far better than a thin single skin that radiates like a loudspeaker panel.
Breakout noise is the sound radiating from the casing itself, which matters when the unit sits near a quiet area; it is controlled by panel mass, damping, and avoiding large flat resonant surfaces that amplify particular frequencies.
The fan is usually the dominant source, so its selection for a low specific noise level, combined with good casing treatment, does more than lining alone, because you cannot line away sound that is generated too loudly at the source.
Material and Design Choices
Internal lining of 25-50 mm of acoustic foam or mineral fibre lowers the unit's emitted sound, but the material must be fire-rated and stable in the airstream without shedding fibres that would contaminate the filter and the downstream space.
Panel stiffness and mass set transmission loss; adding a separate inner skin with an air gap raises performance without making the outer skin impractically heavy, and the gap also helps the thermal break that prevents exterior condensation.
Vibration isolation of the fan and the whole unit stops structure-borne sound travelling through the building, which lining cannot address because it is an airborne-treatment only and leaves the rigid connection as a separate path.
Target a noise criterion such as NC or NR appropriate to the served space; a unit supplying an office needs a lower figure than one in a rooftop plant room, and the criterion should be agreed before the unit is ordered, not discovered after complaint.
| Item | Specification | Note |
|---|---|---|
| Internal lining | 25-50 mm | Absorbs source |
| Transmission | double skin | Mass + gap |
| Breakout | panel stiffness | Avoid resonance |
| Vibration | isolators | Structure-borne |
| Criterion | NC / NR | By space |
| Source | fan SPL | Lowest first |
Selection Checklist
- Choose a fan with a low specific noise level before adding treatment.
- Line the interior with fire-rated acoustic material 25-50 mm.
- Use a stiff double-skin panel for transmission loss.
- Isolate the fan and unit from the structure for vibration.
- Set the NC or NR target from the served space type.
- Verify the combined result against the room criterion.
About the Manufacturer
Keruite Air Conditioning Group, headquartered in Dezhou, Shandong, has more than 30 years of HVAC manufacturing experience and operates an 80,000 m² production site with its own performance testing laboratory. Products are built under ISO 9001:2015 quality management and carry CCC certification, and are supplied to customers in over 50 countries.
Our engineers respond to selection enquiries within 24 hours and can provide project-specific sizing, performance curves, and documentation to support specification and procurement.