Overview - ISO 5135:2020 (Acoustics, air-terminal noise testing)
ISO 5135:2020 specifies general rules for measuring sound power levels of noise from air-terminal devices, air-terminal units, dampers and valves used in air diffusion and distribution systems. It is intended for measurements carried out in a reverberation test room and is based on the precision-grade methods of ISO 3741. The third edition (2020) updates reference standards and adds guidance on measurement uncertainty and test setup elements.
Key topics and technical requirements
- Scope and purpose: Determination of sound power levels for HVAC air-terminal products under steady-state operation; equipment volume limits relative to room volume (applicable up to 5% of room volume; special qualification if >2%).
- Test environment: Use of reverberation test rooms qualified per ISO 3741; room qualification for broadband sound and guidance on simulating reflecting planes with heavy panels.
- Mounting and installation: Defined mounting positions representative of normal use:
- on/against a surface,
- at intersection of surfaces,
- away from surfaces,
- equipment outside the room connected via a duct or opening.
Minimum clearances (commonly 1.0 m to adjacent surfaces) and procedures for equipment located above ceilings are specified.
- Ducted connections: If equipment is outside the room, connect via an unlined duct of at least 2 m or 5 effective diameters, whichever is greater, terminated flush with the test-room surface.
- Airflow and accessories: Include normal air-flow control accessories (dampers, deflectors, straighteners). Airflow measurement methods (ANSI/ASHRAE or EN standards, ISO 5167 for flow metering) and a recommended two-step approach when flow-measuring devices generate noise.
- Measurement details: Precision-grade sound power determination in octave or one‑third‑octave bands (typical mid-bands from 125 Hz to 8 000 Hz; optional lower bands like 63 Hz) and requirements for instrumentation, calculations, uncertainty assessment and reporting.
- Reporting and uncertainty: Test report contents and an explicit clause on measurement uncertainty are included.
Applications and users
- Who uses it: HVAC and ventilation product manufacturers, acoustic test laboratories, certification bodies, building services engineers, and consultants involved in noise performance of air distribution components.
- Practical uses:
- Product R&D and noise optimization of diffusers, dampers and terminal units
- Type testing for product datasheets and compliance
- Comparative evaluation of acoustic performance for HVAC selection and building acoustics design
Related standards (normative references)
- ISO 3741 (reverberation-room sound power methods)
- ISO 7235 (ducted silencers and air-terminal units)
- ISO 5167 (flow measurement)
- ANSI/ASHRAE 70, ANSI/ASHRAE 130
- EN 12238, EN 12239, EN 1751
Keywords: ISO 5135:2020, acoustics, sound power level, reverberation test room, air-terminal devices, dampers, valves, HVAC noise testing, ISO 3741.
Open preview (PDF)Acoustics — Determination of sound power levels of noise from air-terminal devices, air-terminal units, dampers and valves by measurement in a reverberation test room