Overview
ISO 13261-1:1998 specifies procedures for the determination and publication of sound power ratings of outdoor, non-ducted sections of electrically driven, mechanically compressed air‑conditioning and air‑source heat pump equipment. The standard defines how to measure octave‑band and single‑number A‑weighted sound power levels (LWA) for residential, commercial and some industrial outdoor units, and describes reporting of standard and application ratings.
Key topics and technical requirements
- Scope: Applies to non‑ducted outdoor equipment and outdoor sections of factory‑made units; excludes ducted outdoor sections, chillers, variable‑speed compressors and industrial process equipment.
- Rating types: Octave‑band sound power level (LW) and single‑number A‑weighted overall sound power level (LWA). Annex B provides a tone‑adjusted indicator (LWAT) for sound quality information.
- Frequency bands: One‑third‑octave bands from 100 Hz to 10 kHz or full octave bands from 125 Hz to 8 kHz are used (optional 63 Hz octave band with additional requirements).
- Accepted measurement methods: Tests must follow referenced acoustics standards (e.g., ISO 3742, ISO 3743‑1/2, ISO 3744, ISO 3745, ISO 9614‑1/2) and ISO 12001 grading guidance.
- Special procedures: When using sound‑intensity methods (ISO 9614), Annex A describes a special rating procedure and restrictions (data above 6 300 Hz are informational only).
- Measurement controls: Use a foam windscreen on microphones (effect ≤ ±1 dB from 50 Hz–4 kHz; ≤ ±1.5 dB to 10 kHz). Avoid air velocities over microphones exceeding 2 m/s to limit turbulence errors. Equipment must be mounted per manufacturer instructions; heavy masonry walls or auxiliary platforms recommended for wall‑mounted units.
- Data reporting: Sound power levels reported in dB re 1 pW per band; overall A‑weighted values obtained by band‑to‑A weighting conversions and logarithmic summation.
Applications and users
ISO 13261-1:1998 is intended for:
- Test laboratories performing acoustic certification of outdoor air‑conditioning and heat pump units
- Manufacturers publishing declared noise emissions and rating data
- Specifiers, HVAC engineers and facility planners comparing equipment noise performance
- Regulatory bodies and procurement teams setting noise limits or procurement criteria
The standard helps ensure repeatable, comparable sound power ratings for product selection, site planning and regulatory compliance.
Related standards
Keywords: ISO 13261-1:1998, sound power rating, air-conditioning, air-source heat pump, non-ducted outdoor equipment, A-weighted, octave band, ISO 9614, ISO 3744.