Overview
EN ISO 5801:2017/A1:2025 is Amendment 1 to the international CEN-adopted standard ISO 5801:2017, titled Fans - Performance testing using standardized airways. Approved January 2025, this amendment updates definitions, test procedures, calculation methods and uncertainty reporting for aerodynamic performance testing of fans in standardized test ducts (airways). It is published by CEN in collaboration with ISO/TC 117 (Fans) and CEN/TC 156 (Ventilation for buildings).
Key topics and technical requirements
- Revised definitions and symbols: updates to hydraulic diameter, hydraulic mean depth and isentropic exponent; the perimeter symbol is clarified (E).
- “Blow through” verification test: clarified procedure and acceptance criteria for settling means (measurement plane at 0.1 Dh downstream; velocity uniformity threshold: max ≤ 2 m/s or ≤ 125% of average).
- Fan air power calculations: two approved methods
- Polytropic method for compressible flow (detailed formulae and polytropic exponent calculation).
- Simplified method for reference velocities v ≤ 65 m/s (simplified expressions and guidance when impeller power is not measured).
- Static air power and efficiencies: updated formulas for fan static air power and related efficiency computations, with specific guidance for low-speed (v ≤ 65 m/s) conditions.
- Measurement uncertainty & reporting:
- Updated propagation and reporting rules (RSS combination of Type A and Type B elements; return to standard uncertainty).
- Test report must state test value, expanded uncertainty and confidence level (~95%).
- Maximum allowable expanded uncertainties for individual parameters (examples): ambient pressure 0.2%, ambient temperature 0.2%, gauge/differential pressure 1.4%, rotational frequency 0.5%, power input 2%.
- Maximum allowable uncertainties for results (examples): fan air power 2.5%, fan impeller efficiency 3.2%, fan flow rate 2.0%, fan pressure 1.4%.
- Annex updates:
- Nozzle installation, geometry and surface-waviness tolerances for standardized airways.
- Guidance on measuring motor input power with VFDs (annex F) due to harmonic and measurement challenges.
Applications and users
This amendment is essential for:
- Independent test laboratories performing standardized fan performance testing and certification.
- Fan and HVAC manufacturers verifying aerodynamic performance, efficiency and compliance.
- R&D and test engineers developing fan designs and system integrations.
- Certification bodies and regulators requiring traceable test methods and uncertainty documentation.
Practical uses include performance verification, efficiency benchmarking, selection of fans for ventilation and air-conditioning systems, and compliance testing under national CEN implementations.
Related standards
Keywords: fans, performance testing, standardized airways, fan air power, polytropic exponent, hydraulic diameter, measurement uncertainty, nozzle calibration, VFD motor input.
