Reference
Standards and testing
The documents that decide whether a performance number means anything, and which certificate should arrive with the machine. Written plainly, because a specification sheet is only useful if the person ordering the fan understands it.
Performance
Test methods, and why they are not interchangeable
- IS 4894 (BIS)
- Centrifugal fans: the Indian specification covering requirements and tests for fans with directly or indirectly coupled impellers. It is our normal works basis and it is not an equivalent of a certified laboratory rating
- ISO 5801
- Fans – performance testing using standardized airways: the international laboratory method for fans of all types except air-circulation devices
- ANSI/AMCA 210
- Laboratory methods of testing fans for certified aerodynamic performance rating, published in the US and technically aligned with ISO 5801; it is the standard behind an AMCA certified rating
- ANSI/ASHRAE 51
- The US twin of the AMCA laboratory method, published jointly and cited as the test method in rating programmes
Balance
Balance quality and vibration
- ISO 1940-1
- Balance quality of rigid rotors. The grade number is a permissible residual vibration velocity in mm/s: G6.3 allows 6.3 mm/s, G2.5 allows 2.5 mm/s
- Working the grade
- The allowable specific residual unbalance in micron equals 9549 times the grade divided by the speed in RPM, so the same grade becomes a tighter tolerance as speed rises
- ISO 14694
- Industrial fans – balance quality and vibration levels: the fan-specific specification that pairs with ISO 1940-1 when a project states a balance and vibration requirement
- ISO 20816-3
- Mechanical vibration for evaluating machines on site; the Indian adoption is IS 14817-3. Used for in-situ assessment of larger machines rather than for setting a factory balance grade
- Our practice
- G6.3 as standard, G2.5 on high speed or large wheels, with the balance certificate issued with the machine
Sound
Sound ratings
Two numbers get confused constantly. Sound power level is a property of the source, referenced to 1 picowatt, and it is what a fan is rated on. Sound pressure level is what your ear or a meter measures at a position, referenced to 20 micropascals, and it depends on distance and the room. A-weighting, written dB(A), applies the frequency weighting that best represents human hearing.
For a fan, both the blade-passage tone and the broadband noise scale at about the fifth power of blade tip speed, which gives the handy rule that a speed ratio costs or saves 50 times the logarithm of that ratio in decibels, plus 20 times the logarithm of any density change. Halving the tip speed buys roughly 15 dB – which is why a larger, slower fan is the usual answer to a noise complaint.
- ANSI/AMCA 301
- Method for calculating sound power ratings of aerodynamic devices
- ANSI/AMCA 300
- Reverberant room method for sound power determination of fans
- ANSI/AMCA 320
- Laboratory method for determining fan sound power levels in ducts
- Our practice
- Sound data at the confirmed duty on request, with the rating basis stated rather than implied
Elsewhere on the drawing
Materials, motors and supply
- Structural steel
- IS 2062:2011 covers hot rolled carbon-manganese and HSLA structural steel, with E250 and E350 giving minimum yield strengths of 250 and 350 MPa
- Stainless plate and sheet
- IS 6911 is the Indian specification for stainless steel sheet, plate and strip
- Motor efficiency classes
- IEC 60034-30-1 defines IE classes for single-speed line-operated three-phase induction motors, measured to IEC 60034-2-1; in the EU, Regulation 2019/1781 requires IE3 from July 2021 for 0.75 to 1000 kW and IE4 for part of the 75 to 200 kW range from July 2023
- Indian supply
- Low voltage three-phase at 415 V, 50 Hz, with grid frequency operated within roughly 49.2 to 50.3 Hz
- Quality system
- ISO 9001:2015, which is the certification our works holds