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Acoustics Training Chilled Water Terminals

Acoustics Training Chilled Water Terminals. Yves RAIMBAULT EMEIA Product  Manager Terminal Systems - Air Systems. June 2012. Acoustics. Sound definitions Sound weightings Sound power Sound pressure Installation attenuations NR and NC sound ratings Distance attenuations

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Acoustics Training Chilled Water Terminals

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  1. Acoustics Training Chilled Water Terminals Yves RAIMBAULT EMEIA Product Manager Terminal Systems - Air Systems June 2012

  2. Acoustics Sound definitions Sound weightings Sound power Sound pressure Installation attenuations NR and NC sound ratings Distance attenuations Expert link trainings Simple, no big formulas – only the essentials – calculate it yourself Agenda 1

  3. Sound definitions Sound power • Acoustical energy emitted by the sound source • Unaffected by the environment • Formula: • Example from a sound spectrum Sound pressure • Pressure disturbance in the atmosphere • Affected by strength of source, surroundings, and distance between source and receiver Addition of 2 sources at 45 dBA • 2 units side by side with equal sound emission are adding only 3 dB to the overall sound emission From sound power, sound pressure can be calculated in any installation condition 2

  4. C 0 -10 B frequency responses for sound meter weighting characteristics -20 relative response, dB -30 A -40 10,000 20 50 100 200 500 1,000 2,000 5,000 frequency, Hz Sound weightings Attenuation scale is defined to match the response of the human ear to noise 3

  5. Sound power dB(A) For a sound measured at 58.7 dB - the human perception is 42.6 dB(A) Sound power A weighted : Lw(A) • Logarithmic calculation after retrieving the A weight attenuation • The w in Lw stands for Watt • Power is measured in Watt • Attenuation defined attempting to match the response of the human ear to noise • Example 4

  6. Sound pressure dB(A) Sound pressure values are dependant upon installations and sound power Sound perceived after attenuation: Lp(A) • The p in Lp stands for pressure • Types of attenuations: • Laboratory measurements Global Sound Power Lw(A) on terminals • Ducted units measured 3 timesNon-ducted • Inlet • Outlet = LwA Global from Log sumLwA Global measured directly • Radiated • Lp(A) = Lw(A) – attenuations 5

  7. Installation attenuations 9 dB 9 dB 12 dB 12/15 dB 20 dB Non ducted Exposed Generic Rectangular flange Attenuation TRANE model of Rectangular flange Attenuation • Return rectangular flange • Regular 12 dB • Trane flange 15 dB • Discharge Ducted Ducted Return & Discharge Attenuations are proportional to the amount of ductwork (In and Out ) Default attenuations for sound pressure in IRIS Arbitrary • Based on experience Office / Retail Lodging / Residential Office Office Cassette Ducted 20<Pa Ducted 20<Pa Ducted Ducted Cabinet fan coil UniTraneUniTraneUniTraneUniTrane CWS / CWE FCD / FED FCD / FED FCD / FED FCD / FED CFAS FWD FWD FWD FCU / FEU FVC / FCC FCKFWD HFXE / VFXEVFCEHFCEHFCE HFXFVFCFHFCFHFCF 6

  8. Sound data Noise rating curves NR and NC • NR : Noise Rating • NC: Noise Criteria • Developed to determine the acceptable indoor environment for hearing preservation speech communication and annoyance • Most commonly used for offices NR35 in Europe • NC levels are mostly used in US Most selections are completed for a capacity at a given sound level NR and NC sound level 7

  9. NC = 40 NC = 40 Sound data 90 80 70 NC-65 60 NC-60 NC-55 50 octave-band sound pressure level, dB re 20 µPa NC-50 NC-45 40 NC-40 NC-35 30 NC-30 NC-25 Approximatethreshold ofhearing forcontinuousnoise 20 NC-20 NC-15 10 63 125 250 500 1k 2k 4k 8k octave-band center frequencies, Hz Definition • Represent an equal auditory impression of the average human ear • Plot the sound pressure spectrum Lp(A) over the NR and NC curves • NR and NC level are defined based on the most upper tangential curve Equivalent annoyance for 2 different noise emissions with different sound power NR and NC determination 8

  10. Summary NR rating example Exposed Attenuation 9 dB Simple calculation from sound power: apply attenuation based on installation NR and NC determination Rule of thumb • No direct conversion from sound pressure level to NR sound level • Rough estimation: • Lp (dBA) = Lp(NR) + 5 Otherwise said NR is 5 DB lower than sound pressure • NC level is generally 1 or 2 dB lower than NR level Otherwise said, it looks quieter Summary example • Cassette Sound power Lw(A) =50 dB(A) • Sound pressure Lp(A) in the room • Lp(A) = 50 – 9 = 41 dB(A) • Lp(NR) = 41 – 5 = 36 dB(A) • Lp(NC) = 36 – 2 = 34 dB(A) • Error made by this approximation is about +/- 2 dB 9

  11. Distance sound attenuation Sound attenuates with distance from the source The attenuation is function of • The source dimension • The distance Formula • LwA= LpA + Distance attenuation • Distance attenuation in • S is the surface of the volume defined around the source at the measured distance in m² • S0 is 1 m² by definition Formula to use is applicable to any equipment product and installation Effect of distance on noise level 10

  12. Distance sound attenuation 4 way cassette 1 m 1 m 1 m 1 m 1 m 2 m 2 m Noise diffuses in 5 directions • Surface m² • Distance attenuation = dB • It is admitted for Hiwallminisplit 8 dB • For a small product the unit width can be neglected Examples • 4-way cassette measured at 1 m meter 40 dBA • Sound power = 40 + 11 = 51 dBA • Chiller at 10 m with length 4 m x width 2 m x height 2 m • Measured on the long side • Distance from center 11 m • Square around unit 22 x 22 m • Rectangle height 11 m • Surface S = 4 x 22 x 11 + 22 x 22 = 1452 m² • Attenuation is 10 log (1452) = 31.6 dB • Use rounded number 32 dB Surface calculation based on the microphone location around the equipment Example 11

  13. Distance sound attenuation R= 5 m R= 5 m R = 5 m R = 5 m For large unit dimension sound pressure can be taken from several points around a sphere (or a cube) • The sound pressure shall be averaged by the following formula • Where is the quantity of sound pressure measurements at the same distance Noise diffuses in 5 directions • ½ Sphare surface = 314 m² • Distance attenuationdB at 5 m Examples • Small Chiller measured 5 m meter distance from each side • Sound Pressure average • Sound power LwA = 51 + 25 = 76dBA Surface calculation based on the microphone location around the equipment Several points of measurements 11

  14. Expert links Access trainings on Litweb Trainings NR sound tool • Allow to calculate • Sound power from sound pressure data from any distance for any unit type, Fan coil, chiller, etc.. • Noise Criteria NR and NC levels for terminals for exposed or concealed terminals in several ducted installations Available on LitWeb • Link with all terminals • Acoustic trainings terminals • In Tools folder 12

  15. Sound tool Note: all calculations cells are protected but can be Copy / Paste for personal use Enter unit dimensions and sound pressure dB for 1 or more octave band Get started 3 folders Introduction LwACalculate Sound Power LwA of any product from any distance based on one or several sound pressure measurements from any tool (ex Smart Phone) 12

  16. Sound tool Enter unit dimensions and sound pressure dB for 1 or more octave band Get started NR & NCCalculate Noise Criteria base on sound spectrum for terminals 1st utilization Choose installation Enter Sound Pressure dB -> get NR and NC 2nd utilization 12

  17. Sound tool Folder LwA Folder NR & NC Get NR and NC levels directly when LwA data completed Get started NR & NCCalculate Noise Criteria base on sound spectrum for terminals 2nd utilization Choose installation Import data from LwA folder -> get NR and NC 12

  18. Good sales!

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