Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Hvac noise control

5,354 views

Published on

Hvac noise control Details

Published in: Engineering

Hvac noise control

  1. 1. Rensselaer Commercial & Industrial Air Conditioning Architectural Acoustics HVAC Noise Control
  2. 2. Rensselaer Resources • Manufacturers  Trane  Industrial Acoustics  Many others • ASHRAE (American Society for Heating, Refrigerating, and Air- Conditioning Engineers)
  3. 3. Rensselaer Basic HVAC Functionality • Room air is blown over a heat exchanger through which heated liquid (hot water) or cooled liquid (cold water or other refrigerant) liquid is circulated. • Unwanted thermal energy is released outdoors • This requires…
  4. 4. Rensselaer Main HVAC Noise Sources • Fans (to move the air)  Axial  Centrifugal  Propeller • Compressors (to convert gas to liquid)  Piston  Rotary  Scroll  Centrifugal  Screw • Pumps (to circulate liquids) • Diffusers and Ductwork (to distribute air)  Turbulent aerodynamic noise  “Break-out” noise From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  5. 5. Rensselaer Other MEP Noise Sources • Waste and Rain Leader Piping • Transformers • Dimmer Racks • Lights & Ballasts • Elevator Equipment
  6. 6. Rensselaer Noise Control Approaches • Location of equipment • Sealing penetrations • Resilient mounting of equipment & connected services • Flexible connections to equipment • Lower fluid velocities • Internal duct lining and duct attenuators • Routing of ductwork and piping • Enclosing ductwork and piping From Kirkegaard Associates
  7. 7. Rensselaer Fan Coil Units • Opportunity for significant noise issues:  Fan and coil in close proximity: high turbulence  Applications: typically close to “listeners” (hotel rooms, etc.)  Water flow noise From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  8. 8. Rensselaer Packaged Air Handler • Includes fan or fans • Heating coil • Cooling coil • Air filters • Humidifier • Air dampers and controls From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  9. 9. Rensselaer Packaged Air Handler From Kirkegaard Associates
  10. 10. Rensselaer Typical Air-Handler Design MJR Figure 9.3, p. 192
  11. 11. Rensselaer Equipment Location: Rooftop From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  12. 12. Rensselaer Equipment Location: Mechanical Equipment Room • Noise inside the MER • Noise outside the MER • Duct Breakout • Active Noise Control From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  13. 13. Rensselaer Isolator Types Elastomeric Pads
  14. 14. Rensselaer Isolator Types Elastomeric Pads
  15. 15. Rensselaer Isolator Types Neoprene-In-Shear Floor Mount
  16. 16. Rensselaer Isolator Types Neoprene-In-Shear Floor Mount
  17. 17. Rensselaer Isolator Types Neoprene-In-Shear Floor Mount
  18. 18. Rensselaer Isolator Types Open Spring Floor Mount
  19. 19. Rensselaer Isolator Types Open Spring Floor Mount
  20. 20. Rensselaer Isolator Types Restrained Open Spring Floor Mount
  21. 21. Rensselaer Isolator Types Restrained Open Spring Floor Mount
  22. 22. Rensselaer Reciprocating and Centrifugal Chillers Noise • Reciprocating chillers tend to be quieter than centrifugals for the same load From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  23. 23. Rensselaer Fan Noise Components • 1 duct length • 3 duct length • 5 duct length From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 • Aerodynamic noise • Blade-passage noise  fB = (RPM/60) ·N  N = number of blades
  24. 24. Rensselaer Fan Noise Fan noise depends on the fan operation point on the fan curve From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  25. 25. Rensselaer Fan Noise Fan noise depends on the fan operation point on the fan curve From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  26. 26. Rensselaer Estimating Fan Noise • LW = fan sound power level • KW = fan specific value • Q = volume flow rate (cfm) • P = static pressure (in H20) • BFI = blade frequency increment • C = efficiency correction     CBFIPQKL WW  1010 log20log10 From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005          1 log1010 10C  η = Hydraulic efficiency of the fan = Q·P/(6350 · HP)  HP = nominal horsepower of the fan drive motor
  27. 27. Rensselaer Estimating Fan Noise US Army TM 5-805-4 Technical Manual, “Noise and Vibration Control”, Table C-13     CBFIPQKL WW  1010 log20log10
  28. 28. Rensselaer Diffuser Noise • Flow sets the noise level at a given static pressure level forcing the flow • Good aerodynamics are important to low noise from air terminals From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 (Long Fig. 13.23, p. 474)
  29. 29. Rensselaer Indoor Diffusers • Linear or Slot Diffusers • Round or Rectangular Diffusers • Grilles • Registers From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  30. 30. Rensselaer Specifications for Diffuser Noise • Ideal: sound power data in octave bands versus static pressure & CFM • Reality: most manufacturers only provide the NC “rating” at a fixed “room effect” (typically 10 dB) • Sound power from NC: • Sadly, this only provides a noise estimate based on a perfect NC curve (diffusers are typically high-frequency elements, therefore this tends to over-estimate low frequency power) dB10)(  NCLL PW From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 • 400 sabins • 12 feet
  31. 31. Rensselaer Estimating Diffuser Noise • LW = sound power level (dB re. 10-12 Watts) • SD = cross-sectional face area of diffuser (ft2) • UD = flow velocity prior to the diffuser (ft/s) • ξ = normalized pressure-drop coefficient       3.31log60log30log10 101010  DDW USL  2 0 9.334 DU P      ΔP = pressure drop across the diffuser (in. H20)  ρ0 = density of air (0.075 lb/ft3) Long, p. 475
  32. 32. Rensselaer Estimating Diffuser Noise Long, Fig. 13.24, p.476 DWW CLL Oct, • Octave-band power levels can be calculated from the overall level LW 2 13.115.082.5 AACD  2 13.115.082.11 AACD  Generalized Diffuser Spectrum for round diffusers for rectangular diffusers GP Uf  8.48    fNfNA BPB  peak frequency NB(x) = octave-band number of frequency x (32 Hz = 0, 63 Hz = 1, 125 Hz = 2, …)
  33. 33. Rensselaer Recommended Velocity Limits • Plant Rooms 5m/s • Aud. Shafts 4m/s • Within Aud. 2.5m/s Branch Runouts RC-35 2.75 m/s RC-25 2 m/s RC-15 1.25 m/s Terminal velocities are critical because there is nothing after the diffuser to provide additional attenuation! From Kirkegaard Associates
  34. 34. Rensselaer Unlined Ducts • Not much attenuation in unlined ducts  Little absorption from surfaces (although some energy is lost to break-out noise)  Plane-wave propagation → no spreading loss • Plane-wave propagation when duct dimensions (not length) are less than half a wavelength
  35. 35. Rensselaer Attenuation in Unlined Ducts MJR Figure 9.6, p. 193
  36. 36. Rensselaer Duct Liner MJR Figure 9.5 and 9.7, pp. 193 and 194
  37. 37. Rensselaer Duct Liner • Attenuation in lined rectangular ducts can be approximated with this equation  P = duct perimeter (ft)  S = duct cross-sectional area (ft2)  t = thickness of lining (in) D C duct t S P BL        63 125 250 500 1000 2000 4000 8000 B 0.0133 0.0574 0.2710 1.0147 1.7700 1.3920 1.5180 1.5810 C 1.959 1.410 0.824 0.500 0.695 0.802 0.451 0.219 D 0.917 0.941 10.79 10.87 0.000 0.000 0.000 0.000 Octave-Band Center Frequency (Hz) Long, Eq. 14.12, p. 487
  38. 38. Rensselaer Duct Liner MJR Figure 9.5 and 9.7, pp. 193 and 194 x x x x x x x x x x x x x Data from Long’s equation
  39. 39. Rensselaer Duct Liner Data http://www.owenscorning.com/comminsul/documents/FiberglasDuctBoardLiner.pdf
  40. 40. Rensselaer Internal Fiberglass Duct Lining From Kirkegaard Associates Duct Liner
  41. 41. Rensselaer Airflow: Turbulent Noise in Ductwork From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005, (MJR Fig. 9.12, p. 198)
  42. 42. Rensselaer Airflow: Turbulent Noise in Ductwork From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005, (MJR Table 9.1, p. 197)
  43. 43. Rensselaer How Ductwork Radiates Noise (Break Out) From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  44. 44. Rensselaer Duct Shape and Noise Control From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 • Stiffness of round ductwork reduces break-out noise since motion of the duct walls is restricted • However, this means that more noise energy stays within the duct and may produce higher noise levels at the outlet
  45. 45. Rensselaer Long, p. 486 • The ratio of perimeter to cross-sectional area is also important, and can be used to approximate duct attenuation.  P = perimeter (ft)  S = cross-sectional area (ft)  l = duct length (ft)  f = octave-band center frequency between 63 and 250 Hz 3,0.17 85.0 25.0          S P lf S P Lduct 3,64.1 58.0 73.0         S P lf S P Duct Shape and Noise Control
  46. 46. Rensselaer • For octave bands above 250 Hz  P = perimeter (ft)  S = cross-sectional area (ft)  l = duct length (ft) l S P Lduct        8.0 2.0 Long, p. 486 Duct Shape and Noise Control
  47. 47. Rensselaer Long, p. 486 Frequency (Hz) 63 125 250 500 1000 2000 4000 Loss (dB/ft) Circular 0.03 0.03 0.03 0.05 0.07 0.07 0.07 Loss (dB/ft) Square 0.36 0.20 0.11 0.06 0.06 0.06 0.06 • Data for circular duct from Long, Table 14.1 • Data for square duct from previous equations with P/S = 4 Duct Shape and Noise Control
  48. 48. Rensselaer Discharge Noise From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 High noise levels near the discharge of the AHU
  49. 49. Rensselaer Discharge Noise Control • Stiffen the initial 25-50 ft of the discharge duct • Often done by wrapping the duct with gypsum board or loaded vinyl From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  50. 50. Rensselaer Duct Lagging Make the ducts stiff using lagging, typically fire-rated drywall. From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  51. 51. Rensselaer Duct Lagging MJR Figure 9.14, p. 200
  52. 52. Rensselaer Duct Lagging From Kirkegaard Associates
  53. 53. Rensselaer From Kirkegaard Associates Duct Lagging
  54. 54. Rensselaer From Kirkegaard Associates Duct Penetrations
  55. 55. Rensselaer From Kirkegaard Associates Ductwork Crossing an Isolation Joint
  56. 56. Rensselaer Resilient Duct Hangers Elastomeric Hanger From Kirkegaard Associates
  57. 57. Rensselaer Resilient Duct Hangers Spring-and-Neoprene-in Series Isolator (Hanger) From Kirkegaard Associates Precompressed Spring- and-Neoprene-in-Series Isolator (Hanger)
  58. 58. Rensselaer Resilient Duct Hangers Spring-and-Neoprene-in-Series Isolator (Hanger) From Kirkegaard Associates
  59. 59. Rensselaer Resilient Hangers From Kirkegaard Associates
  60. 60. Rensselaer Resilient Hangers From Kirkegaard Associates
  61. 61. Rensselaer Flexible Duct Connections From Kirkegaard Associates
  62. 62. Rensselaer Improvements in Design for Noise Performance From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 Poor Design Better Design
  63. 63. Rensselaer End Effects • Change in cross-sectional area when a duct terminates in a room                88.1 0 10 1log10 fd c Lend                  88.1 0 10 8.0 1log10 fd c Lend  Termination in free space: Termination flush with wall:  c0 = speed of sound  f = frequency  d = duct diameter ( for a rectangular duct)  S d 4  Long, p. 490
  64. 64. Rensselaer Air Plenums, Passive and Active Silencers • Plenum used near equipment outlet; promotes laminar airflow and provides acoustical insertion loss (< 12 dB) • Passive silencers used when large insertion loss is required; must account for pressure drop • Active silencer has no pressure drop, but is typically impractical From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  65. 65. Rensselaer Application of Duct Liner in Underfloor Plenum From Kirkegaard Associates Lined Plenum (For under-floor air supply)
  66. 66. Rensselaer Silencer Location From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  67. 67. Rensselaer Duct Sound Attenuators From Kirkegaard Associates
  68. 68. Rensselaer Active Noise Control in Ducts MJR Figure 9.19, p. 205 Using data from the input microphone, the controller generates a signal to be played by the loudspeaker which is out of phase (180º) with the duct-borne noise at the loudspeaker position. Feedback from the error microphone (which ideally senses no noise) helps fine tune the process.
  69. 69. Rensselaer A Sample Interior Noise Prediction From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005 (MJR Table 9.2, p. 204)
  70. 70. Rensselaer 1/3 vs. 1/1 Octave Band Data From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  71. 71. Rensselaer Fan and Compressor Noise From Paul Henderson, Acoustics for Mechanical Engineers, ASHRAE Expo 2005
  72. 72. Rensselaer

×