ashrae hvac applications
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Title footer may contain company info 5/11/2007
TheTheASHRAE HVAC Applications HandbookASHRAE HVAC Applications Handbook::
What Building Owners and Engineers ShouldWhat Building Owners and Engineers Should
Know AboutKnow About Noise and VibrationNoise and Vibration
Steve Wise
Wise AssociatesMadison, WI608-233-7683
stevewise@att.net
Presentation Title 11/24/2010
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Architects*Understand noise transmission in construction options
Owners*Beware that HVAC Equipment Makes Noise*Set acceptable noise level specifications
Equipment Suppliers*How to provide useful acoustical data
HVAC Engineers
*Maintain noise control design vigilanceContractors*Avoid value-engineering acoustical pitfalls
*Understand impact of subtle installation variances
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CHAPTER 47 - NOISE AND VIBRATION CONTROL
Path Noise Estimation and Control (continued)
Mechanical Equipment Room Sound Isolation
Special Construction Types
Floating Floors and Barrier CeilingsSound Transmission in Return Air Systems
Sound Transmission Through Ceilings
Sound Control for Outdoor Equipment
Fume Hood Duct Design
HVAC Noise Reduction Design Procedures
Vibration Isolation and Control
Vibration Measurements and Criteria
Specification of Vibration Isolation
Internal Versus External Isolation
Isolation of Vibration and Noise in Piping Systems
Seismic ProtectionVibration Investigations
Room Noise Measurements,
Commissioning
Trouble-Shooting
References/ Resources
Data Reliability
Acoustical Design of HVAC Systems
Indoor and Outdoor Sound Criteria
Basic Acoustical Design Techniques
Source Sound Levels
Fans
Terminal Units
Rooftop Mounted Air HandlersAerodynamic Sound in Ducts-
Room Air Devices (GRD)
Chillers / Compressors
Emergency Generators
Path Noise Estimation and Control
Plenums
Ducts, Branches and End Reflections
Duct Silencers
Duct Sound Radiation ( Breakout and Breakin)
Receiver Room Sound Correction
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DATA RELIABILITY
Data in this chapter comes from both from consulting
experience and research studies. Use caution when
applying the data, especially for situations that
extrapolate from the framework of the original research.Although specific uncertainties cannot be stated for each
data set, the sound levels or attenuation data are
probably within 2 dB of measured or expected results.However, significantly greater variations may occur,
especially in low frequency ranges and particularly in
the 63 Hz octave band. Specific data sets may have awide uncertainty range, but experience suggests that, if
done correctly, system estimates that combine data sets
usually compare within about 5 dB of measured levels.
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Paths ofTransmissionSources of Noiseor Vibration
=Sound Level
at Receiver Location
+Where to get data,
or how to estimate it
How to identify and
evaluate them
What is desired, and what will result
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Slide Footer NO Company ID here Slide 61/24/2010Typical Paths of Noise Transmission from HVAC Systems
Path A: Structureborne through floor
Path B: Airborne through supply air system
Path C: Duct breakout from supply air duct
Path D: Airborne through return air system
Path E: Airborne through MER wall
E
A
DC B
Path A: Structureborne through floor
Path B: Airborne through supply air system
Path C: Duct breakout from supply air duct
Path D: Airborne through return air system
Path A: Structureborne through floor
Path B: Airborne through supply air system
Path C: Duct breakout from supply air duct
Path A: Structureborne through floor
Path B: Airborne through supply air systemPath A: Structureborne through floor
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10
20
30
40
50
60
70
31.5 63 125 250 500 1000 2000 4000
Octave Band Frequency (Hz)
Sound Levels From Various HVAC Noise Sources
Fans / AHUs
Fan coils / VAVs
Gril les / Diffusers
Total
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Guidelines for HVAC-Related Background Sound in Rooms
Room Types / Uses RC(N) (QAI
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Guidelines for HVAC-Related Background Sound in Rooms
Room Types / Uses RC(N) (QAI
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0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000 8000
Sound
Pressure
Level(dB)
Octave Band Frequency (Hz)
Noise Criteria (NC) Curves
Room Noise is NC 43
NC-65
NC-60
NC-55
NC-50
NC-45NC-40
NC-35
NC-30
NC-25
NC-20
NC-15
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0
10
20
30
40
50
60
70
80
90
16 31 63 125 250 500 1000 2000 4000
Sound
Pres
sure
Level(dB)
Octave Band Frequency (Hz)
Room Criteria (RC) Curves
Room Noise is RC 35 rumbly
RC Rating Curve
RC55
RC50RC45
RC40
RC35
RC30
RC25
RC20
A - clearly noticeable vibrations
B - mildly noticeable vibrations
A
B
LF MF HF
RC-35
Rumbly
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Guidelines for HVAC-Related Background Sound (2011?)
Room Types / Uses RC/NC
Residences, Apartments, Condos
Bathrooms, kitchens, utility space
Performing Arts Spaces
Drama theaters, concert and recital halls
Music teaching studios
Music practice rooms
Office Buildings
Executive and private offices
Conference roomsTeleconference rooms
Open-plan offices
With sound masking
Corridors and lobbies
30
3025
40
35
45
25
25
30
30
35
dBA
35
3530
45
40
50
30
30
35
35
40
dBC
55
5550
65
60
70
50
50
55
55
60
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Sound Source Path No.
Circulating fans; grilles; registers; diffusers; unitary equipment in room 1
Induction coil and fan-powered VAV mixing units 1, 2
Unitary equipment located outside of room served; remotely located air-handling equipment,
such as fans, blowers, dampers, duct fittings, and air washers
2, 3
Compressors, pumps, and other reciprocating and rotating equipment (excluding air-
handling equipment)
4, 5, 6
Cooling towers; air-cooled condensers 4, 5, 6, 7
Exhaust fans; window air conditioners 7, 8
Sound transmission between rooms 9, 10
No. Transmission Paths Noise Reduction Methods
1 Direct sound radiated from sound source to ear Direct sound can be controlled only by selecting
quiet equipment.
Reflected sound from walls, ceiling, and floor Reflected sound is controlled by adding soundabsorption to room and to equipment location.
2 Air- and structureborne sound radiated from casingsand through walls of ducts and plenums is
transmitted through walls and ceiling into room
Design duct and fittings for low turbulence; locatehigh-velocity ducts in noncritical areas; isolate
ducts and sound plenums from structure withneoprene or spring hangers.
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63 125 250 500 1000 2000 4000
Mineral fiber 1 0.625 13 16 18 20 26 31 36
0.5 0.625 13 15 17 19 25 30 33Glass fiber 0.1 0.625 13 16 15 17 17 18 19
0.6 2 14 17 18 21 25 29 35
Glass fiber
with TL
backing
0.6 2 14 17 18 22 27 32 39
Gypsumboard tiles
1.8 0.50 14 16 18 18 21 22 22
Solid gypsum
board ceiling
1.8 0.50 18 21 25 25 27 27 28
2.3 0.625 20 23 27 27 29 29 30
Double layer
of gypsumboard
3.7 1 24 27 31 31 33 33 34
4.5 1-1/2 26 29 33 33 35 35 36
Mineral fiber
tiles,
concealed
spline mount.
0.5 to 1 0.625 20 23 21 24 29 33 34
Tile Type
Density,
lb/ft2
Thickness,
in.
Octave Midband Frequency, Hz
Ceiling/Plenum/Room Attenuations in dB for Generic Ceiling
in T-Bar Suspension Systems
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Sound Transmission Class (STC) and Transmission Loss Values of
Typical Mechanical Equipment Room Wall, Floor, and Ceiling Types,dB
63 125 250 500 1000 2000 4000
8 in. CMU* 50 35 35 41 44 50 57 64
8 in. CMU with 5/8 in. GWB* on
furring strips53 33 32 44 50 56 59 65
5/8 in. GWB on both sides of 3 5/8
in. metal studs38 18 16 33 47 55 43 47
5/8 in. GWB on both sides of 3 5/8
in. metal studs with fiberglass
insulation in cavity
49 16 23 44 58 64 52 53
2 layers of 5/8 in. GWB on both
sides of 3 5/8 in. metal studs withfiberglass insulation in cavity
56 19 32 50 62 67 58 63
Double row of 3 5/8 in. metal studs,
1 in. apart, each with 2 layers of 5/8
in. GWB and fiberglass insulation in
cavity
64 23 40 54 62 71 69 74
6 in. solid concrete floor/ceiling 53 40 40 40 49 58 67 76
6 in. solid concrete floor with 4 in.
isolated concrete slab and
fiberglass insulation in cavity
72 44 52 58 73 87 97 100
6 in. solid concrete floor with two
layers of 5/8 in. GWB hung on
spring isolators with fiberglass
insulation in cavity
84 53 63 70 84 93 104 105
Room Construction Type STC
Octave Midband Frequency, Hz
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Note 22. Steel springs are the most popular and versatile isolators for HVAC applications
because they are available for almost any deflection and have a virtually unlimited life.
Spring isolators may have a rubber acoustical barrier to reduce transmission of high-
frequency vibration and noise that can migrate down the steel spring coil. They should be
corrosion-protected if installed outdoors or in a corrosive environment. The basic types
include:
Note 23. Open spring isolators (type 3) consist of top and bottom load plates withadjustment bolts for leveling equipment. Springs should be designed with a horizontal
stiffness of at least 80% of the vertical stiffness (kx/ky) to ensure stability. Similarly, the
springs should have a minimum ratio of 0.8 for the diameter divided by the deflected
spring height.
Note 24. Restrained spring isolators (type 4) have hold-down bolts to limit vertical as
well as horizontal movement. They are used with (a) equipment with large variations
in mass (e.g., boilers, chillers, cooling towers) to restrict movement and prevent strain
on piping when water is removed, and (b) outdoor equipment, suchas condensing
units and cooling towers, to prevent excessive movement due to wind loads. Spring
criteria should be the same as open spring isolators, and restraints should have
adequate clearance so that they are activated only when a temporary restraint isneeded.
Closed mounts, orHoused spring isolators consist of two telescoping housings
separated by a resilient material. These provide lateral snubbing and some vertical
damping of equipment movement, but do not limit the vertical movement. Care
should be taken in selection and installation to minimize binding and short-circuiting.
LENGTHY SECTION ON TYPES OF VIBRATION ISOLATORS
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Table 3 Maximum Recommended Duct Airflow Velocities to Achieve Specified
Acoustic Design Criteria
Main Duct Location
Design
RC(N)
Maximum Airflow Velocity,
fpm (m/s)
Rectangular
Duct Circular Duct
In shaft or above drywall ceiling 45 3500 5000
35 2500 3500
25 1700 2500
Above suspended acoustic ceiling 45 2500 4500
35 1750 300025 1200 2000
Duct located within occupied space 45 2000 3900
35 1450 2600
25 950 1700
Aerodynamically
Generated
Sound
in
Ducts
Aerodynamic sound is generated when airflow turbulence occurs at duct elements such as duct
fittings, dampers, air modulation units, sound attenuators, and room air devices. For details on airmodulation units and sound attenuators, see the sections on Variable Air Volume Systems and
Duct Silencers.
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Description
Supply air fan, 7000 cfm, 2.5 in. of water
22 in. dia., 90 rad. unlined elbow
22 44 in. long sound attenuator
22 in. dia., 8 ft long unl ined duct
10 in. dia. branch, 22 in. dia. main, branch path
10 in. dia. branch, 22 in. dia. main, main path
10 in. dia., 6 ft long unl ined duct
VAV terminal
10 in. dia., 2 ft long unl ined duct
10 in. dia., 90 rad. unlined elbow
10 in. dia. diffuser, end reflection15 15 in. rectangular diffuser
ASHRAE room correction: point source
Path Element Sound Calculation Reference
Data Source Reference
Manufacturers data
Attenuation: Table 18
Manufacturers data
Attenuation: Table 11
Attenuation: Table 22
Attenuation: Table 22
Attenuation: Table 11
Manufacturers data
Attenuation: Table 11
Attenuation: Table 18
Attenuation: Table 24Manufacturers data
Equation (22), Tables 32 and 33
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,
Estimated Sound Level Build-Up in Mechanical
Rooms for ARI 575 Chiller Sound Levels
Example:
For ARI 575 test area 15 x 30 x 10
and a room area 30 x 40 x 16
Area ratio =19200/4500 = 4.25
If the room is LIVE (block walls)
the sound level could be 13 dB
louder than ARI submittal sound
rating.
Absorptive wall treatments may
reduce the sound by 10 dB+.
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Troubleshooting (Oops)
Determining Problem Source
Fans, Diffusers, etc.
Determining Problem Type
Noise or Vibration
Testing Vibration Isolator Systems
Floor Flexibility Problems
Vibration Isolation System Resonance
Building Resonances
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