using simulation to determine attenuation of hvac ductwork

David HerrinUniversity of Kentucky

Using Simulation to Determine Attenuation of HVAC Ductwork

University of Kentucky

March 18, 2021

Vibro-Acoustics Consortium

March 18, 2021

2

Overview

• Unlined and Lined Duct Insertion Loss

• Elbow Insertion Loss

• Plenum Insertion Loss

• Duct Breakout Noise


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3

Prior ASHRAE Sponsored Work• Vér, I.L. 1978. A review of the attenuation of sound in straight lined and

unlined ductwork of rectangular cross section. ASHRAE Transactions84(1):122-149.

• Kuntz, H.L. and R.M Hoover. 1987. The interrelationships between the physical properties of fibrous duct lining materials and lined duct sound attenuation. ASHRAE Transactions 93(2):449-470.

• Reynolds, D.D. Reynolds, D.D. and J.M. Bledsoe. 1989a. Sound attenuation of unlined and acoustically lined rectangular ducts. ASHRAE Transactions 95(1):90-95.

• J.M. Bledsoe. 1989b. Sound attenuation of acoustically lined circular ducts and radiused elbows. ASHRAE Transactions 95(1):96-99.

Limitation Measurement-based studies based on a limited number of duct cross-sectional areas and lining lengths.


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4

RP-1408 Campaign

Receiving Room (Reverberant Room)

Test Duct

Source Room with Loudspeaker Array

ASTM E477

Source Room

ReceivingRoom


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Modeling Approach

20 Monopoles

Automatically Matched Layer

Structural FEMRigid Ductwork

Acoustic FEM




Poroelastic FEM

Acoustic FEM

Acoustic FEM


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Modeling Approach

Poroelastic Mesh

Structural Mesh

Acoustic Mesh


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Sound Absorptive Material Properties

0.0

0.2

0.4

0.6

0.8

1.0

0 1000 2000 3000 4000 5000

Soun

d Ab

sorp

tion

Frequency (Hz)

Measurement Curve Fit

• Johnson-Champoux-Allard model (Allard and Atalla 2009)• Curve fit (using ESI Foam-X software) used to identify the flow

resistivity, characteristic viscous length, characteristic thermal length, and mass density for the fiber.

• Alternative sound absorbing models can be used with little impact.


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Metrics for Duct Attenuation

Insertion Loss – Difference in sound pressure level in receiving room without and with absorbing lining.Noise Reduction – Difference in sound pressure level between source and termination (independent of source).Transmission Loss – Difference between incident and transmitted sound power (independent of source and termination).

Source Room

Noise Control Treatments


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Noise Reduction – Unlined Duct

24 in x 24 in (0.61 m x 0.61 m), 10 ft (3.05 m) Length Square Duct

-5

0

5

10

15

62.5 125 250 500 1000 2000 4000

Noi

se R

educ

tion

(dB)

Frequency (Hz)FEM (Rectangular) ASHRAE Handbook (Rectangular)


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10

Noise Reduction – Unlined Duct24 in (0.61 m) Diameter, 20 ft (6.10 m) Length Circular Duct

-5

0

5

10

15

62.5 125 250 500 1000 2000 4000

Noi

se R

educ

tion

(dB)

Frequency (Hz)FEM (Circular) ASHRAE Handbook (Circular)


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Insertion Loss – Lined Duct24 in x 24 in (0.61 m x 0.61 m), 10 ft (3.05 m) Length Square Duct2 in (5 cm) fiber lining)

0

10

20

30

40

50

60

50 100 200 400 800 1600 3200 6400

Inse

rtion

Los

s (d

B)

Frequency (Hz)

FEM Measurement (RP-1408)


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+

-

+

+

-

Insertion Loss – Lined Duct

𝑓𝑐

2𝑑

𝑓 𝑐𝑑


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13


0102030405060708090

50 100 200 400 800 1600 3200 6400

Inse

rtion

Los

s (d

B)

Frequency (Hz)

FEM Measurement (RP-1408)

24 in x 24 in (0.61 m x 0.61 m), 30 ft (9.15 m) Length Square Duct2 in (5 cm) fiber lining)


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Likely Flanking Path



Flanking Path


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0

10

20

30

40

50

60

70

80

50 100 200 400 800 1600 3200 6400

Inse

rtion

Los

s (d

B)

Frequency (Hz)FEM Measurement (RP-1408)

24 in (0.61 m) Diameter, 20 ft (6.10 m) Length Circular Duct2 in (5 cm) fiber lining)


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Attenuation vs. Length

010

20

3040

50

6070

80

90

0 5 10 15 20

Atte

nuat

ion

(dB)

Distance (Acoustic Wavelengths)315 Hz (10 ft) 630 Hz (10 ft) 800 Hz (10 ft) 1250 Hz (10 ft)315 Hz (30 ft) 630 Hz (30 ft) 800 Hz (30 ft) 1250 Hz (30 ft)


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Overview

• Unlined and Lined Duct Insertion Loss





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Introduction

Airborne direct path

Airborne indirect path or duct breakout

Structure‐borne path

HVAC Building Equipment


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Prior Elbow Work• Vér, I.L. 1983. Noise generation and noise attenuation of duct fittings

– a review: Part II (RP-265). ASHRAE Transactions 90(2A):383-390.

• Mechel, F. 1975. Mufflers, Chapter 19, Pocket Book of Technical Acoustics. Ed. H. Heckl and M.A. Mueller, Springer (in German).

• VDI.2001. VDI Technical Report 2081. Noise Generation and Noise Reduction in Air-Conditioning Systems.

Limitation Studies limited to certain duct sizes, bend angles, and specific sound absorptive linings.


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Modeling Approach

20 Monopoles

Rigid Ductwork

Acoustic FEM Poroelastic FEM

Structural FEM


Acoustic FEM

Acoustic FEM





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Modeling Approach

Acoustic Mesh with Automatically Matched Layers

Structural Mesh

Poroelastic Mesh


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Elbow Insertion Loss

Source

Source

𝐿 ,

𝐿 ,

𝐼𝐿 𝐿 , 𝐿 ,


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Insertion Loss – Unlined Elbow

23

24 in x 24 in (0.61 m x 0.61 m)

-5

0

5

10

15

20

50 100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Frequency (Hz)

FEM ASHRAE Handbook


March 18, 2021

Insertion Loss – Lined Elbow

24

24 in x 24 in (0.61 m x 0.61 m)1 in (2.5 cm) fiber lining

-5

0

5

10

15

20

50 100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Frequency (Hz)

FEM ASHRAE Handbook


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Lined Elbow Insertion Loss

Source

Source

𝐿 ,

𝐿 ,

𝐼𝐿 𝐿 , 𝐿 ,


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Insertion Loss – Lined Elbow24 in x 24 in (0.61 m x 0.61 m)1 in (2.5 cm) fiber lining

-10

0

10

20

30

40

50 100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Frequency (Hz)

FEM ASHRAE Handbook


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Overview

• Lined Duct Insertion Loss





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𝐼𝐿 10 log 𝑆𝑐𝑜𝑠𝜃2𝜋𝑑

1𝑅

Above the cutoff frequency

𝑑 𝐿 𝑙 𝐻 )

cos𝜃 𝐻/𝑑

𝑆 𝑙𝑊

𝑅 𝑆𝛼 1 𝛼⁄ )

Wells, 1958

𝑙

𝐿

𝐻 𝑊

Unlined and Lined Plenums


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Mouratides and Becker, 2003


𝐼𝐿 𝐴 𝑆 𝑊 𝐸

Below the cutoff frequency

𝐴 ~ empirically defined surface area coefficient𝑆 ~ total inside surface area of plenum less the inlet and outlet areas𝑊 ~ wall effect (dB)𝐸 ~ offset angle effect (dB)


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Mouratides and Becker, 2003


Above the cutoff frequency

𝐼𝐿 𝑏𝑆 𝑄4𝜋𝑟

𝑆 1 𝛼𝑆𝛼 𝐸

𝑆 ~ outlet cross-sectional area𝑆 ~ surface area of the plenum𝑟 ~ distance between the centers of the inlet and outlet sections𝑄 ~ directivity factor, and 𝛼 is the average absorption coefficient in the plenum𝑏, 𝑛 ~ empirically determined constants (3.505 and -0.359)𝐸 ~ offset angle effect (dB)


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Finite Element Model

Poroelastic Mesh

Structural Mesh

Acoustic Mesh

Automatically Matched Layers


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Insertion Loss – Unlined Plenum

4 ft x 6 ft x 5 ft

unlined plenum

0

5

10

15

20

100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Freqeuncy (Hz)

Measurement (RP-1026)FEMMouratidis and Becker (2004)Wells (1958)


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Insertion Loss – Lined Plenum

0

10

20

30

40

100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Freqeuncy (Hz)

Measurement (RP-1026)FEMMouratidis and Becker (2004)Wells (1958) 4 ft x 6 ft x 5 ft lined

(2 in fiber) plenum


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0

10

20

30

40

100 200 400 800 1600 3200

Inse

rtion

Los

s (d

B)

Freqeuncy (Hz)

Measurement (RP-1026)FEMMouratidis and Becker (2004)Wells (1958)

Insertion Loss – Lined Plenum with Right Angle

4 ft x 6 ft x 5 ft lined

(2 in fiber) plenum

Inlet and outlet ducts at right angles


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Overview

• Lined Duct Insertion Loss





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Prior Breakout TL Work

36

• Vér, I.L. 1983. Prediction of Sound Transmission through Duct Walls; Breakout and Pickup. ASHRAE TRP-319.

• Cummings, A. 1983. Acoustic noise transmission through the walls of air conditioning ducts. Final Report, Department of Mechanical and Aerospace Engineering, University of Missouri, Rolla.

• Cummings, A. 1985. Acoustic noise transmission through duct walls. ASHRAE Transactions 91(2A):48-61.

• Cummings, A. 2001. Sound transmission through duct walls. Journal of Sound and Vibration 239(4):731-765.

• Lilly, J. 1987. Breakout in HVAC duct systems. Sound & Vibration 21(10).

Limitation Studies limited to certain duct sizes and specific sound absorptive linings.


March 18, 2021

Measurement (Cummings, 1985)

Receiving Room (Reverberation Room)


Sound Absorptive Termination

𝑇𝐿 𝐿 𝐿 10 log𝑆𝑆

Method 1 (low frequencies)


March 18, 2021Measurement of Breakout Transmission Loss (Cummings,

1985)



Method 2 (high frequencies)

Measure sound pressure in reverberation room with cap as on prior slide then measure again with horn.

Measurement (Cummings, 1985)


March 18, 2021

Modeling Approach

39

20 Monopoles


Structural FEM

Rigid Ductwork

Acoustic FEM




Poroelastic FEM

Acoustic FEM

Acoustic FEM


March 18, 2021

Structural FEM Models

40

30 ft (9.15 m) Rectangular Duct

20 ft (6.10 m) Circular Duct


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Damping Properties

41

Accelerometers

Data Acquisition

Rectangular Duct


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Measured Damping

42

Measured Damping Loss FactorsCircular Rectangular

Frequency (Hz)10 in Diameter

(25.4 cm)10 in × 10 in

(25.4 cm × 25.4 cm)16 in × 16 in

(40.6 cm × 40.6 cm)32 in × 32 in

(81 cm × 81 cm)Unlined Unlined Unlined Lined Unlined Lined

63 0.016 0.011 0.012 0.014 0.012 0.021125 0.010 0.006 0.009 0.038 0.007 0.011250 0.007 0.004 0.006 0.036 0.004 0.030500 0.016 0.003 0.010 0.026 0.003 0.026

1000 0.008 0.003 0.007 0.022 0.003 0.0222000 0.004 0.003 0.004 0.012 0.002 0.0144000 0.002 0.004 0.004 0.007 0.002 0.0098000 0.001 0.002 0.002 0.005 0.002 0.006


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Rectangular Duct Breakout TL Curve

From Vér, I.L. 1983


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Breakout TL – Rectangular Duct

44

16 in x 48 in (0.4 m x 1.2 m) Rectangular Duct; 10 ft (3.1 m) Length2 in (5 cm) Fiber Lining

10

20

30

40

50

60

70

50 100 200 400 800 1600 3200 6400

Brea

kout

Tra

nsm

issi

on L

oss

(dB)

Frequency (Hz)

FEM (Unlined) FEM (Lined)ASHRAE Handbook (Unlined) Cummings (1983)


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45

Circular Duct Breakout TL Curve

From Vér, I.L. 1983


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Breakout TL – Circular Duct24 in (0.61 m) Diameter Duct; 20 ft (6.1 m) Length2 in (5 cm) Fiber Lining

20

30

40

50

60

70

80

90

100

50 100 200 400 800 1600 3200 6400

Brea

kout

Tra

nsm

issi

on L

oss

(dB)

Frequency (Hz)

FEM (Unlined) FEM (Lined)ASHRAE Handbook (Unlined) ASHRAE Handbook (Lined)Cummings (1983)


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47

Importance of Breakout TL

0

10

20

30

40

50

60

50 100 200 400 800 1600 3200 6400

Atte

nuat

ion

(dB)

Frequency (Hz)

Insertion Loss Breakout Transmission Loss (Unlined)Breakout Transmission Loss (Lined)


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Summary

• FEA approach qualified for predicting insertion loss of unlined and lined ducts, elbows, and plenums.

• FEA approach qualified for predicting breakout transmission loss.

• Approach can be used for design purposes and to fill in the gaps in the ASHRAE Handbook.


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References• K. Ruan and D. W. Herrin, “A Simulation Approach to Determine the

Insertion and Transmission Losses of Unlined and Lined Ducts (RP-1529),” ASHRAE Transactions, Vol. 122, Part 1 (2016).

• K. Ruan and D. W. Herrin, “Using Simulation to Determine Elbow and Side Branch Attenuation and Duct Breakout Transmission Loss (RP-1529),” ASHRAE Transactions, Vol. 122, Part 1 (2016).

• D. W. Herrin and K. Ruan, “A Review of Prior ASHRAE Research Efforts to Characterize Noise Propagation in Ducts,” ASHRAE Transactions, Vol. 125, Part 1 (2019).

using simulation to determine attenuation of hvac ductwork

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