The Taming of the Screw:Screw Chiller Noise Sources and Their Mitigation

ASHRAE Seminar 07Sponsored by TC 2.6

Patrick Marks

Staff EngineerCarrier Corporation, Syracuse, NY

28 January 2001

A United Technologies Company

Carrier

Return to www.enoisecontrol.com

Seminar 07, 28 January 2001

Screw Chiller Noise Sources and Their Mitigation

q Review of Screw Compression Technologyq Types of Screw Chillersq Screw Compressor Noise Generation Mechanismsq Chiller Noise Sourcesq Component Level Mitigationq System Level Mitigation

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Screw Compression Technology

q Advantages of Screw Compression:è Positive Displacementè Few Moving Partsè Efficient

q Disadvantages of Screw Compression:è Complex Machining Requirements (Tight Tolerances)è Oil Sealsè Noise - Pure Tones at Relatively High Frequencies

(Sound Quality)

ASHRAE TC 2.6

Seminar 07, 28 January 2001

è Compressor(s)è Evaporatorè Pipingè Oil Separator(s)è Fans

Screw Chiller Types & Noise Sourcesq Water-Cooled

è Compressor(s)è Heat Exchangersè Pipingè Oil Separator(s)

q Air-Cooled

Compressor Oil Separator

Lw

Evaporator Piping

Lw

Vibration

Pulsation

Vibration

Vibr

atio

n

Puls

atio

n

Vibration

Pulsation

Lw Lw

LwVi

brat

ion

Puls

atio

n

Lw

Fan

Compressor Oil Sep.

Lw

Evaporator Piping

Lw

Condenser

Vibration

Pulsation

Vibration

Vibr

atio

n

Puls

atio

n

Vibration Vibration

Pulsation Pulsation

Lw Lw

LwLw

Vibr

atio

n

Puls

atio

n

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Screw Compression Noiseq Pressure Pulsations (Unsteady Mass Flow)q Unsteady Forcesq Tonal - Lobe Passage Frequency (LPF)q Two Paths:

è Gas-Bornem Compressor Shellm Pipingm Heat Exchangers

è Structure-Bornem Heat Exchangers / Piping

q At Typical Screw Compressor LPF’s, Shell andTube Heat Exchangers are Very Responsive.

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Gas-Borne Excitationq Pressure Pulsations in Refrigerant

è Discharge Side Symptoms:m Oil Separator(s)m Compressor Discharge Plenumm Discharge Pipingm Condenser

è Suction Side Symptoms:m Evaporatorm Suction Piping

è “Taming” Procedure:m Muffling (Usually difficult for an installed problem, more of

a design fix)m Lagging - Mass and Decoupling Layer

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Structure-Borne Excitationq Compressor Vibration Transmitted to Other

Componentsè Symptoms:

m Components Directly Connected to the Compressorm Heat Exchangersm Stiff Piping

è “Taming” Procedure:m Component Structural Modification (OEM fix only -

must be qualified)m Lagging - Mass and Decoupling Layer (Radiating

Component)

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Taming of the Screw - Lagging

q Limp Mass with Absorptionq f > 250 Hzq Mass > 1.0 lb./ft2 (4 kg/m2)q 0.5 < ρ < 2.0 lb./ft3 (8 to 32 kg/m3)

Impervious Outer Layer

Adhere this side to chiller

Absorptive Material

0

2

4

6

8

10

100 200 400 800 1600 3150 6300

One-Third Octave Band Center Frequency (Hz)

Typi

cal I

L (d

B)

A

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Water Cooled - System Level Noise Controlq Enclosures

è Rigidm Panelsm Absorption

è “Flexible”m Quilted Barrierm Absorption and

TL Combined

0

2

4

6

8

10

12

14

16

18

20

125 250 500 1000 2000 4000 8000 A

Octave Band Center Frequency (Hz)

Typi

cal I

nser

tion

Loss

(dB

)

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Water Cooled - System Level Noise Controlq Sealing of Leaks is Critical

05

1015202530354045

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75Shield Sound I.L. with No Openings, dB

Shie

ld S

ound

I.L.

with

Ope

ning

s, d

B

.01 %

50 %

10 %

5.0 %

1.0 %

.50 %

.05 %

.10 %% open-

area

ASHRAE TC 2.6

Seminar 07, 28 January 2001

Air Cooled Chiller Noise Mitigationq Fan Noise Control

è Reduce Fan Speedè Reduce System

Lossesè Swept Bladesè Reduce Inflow

Distortion

0

2

4

6

8

10

12

14

16

18

20

125 250 500 1000 2000 4000 8000 A

Octave Band Center Frequency (Hz)

Typi

cal I

nser

tion

Loss

(dB

)

q Partial Enclosure (Fans andRefrigerant System Noise)è Louversè Sound Traps above Fan Deckè Barriers

ASHRAE TC 2.6

Seminar 07, 28 January 2001

The Taming of the Screw - Summary

q Screw Chillers Produce Predominantly TonalNoise

q Two Paths:è Structure-borneè Gas-borne

q Taming:è Components - Laggingè Water-Cooled System - Enclosureè Air-Cooled System - Partial Enclosure

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eASHRAE TC 2.6