Screw Chiller Noise Sources and Their Mitigation

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The Taming of the Screw:
Screw Chiller Noise Sources and Their Mitigation
ASHRAE Seminar 07
Sponsored by TC 2.6
Patrick Marks
Staff Engineer
Carrier Corporation, Syracuse, NY
28 January 2001
Carrier
A United Technologies Company
Screw Chiller Noise Sources and Their Mitigation
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Review of Screw Compression Technology
Types of Screw Chillers
Screw Compressor Noise Generation Mechanisms
Chiller Noise Sources
Component Level Mitigation
System Level Mitigation
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Screw Compression Technology
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Advantages of Screw Compression:
è Positive Displacement
è Few Moving Parts
è Efficient
Disadvantages of Screw Compression:
è Complex Machining Requirements (Tight Tolerances)
è Oil Seals
è Noise - Pure Tones at Relatively High Frequencies
(Sound Quality)
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Screw Chiller Types & Noise Sources
Vibration
Evaporator
Lw
Vibration
Vibration
Pulsation
Vibration
Seminar 07, 28 January 2001
Vibration
Piping
Fan
Oil Separator
Pulsation
Pulsation
Piping
Lw
Pulsation
Lw
Lw
Evaporator
Vibration
Vibration
Pulsation
Compressor
Vibration
Lw
Lw
Condenser
Pulsation
Pulsation
Air-Cooled
è Compressor(s)
è Evaporator
è Piping
è Oil Separator(s)
è Fans
Lw
Lw
Lw
Pulsation
Vibration
Oil Sep.
Pulsation
Vibration
Lw
Lw
Vibration
Compressor
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Lw
Water-Cooled
è Compressor(s)
è Heat Exchangers
è Piping
è Oil Separator(s)
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ASHRAE TC 2.6
Screw Compression Noise
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Pressure Pulsations (Unsteady Mass Flow)
Unsteady Forces
Tonal - Lobe Passage Frequency (LPF)
Two Paths:
è Gas-Borne
Compressor Shell
m Piping
m Heat Exchangers
m
è Structure-Borne
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Heat Exchangers / Piping
At Typical Screw Compressor LPF’s, Shell and
Tube Heat Exchangers are Very Responsive.
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Gas-Borne Excitation
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Pressure Pulsations in Refrigerant
è Discharge Side Symptoms:
Oil Separator(s)
m Compressor Discharge Plenum
m Discharge Piping
m Condenser
m
è Suction Side Symptoms:
Evaporator
m Suction Piping
m
è “Taming” Procedure:
Muffling (Usually difficult for an installed problem, more of
a design fix)
m Lagging - Mass and Decoupling Layer
m
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Structure-Borne Excitation
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Compressor Vibration Transmitted to Other
Components
è Symptoms:
Components Directly Connected to the Compressor
m Heat Exchangers
m Stiff Piping
m
è “Taming” Procedure:
Component Structural Modification (OEM fix only must be qualified)
m Lagging - Mass and Decoupling Layer (Radiating
Component)
m
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Taming of the Screw - Lagging
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Limp Mass with Absorption
f > 250 Hz
2
2
Mass > 1.0 lb./ft (4 kg/m )
3
3
0.5 < ρ < 2.0 lb./ft (8 to 32 kg/m )
Absorptive Material
Adhere this side to chiller
10
8
Typical IL (dB)
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6
4
2
0
100
200
400
800
1600
Impervious Outer Layer
3150
6300
One-Third Octave Band Center Frequency (Hz)
Seminar 07, 28 January 2001
A
ASHRAE TC 2.6
Water Cooled - System Level Noise Control
Enclosures
è Rigid
Panels
m Absorption
m
è “Flexible”
Quilted Barrier
m Absorption and
TL Combined
m
20
18
Typical Insertion Loss (dB)
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16
14
12
10
8
6
4
2
0
125
250
500
1000
2000
4000
8000
Octave Band Center Frequency (Hz)
Seminar 07, 28 January 2001
ASHRAE TC 2.6
A
Water Cooled - System Level Noise Control
Sealing of Leaks is Critical
Shield Sound I.L. with Openings, dB
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45
40
.01 %
35
.05 %
30
.10 %
25
.50 %
20
1.0 %
15
5.0 %
10
10 %
5
% openarea
50 %
0
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Shield Sound I.L. with No Openings, dB
Seminar 07, 28 January 2001
ASHRAE TC 2.6
Air Cooled Chiller Noise Mitigation
Fan Noise Control
è Reduce Fan Speed
è Reduce System
Losses
è Swept Blades
è Reduce Inflow
Distortion
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Partial Enclosure (Fans and
Refrigerant System Noise)
è Louvers
è Sound Traps above Fan Deck
è Barriers
20
18
Typical Insertion Loss (dB)
q
16
14
12
10
8
6
4
2
0
125
250
500
1000
2000
4000
8000
Octave Band Center Frequency (Hz)
Seminar 07, 28 January 2001
ASHRAE TC 2.6
A
The Taming of the Screw - Summary
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Screw Chillers Produce Predominantly Tonal
Noise
Two Paths:
è Structure-borne
è Gas-borne
Taming:
è Components - Lagging
è Water-Cooled System - Enclosure
è Air-Cooled System - Partial Enclosure
Seminar 07, 28 January 2001
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