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Back to basics: Acoustics HVAC installations for vibration reduction - - PDF document
Back to basics: Acoustics HVAC installations for vibration reduction - - PDF document
Back to basics: Acoustics HVAC installations for vibration reduction Presented by Clem Sturgess Causes of vibration Vibration is generally transferred into the structure from out of balance or misaligned rotating equipment www.
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Effect of vibration on humans
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Pipework Support
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It is important to isolate pipework that is connected to sources of vibration. Generally the pipes should be supported up to 100 pipe diameters from the source of the vibration.
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Pipework Support
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The spacing of pipework hangers is dependant on the size of the pipework, however, the pipework should be supported at all changes of direction.
Pipework Support
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Pipework should still be isolated even if a flexible connection is used. Water can take a large distance to settle into even laminar flow in pipework. Also under high pressures, the flexible connection may be not that flexible
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Under normal operation, seismic mounts act like standard
- pen springs
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Seismic vibration mount
- How they work
3mm gaps between central block and rubber provide support in the event of seismic activity
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Seismic vibration mount
- How they work
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Force transmitted through to structure
3mm gaps between central block and rubber provide support in the event of seismic activity
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Seismic loading on equipment
Seismic vibration mount
- How they work
Isolation Sleeves
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Prevents bridging the rubber on the base of the mount
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How Vibration Isolation Works
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Natural Frequency
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When an object is struck. It will vibrate at its natural frequency.
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Static deflection
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The more a spring or rubber deflects under load, without compressing to solid, the lower the natural frequency of the mount. This is called the static deflection.
Resonance
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If an object is given repeated pushes at its natural frequency it will go into
- resonance. It will move slightly more each time until it gets out of control.
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Startup Issues
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As a motor ramps up from stopped to operating speed, it must pass through the resonant frequency. The equipment may require some restraint
Effect of height
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The higher storeys are inherently less stable than lower storeys. So the higher in the building, the more isolation is required.
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Important factors in vibration isolation selection
Isolation Efficiency Chart Static Deflection Guide
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The 6 most common vibration problems
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1: Fixed Pipe Stands
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Problem: Well isolated pumps or chillers connected to pipes with fixed stands
1: Fixed Pipe Stands
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Problem: Well isolated pumps or chillers connected to pipes with fixed stands
Isolated Equipment Isolated Equipment Fixed pipe mounting Fixed pipe mounting
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1: Fixed Pipe Stands
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Solution: Install spring mounts on the pipe stand base so that they match pump spring deflection
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Support the top of the pipework using isolation hangers and remove pipe stand
Pipe stand SHS spring hanger
1: Fixed Pipe Stands
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Pipe stand spring hanger
Solution: Install spring mounts on the pipe stand base so that they match pump spring deflection
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Support the top of the pipework using isolation hangers and remove pipe stand
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2: Noise transmitted from isolated pumps
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Problem: Noise transmitted from isolated pumps
Pumps on isolated inertia bases Pumps on isolated inertia bases
2: Noise transmitted from isolated pumps
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Solution: Check under inertia base for nuts, bolts or other debris or adjust springs to raise pumps
Shifter Nut Bolt
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3: Pipework hard fixed into wall or ceiling
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Problem: Noise transmitted from pipework passing through a wall or ceiling
Spring mounted pipework next to a hard grouted wall connection Spring mounted pipework next to a hard grouted wall connection
3: Pipework hard fixed into wall or ceiling
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Solution: Seal around openings for pipework with flexible mastic or insulation
10-15mm clear gap around pipe, filled for a depth of 12mm with non-setting flexible mastic similar to Bostik Fireban One. 10-15mm clear gap around pipe, filled for a depth of 12mm with non-setting flexible mastic similar to Bostik Fireban One. 25mm thick Rockwool sectional pipe sleeve insulation around pipe. Rockwool is to be encapsulated to prevent loss of fibres 25mm thick Rockwool sectional pipe sleeve insulation around pipe. Rockwool is to be encapsulated to prevent loss of fibres 1.2mm thick steel or copper sleeve grouted into wall with non-shrinking grout 1.2mm thick steel or copper sleeve grouted into wall with non-shrinking grout 75mm
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4: Bridging of spring hangers
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Problem: Rod is touching the side of the hanger cage, causing bridging of isolation element
Bridging Bridging
4: Bridging of spring hangers
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Solution: Realign pipe clip or hanger cage so rod is central to the hole in the hanger cage
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5: Hard bolted pipework
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Problem: Condenser pipework hard bolted to floor or walls
5: Hard bolted pipework
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Solution: Suspend pipework from raised frame
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5: Hard bolted pipework
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Solution: Install new wall bracket and suspend pipes from the bracket.
6: Generator vibration transmission
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Problem: Incorrectly adjusted spring mounting
Springs not taking the generator load Springs not taking the generator load
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