Vibro-Acoustics_bySwegon_White
Vibro-Acoustics_bySwegon_White

Cooling towers are among the heaviest pieces of equipment typically located on the roof. Their change in operating weight (wet vs. dry) poses a challenge when isolating cooling towers for vibration and restraining them for wind or seismic activity.

PDFRegular Details (Broken Link)
PDFSeismic Details (Broken Link)

Vibro-Acoustics' flex connectors are applied to piping connections with vertical inline pumps to isolate the connecting piping and reduce structure-borne noise.

Vibro-Acoustics Seismic Restrained Spring (SCSR) series provide vibration isolation for mechanical systems and equipment. These welded housed isolators are designed to limit vertical and lateral movement of the top support plate caused by equipment operation or wind loading.

Vibro-Acoustics’ Cooling Tower Bases provide support for cooling towers to increase rigidity and provide a method of attachment for vibration isolators.

Steel bases are designed to fit the equipment and are available in any shape and size. Based on the application, cooling tower base designs can work with any of Vibro-Acoustics’ floor-mounted isolators.

Slab on Grade Design Considerations

Structure-Borne Vibration

Problem: This is noise traveling through the structure instead of the air. Vibration from the fans is transferred to the structure and can create noise problems in different areas of the building. Unlike airborne noise, structure-borne noise is very difficult to diagnose post design.  

Solution: Isolate Equipment. Due to the potential change in the operating weight of the cooling tower, restrained isolators are recommended. A minimum of 2-inch deflection is suggested so that the springs are operating at a high efficiency.

Solution: Isolate Connecting Piping. Spring hangers or restrained spring isolators are recommended on the inlet and discharge piping until the vibration is dissipated. Depending on pipe size, this set-up usually requires 3 to 5 hangers on either side. Proper calculations should be performed for quantity and locations of the hangers.

Problem: Some Cooling Towers are not designed to be point loaded on isolators.

Solution: Structural base is required.



Weight Issues

Problem: Unit must be drained for cleaning at required intervals.

Solution: Restrained isolators with upward limit stops must be used to keep unit from becoming displaced and damaging piping connections.

Seismic/Wind Requirements

Problem: Horizontal and vertical forces due to wind and/or seismic forces applied at the center-of-gravity of the unit require proper design of the attachment of the unit and/or vibration isolators to the structure. Typically wind forces are higher than seismic, excluding high seismic areas like California.

Solution: Restrained springs must be used and a certain number of springs may be required to distribute the load properly to the structure.

Problem: Forces are determined by a number of factors including: project location, site class, risk category, component importance factor and equipment location equipment relative to the overall height of the building.

Solution: Certified anchorage calculations must be submitted to verify loading conditions are met for each piece of equipment.

Problem: The complete load path must be followed.

Solution: All connections must be checked including anchorage of unit to base or isolators, attachment of base to isolators and isolators to structure.

Problem: Poor installation of concrete anchors.

Solution: Omega Naught Factor (Horizontal forces multiplied by 2.5).

Problem: Differential motion due to equipment on isolators and piping attached to structure.

Solution: Flexible connectors are required to reduce equipment nozzle loads.

Cooling towers are among the heaviest pieces of equipment typically located on the roof. Their change in operating weight (wet vs. dry) poses a challenge when isolating cooling towers for vibration and restraining them for wind or seismic activity.

PDFRegular Details (Broken Link)
PDFSeismic Details (Broken Link)

Vibro-Acoustics’ Cooling Tower Bases provide support for cooling towers to increase rigidity and provide a method of attachment for vibration isolators.

Steel bases are designed to fit the equipment and are available in any shape and size. Based on the application, cooling tower base designs can work with any of Vibro-Acoustics’ floor-mounted isolators.

Vibro-Acoustics Seismic Restrained Spring (SCSR) series provide vibration isolation for mechanical systems and equipment. These welded housed isolators are designed to limit vertical and lateral movement of the top support plate caused by equipment operation or wind loading.

Vibro-Acoustics' flex connectors are applied to piping connections with vertical inline pumps to isolate the connecting piping and reduce structure-borne noise.

Upper Floor Design Considerations

Structure-Borne Vibration

Problem: Fans are the most common noise source in HVAC systems. If this vibration is transferred to the structure, it can create serious noise problems in many different.

Solution: Isolate Equipment. Inertia base with proper selection of isolators. Ref. Isolation Table for recommended spring deflection.

Problem: Lateral forces due to torque and static.

Solution: Isolate Connection Piping Spring hangers are recommended on the inlet and discharge piping before the drop and until the vibration is dissipated. Depending on pipe size, this set-up usually requires 3 to 5 hangers on either side. Proper calculations should be performed for quantity and locations of the hangers.



Uneven Weight Distribution

Problem: Motor location causes center-of-gravity to be off-center.

Solution:It is important to perform a center-of-gravity calculation and select the appropriate isolators for each location on the inertia base to avoid over- or under-loading isolators.

Seismic/Wind Requirements

Problem: Horizontal and vertical forces applied at the center-of-ravity of the unit require proper design of the attachment of the unit and/or vibration isolators to the structure.

Solution: Restrained springs must be used.

Problem: Forces are determined by a number of factors including: project location, site class, risk category, component importance factor and equipment location equipment relative to the overall height of the building.

Solution: Certified anchorage calculations must be submitted to verify loading conditions are met for each piece of equipment.

Problem: The complete load path must be followed.

Solution: Often overlooked is the proper reinforcement and doweling in of the housekeeping pad to the structural slab.

Problem: Poor installation of concrete anchors.

Solution: IBC 2015 requires ICC-ES approved anchors for cracked concrete and Omega Naught Factor (Horizontal forces multiplied by 2.5).

Problem: Differential motion due to equipment on isolators and piping attached to structure

Solution: Flexible connectors are required to reduce equipment nozzle loads.

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