This article on vibration isolation covers the supply, delivery, installation, and testing of noise and vibration control equipment used to isolate various mechanical devices in HVAC systems.
The purpose of this specification is to ensure that noise levels from mechanical equipment and related services meet the design objectives in all occupied areas specified. The requirements outlined are the minimum necessary precautions to achieve these objectives. The entire installation must operate without objectionable noise and vibration, as determined by the Engineer.
This specification includes the supply, delivery to site, installation, commissioning, and a two-year warranty for noise and vibration control equipment, as detailed in the specification, including schedules of vibration control equipment and drawings.
Vibration Isolation: Sub-Contractor Responsibilities
The Sub-Contractor shall select and provide all mechanical equipment according to the specification, focusing particularly on balancing equipment, aligning driving and driven units, and operating speed.
The Sub-Contractor is responsible for installing all mechanical plant and services in accordance with the specified installation practices and additional precautions necessary to ensure the plant operates without exceeding noise levels or vibration amplitudes specified.
Before starting work on the Project, the Sub-Contractor must review all drawings and specifications and report any features or characteristics that may impact achieving the design objectives to the Engineer.
The Sub-Contractor shall warrant that the complete plant and installation, when performed within design standards, will meet the noise standards specified in this section.
During construction or after completing the works, the Sub-Contractor is responsible for any corrective actions needed to meet all design objectives.
Design Objectives
The octave band sound pressure levels at various parts of the building and specific locations outside the building, due to equipment operation, shall not exceed the noise level ratings specified in the schedule below.
In case of disputes regarding the classification of areas per the schedule, the area classification determined by the architect shall be final:
| SPACE/AREA | NOISE CRITERIA (NC) | dBA |
|---|---|---|
| Food Court, Hawkers Areas, Atrium, Lobbies, Corridors | 45 | 53 |
| Supermarket, Shop Lots, Retail Departmental Stores | 45 | 53 |
| General Office and Clerical Areas | 40 | 49 |
| Toilets | 50 | 58 |
| Car Parks, Kitchens | 55 | 62 |
| Exterior Areas at Property Boundaries | 60 dBA daytime, 55 dBA nighttime | 62 |
| Hotel Guest Rooms | 27 | 32 |
| Hotel Guest Bathrooms | 35 | |
| Hotel Public Rooms | 35-40 | |
| Hotel Meeting/Board/Ball Rooms | 35 | |
| Private Offices | 35 |
Vibration Isolation: Space/Area Noise Standards (NC) dBA
The specified noise level limits apply to locations 1 m to 2 m above the floor and not closer than 1.5 m from any air outlet or equipment.
Environmental external noise limits are imposed on all equipment operations to control noise disturbance from outside equipment.
Standards for environmental vibration levels should be nearly imperceptible to most people, with reradiated structure-borne noise levels not exceeding approximately NC 35 to minimize contribution to airborne noise in the audible range.
Vibration levels should be below minus 60 dB Re 1G from 2 Hz to 10 Hz and minus 55 dB Re 1G from 10 Hz to 31.5 Hz.
Vibration Isolation: Anti-Vibration Equipment/Techniques
The following summarizes the types and methods of noise and vibration control equipment used to isolate various mechanical equipment:
Steel Springs in Series with Neoprene Pads
Unless otherwise specified, the spring type isolator shall be non-housing, laterally fixed with leveling bolts firmly bolted to the inertia blocks/base frames. The diameter should be comparable to the compressed height at rated load, with horizontal spring stiffness equal to vertical stiffness.
The spring should have a minimum excess travel per solid equal to 50% of the rated deflection, ensuring the elastic limit is not exceeded.
All springs must be mounted with adequate clearance from the brackets and must be visible or subject to critical inspection.
Examples of spring types include:
- Mason Type SLFH
- Vibron Engineering (M) Sdn Bhd 86B, 2nd Floor, Jalan SS 15/4 47500 Petaling Jaya, Selangor
- Kinetics Type S (preferably Type FDS)
- Mecomb Malaysia Sdn Bhd Lot 20, Jalan 225 PO Box 24, 46700 Petaling Jaya, Selangor
Other makes/types of isolators with known load/deflection curves may be used with the Engineer’s approval.
For restricted mounts, use housing with vertical limit stops, maintaining a clearance of at least 10 mm around bolts and between housing and spring to prevent interference. Mounts used outdoors should be hot-dipped galvanized.
Common choices include: Kinetics FLS Corefund WSCL, Mason SLR, WMC, AWR.
All steel springs must be installed in series with two layers of neoprene ribbed or waffle pattern pads (minimum 8 mm thickness).
Springs should support calculated loads with specified minimum spring deflections without exceeding the manufacturer’s maximum rated loads.
The mechanical contractor must consider the weight distribution of equipment, unsupported pipes/vessels, and dynamic forces from fluid movement, torque reaction, and starting/stopping. Shop drawings, make, and model numbers of selected isolators, and their calculated loads must be submitted.
Inertia Blocks
Inertia blocks are installed as specified. Mechanical devices must be bolted directly to integral concrete inertia blocks. The concrete should have a minimum density of 2240-2400 kg/cu m (140-150 lb/cuft).
Generally, the length and width of the inertia block should be at least 50% greater than the supported equipment. The inertia is determined by the block’s weight and thickness.
The base consists of a concrete slab on a welded steel base frame assembly. Frames should be welded steel channels with a minimum thickness of 150 mm (6″) or equivalent, reinforced with 12 mm (½”) steel reinforcing rods or angles welded at 150 mm (6″) centers. Anchor bolts should allow minor location adjustments. Bolts are placed in sleeves or pockets cast into the block for later insertion.
Provide a minimum 10 mm plywood or equivalent to form the slab. Steel channel isolator brackets must be welded to the channel frames and adjusted to the height of the deflected springs and inertia block clearance with the plinth.
Ensure sufficient clearance (min. 20 mm) across the spring to avoid contact with any part of the mounted assembly. Clearance between inertia block and floor/plinth should be at least 75 mm (3”).
The Sub-Contractor shall supply and install all required welded structural steel and reinforcement for inertia blocks and coordinate with the main contractor for concrete supply. Installation works are included in this sub-contract.
Ribbed or Waffle Pattern Neoprene Pads
Use 40 durometer pads 8 mm (5/16″) – 9.5 mm (3/8″) thick as supplied by the manufacturer.
For typical applications, 40 durometer neoprene pads should support a surface weight of approximately 35,000 kg/sq.m (7150 lb/sq ft).
When using multiple layers of neoprene pads, separate individual layers with 1 mm (20 g) thick steel shims.
Vibration Isolation: Resilient Hangers
Elastic hangers are used for the suspension of pipes and ducts where specified. For deflections above 6 mm (¼”), the hangers should be multi-disked or coil spring, allowing vertical movement of 6 mm (¼”) without generating excess noise or vibration.
Ensure hangers are suitable for the installation, including dynamic vibration loads from moving parts, and meet the specified isolation criteria.
Acoustic Mufflers
Install acoustic mufflers to reduce noise levels in ductwork. Mufflers should be constructed with sound-absorbing materials and installed as specified to meet the desired noise reduction levels.
Ensure mufflers are tested and rated according to standards and comply with specified noise criteria.
Testing and Acceptance
Following installation, conduct vibration testing to ensure compliance with specified limits. Testing should include vibration amplitude measurements and verification against the provided standards. The Contractor must correct any deviations and retest as necessary to meet requirements.
All equipment, installation practices, and control measures must be validated to ensure that the completed work meets the noise and vibration criteria specified. The Engineer’s approval is required before final acceptance.
Conclusion
Effective vibration isolation is crucial for maintaining a quiet and comfortable environment in buildings. By following the specifications for the supply, installation, and testing of noise and vibration control equipment, and ensuring all components meet the specified standards, the Sub-Contractor ensures that the mechanical systems operate smoothly and quietly, meeting the design objectives and enhancing overall building performance.
About The Author
Omprakash Ramagiri; as the Founder of HVAC Technocrats, I bring over 18 years of experience as a Mechanical Engineer specializing in HVAC (Central Air-conditioning) for commercial, cleanrooms, data centers, and Petrochemical industries. Throughout my career, I’ve held pivotal roles at companies like TATA Consulting Engineers, MW Zander (for Cleanroom solutions), Bluestar Malaysia, and ETA in Dubai. I’ve managed international HVAC projects and gained valuable exposure in dynamic markets like Dubai and Saudi Arabia. With a passion for excellence and a commitment to innovative solutions, I specialize in designing Class 10K & 100K Cleanrooms for various industries. Connect with me to explore collaborations in HVAC design, project sales, and consultancy. Click to visit the Author’s Linkedin page
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