Because HVAC systems involve many moving components, it is normal to experience some vibration and noise, even in a correctly installed and well-maintained system. However, excessive vibration and noise indicate that a facility is due for maintenance and can also lead to other performance problems.
Vibration and noise are typically addressed together because they are closely related; the second is often a consequence of the first. Some homeowners just focus on noise and use a lot of sound insulation, but this isn't the best approach because it doesn't solve the underlying problem.
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Common Sources of Vibration
In HVAC installations, vibration often originates from rotating machinery or mass air movements. Vibration tends to increase over time as system components wear, but it can also be present in new installations as a consequence of poor design decisions:
- Excessive vibration can be caused by an oversized compressor or cooler . This also leads to extra capital expenditure, additional power requirements and a shorter equipment lifespan – oversized units cycle on and off more frequently.
- Oversized fans and blowers can also cause excessive vibration.
- In HVAC systems that utilize hydronic piping, water pumps can also be a source of vibration. As with compressors and chillers, the effect can be minimized with proper equipment selection and the use of damping pads.
- Even if the equipment is properly sized, vibration problems can arise due to the use of inadequate supports. There are neoprene and fiberglass pads that minimize vibration transmitted between moving equipment and the underlying structure.
- Poorly designed air ducts can experience high air pressure or velocity, and this can also be a source of vibration.
- In general, any equipment that rotates can produce vibration if the shaft is not aligned correctly. Special attention should be paid to shaft couplings between different equipment, for example between an electric motor and a centrifugal pump. The centerlines of both axles should coincide as much as possible to minimize vibration.
Vibration can only be felt directly in some cases – humans are more likely to perceive vibration when the frequency is low and the magnitude is high. However, the negative consequences begin before this point is reached: many mechanical components are very susceptible to vibration, especially the bearings of rotating machines.
The best way to control vibration is to prevent it with smart design choices . In existing installations, it can be minimized with proper maintenance and installation of shock absorbers or spring supports for rotating machines. Keep in mind that it is not possible to completely eliminate vibration, but it can be reduced and isolated to a point where its effects are negligible.
In general, excessive vibration increases the cost of ownership of construction systems. Maintenance expenses and downtime tend to increase, and the associated noise can be distracting in work environments. In the industrial sector, uncontrolled vibration can lead to product quality problems. For example, propagated vibration can affect the performance of machining equipment, leading to incorrect product dimensions and other similar defects.
Propagated vibrations and noise
When troubleshooting vibration, remember that vibration can propagate. In many cases, most of the noise is produced by building components that are affected by vibration propagated from other sources. False ceiling grids can become very noisy when subjected to vibrations, as they have many points of contact with ceiling tiles and lighting fixtures.
In new construction, a good recommendation is to define a building layout where the occupied areas are not adjacent to mechanical rooms or other sources of noise and vibration. This provides comfort to occupants, while also reducing the need for sound insulation between different areas of the building.
Dealing with noise from aerodynamic effects
Excessive wind speed and turbulence can also cause noise, and direct exposure to air currents is uncomfortable and harmful to health. These effects can be minimized by correctly sizing ventilation equipment but owners of existing buildings can also control fan speeds with variable frequency drives.
Many installations with oversized fans use air dampers to regulate flow, often causing excessive pressure and hissing sounds. Furthermore, this represents a waste of energy. Reduced speed operation consumes less energy and produces less noise than restricting airflow from an oversized fan running at full speed.
For air ducts in new construction, avoid 90° turns whenever possible, as these tend to cause turbulence and noise. When air ducts need to change direction, the best option is to use consecutive 45° bends or bends rather than a sudden 90° angle.
Upgrading equipment to improve efficiency and reduce vibration
Equipment becomes more prone to vibrations as it ages, and in many cases it makes sense to consider a new unit. This is especially true if existing equipment also consumes a lot of energy. For example, modern chillers with variable speed compressors can achieve savings of over 50% when replacing older units.
If you are planning to replace fan and pump motors, consider high-efficiency units with speed control:
- For fractional horsepower applications, consider electronically commutated motors (ECMs), also known as brushless motors. They are highly efficient and come with built-in speed control.
- For higher power applications, consider NEMA Premium Efficiency motors equipped with variable frequency drives. Consider that many types of VFDs can drive three-phase motors with single-phase input, so there is no reason to limit your options to single-phase motors.
Final Recommendations
Vibration and noise can be addressed through prevention or mitigation. In projects that are still in the design phase, it is important to ensure that the machinery is properly sized and specified with appropriate supports. Also remember that some degree of vibration is normal, so be sure not to place mechanical rooms near sensitive areas. Ideally, mechanical rooms should be isolated from hallways, service areas, storage rooms, or other types of rooms that are not permanently occupied.
In existing buildings, vibration and noise problems can be controlled with effective maintenance. Equipment that generates vibration can be mounted on springs or dampers, and speed control can be implemented for pumps and blowers. If a piece of equipment is very old and produces a lot of vibration, consider replacing it to also improve energy efficiency.
