How are vibrations generated in thermo-hydraulic systems?
Basically, the vibrations are produced either by a rotor which, during its operation, undergoes friction with consequent removal of material. This removal causes an imperfect balancing of the rotor itself with consequent onset of vibrations. Any pump has at least one rotor inside it. Vibrations can also arise as pulsations: imagine a tube inside which a pressurized fluid (a gas or a liquid) flows: if the tube is sufficiently elastic it is possible that it starts to pulsate under the effect of the pump that puts the fluid under pressure, a bit like when you feel the heartbeat by touching a vein.
What limits must the vibrations produced by these systems respect?
To date, there is still no legal provision that sets limits on the levels of vibration that can be tolerated in the living environment; There are Standard Hygiene Regulations, issued by the Regions and then usually adopted by the Municipalities. These regulations cite the international ISO 2631 standards which in turn were then implemented in Italy by the UNI, among which the following are mentioned:
• UNI 9614:2017 standard “Measurement of vibrations in buildings and disturbance evaluation criteria”;
• UNI 9916:2014 standard: “Criteria for measurement and evaluation of the effects of vibrations on buildings”.
Generally, as regards damage to buildings, the levels considered by the regulations are higher than those which cause disturbance or alarm to people.
Vibration measurement is a fairly complex practice since multi-channel instruments are required (at least 3 for each measurement point: X, Y and Z) and the subsequent post-processing required by the regulations is rather complex. Today there are few structures on the market capable of carrying out vibrometric analyses.
How are vibrations attenuated?
The vibrations produced by the operation of a system must be attenuated before they propagate to the structure of the building by interposing systems capable of dampening them between the machine and the structure.
There are two types of support: point or plate.
Punctual supports are usually applied to medium-sized systems (AHU, refrigeration units, etc...); the type depends on the range of frequencies that must be attenuated: rubber elements are effective at frequencies that are not "very low" while elements with coil springs or pneumatic elements can effectively reach even very low frequencies.
The sheet supports can be applied to any type of system and are useful for their versatility and very low thickness. They are applied from the foundations of buildings to the support of small systems.
All systems must be appropriately sized; in fact, vibration isolation occurs if the elastic support is partially crushed (static sagging) by the weight of the mass above. If it is too compressed or not at all, the insulating effect is compromised.
To put it in engineering terms, the springs must have an elastic constant K which depends on the way the machine vibrates and must have almost zero damping, which can be achieved by using high quality steels; the plates must have a specific dynamic rigidity depending on the air mass of the system and a high resilience.
One of the most common mistakes in mounting anti-vibration mounts is leaving rigid connections between the machine and its foundation. In this case, despite all the attention paid to the choice of supports, these will be practically ineffective. Another aspect of fundamental importance is that all machine connections (electrical, hydraulic, aeraulic, etc...) must be made with flexible elements. Flexible fittings adaptable to numerous needs, temperatures and pressures are commercially available.
How are vibrations generated in thermo-hydraulic systems?
Basically, the vibrations are produced either by a rotor which, during its operation, undergoes friction with consequent removal of material. This removal causes an imperfect balancing of the rotor itself with consequent onset of vibrations. Any pump has at least one rotor inside it. Vibrations can also arise as pulsations: imagine a tube inside which a pressurized fluid (a gas or a liquid) flows: if the tube is sufficiently elastic it is possible that it starts to pulsate under the effect of the pump that puts the fluid under pressure, a bit like when you feel the heartbeat by touching a vein.
What limits must the vibrations produced by these systems respect?
To date, there is still no legal provision that sets limits on the levels of vibration that can be tolerated in the living environment; There are Standard Hygiene Regulations, issued by the Regions and then usually adopted by the Municipalities. These regulations cite the international ISO 2631 standards which in turn were then implemented in Italy by the UNI, among which the following are mentioned:
• UNI 9614:2017 standard “Measurement of vibrations in buildings and disturbance evaluation criteria”;
• UNI 9916:2014 standard: “Criteria for measurement and evaluation of the effects of vibrations on buildings”.
Generally, as regards damage to buildings, the levels considered by the regulations are higher than those which cause disturbance or alarm to people.
Vibration measurement is a fairly complex practice since multi-channel instruments are required (at least 3 for each measurement point: X, Y and Z) and the subsequent post-processing required by the regulations is rather complex. Today there are few structures on the market capable of carrying out vibrometric analyses.
How are vibrations attenuated?
The vibrations produced by the operation of a system must be attenuated before they propagate to the structure of the building by interposing systems capable of dampening them between the machine and the structure.
There are two types of support: point or plate.
Punctual supports are usually applied to medium-sized systems (AHU, refrigeration units, etc...); the type depends on the range of frequencies that must be attenuated: rubber elements are effective at frequencies that are not "very low" while elements with coil springs or pneumatic elements can effectively reach even very low frequencies.
The sheet supports can be applied to any type of system and are useful for their versatility and very low thickness. They are applied from the foundations of buildings to the support of small systems.
All systems must be appropriately sized; in fact, vibration isolation occurs if the elastic support is partially crushed (static sagging) by the weight of the mass above. If it is too compressed or not at all, the insulating effect is compromised.
To put it in engineering terms, the springs must have an elastic constant K which depends on the way the machine vibrates and must have almost zero damping, which can be achieved by using high quality steels; the plates must have a specific dynamic rigidity depending on the air mass of the system and a high resilience.
One of the most common mistakes in mounting anti-vibration mounts is leaving rigid connections between the machine and its foundation. In this case, despite all the attention paid to the choice of supports, these will be practically ineffective. Another aspect of fundamental importance is that all machine connections (electrical, hydraulic, aeraulic, etc...) must be made with flexible elements. Flexible fittings adaptable to numerous needs, temperatures and pressures are commercially available.