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Noise can then vary according to the type of belts:
synchronous belts (i.e. toothed belts) are less silent How to limit noise emission
than V-type belts because of the continuous impacts of Air Cooled Heat Exchangers
of the belts teeth to the pulleys teeth, and because
of the very fast evacuation of air, which occur Many factors can be applied to design low noise air
continuously during operation, when the belts teeth coolers. Some of them affect the capability of the
match the pulleys teeth. equipment to transfer heat to the ambient air (e.g.,
Noise emitted by electric motors is due to different reduced ambient air flow through the heat exchanger)
components/mechanisms like mechanical noise and shall therefore be balanced by oversizing the heat
related to bearings, electromagnetic noise, and exchange surface, with impact on CAPEX. Other
noise due to the cooling fans. In case of ultra low expediencies are instead related to detailed design and
noise applications, electric motors noise can be of applied based upon experience or specific calculations,
the same magnitude of that of the fans, requiring when convenient. Some examples are the attention to
particular attention to their selection. A further the correct positioning of the safety nets, the use of
aspect taken into account when designing air vibration isolators, and the adoption of bell-shaped
coolers is that motors driven by variable frequency fans rings.
drives (i.e., inverters) emit more noise than motors Not only that, the collaboration between the
directly connected on-line. This is due to the manufacturer and the EPC / plant operator may allow
harmonics resulting from the variable frequency creative solutions to be identified and implemented, not
drives. strictly related to the design of the equipment but to the
way it is used and controlled by the plant control
While designing air coolers, consideration is given to system as well. For instance, a possibility could be to
the presence of any obstacles upstream and design the air cooler for fulfilling the noise requirements
downstream from the fans like the safety nets aimed set for daytime, and to turn off some fans during
at maintenance personnel avoiding getting into nighttime, when the noise limitations are usually more
contact with the rotating parts. Provisions like these stringent. Depending on the application, this might be
affect the noise performance of air coolers because convenient as the capability of air coolers to dissipate
of both the additional static pressure required by the heat increases, the lower the ambient temperature.
fans, and because of the turbulence therein
generated. Table 1 lists some of the main strategies usually
applied to reducing air coolers noise. Further comments
Finally, any excess of vibration of the structural parts and notes are reported in the history case that follows,
should be avoided by designing the equipment for which a detailed analysis has been conducted to
correctly and selecting fans suitable for the application. identify and rank the noise control measures to be

STRATEGY PROS CONS
Increased loads on steel structures,
Use of Low noise type fans
1 Straight noise reduction Higher electrical consumption,
vs. standard fans
Higher cost
Increase of footprint and piping
Increase of heat exchange Decrease of fan static pressure and
2 length,
surface electric power absorption
Increased weight of equipment
Use of V-belt type
3 Slight noise reduction -
transmissions

Turn-off some fans during Relevant reduction in case of very low Increased complexity of the control
4
nighttime ambient temperatures system
Possibility of reducing fans speed dur-
5 Add Inverters for motors Impact on CAPEX
ing night time
Add precautions on Reduced noise, by avoiding excess of Increase of steel structures weight
6
structural components vibration and air turbulence and complexity

Table 1: Main strategies for reducing air coolers noise.

IndustrIal Plants - May 2022
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