Quiet, work in progress: reducing the noise pollution of industrial refrigeration plants
Noise pollution is one of the main design variables in modern industry. It is no longer an accessory requirement or an after-the-fact check, but a parameter that directly affects regulatory compliance, the quality of the working environment and the plant’s relationship with the context in which it is placed.
In the industrial refrigeration landscape, the need to reconcile high thermal performance with increasingly stringent acoustic constraints has led to a significant evolution of design solutions. This is particularly true for applications in the food, pharmaceutical and chemical sectors, as well as for installations near residential areas or sensitive receptors, where noise is one of the main critical factors.
The acoustic problem in technological plants
The noise generated by a refrigeration plant derives from the interaction between different sources, propagation mechanisms and emission-spectrum characteristics. For correct acoustic design, it is therefore necessary to consider the origin, frequency and path of the sound.
The main acoustic sources in industrial refrigeration plants are
- the fans, whose aerodynamic contribution is linked to airflow turbulence, vortex shedding from the blade edges and interaction with grilles and cowls;
- the compressors, where mechanical and electromagnetic components prevail, with emissions ranging from the low frequencies associated with high-power motors to the higher frequencies typical of scroll or screw systems;
- the auxiliary equipment (pumps, valves, control devices and support systems), whose acoustic contribution is not intrinsic to the single component but depends on the technology chosen, the operating regime and the coupling with the plant’s structures.
From the propagation standpoint, noise can be transmitted both through the air and structurally. Vibrations transmitted to bases, supports and piping can turn building and structural elements into radiating surfaces, amplifying the acoustic disturbance even at significant distances from the source.
A particularly critical aspect is linked to the nature of the acoustic emissions generated by the different sources. The fans are frequently responsible for low-frequency components, perceived as a “rumble”, difficult to attenuate and often at the origin of the main environmental issues. Pumps and compressors instead tend to generate higher-frequency components, generally more manageable through absorption and confinement solutions.
For this reason, the acoustic design of a plant cannot be limited to a global assessment of the sound level, but must start from identifying the dominant sources and the prevailing frequencies, so as to adopt targeted, effective solutions already at the design stage.
State-of-the-art technologies for reducing noise at the source
The most effective and economically sustainable strategy for achieving a quiet plant is to act directly on the primary noise sources. This approach makes it possible to avoid bulky barriers, oversized silencers or corrective measures that often penalise the plant’s energy efficiency and flexibility.
The Refteco approach is based on this principle: to design components and refrigeration units so that noise is kept to the minimum level compatible with the required performance.
Fans with EC motors
In industrial refrigeration systems, the fan is one of the main noise sources, particularly for the aerodynamic component. The sound generation is closely linked to the rotation speed and to the management of the airflows within the unit, making the ability to operate at low speeds a decisive design factor for controlling acoustic emissions.
The use of fans with EC motors allows continuous regulation proportional to the real load, avoiding over-ventilation and sub-optimal operating conditions. From an acoustic standpoint, even moderate reductions in rotation speed produce significant benefits, especially in the most critical conditions, such as night-time operation.
This approach finds direct application in Refteco solutions: in the unit coolers and air coolers intended for environments with operators present, such as food and pharmaceutical processing rooms, the dual-flow REDI, RBDI, RADI and RGDI series combine EC fans and uniform air distribution to limit local velocities and reduce perceived acoustic disturbance. The goal is not to attenuate the noise, but to prevent it from exceeding values that can create discomfort for those working.
A similar principle is adopted in the RN-series industrial cubic unit coolers, where aerodynamically optimised cowls and EC fans with 6-pole motors make it possible to operate at low rotation speeds, reducing aerodynamic hiss without penalising thermal output.
Quiet compressors and inverter control
The acoustic contribution of the compressor is mainly linked to mechanical vibrations and to operating transients. More than the steady-state sound level, it is often the start-ups, shutdowns and rapid load variations that generate the most critical noise peaks and structural stresses.
The evolution of new-generation compressors has reduced the intrinsic vibrations compared with traditional models. However, from an acoustic standpoint, the real design variable is not the compressor itself, but the way its capacity is managed within the system.
Integrating inverter technology allows the compressor to continuously modulate its operating regime according to the real cooling demand. This avoids continuous on–off cycles, reduces the acoustically most critical transients and limits the transmission of vibrations to the plant’s structure.
In continuously running applications, typical of the food, pharmaceutical and chemical sectors, capacity modulation makes it possible to reconcile two often conflicting needs: noise containment, particularly at night, and the stability of the process thermal conditions. In this context, inverter control is a fundamental design lever for the plant’s overall acoustic management, especially when integrated with EC fan regulation. This approach finds application in high-efficiency units such as the gas coolers RKVD and RKVM, in the air-cooled condensers RCVD and RCVS and in the liquid coolers of the RDVM, RDVS and RDVD series.
Other solutions: structure, aerodynamics and structural noise
In many plants, a significant portion of the acoustic disturbance is not generated directly by the primary source, but by the transmission of vibrations to the structure. Frames, bases, floors and distribution networks can amplify the phenomenon, turning into radiating surfaces and rendering measures limited to airborne noise alone ineffective.
For this reason, alongside the choice of low-noise components, managing the machine–structure coupling is a decisive design variable: anti-vibration mounts correctly sized according to the machine’s characteristic frequencies, flexible connections on piping and ducts and, in the most demanding cases, the use of inertia bases make it possible to effectively limit the propagation of vibrations to the building.
This structural approach is an integral part of the design of Refteco units. In the RDDL flat liquid coolers, the long-frame geometry improves the overall air-handling efficiency, allowing operation with low-speed fans and simultaneously reducing airborne noise and the mechanical stresses transmitted to the structure.
In the RDVM, RDVS and RDVD series, the tube suspension system avoids direct contact between the coil and the frame, limiting the transmission of vibrations and concretely contributing to the reduction of structural noise, as well as improving the unit’s durability over time.
Alongside these solutions, when necessary, there are customised configurations: oversizing the exchangers to operate in “silent” mode, adopting specific anti-vibration mounts, optimising the layout and the plant connections. Measures that do not act as after-the-fact corrections, but as an integral part of the overall acoustic design.
In this sense, noise and vibration control fully belongs, for Refteco, among the “other solutions”: not because they are secondary, but because they are cross-cutting, to be integrated only when the context requires it, and always within a systemic vision of the plant.
Refteco supports designers and end users in developing refrigeration solutions in which thermal performance, reliability and acoustic compatibility are addressed in a coordinated way, right from the initial design stages.
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