Category: Blauberg

Inline duct fans are widely used in residential buildings, commercial facilities and auxiliary industrial ventilation systems. Installed directly within the ductwork, they support supply air, exhaust air, local ventilation and equipment cooling.

One of the most visible differences between fan models is the housing material. Some use engineering plastics, while others are manufactured from galvanized or coated steel. From an engineering perspective, however, housing material alone does not determine fan performance.

The main differences between metal and plastic housings relate to structural rigidity, weight, corrosion resistance, temperature capability and maintenance requirements. A suitable selection must also take into account the required airflow, system resistance, air characteristics, acoustic limits and control strategy.

Housing material is only one part of the fan design

Plastic inline duct fans commonly use polypropylene or other engineering plastics for the housing, airflow guides and connection spigots. The motor, bearings, fasteners and supporting components may still be made of metal.

Metal duct fans are generally constructed with galvanized or coated steel housings. Their impellers may be made from metal or engineering plastic, depending on the design.

The terms “metal fan” and “plastic fan” therefore refer mainly to the housing or primary structural material. They do not imply that the impeller, motor and control system use the same material configuration.

Within Blauberg’s inline duct fan range, for example, some mixed-flow models combine a plastic inner housing with a steel acoustic casing, while certain box-type models use galvanized steel housings, backward-curved centrifugal impellers and EC motors. These material combinations are selected to address specific requirements for pressure performance, acoustic treatment, installation and maintenance.

Aerodynamic selection should be based on the operating point

Inline duct fan selection begins with two parameters: the required airflow and the system resistance.

The maximum airflow shown in a product catalogue is generally measured under low-resistance conditions. Once the fan is connected to an actual duct system, it must overcome pressure losses generated by straight duct sections, bends, transitions, dampers, filters, grilles and heat exchangers.

For a conventional ventilation system, resistance can be approximated as:

Δp = KQ²

where Δp is the pressure loss, Q is the airflow rate and K represents the combined resistance of the ductwork and its components.

The point at which the fan performance curve intersects the system resistance curve is the actual operating point. Two fans with similar connection sizes and nominal maximum airflow may therefore deliver different airflow rates when installed in the same system.

Impeller type, blade geometry, impeller diameter, rotational speed and internal airflow guidance all influence the pressure–airflow characteristic.

Axial or mixed-flow fans may be suitable for short duct runs with limited resistance. For longer duct systems, multiple filters or higher static-pressure requirements, mixed-flow or centrifugal designs should be evaluated against their complete performance curves. Maximum airflow alone does not provide a reliable indication of installed performance

Engineering characteristics and limitations of plastic housings

Engineering plastics can be injection-moulded into complex airflow guides, reinforcing ribs and connection structures. This allows several functions to be integrated into the housing while reducing the number of separate components and maintaining consistent internal geometry.

Plastic housings are also relatively lightweight. This can reduce the load placed on suspended ceilings, mounting brackets and duct connections, making them suitable for compact circular duct systems with limited installation space.

Unlike unprotected carbon steel, plastic does not undergo conventional electrochemical corrosion. Plastic inline fans are therefore commonly used for bathroom exhaust, residential fresh-air systems, storage-room ventilation and general equipment cooling.

However, resistance to rust should not be confused with universal resistance to corrosive environments. Different polymers respond differently to high temperatures, ultraviolet exposure, oil mist, solvents, acids and alkaline substances.

Under prolonged heat or continuous mechanical load, some plastics may also experience creep, resulting in gradual deformation or dimensional change.

Selection should therefore consider:

● The exact housing and impeller material

● Permissible ambient and air-stream temperatures

● Material flammability classification

● Chemical compatibility

● Installation orientation

● Support and fastening requirements

A low-flammability material classification describes material behaviour under defined test conditions. It does not replace whole-product approval for high-temperature operation or smoke-extraction duty.

Structural characteristics and corrosion considerations of metal housings

Metal housings offer relatively high structural rigidity and are well suited to flanged connections, access panels, support frames and larger enclosure designs.

For rectangular duct systems, higher-airflow applications or mechanical rooms requiring regular inspection, metal housings can be integrated more readily with ductwork, vibration isolation and maintenance access.

Metal casings can also incorporate perforated panels, mineral wool or other acoustic materials to reduce noise radiated through the housing. The resulting acoustic performance depends on the combined design of the impeller, airflow path, casing and sound-absorbing structure. It should not be assumed that a metal fan is inherently quieter.

Galvanized steel provides a degree of surface protection, but cut edges, welds, fixing holes and damaged coatings may still become corrosion initiation points. In humid, saline or chemically aggressive environments, the coating system and maintenance interval should be assessed in relation to the expected corrosion category.

When cold air is transported, the metal housing may fall below the surrounding air’s dew point and develop surface condensation. Thermal insulation, vapour control and condensate management may therefore be required.

Fire safety, high-temperature capability and noise must be assessed at product level

A standard metal inline fan is not automatically suitable for high-temperature smoke extraction.

High-temperature performance depends on more than the casing material. The impeller, motor insulation, bearing lubrication, cables, seals, electronic controls and mounting structure must all remain functional under the specified temperature and operating duration.

Similarly, a plastic fan cannot be assessed for fire-related applications solely on the basis of the material’s flammability rating.

Smoke extraction, commercial kitchen ventilation, drying equipment and high-temperature process exhaust systems require purpose-designed products. Selection should be based on air temperature, exposure duration, contaminant type, project specifications and the relevant test documentation for the specific model.

Housing material may be used as an initial screening factor, but it cannot replace whole-product testing and certification.

Fan noise should also be evaluated as a system characteristic. Typical sources include impeller rotation, motor operation, airflow separation and structure-borne transmission.

When comparing acoustic data, it is important to distinguish between sound power level and sound pressure level. Test distance, fan speed, airflow, static pressure and installation conditions must also be consistent.

An inlet located immediately after a bend, an abrupt transition, undersized ductwork or the absence of flexible connectors can increase noise at the installation site.

For meeting rooms, classrooms, hotel rooms and other acoustically sensitive spaces, the fan, duct velocity, silencers, flexible connections, vibration isolators and installation position should be considered as one integrated system.

EC control should be treated as a separate selection criterion

EC motor technology is available with both plastic and metal inline duct fans. Its main engineering value lies in speed control and system connectivity rather than housing material.

Depending on the model, an EC fan may accept a 0–10 V control signal and connect to temperature, pressure or indoor-air-quality sensors, as well as a building management system. This allows fan speed to be adjusted in response to actual ventilation demand.

Under geometrically similar conditions and approximately constant air density:

● Airflow is approximately proportional to rotational speed

● Pressure is approximately proportional to the square of rotational speed

● Shaft power is approximately proportional to the cube of rotational speed

Actual electrical input, however, also depends on motor efficiency, controller losses, system operating point and the duration of operation at each speed. A single energy-saving percentage should therefore not be applied without reference to a defined system and operating profile.

For applications with variable loads, EC control provides a technical basis for demand-controlled ventilation and system regulation. Selection should also confirm the required control signal, communication protocol, protection functions, minimum stable speed and compatibility with sensors or building automation systems.

Conclusion

Plastic inline duct fans offer advantages in weight, component integration and resistance to conventional rust. They are well suited to systems with clearly defined air conditions, stable temperatures and restricted installation space.

Metal inline duct fans provide greater flexibility for structural reinforcement, flanged connections, acoustic enclosures and maintenance access. They are commonly considered for larger systems, higher duct resistance or projects with more demanding structural and service requirements.

A sound selection process should establish the required airflow and static pressure first, followed by the air characteristics, temperature range, material compatibility, available installation space, acoustic limits, fire requirements and control strategy.

The final decision should be based on the performance curves, technical specifications and test documentation of the specific fan model.

There is no universal advantage of metal over plastic, or plastic over metal, when the operating conditions are not defined. A meaningful engineering comparison must consider the housing material together with the impeller design, motor configuration, system resistance and operating environment.

When selecting a centrifugal fan, airflow, static pressure, efficiency and noise are usually the first parameters considered. Impeller material, however, is often reduced to a simple assumption: metal is stronger, while plastic is lighter.

In practice, impeller material affects structural strength, dimensional stability, manufacturing methods and environmental suitability. It should not be evaluated independently of blade geometry, impeller diameter, operating speed or temperature.

In this article, metal impellers mainly refer to the steel, aluminum-alloy and stainless-steel impellers commonly used in industrial centrifugal fans. Plastic impellers mainly refer to components made from glass-fiber-reinforced engineering plastics such as PA6-GF. Performance can vary significantly according to material grade, glass-fiber content and structural design. Final selection should therefore be based on the technical documentation and test results for the specific fan model.

Comparison of the structural and material characteristics of metal and engineering-plastic centrifugal impellers

Fire Safety: Material Properties Are Not the Same as Whole-Fan Fire Resistance

Under normal fan operating conditions, steel and aluminum-alloy impellers do not exhibit the softening and dripping behavior associated with thermoplastics. Their metallic base materials also do not produce smoke through the thermal decomposition of a polymer matrix.

Metal impellers can therefore offer a material-level advantage in applications where combustible materials are restricted, or where smoke generation and molten dripping are particular concerns.

A metal impeller, however, should not automatically be regarded as suitable for smoke extraction. At elevated temperatures, the mechanical strength of steel and aluminum alloys may decrease, and thermal deformation may occur. Surface coatings, motor insulation, bearing lubricants, cables and electronic controls must also be assessed for high-temperature operation.

Some engineering plastics can be compounded with flame retardants to achieve specified flammability ratings. These ratings describe how a standardized material specimen performs under defined test conditions. They do not, on their own, demonstrate that the complete fan is suitable for smoke extraction or has achieved a particular fire-resistance classification.

For smoke extraction, high-temperature air handling or applications with defined fire-resistance requirements, suitability should be determined through whole-fan testing at the specified temperature and duration, rather than by impeller material alone.

The fire safety and structural reliability of a metal impeller must be verified together with the complete fan under defined high-temperature test conditions

Structural Strength: Focus on Allowable Tip Speed and Long-Term Stability

At comparable temperatures and with appropriate structural design, metals generally offer a higher elastic modulus and better dimensional stability. This can provide greater design flexibility for larger impellers, higher allowable tip speeds and greater centrifugal loads.

Even so, the reliability of a metal impeller is not determined by material strength alone. Stamping, bending and welding may introduce local deformation or residual stress. Blade attachment points, weld quality and balancing accuracy can all affect long-term operation.

For high-speed impellers, structural safety margins may also need to be assessed through finite-element analysis, overspeed testing and fatigue validation.

Plastic impellers are commonly manufactured from glass-fiber-reinforced engineering plastics such as PA6-GF. Glass fibers can improve stiffness and mechanical strength, but actual performance depends on fiber content, fiber orientation, wall-thickness design, ambient humidity and molding conditions.

Injection molding allows blades, backplates and connecting structures to be formed as a single component, making complex three-dimensional blade geometries easier to produce. At the same time, designers must control molding shrinkage, warpage and anisotropic behavior caused by fiber orientation.

For impellers operating continuously at elevated temperatures or under sustained mechanical loads, creep and long-term material aging must also be considered.

Aerodynamic Performance: Blade Design Matters More Than Material Choice

The aerodynamic efficiency of a centrifugal fan is not determined directly by whether the impeller is made from metal or plastic.

Blade curvature, impeller diameter, blade count, inlet geometry, volute or airflow-path matching, and the clearance between the impeller inlet and inlet cone all influence flow separation, recirculation losses and pressure development.

Injection molding is well suited to complex surfaces and smooth geometric transitions. When tooling, material and processing conditions are stable, it can also provide consistent geometry across large production volumes. For this reason, molded plastic impellers are widely used in small and medium-sizedproduced in larger quantities.

Advances in metal forming and joining technologies have also made three-dimensional blade designs possible in metal impellers. Some product generations have improved efficiency, allowable speed and acoustic performance through optimized blade profiles, inlet matching and stress distribution.

These results, however, are usually associated with the development of specific products. They should not be interpreted as evidence that metal impellers are universally more efficient than plastic alternatives.

The two options should be compared under the same test standard and operating conditions, using airflow–static pressure curves, total or static efficiency, input power and sound power data.

Impeller material should be matched with the motor, airflow path, heat-exchange components and actual operating conditions

Noise and Vibration: Material Alone Does Not Determine Acoustic Performance

Engineering plastics generally provide greater material damping, while metals usually offer a higher elastic modulus. These characteristics can influence structural behavior, but neither directly determines the overall noise level of a fan.

The acoustic performance of a centrifugal fan is also affected by blade-pass frequency, flow separation, impeller balance, installation stiffness, structural modes and the selected operating point.

When a fan operates close to stall or near a structural resonance speed, noise and vibration may increase significantly even when the impeller material remains unchanged.

Statements such as “plastic impellers are always quieter” or “metal impellers are always more stable” are therefore too broad. Low-noise selection should be based on sound power data at the specified operating point, together with the operating-speed range and the airflow path inside the equipment.

Corrosion Resistance and Environmental Compatibility: Verify Material Suitability Case by Case

Plastic impellers do not suffer from conventional metallic oxidation or rust and generally require no additional anti-corrosion coating in ordinary humid environments.

However, plastic is not resistant to every medium. Oil mist, solvents, cleaning chemicals, ultraviolet exposure, high temperatures and high humidity can all affect material properties.

Metal impellers can be manufactured from galvanized steel, coated steel, aluminum alloy or stainless steel, depending on the operating environment. Corrosion resistance varies substantially between different metal grades and surface treatments.

Where salt spray, chemical gases or condensate may be present, material selection should be based on the actual medium and verified accordingly.

Manufacturing Cost: Production Volume and Size Determine Overall Value

Plastic impellers usually require a relatively high initial investment in injection-molding tools. Once stable mass production has been established, however, they can offer short molding cycles, fewer individual parts and good batch-to-batch consistency. This makes them well suited to small and medium-sized products manufactured in larger volumes.

Metal impellers may require cutting, forming, welding, surface treatment and balancing. Although this involves more individual processing steps, metal construction often provides greater flexibility for large impellers, special dimensions and low-volume customized projects.

Cost comparisons should therefore extend beyond the purchase price of a single impeller. Tooling investment, production volume, transport weight, maintenance conditions and expected service life should all be considered.

Selection Must Begin with the Actual Operating Conditions

When selecting an impeller material for a centrifugal fan, engineers should verify several key conditions:

Does the applicable equipment standard restrict combustible materials? What are the ambient temperature and conveyed-air temperature? What are the maximum operating speed and allowable impeller tip speed? Does the airstream contain moisture, salt spray, oil mist, dust or chemical substances? Will the fan operate continuously? What safety tests and market-access requirements must the complete fan satisfy?

Across its centrifugal fan range, Blauberg uses different impeller materials according to impeller diameter, operating speed and application environment. Model-specific documentation identifies parameters such as impeller material, motor protection, control options and performance data.

Some models use PA6-GF impellers, while others use metal impellers. The exact configuration and scope of protection should always be confirmed in the technical specification for the relevant model.

This product-development approach reflects an important principle: impeller material should be treated as one element of system selection and evaluated together with the motor, operating speed, airflow path, control method and application environment.

Metal impellers are often worth considering where equipment standards restrict combustible materials, where tip speeds are relatively high, or where dimensional stability is a priority.

Engineering-plastic impellers may be suitable where weight reduction, complex molded blade geometry and production consistency are important.

The comparison should not be viewed as a contest between a “higher-grade” and a “lower-grade” material. The better choice is the impeller that suits the operating conditions, has been properly validated and is correctly matched to the complete fan system.

The same fan architecture, but very different control capabilities

Cross-flow fans, also known as tangential fans, typically use a long cylindrical impeller. Air enters the impeller radially, passes across its interior, and then flows through the blades a second time before being discharged. This creates a broad, relatively uniform airflow pattern across the length of the fan.

Their low-profile design makes cross-flow fans well suited to applications where installation space is limited but a wide air outlet is required. Typical uses include air curtains, fan coil units, heating appliances, terminal HVAC equipment, refrigerated display cases, and selected electronics-cooling systems.

Cross-flow fans are generally used in applications requiring relatively high airflow at low pressure. Their actual aerodynamic performance, however, depends not only on the motor but also on impeller length, tongue clearance, inlet and outlet geometry, and the overall resistance of the host equipment.

AC, DC, and EC cross-flow fans differ in power supply, speed-control capability, and ease of system integration. Strictly speaking, however, these are not three fully parallel motor classifications. AC and DC mainly describe the input power supply, while EC refers to electronic commutation. Many low-voltage brushless DC fans therefore also use electronically commutated motors in principle.

In practical fan selection, the industry commonly uses “AC fan” for conventional motors connected directly to an AC supply, “DC fan” for low-voltage direct-current products, and “EC fan” for electronically controlled permanent-magnet solutions, often designed for direct connection to AC mains. This article follows that widely used convention.

AC cross-flow fans: straightforward control for stable operating conditions

AC cross-flow fans are normally powered directly from an alternating-current supply. Common motor types include shaded-pole motors, permanent-split-capacitor motors, and other AC induction-motor designs.

Their mechanical and electrical configurations are well established. For equipment that only requires on/off operation, a fixed speed, or a small number of preset speed levels, the overall system can remain relatively simple.

AC fans are not necessarily limited to one speed. Depending on the motor and product design, some single-phase AC motors can use tapped windings, transformers, series capacitors, or voltage-control methods to provide stepped speed adjustment. Compatible three-phase motors may also be controlled by a variable-frequency drive.

These methods can affect motor temperature, available torque, and acoustic performance. Their suitability should therefore be confirmed against the motor specification and through testing of the complete appliance.

For entry-level air curtains, heating appliances, and air-circulation equipment that operate for long periods at a stable duty point, an AC solution may still be a practical choice. Its main advantages are fewer control components and a relatively straightforward initial configuration—not universally lower cost or higher efficiency under every operating condition.

When an application requires frequent airflow adjustment or prolonged operation at low speed, a conventional AC control arrangement may offer a limited control range. It may also experience changes in low-speed torque or electromagnetic noise. These effects vary by motor design, so AC fans should not be treated as though they all behave in the same way.

DC cross-flow fans: a natural fit for low-voltage systems

DC cross-flow fans commonly operate from low-voltage supplies such as 12, 24, or 48 VDC, although the available voltage range depends on the specific design.

Most modern DC fans use brushless motors with electronic commutation. This allows for compact construction, fast control response, and convenient integration with an equipment controller or main circuit board.

In this context, “DC fan” is primarily a product and power-supply classification. It does not mean that DC and EC motors are fundamentally unrelated. A low-voltage brushless DC motor can also be electronically commutated. In practice, the main differences usually involve the input supply, where power conversion takes place, the available control interfaces, and the intended application platform.

Depending on the model, a DC cross-flow fan may support speed control through a dedicated PWM input, an analog control signal, or adjustment of the supply voltage within the permitted operating range. Some models may also provide FG or tachometer feedback, alarm outputs, locked-rotor protection, or reverse-polarity protection.

These functions should not be assumed to be standard across all products. The specification sheet and wiring documentation for the selected model must always be checked.

Where the equipment already includes a DC bus or switch-mode power supply—such as in vehicle HVAC systems, electronic equipment, charging systems, or compact heating and cooling appliances—a DC fan is often easier to integrate into the electrical architecture.

Where the host system is supplied only by AC mains, the efficiency, capacity, thermal management, and cable-voltage drop of the AC/DC power supply must also be included in the system assessment.

EC cross-flow fans: designed for variable-speed operation and system integration

EC stands for electronically commutated. In fan applications, an EC motor generally combines a permanent-magnet rotor, stator windings, and an electronic controller. The controller energizes the windings in sequence according to rotor position, creating the rotating magnetic field required to drive the motor.

In an EC fan designed for direct connection to AC mains, the incoming AC supply is typically rectified to create a DC bus. Power electronics then control the motor. The motor, drive electronics, and control functions can be integrated into a compact assembly, so a separate variable-frequency drive is usually not required.

The main value of an EC solution lies in its wide speed-control range and its ability to operate efficiently under part-load conditions. Fan speed can be adjusted in response to temperature, equipment load, or commands from the main control system, reducing unnecessary input power when full-speed operation is not required.

Depending on the model, an EC fan may accept PWM, 0–10 V, 4–20 mA, or digital communication signals. It may also provide speed, operating-status, and fault feedback.

Functions such as Modbus communication, RS485 connectivity, PID control, or constant-airflow operation are model-dependent or optional. They should not be presented as standard features of every EC cross-flow fan.

For air curtains, fan coil units, and heating or cooling equipment that operate continuously, experience significant load variation, or need to communicate with a central controller, EC technology generally makes demand-based speed control easier to implement.

The electronic section still requires careful attention to electromagnetic compatibility, ambient temperature, cooling, signal compatibility, and electrical protection. Fan selection should therefore not be based on rated airflow alone.

Efficiency comparisons must be made at the actual operating point

AC, DC, and EC cross-flow fans should not be compared only by motor nameplate efficiency or maximum airflow.

The final performance of the system depends on the motor, power electronics, impeller, scroll or airflow guide, and the complete internal airflow path of the equipment.

A more meaningful comparison is made under the same installation boundary conditions, at the same air density and operating point. Input power, airflow, pressure rise, and acoustic performance should all be measured under equivalent conditions.

For cross-flow fans, airflow distribution along the full impeller length is also important. Restricted inlet sections, uneven internal geometry, or incorrect tongue clearance may cause airflow distortion, recirculation, and additional noise.

The benefit of EC technology under variable-load conditions does not come from the motor alone. It also comes from the ability to reduce speed when full airflow is unnecessary.

If a system always operates at one duty point, a properly matched AC or DC solution may still satisfy both performance and cost requirements. If the equipment spends long periods at part load or requires frequent airflow adjustment, an EC solution usually provides greater scope for system-level optimization.

Where each option fits best

An AC cross-flow fan is generally suited to equipment with an AC supply, relatively stable operating conditions, and limited control requirements.

A DC cross-flow fan is a good fit for products that already have a low-voltage DC supply, limited installation space, and a need for integration with an electronic control board.

A mains-powered EC cross-flow fan is typically better suited to applications with variable loads, continuous speed control, operating feedback, or communication requirements.

Final selection should also account for target airflow, pressure requirement, impeller length, mounting orientation, inlet and outlet clearance, operating temperature, noise limits, supply voltage, and control interface.

Choosing the correct motor type does not automatically guarantee the expected performance of the complete appliance. The match between the fan, impeller, housing, and airflow path remains equally important.

For suppliers such as Blauberg, whose product portfolio includes fan, motor, and control technologies, technical discussions should go beyond a simple “AC or EC” comparison. The selected solution should be based on the actual duty point, available power supply, installation conditions, and control requirements.

For any specific cross-flow fan, the final decision should always be confirmed against the relevant performance curves, wiring diagrams, and technical data sheet.

Dry coolers and cooling towers are typically installed outdoors on rooftops, equipment platforms, or at industrial facilities

Outdoor Cooling Equipment Places Greater Demands on Fan Performance

Dry coolers and cooling towers play an important role in rejecting excess heat from data centers, industrial refrigeration systems, energy centers, process cooling applications, and large commercial buildings.

A dry cooler uses ambient air flowing across a finned heat exchanger to cool the circulating fluid inside the system. A cooling tower removes heat through the combined movement of air and heat exchange with circulating water. Although the two types of equipment differ in structure and operating principle, both depend on continuous and reliable airflow. Axial fans provide the driving force required to move air through the heat exchange area.

Unlike ventilation equipment installed indoors, dry coolers and cooling towers are typically located on rooftops, equipment platforms, or open outdoor sites. Their fans may be exposed to high summer temperatures, freezing winter conditions, rain, humidity, dust, crosswinds, and prolonged sunlight. Some industrial applications may also involve corrosive atmospheres, frequent start-stop cycles, or continuous year-round operation.

For this reason, fan selection should not be based on rated airflow alone. The ability to operate reliably under changing environmental conditions, while working effectively with the heat exchanger, fan housing, and control system, is often more important over the equipment’s service life.

Why Axial Fans Are Commonly Used in Dry Coolers and Cooling Towers

Dry coolers and cooling towers generally require high airflow volumes. Most of the system resistance comes from finned coils, fill media, louvers, protective guards, and the internal structure of the equipment.

Axial fans move air in a direction parallel to the fan shaft. Their compact construction, shallow installation depth, and ability to move large volumes of air make them well suited for installation above or beside heat exchangers, as well as within modular fan housings.

For larger cooling systems that use multiple fans in parallel, axial fan configurations also support modular equipment design and more convenient maintenance.

Schematic of airflow paths and axial fan operation in dry coolers and cooling towers

However, selecting a suitable fan involves more than comparing catalogue performance data.

The distance between the fan and the heat exchanger, the clearance between the impeller and the fan housing, restrictions around the air inlet, and the possibility of exhaust air recirculation can all affect actual airflow and heat rejection performance.

If airflow is concentrated in only part of the heat exchanger, some sections of the coil or fill media may not be used effectively. If warm discharge air is drawn back into the equipment, cooling capacity may decline even when the fan continues to operate at a relatively high speed.

The fan, housing, inlet grille, and heat exchanger should therefore be considered as one complete air-moving system. Well-designed airflow distribution is often more valuable than simply increasing motor power.

More Airflow Is Not Always Better

Cooling demand in dry coolers and cooling towers is rarely constant.

Outdoor temperature, the number of operating units, process heat loads, supply and return water temperatures, and system setpoints can all change throughout the day and across different seasons.

During hot summer conditions, the equipment may require a higher airflow rate. In cooler weather or during periods of reduced demand, operating every fan continuously at full speed can result in unnecessary energy use and higher noise levels.

If the fan is undersized, the heat exchanger may not receive enough airflow. As a result, the circulating fluid temperature may rise and the cooling system may operate under greater load.

An oversized fan, on the other hand, may increase initial cost, operating noise, and energy consumption without providing a meaningful improvement in system performance.

A more effective approach is to determine the fan duty point according to the resistance of the heat exchanger, the required airflow, and the expected operating range. Appropriate allowances should also be made for high ambient temperatures, dirt accumulation, crosswinds, and other adverse conditions.

The objective is not to select the fan with the highest airflow rating, but to select one that matches the actual system requirements.

EC Speed Control Allows Cooling Capacity to Follow Demand

Traditional fixed-speed fans often regulate cooling capacity through on-off operation or staged fan control. When system demand moves between control stages, this approach may lead to temperature fluctuations, frequent switching, and noticeable changes in noise.

EC axial fans can be integrated with control systems to adjust operation according to cooling demand

EC fans allow speed to be adjusted continuously according to temperature, pressure, or cooling load.

At lower loads, the fan speed can be reduced to limit unnecessary energy consumption. As ambient temperature or system demand increases, airflow can be raised gradually so that cooling output remains aligned with actual operating requirements.

In dry coolers and cooling towers equipped with multiple fans, EC technology also enables more flexible control strategies.

Several fans can operate simultaneously at reduced speed to provide more even airflow across the heat exchanger. Fans can also be controlled by section or operating zone according to changes in load.

Compared with running only a small number of fans at high speed, this approach can help reduce local airflow variation and limit the mechanical and electrical stress associated with frequent start-stop operation.

Where communication interfaces are available, the fans can also be integrated into the equipment control system. This allows fan speed settings, operating status, and fault information to be monitored centrally, providing useful data for maintenance and system management.

Outdoor Applications Require Greater Attention to Protection and Reliability

Fan selection for harsh outdoor environments should begin with the actual installation conditions.

Outdoor axial fans must withstand rain, humidity, dust, and temperature fluctuations

In hot climates, the permitted ambient temperature of the motor and electronic components must be checked carefully. In cold regions, low-temperature starting, snow accumulation, and icing should be considered.

For coastal or high-humidity locations, attention should be given to the corrosion resistance of the impeller, guard, fasteners, motor housing, and surrounding structural components.

Rainwater and dust are equally important considerations. Fans and electrical connections should provide a level of protection appropriate for the installation environment. Wiring, controllers, and sensors should also be positioned to avoid long-term exposure to standing water or contamination.

For equipment intended to operate continuously throughout the year, bearing life, motor protection, vibration monitoring, and maintenance access all influence long-term reliability.

A fan that is difficult to remove or inspect may increase downtime during cleaning, servicing, or replacement, even when its initial performance is suitable.

Multi-fan systems should also include adequate service access and provisions for isolating individual fans, allowing maintenance work to be carried out without unnecessarily shutting down the complete cooling system.

From Individual Fan Performance to Overall System Efficiency

A fan solution for a dry cooler or cooling tower should not be assessed only by its airflow, power input, or sound level at a single rated operating point.

Under real operating conditions, the equipment may be affected by heat exchanger fouling, changes in ambient temperature, natural wind, and fluctuating cooling loads.

The suitability of a fan solution can only be evaluated properly when fan performance, airflow distribution, control strategy, and maintenance conditions are considered together.

During the design stage, engineers can select the appropriate impeller size, installation arrangement, and control method according to the resistance of the heat exchanger and the structure of the equipment.

During operation, fan speed can be adjusted according to fluid temperature and system load, reducing the need for prolonged full-speed operation.

Fan manufacturers such as Blauberg continue to develop solutions around axial impeller design, EC drive technology, and communication-based control, providing more flexible options for dry coolers, cooling towers, and other heat rejection equipment.

Dry coolers and cooling towers may operate behind the scenes, but they directly influence the efficiency of primary equipment, process stability, and long-term operating costs.

In environments affected by heat, cold, humidity, and dust, the role of the axial fan goes beyond simply moving air. It must provide the airflow required by the heat exchanger consistently and reliably over time.

By considering aerodynamic matching, demand-based speed control, outdoor protection, and maintenance requirements as part of one complete system, cooling equipment can operate more reliably and efficiently under challenging outdoor conditions.

Airtight Buildings Need Well-Designed Ventilation

As buildings become better insulated, quieter, and more airtight, less air is exchanged naturally through gaps around windows and doors. In homes, moisture, odors, and carbon dioxide may build up in bathrooms, walk-in closets, and storage rooms. Similar issues can occur in offices, meeting rooms, retail spaces, and service rooms as a result of occupancy and everyday activities.

Improving indoor air quality cannot depend solely on opening windows or running fans continuously at high speed. Natural ventilation is affected by outdoor weather, noise, and air quality, while excessive mechanical ventilation may increase electricity consumption, system noise, and heating or cooling loads.

A more practical approach is to establish a stable and controllable airflow path based on the function of each space and its actual ventilation demand.

Inline duct fans are installed within ductwork and can be used for supply air, extract air, or general air movement. They can be connected to one or more air terminals and installed above suspended ceilings, in service areas, or in other concealed locations. This makes them suitable for centralized residential extract systems and small to medium-sized commercial ventilation applications.

It is important to note that an inline duct fan is only the air-moving component of a ventilation system. Indoor air quality also depends on the position of outdoor air inlets and exhaust points, supply and extract airflow rates, airflow direction, filtration, and regular maintenance. Installing an extract fan alone is not the same as providing a complete mechanical ventilation system with outdoor air supply.

Residential and Commercial Inline Duct Ventilation Applications

Actual Airflow Depends on System Resistance

The maximum airflow stated on a fan nameplate or in product documentation is normally measured under specified test conditions. It does not necessarily represent the actual airflow after the fan is connected to a duct system.

As air moves through ductwork, it must overcome resistance created by duct length, elbows, transitions, dampers, grilles, filters, silencers, and other components. As system resistance increases, the actual operating point may move further away from the published maximum airflow.

For this reason, an inline duct fan should not be selected solely by its connection diameter or maximum airflow rating. The required design airflow, total system pressure loss, and the fan performance curve should all be considered.

Common inline duct fan designs include mixed-flow and centrifugal configurations. Mixed-flow fans generally combine useful airflow and pressure capability in a compact design, making them suitable for many circular duct systems with moderate resistance.

Centrifugal inline fans typically provide greater pressure capability and are often better suited to longer duct runs, systems with multiple bends, or applications that include filters and other resistance-producing components. The final selection should always be based on the required operating point rather than the fan type alone.

Inline Duct Fan Design and Airflow

Blauberg’s inline duct fan range covers both circular and rectangular duct systems, with mixed-flow, centrifugal, EC-driven, and acoustically insulated configurations available. These options allow the fan to be matched to project requirements for airflow, static pressure, installation space, and control.

Ventilation Requirements Vary by Application

In residential buildings, inline duct fans can be used for bathroom extract, moisture removal, and the ventilation of walk-in closets and storage rooms. A single fan may also serve several bathrooms or auxiliary spaces as part of a centralized extract system.

Residential applications usually place greater emphasis on nighttime noise, compact installation, low-airflow operation, and convenient maintenance access.

In kitchens, general room ventilation must be distinguished from grease-laden cooking exhaust. Standard inline fans intended for comfort ventilation should not be used directly for airstreams containing grease, elevated temperatures, or highly corrosive substances.

Where grease, high temperatures, or corrosive gases are present, the fan, ductwork, and cleaning and maintenance strategy must be selected specifically for those operating conditions.

Commercial buildings often experience wider variations in occupancy and operating hours. Offices and meeting rooms may require ventilation rates that respond to the number of occupants. Retail stores and training spaces need to accommodate changing visitor levels, while washrooms, stockrooms, and service rooms may require continuous extract or odor control.

Standard comfort-ventilation products should not be applied directly to industrial dust, flammable or explosive atmospheres, high-temperature air, or highly corrosive airstreams. Such applications require equipment selected according to the characteristics of the conveyed air, applicable safety requirements, and the necessary protection rating.

EC Speed Control Supports Demand-Controlled Ventilation

Traditional duct fans often operate at a fixed speed or with only a limited number of speed settings. When ventilation demand is low, maintaining a high airflow may waste electricity and increase heating or cooling losses. When occupancy or humidity rises, a fixed airflow may no longer be sufficient.

EC motors use electronic commutation and allow fan speed to be adjusted in response to a control signal. When the fan and control system are properly selected, airflow can be reduced during low-demand periods and increased when ventilation demand rises.

When humidity, carbon dioxide, or other indoor air quality sensors are integrated into the system, fan speed can be adjusted according to predefined setpoints. For example, extract airflow can increase when bathroom humidity rises, ventilation can be boosted as more people enter a meeting room, and airflow can be reduced during unoccupied periods.

The purpose of demand-controlled ventilation is not to operate the fan continuously at full speed, but to provide the required airflow while avoiding unnecessary overventilation.

Constant-airflow or constant-pressure operation also requires suitable sensors, controllers, and control logic. These functions cannot be achieved simply by using an EC motor. EC technology provides the basis for continuous speed control, but the overall energy performance of the system still depends on the fan operating point, duct resistance, control strategy, and operating hours.

Low-Noise Operation Depends on the Whole System

Installing an inline duct fan away from occupied areas can reduce the direct impact of fan noise, but it does not guarantee a quiet ventilation system.

Actual sound levels are also affected by fan speed, operating point, duct dimensions, air velocity, bend locations, structural vibration, and the design of grilles and diffusers.

Undersized ducts, excessive air velocity, sharp bends close to the fan inlet or outlet, and abrupt changes in duct cross-section can all generate additional aerodynamic noise. An oversized fan that is heavily throttled with dampers may also create unnecessary energy consumption and noise.

During installation, the inlet and outlet conditions recommended by the manufacturer should be maintained wherever possible. The fan should be securely supported, with vibration-isolating connections used where necessary. Adequate access should also be provided for cleaning, inspection, and component replacement.

In systems located close to bedrooms, hotel rooms, or office areas, acoustically insulated fan housings or silencers may be used where appropriate. However, these measures cannot compensate for incorrect airflow calculations or unsuitable duct sizing.

Moving from Fan Selection to System Matching

Inline duct fans provide a flexible solution for moving air through residential and commercial buildings, but ventilation performance is not determined by the fan alone.

The design process should begin by defining the function of the space and its ventilation requirements. The duct-system resistance can then be calculated so that the required airflow, static pressure, acoustic performance, and control method can be specified.

For applications with long operating hours or significant load variation, EC speed control and sensors can be used to adjust fan output as demand changes. For simpler spaces with predictable usage patterns, adding an unnecessarily complex control system may offer limited practical benefit.

Fan selection, duct layout, controls, installation, and maintenance all influence the final performance. Matching the fan operating point to the actual system helps improve the indoor environment while keeping ventilation energy use under reasonable control.

As Liquid Cooling Gains Momentum, Why Does Air Cooling Still Matter?

The rapid growth of artificial intelligence, high-performance computing and cloud services is driving server power density to new levels. In AI infrastructure in particular, rack power continues to rise, making thermal management a critical factor in data center availability and operational stability.

Liquid cooling has therefore attracted increasing attention. Technologies such as direct-to-chip cold-plate cooling and immersion cooling can remove heat more directly from high-heat-flux components, including CPUs and GPUs, making them important solutions for increasingly dense computing environments.

However, the growth of liquid cooling does not mean that air cooling is becoming obsolete. In real-world data centers, thermal management strategies vary according to server type, facility design and operational requirements. Liquid cooling may remove most of the heat generated by processors and accelerators, but other server components, network equipment, storage systems and supporting electronics may still depend on airflow.

Air-side systems are also needed to control room temperature and humidity, maintain appropriate air circulation and manage the heat that remains outside the liquid-cooling loop.

Liquid cooling therefore changes how heat is transferred, rather than eliminating the need for air-side thermal management. As a key component of air-handling systems, EC centrifugal fans continue to play an important role in environmental control, auxiliary cooling and airflow management across the data center.

Liquid and Air Cooling Working Together to Build Efficient Data Center Cooling Systems

From High-Volume Air Delivery to Precision Airflow Management

Traditional data centers commonly use CRAC units—computer room air conditioners—or CRAH units—computer room air handlers—to supply conditioned air to server areas. Historically, many systems were designed around relatively high airflow rates and operated continuously to maintain acceptable room temperatures.

As facilities grow larger and IT loads become more dynamic, fixed operating strategies are becoming less suitable for precise thermal management. In hybrid environments where liquid and air cooling operate together, the role of the air-side system is also changing.

Fans are no longer expected simply to move large volumes of air. They must respond to changes in IT load, room temperature and system pressure, delivering airflow where and when it is needed. Airflow can be reduced in lower-load zones and increased in areas with higher thermal demand, helping distribute cooling capacity more effectively.

This creates a broader set of requirements for fan technology. Fans must provide stable airflow, overcome the resistance of filters, cooling coils and ductwork, and remain efficient across a wide operating range.

EC centrifugal fans are well suited to these requirements. Their static-pressure capability, compact design and variable-speed control make them suitable for CRAH units, precision cooling equipment and other data center air-handling applications that require stable operation and flexible control.

EC Technology Enables More Responsive Operation

Data center cooling systems operate around the clock, which means fan energy consumption can make a meaningful contribution to total facility power demand.

In fixed-speed AC fan arrangements, airflow is often adjusted through dampers or other system components. When cooling demand falls, the fan may continue operating at or near full speed, while part of the available energy is lost through throttling.

EC motors provide a more direct and flexible approach to airflow control. EC fans can be speed-controlled and integrated into a building management system or cooling control platform through interfaces such as 0–10 V, PWM and Modbus communication.

When the IT load decreases, fan speed can be reduced. When cooling demand rises, the control system can increase fan speed and airflow accordingly. This demand-based approach can lower energy consumption and reduce unnecessary operation at full load.

For data centers running continuously throughout the year, controllable and efficient fan operation also supports long-term reliability by reducing avoidable mechanical and thermal stress.

Reliability Matters Even More in Hybrid Cooling Environments

Future data center cooling architectures are unlikely to rely exclusively on either liquid cooling or air cooling. A hybrid approach is more practical for many facilities.

High-power AI servers may use liquid cooling to remove most of the heat generated by CPUs and GPUs. Conventional servers, storage equipment, network devices and auxiliary electronics may continue to depend on air cooling. Air-handling systems will also remain responsible for maintaining room temperature, humidity and overall airflow conditions.

Air-side equipment must therefore provide more than cooling capacity. It must also support operational continuity and system resilience.

A modular fan array, often referred to as a FanGrid or fan wall, uses multiple EC centrifugal fans operating in parallel. The number of active fans and their operating speeds can be adjusted according to real-time demand.

When one fan requires maintenance, the remaining units can continue to provide essential airflow, depending on the redundancy designed into the system. This modular architecture can improve serviceability and reduce the risk associated with a single large fan.

It also makes future expansion easier. Fan capacity can be planned or upgraded in stages as IT loads and cooling requirements evolve.、

Modular FanGrid Solutions Improve System Reliability and Maintainability

Data Center Fan Selection Is About More Than Airflow

In data center applications, fan selection should never be based on maximum airflow alone.Engineers must also consider available static pressure, efficiency at partial load, control and communication capabilities, motor protection, acoustic performance and access for maintenance. The selected fan should also operate reliably across the expected system curve rather than at a single nominal duty point.

These factors collectively determine how the cooling system performs over its full service life. For mission-critical infrastructure operating continuously, the value of a fan lies not only in peak performance, but also in long-term stability, controllability and maintainability.

Fan manufacturers such as Blauberg Motoren are continuing to develop EC fan technologies with higher efficiency, greater integration and more advanced control capabilities. For data center cooling, air-handling units and precision climate-control equipment, Blauberg Motoren offers EC centrifugal fans across a range of sizes and performance levels.

Available options can include communication control, enhanced ingress protection and integrated operating safeguards, giving equipment manufacturers greater flexibility when designing and integrating cooling systems.

Redefining the Role of Air Cooling

The evolution of data center cooling is not a simple transition from air cooling to liquid cooling. It is a move toward more efficient combinations of technologies, selected according to heat density, equipment design and operating conditions.

Liquid cooling is well suited to removing heat from high-power processors and accelerators. Air cooling continues to support other electronic components, room-level environmental control and overall system balance. The two technologies are complementary rather than mutually exclusive.

For EC centrifugal fans, future value will extend beyond moving air. These fans will increasingly connect cooling performance with energy management, intelligent control, redundancy and system reliability.

Air cooling will not disappear in the liquid-cooling era. Instead, it will become more targeted, more responsive and more closely integrated into the overall data center thermal-management strategy.

Entrances in shopping centres, hotels, office buildings, hospitals, restaurants and some industrial facilities often remain open for extended periods or operate with frequent door cycles. While this makes the movement of people and goods more convenient, it also allows air to move continuously between indoor and outdoor spaces under the combined effects of temperature differences, pressure imbalances and wind.

During summer, conditioned indoor air can escape through the opening. In winter, indoor heat may be lost in the same way. Outdoor dust, odours and insects may also enter with the moving air.

At times of heavy foot traffic, temperature fluctuations and draughts around the entrance can become more noticeable. This may affect the comfort of people passing through and make conditions around the entrance more difficult to manage.

An air curtain is typically installed above the doorway and delivers a continuous jet of air vertically or at a slight angle across the opening, creating an aerodynamic barrier. It cannot separate indoor and outdoor spaces in the same way as a closed physical door. However, when correctly designed, selected and installed, it can help reduce the exchange of warm and cold air and support indoor climate control around the entrance.

Actual performance depends on whether the airflow covers the width and height of the doorway, as well as on discharge velocity, airflow direction, indoor-to-outdoor pressure differences and surrounding wind conditions.

Air Curtain Application at a Commercial Building Entrance

Air Curtain Performance Is About More Than “How Strong the Air Feels”

The performance of an air curtain should not be judged solely by its rated airflow or by how strong the air feels directly beneath the unit. More important considerations include whether the airflow remains continuous across the full outlet, whether the velocity distribution is reasonably uniform and whether the discharge jet can reach the lower part of the doorway.

If airflow is concentrated in the centre of the unit while the ends remain weak, air may still pass through the sides of the opening. Simply increasing fan speed is not always the right solution. It may increase draught discomfort and operating noise, while airflow striking the floor, door frame or nearby walls may produce recirculation and turbulence that disrupt the continuity of the air barrier.

For an air curtain, a reasonably uniform band of air distributed across the doorway is often more useful than a powerful jet concentrated in one area. The fan must provide airflow appropriate for the doorway, but the outlet grille, guide vanes, internal air path and installation angle also have a direct influence on overall performance.

Why Cross Flow Fans Are Well Suited to Wide Air Outlets

Cross flow fans, also known as tangential fans, generally use a long cylindrical impeller with blades arranged along the axis of rotation. Air enters through one side of the impeller, flows across its interior and passes through the blade region a second time before being discharged from the opposite side. This produces a broad airflow pattern along the length of the impeller.

The design is well suited to the long, slim housings commonly used for air curtains. A cross flow impeller can be installed within a relatively shallow unit while delivering airflow across a wide section of the doorway. Cross flow fans are also used in air-conditioning units, heating appliances and other equipment where installation depth is limited and broad airflow distribution is required.

However, cross flow fans are not the default choice for every air curtain. Their compact dimensions and wide discharge pattern can be a good fit for commercial entrances with moderate installation heights and limited crosswinds.

For taller doorways, locations with larger indoor-to-outdoor pressure differences or units with higher internal resistance, the fan arrangement should be assessed against the required airflow, pressure, discharge velocity and throw distance. In some cases, centrifugal fans or other configurations may be more suitable.

 Airflow Organization of a Cross Flow Fan in an Air Curtain

The Complete Air Path Matters, Not Just the Fan

The fan is one of the components that generates the air curtain. Before the air leaves the unit, it may pass through the inlet, internal guide structures, heating components, outlet grille and adjustable vanes. Excessive resistance or poorly designed transitions at any point can affect both the delivered airflow and its distribution.

A cross flow fan should not simply be installed inside a housing without considering the surrounding geometry. The impeller length should match the effective outlet width, while the clearances between the impeller, cutoff and housing need to be carefully designed. The inlet area should also remain unobstructed by decorative panels, suspended ceilings or mounting structures.

If part of the inlet is restricted, the fan may still meet its catalogue specifications in isolation, yet the complete unit may produce uneven airflow at the ends, higher operating noise or a working point that differs from the intended design.

For heated air curtains equipped with electric heating elements or hot-water coils, airflow distribution through the heating section must also be considered. Insufficient or uneven airflow may affect component cooling and create variations in discharge-air temperature.

The fan, heating section, housing and internal air path should therefore be developed as an integrated system during product design.

 Internal Structure and Airflow Performance of an Air Curtain

Installation Conditions Determine Whether the Airflow Reaches the Lower Doorway

The effective discharge width of an air curtain should normally cover the full width of the doorway. Wider openings may require several units installed side by side, but attention should be paid to the areas where adjacent airflow streams meet, as gaps may reduce the continuity of the air barrier.

The position of the unit relative to the doorway also matters. If it is installed too far away from the opening, the jet may begin to spread before reaching the area where separation is required.

As doorway height increases, the airflow must remain coherent over a greater distance. This generally places higher demands on discharge velocity, direction and jet stability. Building orientation, indoor and outdoor temperature differences, door-opening frequency, crosswinds and negative pressure created by extract systems may also influence performance.

An air curtain can help manage air exchange through an open entrance, but it cannot correct every airflow or pressure problem within a building.

Cold stores, food-processing facilities and industrial passages may involve more demanding operating conditions, including condensation, dust, corrosive atmospheres and extended running hours. Fan and air curtain selection should therefore be based on actual site conditions, protection requirements and expected operating cycles rather than on a standard commercial configuration.

 

Air Curtain Application at an Industrial Passage and Loading Bay

 

Moving from Fixed Airflow to Demand-Based Control

An air curtain does not necessarily need to operate at the same speed at all times. Multi-speed or continuously variable control allows airflow to be adjusted according to operating hours, door position and changing environmental conditions, helping to avoid unnecessary high-speed operation.

Where the selected fan or motor supports PWM, 0–10 V or other control signals, it may be integrated with door switches, temperature controllers or equipment control systems. When the door is closed or traffic is light, the unit may reduce speed or stop according to the programmed control strategy. When the entrance opens, it can return to the required operating condition.

Variable-speed capability, however, does not automatically guarantee an effective air curtain. Airflow, operating sound and throw distance at different speeds should still be verified through prototype testing.

During product development, engineers should assess not only the catalogue performance of the fan but also its behaviour after installation in the complete unit. Airflow, sound levels, temperature rise and operating stability should be validated at the actual system working point.

Matching the Fan to the Requirements of the Entrance

For air curtains, air coolers and other equipment requiring wide airflow distribution, Blauberg can provide cross flow fan selection support based on housing design and operating conditions.

The selection process should take into account the effective outlet width, target airflow, system resistance, sound requirements, control method and installation environment, rather than relying only on rated power or maximum speed.

A continuous air curtain is created by several elements working together, from impeller geometry and motor drive to housing design and airflow control. The value of a cross flow fan lies in its ability to distribute air across a wide outlet within a slim, compact structure.

It cannot replace a physical door or eliminate all air exchange between indoor and outdoor spaces. In suitable applications, however, it can help establish a relatively continuous and stable aerodynamic boundary across an open entrance.

In Heat Pump Operation, the Fan Is a Key Gateway to Heat Exchange Efficiency

Driven by the demand for clean heating, building energy efficiency and low-carbon renovation, air-source heat pumps are widely used in residences, apartments, hotels, schools, office buildings, hospitals and commercial buildings. They provide heating, domestic hot water and, in some systems, cooling support. For end users, the performance of a heat pump is not judged only by heating capacity. Energy consumption, nighttime noise and stable operation in low-temperature conditions are equally important.

In the outdoor unit of an air-to-water heat pump, the axial fan organizes outdoor airflow through the evaporator, allowing the air to fully interact with the heat exchanger. Whether the airflow is sufficient and evenly distributed can affect evaporator heat exchange efficiency, defrosting cycles and the overall operating condition of the unit. If the fan is undersized, the heat exchanger may not fully utilize the available heat in the outdoor air, which can increase the compressor load. If the fan is selected too large without proper system matching, it may lead to higher power consumption, increased noise and structural vibration.

Therefore, the heat pump fan is not just a supporting component. It is a key part of the heat exchange system that requires careful matching. It connects overall system efficiency, operating sound level and long-term user experience.

Why Axial Fans Are Suitable for Heat Pump Outdoor Units

Air-source heat pumps need to continuously extract heat from outdoor air. This means the outdoor unit usually requires a relatively high air volume. At the same time, the system resistance of the evaporator is typically within a low to medium range, making axial fans a suitable choice for airflow management.

An axial fan moves air along the axis of the motor. The airflow path is direct, and the overall structure is relatively compact. This makes it easier to integrate the fan with finned heat exchangers, inlet rings, protective grilles and the outdoor unit housing. For heat pump units installed in gardens, on rooftops, on equipment platforms or beside building façades, this structure helps create a stable air inlet and outlet path within a limited installation space.

However, the role of an axial fan in a heat pump is not limited to “providing airflow”. Once installed in the unit, the fan must also support stable air volume, acceptable noise levels, speed control and outdoor operating conditions. In residential and commercial applications, fan performance often influences how users perceive the quality of the entire heat pump system.

Efficiency: From Fixed Speed to Demand-Based Operation

When the fan becomes part of the heat exchange system, efficiency cannot be evaluated only at a single rated operating point. Air-to-water heat pumps operate under changing conditions throughout the year. The required airflow may vary between day and night, early winter and severe cold, heating operation and defrosting conditions.

If a fan runs continuously at a fixed speed, it may cause unnecessary energy consumption and make it harder for the system to maintain appropriate performance under partial-load conditions.

The value of EC axial fans lies in their ability to adjust speed according to heat pump load. Through 0–10V, PWM or communication-based control, fan speed can be adapted to the operating status of the unit. At low load or during night-time operation, the fan can run at a lower speed to help manage energy use and noise. When the load increases or frosting causes higher resistance, the fan can maintain the required airflow to support evaporator performance.

Of course, fan efficiency is not determined by the motor alone. Impeller diameter, blade angle, tip clearance, inlet ring geometry and the available inlet and outlet space all affect the real performance of the fan once it is installed in the heat pump unit. A good laboratory curve does not necessarily mean the same result after integration into the final housing. A mature fan solution should consider the motor, impeller, airflow guidance and the system boundary of the outdoor unit together.

Noise: Details Matter More at Night

Efficiency affects operating cost, while noise directly affects user experience. Air-to-water heat pumps are often installed close to bedrooms, neighbouring windows or shared outdoor areas. During the day, fan noise may be less noticeable due to background sound. At night, however, airflow noise, low-frequency vibration or speed fluctuations can become much easier to perceive.

Noise reduction for heat pump fans should not be judged by a single decibel value alone. Tonality, sharpness, periodic fluctuations and overall sound quality also matter. Blade profile, leading-edge design, impeller balancing, inlet ring matching and motor control strategy can all influence the final acoustic impression.

A well-designed aerodynamic structure helps reduce flow separation and vortex-related noise, resulting in a smoother sound profile. Smooth EC motor speed control can also support reduced fan speed in night mode, helping to limit disturbance to the surrounding environment. For heat pumps used in residential, hotel and commercial projects, low-noise operation has become an important part of product experience rather than a secondary feature.

Reliability: Winter Operation Shapes Long-Term Reputation

While efficiency and noise affect daily experience, reliability determines whether the equipment can operate stably over time. Heat pump outdoor units are exposed to rain, moisture, dust, temperature fluctuations and frequent start-stop cycles. In winter, frost may form on the evaporator surface, narrowing the air passage and changing system resistance.

Under such conditions, the fan needs a certain pressure reserve to handle resistance changes caused by frost, dust build-up or changes in inlet and outlet conditions. After defrosting, condensate drainage, base pan icing or ice accumulation on the grille may also affect the next start-up.

For this reason, fan reliability should not be assessed only by rated data. Bearing life, insulation class, protection performance, material weather resistance, low-temperature start capability and long-term dynamic balance all deserve attention. As R290 and other low-GWP refrigerants are adopted in some heat pump products, the motor structure, control electronics and installation position of the fan also need to be considered as part of the overall safety design.

Selection: From Component Purchasing to System Matching

When selecting axial fans for heat pump applications, manufacturers should focus on several practical questions: Is the static pressure sufficient at the target air volume? Can noise be controlled after installation? Is there enough margin under frosting conditions? Can the speed control method be integrated with the main control board? Are motor temperature rise and bearing life suitable for long-term operation? Are the housing, grille and airflow guidance structure convenient for unit assembly?

These questions are closer to real applications than simply comparing air volume, power and price. The heat pump industry is moving from parameter-based competition toward system-level performance. Whether a fan supplier understands the actual operating conditions of the unit can influence the final product performance.

Blauberg Motoren has long focused on motors and fans, with product directions covering EC, AC and DC motors, as well as axial and centrifugal fan solutions. For heating, refrigeration, air conditioning and ventilation applications, Blauberg can provide fan-matching references from the perspectives of motor efficiency, impeller design, control method and application boundary.

For air-to-water heat pump manufacturers, selecting the right axial fan can help improve overall efficiency performance, manage operating noise and support stable operation in low-temperature environments. A heat pump with a good user experience is rarely the result of one core component alone. It comes from the careful matching of multiple key components. The axial fan is one of the parts that deserves close evaluation.

Kitchen fume emissions are becoming a major concern in the rapidly expanding catering sector. The global market for kitchen ventilation systems is expected to expand at a compound annual growth rate (CAGR) of 6.4%, from $4.51 billion in 2025 to $7.79 billion in 2034. In the meanwhile, the recently updated “Emission Standard for Catering Industry Fume” has raised the bar for noise control, purification rate, and exhaust efficiency. Blauberg has introduced Dual Inlet Blower fan that offers an integrated high-performance centrifugal fan solution for kitchen fume extraction at this crucial point of industry transition by utilizing its fundamental German technological advantages.

Blauberg’s Industrial Fans business, a top producer of ventilation equipment worldwide, is dedicated to offering a complete range of products, including axial and centrifugal fans, covering a variety of applications such heavy equipment cooling, HVAC, and industrial ventilation systems. The recently introduced Dual Inlet Blower series is the result of the group’s years of technological accumulation in the ventilation area, and it has over 700 international patents.

The Dual-Inlet Fan is the Best Choice for Kitchen Fume Exhaust

Dual-inlet blower fan is a centrifugal fan that has air intakes on both sides of the impeller. Air simultaneously enters the impeller from both sides, concentrates, is driven by the volute, and then leaves through the outlet. It has a complete advantage over single-inlet volute fans in managing kitchen odors because of its structural construction.

The dual-side air intake’s greater airflow impact is, in theory, completely used by the dual-inlet volute fan. It simultaneously achieves a triple balance of high air pressure, big air volume, and low noise through enhanced volute flow channels and impeller aerodynamic design. The Blauberg Dual Inlet Blower fan is particularly suitable for complicated kitchen situations where it is necessary to overcome many resistances from fire dampers, elbow ducts, and fume hoods. Compared to conventional single-inlet fans, it has a more uniform airflow distribution, reduced vibration, and a 40% increase in airflow at the same rotating speed.

Why Select dual inlet fans: Four Principal Benefits

1. Greater Airflow, More Complete Elimination of Smoke

Everyone’s health and the working environment are directly impacted by how quickly kitchen gasses are expelled. Our dual-intake volute fan efficiently draws in vapors from two inlets at once by allowing air to enter from both sides. The volume and area of the air intake are increased as a result. It produces a greater exhaust volume, extracts fumes more quickly, and eliminates them more successfully than a single-intake centrifugal fan with the same impeller size and rotation speed.

2. Increased Energy Efficiency Driven by EC Motor Technology

Energy expenses are a major problem since commercial kitchen fans sometimes need to run continuously for long periods of time. An EC (Electrically Commutated) brushless DC motor is an option for the Blauberg double inlet blower fan. EC motors can reduce power consumption by up to 70% when compared to conventional AC fans. By using electronic commutation technology to eliminate brush friction losses, Blauberg’s in-house EC motor maintains over 85% efficiency even under partial load situations, improving efficiency by 25% to 30% over conventional induction motors. In the meanwhile, the EC motor offers 0-10VDC/PWM dual-mode stepless speed regulation, which enables “ventilation on demand” and prevents energy loss from fixed-speed operation by adjusting the air volume in real time based on the actual oil fume concentration in the kitchen.

3. A Better Kitchen Environment with Less Noise

Due to their enormous volume, traditional kitchen fans frequently generate issues for their operators, particularly in restaurants housed in residential buildings where noise complaints are frequent. The structural design of dual-intake volute fans naturally reduces noise since intake from both sides guarantees a more uniform and stable airflow distribution, which lowers turbulence and impact losses during intake and exhaust. When combined with Blauberg’s triple noise reduction technology (noise-reducing holes, sound-insulating materials, and optimized volute design), the Blauberg double inlet blower fans’ operating noise can be controlled between 53 and 57 dB(A), which is significantly lower than the industry average and makes working in the kitchen more comfortable.

Which type of volute fan is better for  kitchens, a single-inlet or a double-inlet?

To help customers make more informed decisions, we provide a comprehensive comparison of single-inlet and double inlet blower fans from several perspectives. In addition to  kitchens, our clients may select the best fan for their sector.

Airflow: Due to its single intake, single inlet blowers provide modest airflow. Double inlet blowers are better suited for medium-sized to large-sized  kitchens with larger exhaust volume needs since they feature two inlets that increase airflow by around 40% at the same rotating speed.

Pressure: For high-rise smoke extraction or long-distance ducting, single inlet blower fans provide higher pressure. Because of their superior volute flow channel design,double inlet blower fans also perform very well in terms of pressure, sustaining stable operation at medium to high static pressure circumstances (845Pa).

Noise Level: By using cutting-edge aerodynamic design and noise reduction technologies, our double inlet centrifugal blower fan has greatly reduced its noise level, consistently enhancing its overall noise management capabilities.

Maintenance and Cleaning: double inlet centrifugal blowers usually have a bottom drain outlet (oil valve) that permits condensed waste oil to naturally flow along the curved casing to the bottom for discharge, reducing buildup. The impeller design also makes cleaning and disassembly easier.

Blauberg’s IoT-Enabled Solutions for the Smart Kitchen Era

Intelligent technology is becoming a necessary trend for effective kitchen ventilation as the industry speeds up its transition to “fully automated, low-emission, and highly integrated” systems. Blauberg’s double inlet centrifugal fan seamlessly interacts with Industry 4.0 platforms and smart home systems thanks to an integrated IoT-ready controller that supports the RS485 communication standard. In order to provide intelligent smoke control, energy management, and predictive maintenance, the fan may modify operating settings in real time depending on sensor data. This lowers operational expenses for catering companies while satisfying ever-tougher environmental regulations.

Intelligent ventilation solutions are quickly becoming more and more popular in the global market for kitchen ventilation systems. Innovative technologies like demand-controlled variable speed fans, IoT-enabled real-time air quality monitoring systems, and heat recovery devices are being adopted at an increasing rate. A standard device that fits this technical trend is Blauberg’s dual-inlet volute fan.

Blauberg double inlet double with centrifugal fans are utilized in key areas of  kitchens, such as star-rated hotel kitchens, central kitchens, chain fast food restaurants, school canteens, large supermarket food courts, and hospital catering centers. They have a broad range of applications and promising global market prospects. Customers both domestically and abroad have acknowledged the product performance and technical dependability of this series of centrifugal fans, which are also widely used in air conditioning systems, purification equipment, industrial ventilation, refrigeration equipment, and fresh air units.

According to market research, as the global QSR (fast food) business grows and indoor air quality regulations tighten, the  kitchen ventilation system market will continue to rise quickly. Using a four-in-one technological innovation approach—high efficiency, energy saving, quiet operation, and intelligent technology—Blauberg will continue to capitalize on its German technological heritage and localized manufacturing advantages to offer top-notch centrifugal fan products and ventilation solutions to customers worldwide.

Please visit the official Blauberg product page or get in touch with our knowledgeable staff via our website for specialized kitchen ventilation solutions to find out more about Blauberg’s double inlet centrifugal blower fan and complete line of centrifugal fans.