There are several intrinsically different fan types and each offers different performance characteristics. Many questions need to be answered in order to determine the correct fan shape selection.
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This post will give an overview of the different fan types available, and the questions you need to consider when selecting a fan.
The axial fan has various blade shapes including Aerofoil, Sickle, Paddle, and Variable pitch. Axial fans are used for relatively high flow rates and low pressures with flow parallel to the axis of fan. They also have lower power input.
Axial fans are generally selected for simple extraction or cooling applications with very low system resistance, such as moving air from one large space to another (i.e. from factory to outside), desk fans and condenser cooling in refrigeration.
These barrel-shaped fans have curved forward blades that are generally many times longer than any given diameter. Tangential fans tend to scoop the air up and deliver it at relatively low pressure over a longer length, ideal for cabinet cooling or process air coverage.
The main advantage of tangential over axial fans is that they provide extremely smooth laminar airflow over the whole frame width. This makes them suitable for applications such as air conditioning systems, air curtains, computer systems, instrument racks, convector fans, ovens, de-humidifiers and ventilators.
Typical impeller blade construction types include Paddle, Radial, Backward Curved and Forward Curved. Characteristics are low flow rates and high pressures with flow perpendicular to blower axis. Air enters around the centre of the fan and exits around the outside.
Centrifugal fans with Paddle impellers are used when debris will pass through the system because this configuration prevents any clogging.
Fans with backward curved blades produce less air volume than Axial units, but generate considerably more pressure and are the least hungry for power in the centrifugal range. They can also be produced as multistage units to give even higher pressures.
By comparison, the Centrifugal Fans with Forward curved blades develop the best airflow and pressure requirement in size by size comparison, although they will require extra motor power.
Typical applications for centrifugal fans include air handling units, process heating and cooling, electronic cooling and boiler combustion air.
Knowing if your application requires high volumes of airflow but low pressure or high pressure and low volumes is just one of the questions that need to be answered in order to determine the correct industrial fan selection.
It is important to also take into consideration factors such as:
When determining the pressure required it is important to consider system restrictions. For example, additional pressure may be required to achieve flow across a filter, or to compensate a pressure drop due to length, size and complexity of ducting.
All ducting will have an effect on the air passing through a system and this will nearly always take the form of a restriction to the flow and therefore have an influence on pressure requirements.
At the earliest stage in the design process the ducting should be carefully evaluated and made as efficient as possible. This will reflect beneficially on the final design in the overall cost, the compactness of the fan and the running costs.
In reality, there are many factors that impact upon fan specification and applications that demand particular air movement characteristics for cooling, exhausting, aerating, ventilating and drying should undergo a ‘system resistance’ assessment. Only by evaluating all the impacting factors (flow resistance, power units, size, space envelope) is it possible to ensure maximum efficiency and reliability of both the fan and the equipment involved.
To help ensure that all aspects of fan sizing have been considered the following checklist may be useful:
Velocity Required.
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Does this take into account the worst case open area?
Density of the air being moved (temperature or different gas).
Pressure required to generate desired flow through open area.
Pressure drop across filter.
Pressure drop due to ducting.
Are there any special hazards (e.g. flammable gas, corrosion, agents etc)?
Noise level restrictions.
Inlet and discharge configuration.
Electrical supply – is speed control required?
What are the physical size constraints?
Even flow across aperture – if a large area then poor distribution could occur.
Dwell time – is the velocity across the filter giving desired dwell times.
While Moffitt has always specialized in natural ventilation, we don’t hesitate to recommend factory exhaust fans when necessary. With over 50 years of experience with industrial fan and industrial ventilation, we can find the help you find the perfect ventilation solution. The powered ventilation series includes a complete line of axial fans. Moffitt provides the best selection of industrial axial fans including rooftop exhaust fans, wall fans, upblast fans, and tube fans on the market today.
Look at the rooftop of any industrial building and you will see a hooded roof fan. Hooded roof fans move a lot of air while producing little noise and using little power. The watertight, overlapping seams and heavy gauge materials help prevent leakage.
Model H hooded roof axial fans are available with direct drive motors while model fans come with belt drive motors. Both are available with blades as small as 12″ and as large as 120″. These fans can fit almost any roof type and at any capacity required. Furthermore, optional stainless-steel construction ensures that they can withstand even the harshest of conditions.
Industrial Axial Wall Fans are extremely popular for general building ventilation. They can be used in both commercial and industrial applications and can be positioned to provide supply or exhaust. The key benefit of the Moffitt Model and fans is that they are both standardized and customizable. They can be designed to match any needs you may currently have while also providing what you know and expect out of a wall fan. A small crew can install these fans in a matter of hours. Wall axial fans have both direct and belt drive options.
Upblast fans are especially useful in areas with hot, stagnant air. They move the stifling air out of a small space and provide general ventilation in almost any area. Their chief benefit is that they can remove a lot of air at a fast pace. These types of fans work best in kitchens, workshops, and other smaller, enclosed areas. These axial fans are fully contained in a drum housing. Upblast fans are available in sizes ranging from 24″ to 120″.
Moffitt tube axial fans, model TA- and TA-, have fan wheels located in cylindrical tubes and come without dampers to ensure maximum air flow. They are useful in commercial buildings as well as general building HVAC. These units have either a direct drive motor or a belt drive. Additionally, they come in a variety of shapes and styles.
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