12 November 2019

How to choose the best impeller for your needs

By Elta Fans Asia

12 November 2019

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About the Impeller

The first Elta Fans axial impeller fan was manufactured in 1972. Since then the axial technology has been tested, improved, and optimised. It is the most energy-efficient fan of its kind, capable of significantly reducing energy costs for buildings around the world.

The reliable long term performance and increased efficiency of our impellers has earned it an unrivalled reputation within the global HVAC markets. It is increasingly being specified on large scale green or sustainable building projects around the globe including the United Kingdom, Australia, and South Africa.

Our impellers are providing air movement and ventilation solutions across a wide range of industries and are often performing in some of the harshest and most demanding environments.

The Elta Fans range of axial fans is licensed to carry the AMCA seal and has over 800 different models available, capable of being configured to suit any specific need or requirement.


Material

Elta Fans adjustable pitch aerofoil impellers comprise of blades manufactured from high quality cast aluminium, Glass Reinforced Polypropylene (GRP), or carbon loaded composite.

Which material is used depends on the fan’s intended application and specification requirements. Typical blade materials used by Elta fans include GRP, Aluminium, Nylon, and Anti-Static Plastic. The properties of each material used are detailed in the below table.

GRPAluminiumNylonAnti-Static
Temperature Limits
(continuous duty)
-40°C to 100°C-40° to 250°C-40°C to 110°C-40°C to 70°C
Strength RatingLowHighestMediumLowest
Corrosion ResistanceVery GoodGoodVery GoodVery Good
Stressors

When selecting the correct blade material for your needs, both temperature and stressors need to be considered.

A rotating impeller blade will be exposed to a number of stressors including centrifugal and bending stressors during the fan start-up and operation. The strength of the material plays a big part in how the fan handles such stressors and can determine whether or not your chosen fan will be suitable for its intended application.

For example, though Aluminium has the highest strength levels, GRP blades contain fibre reinforced compounds that improve stress tolerance (even on large fans) and are cost-effective so could be a more suitable choice.

Manually calculating stressors requires in-depth knowledge of blade profiles, airflow, pressure, blade length, motor torque, speed, and temperate.


Temperature

Generally, when temperatures are increased, material strength is decreased. GRP blades can safely handle temperatures up to 70 °C while aluminium blades can handle temperatures up to 110 °C, however as shown in the above table, these temperatures can be greatly exceeded. This is the case if the blades are de-rated from a stress perspective.

When selecting a fan for high-temperature applications such as a smoke spill, aluminium should be used in order to cope with the higher temperatures. During a smoke spill test, temperatures can be up to 400 °C.

Elta Fans testing has shown that the aluminium fan blades can withstand these temperatures for short periods of time, but only if the blades are not highly stressed.

In some circumstances, under high temperatures, aluminium blades can exhibit a phenomenon called creep. Creep is where the centrifugal force causes the blades to stretch. When creep occurs, particular attention needs to be paid to blade tip clearances to avoid blades tipping against the fan casing when a smoke spill event occurs.


Casing Options

The axial impeller fan comes with both short and long casing options. Both casings are made of durable hot-dipped galvanised steel or pre-galvanised steel.

Short cased axial units use mounting flanges at each end of the casings. fThe configuration of the short cased fans are designed to suit end-of-duct OEM applications or where the application has limited space.

The configuration of this fan allows the rear of the platform mounted motor to partially protrude beyond the flange and for ease of wiring installation, an external duct mounted terminal box I can also be included. Long cased axial fans are more standard than their short-cased counterparts and have integral mounting flanges with industry standard hole drillings.

The configuration of the long case allows for an easy fan removal from inline dust applications. The centrally mounted motor is wired to an IP55 protected, duct mounted terminal box fitted on the outside of the fan casing, using a flexible weatherproof cable.


Size and Blade Combinations

The size of the fan is also an important consideration in specifying the correct fan for your needs. The Elta Fans axial impeller range includes seventeen different sizes ranging from 315 mm to 2000 mm in diameter.

The size of the fan can affect the performance of the fan in terms of how much airflow it provides, and the speed of the air being ventilated.

Impellers have adjustable pitch allowing for a variety of performance characteristics but are factory set an angle that provides desired performance. The number of blades on an impeller can also be varied in order to provide varied results to best suit the application.

Fitting a lower amount of blades reduces the peak pressure development and the peak efficiency point moves to a lower pressure. It can also affect the noise levels produced by the fan. A lower number of blades allows for motors of lower output to be fitted, due to the reduced solidity which can ultimately save on operation costs.


To sum it up

There are many variables to consider when choosing the best impeller fan for you. Elta Fans provide a comprehensive Fan Selection Software that is capable of automatically calculating the specifications of your required fan, as required by your application. It is a quick and easy way to ensure you are getting the best impeller for your needs. 

If you are still unsure of which impeller you need for your application, our knowledgeable sales team can talk you through everything you need to know and recommend a range of products and solutions for any application. Contact them here https://www.eltafans.asia/contact/

If you would like to know more about our axial impeller range you can find more information on the manufacturing process and product options here https://www.eltafans.asia/solutions/our-axial-impeller/

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