10 August 2022
Impeller design and specification is critical to fan performance in all applications, and especially when operating in harsh operating environments. Phil Kirkham, engineering manager at Elta Fans Applied Technology, explains what to look for when specifying these components.
The importance of procuring the right fan and impellers for the application cannot be understated. Without careful consideration, a host of issues can happen, including reduced lifespan, higher costs from servicing and maintenance, as well as lost operating time and money through unnecessary downtime. The fan may also perform at lower capacity, resulting in higher energy costs. To ensure these detriments do not occur, impellers must be accurately designed, specified and manufactured.
Design and specification
There are numerous conditions to be considered during the design process, including necessary air volume and pressure, air density and temperature ranges they need to work to. Any other operational conditions such as ATEX (hazardous, explosive materials) or smoke ventilation can affect selection, and should therefore be factored in as well.
Navigating these parameters is evidently a meticulous process, which is why Elta Fans offers a Fan Selection Programme for greater ease. Users are able to determine the correct impeller for their application requirements through airflow, pressure, sound and efficiency requirements. Impeller stress calculations are also built into the programme to ensure safe selections.
Once all elements have been determined, ventilation professionals can select the appropriate impeller and design the correct fan in line with customer needs. Different types of blades should be considered, depending on the required application. For example, in marine environments, glass reinforced plastic, certain grades of aluminium and anti-static impellers could be suitable. Across all material choices it’s important that blade design incorporates adjustable pitch and solidity for a wider range of options.
Coating and resistive properties should also be appropriately decided to provide an effective solution. In specific applications where impellers need additional protection, they can be painted, flame sprayed or anodised to prevent corrosion or wear and tear.
Performance testing and quality control
Once an accurate specification has been agreed, it is important that quality and performance is guaranteed in the subsequent manufacture process. Here, the critical measure is what factory production controls are in place to provide assurance that all fans built are being run-tested to check for vibration, running current, and speed. Thorough testing is vital to achieve optimum performance and should be carried out in line with applicable regulations. Ventilation specifiers should look to fan suppliers that test in accordance with key industry standards, such as BS ISO 5801.
Acoustics and airflow are also key factors to accommodate. The principal standards to adhere to are air performance (ISO 5801 and AMCA 210) and sound (ISO 13347-2, ISO 5136, AMCA 300), for which all impellers should be fully tested to. Third party testing is also a key sign of quality, and at Elta, testing is performed in the company’s own laboratory which is accredited by AMCA for performance and sound. The option of customer witness testing can also provide added peace of mind here.
Alongside the testing of the individual components, when building the fan, impellers need to be dynamically balanced to operate correctly and thus prevent vibration back to the fan, motor, bearings, and surrounding structure. Again, regulatory testing must be conducted to meet the conditions of ISO 14694, along with providable certificates for credibility.
Quality is equally important when introducing new products to the market. In the interests of quality assurance, many of Elta Fans components are manufactured at foundries in the UK. As well as materials, comprehensive ‘start’ testing and over-speeding to verify stress limitations is a crucial step to ensure performance and reliability.
For any application, preventing downtime and unnecessary maintenance is a key part of ensuring optimum performance. To maximise lifespan, it is therefore paramount that impellers are carefully considered as part of fan systems. By applying design and specification principles in tandem with performance testing and quality assurance, the right solution can be achieved.