Performance Testing of Industrial Fans
How do you gauge the performance of a fan? You need to view fan selection, at the onset, in terms of your requirements and the needs of your processes. This goes beyond simply looking at the models and types available.
Rather, you need to make sure that the industrial fan‘s performance is at par with the required air flow rate and the time it would take to fully distribute, replenish, exchange, or redirect that airflow. Considering these factors will make the industrial fans more cost-effective in the long run.
Fan Performance Measures & Fan Curves
Across the industry, industrial fan manufacturers showcase their products side by side the performance rating tables in catalogs. This particular performance table captures the necessary information that matches the customer’s desired performance.
However, to ensure that all manufacturers adhere to the same standard, AMCA or the Air Movement and Air Control Association International, Inc. defined laboratory test methods for industrial fans under ANSI-AMCA STANDARD 210 (or the Laboratory Methods of Testing Fans for Certified Aerodynamic Performance)or ISO Standard 5801. These typical tests are aimed to capture performance ratings and these standards define a uniform approach in measuring that. For industrial fans, these types of information are depicted in fan performance curves.
In a fan performance curve, the graph shows 3 axes, namely:
● Volumetric Flow Rate
● Static Pressure
● Brake Horsepower
By breaking down these measures, you should be able to understand the 3 key aspects you need to look out for in terms of a fan’s capability.
Volumetric Flow Rate
The first consideration is the fan’s airflow or its volumetric flow rate, usually measured in CFM or cubic feet per minute. Airflow requirements vary on the specific setup but are usually dependent on the volume of space that requires air to move through. This is particularly important in industrial areas where a steady airflow is required to remove generated fumes. This keeps the air clean, so you need a fan system that can move up to 300 to 600 CFM for 2000 ft3 space. Airflow is measured from the operating static pressure relative to the fan speed (or RPMs).
Air pressure is the resistance pressure that the fan has to blow against in order to carry the air towards the intended direction, usually measured in water gauge (in. wg) or in Pascals (Pa). It’s friction created from air passing through ducts and pipes. Pressure-indicating instruments, such as manometers, are used to capture the measurement of air pressure. In the graph below, the manometer makes use of liquid pressure to determine “h” = the displacement of the liquid caused by airflow generated in the form of pressure or a vacuum.
Fig. Manometer reading [Dwyer Instruments, Inc (2020)]
However, there are factors that may impact the ability to measure this consistently, such as whether air density is kept as static. Fan performance is directly correlated to this, in the sense that performance changes the moment air density becomes higher or lower. Furthermore, air density is affected by 3 key components: temperature, altitude, and humidity. For the purpose of gauging fan performance, air density is assumed to be standard. Standard Air Conditions are the assumption that air has a density of about 0.075 pounds per cubic foot, at 70F, at sea level, with 0% relative humidity.
Lastly, fan performance is tested with regard to its brake horsepower, or its rotational speed which is measured in terms of RPMs by a tachometer. Fan speed, in this regard, is the rotation speed of the impeller, which has to be considered and levelled against other factors such as the variation in fan load (its speed relative to the density of the air it carries through), temperatures in the air, and machine-generated noise.
Collection of Data & Testing
With these 3 key components, it’s important to record these under controlled environments and conditions so that these measurements come out much more reliable. Several manufacturers build test chambers to help generate fan performance metrics when certain variables are changed, such as airflow – a free field vs. with airflow impedance. All these test setups and equipment are listed by the AMCA to ensure that the collection of information is accurate and standard across the industry.
Fan Performance Curve
Once collected, all 3 components (air flow, static pressure, and brake horsepower) are measured individually and plotted in a fan performance curve.
While fan curves vary depending on the fan type, below is an example of a fan curve for an axial fan.
Vu, Thanh &Litomisky, Ales (2020). [Picture of a Fan Curve]
With this, the fan curve (denoted by the downward sloping line – static pressure curve) represents the performance of an industrial fan. It depicts the pressure loss against the volumetric flow rate increasing the further you move along the axis.
Best operating conditions are regarded as the operating point, where the system line and the fan curve intersect. At least in terms of understanding the fan design, performance rated in these graphs shows the capacity of the industrial fan to meet a certain flow rate, characterized by lesser air resistance while it runs at a particular fan speed. However, if the static pressure, impeded by a change in air density, increases or decreases, the entire fan curve too moves relative to this.
Selecting an industrial fan operating at the required air volume (CFM) and static pressure enables you to maximize its operating efficiency, and this is one of the main reasons that beyond cost, performance measures need to be considered in fan selection.
Importance of Performance Measures
After covering the important performance measures that industrial fans are usually gauged by, it is also important to discuss why they need to be tested.
Performance testing, from the point of view of manufacturers, helps to identify the performance levels of their industrial fans as they vary by type and size. In doing so, they are able to offer solutions that cater ultimately to the needs of the client. While fans are able to reach a range of air flow, the overall performance has to be looked at. Fans that are oversized compared to what their service requirements are for don’t quite operate at their peak efficiency points.
From the point of the view of customers, given that the published performance metrics of these industrial fans are assumed to be at standard air density and unperturbed air flow, that changes once these machineries are installed in a duct system. The variability between the published performance generated in controlled conditions compared to the actual capacity is distinctly noted as a system effect. These are plotted to show the losses brought about by the introduction of components such as dampers, filters, elbows.
Fan systems should then be recalibrated, taking into consideration the adjustments to be made as an effect of change in environment conditions. These include things such as temperature and air density, and components that inhibit a laminar air flow.
With various industrial applications, fans are regarded as the backbone of these sectors, largely due to their impact on the ventilation systems and overall process support. Therefore, the selection process is an interplay of various factorsthat are relative to the performance of each industrial fan.
Ferrari Ventilation has been manufacturing top quality industrial fans since 1963.