The Basics of Ventilation Fan in Singapore

  • Ja Redden
  • March 31, 2024
  • Blogs
JA Redden Pte. Ltd.

Ventilation fans in Singapore are an indispensable component of the industrial field. They play a pivotal role in maintaining air quality, regulating temperature, and ensuring safety by removing airborne contaminants. Whether you're an industry professional or simply curious about how these systems work, this article will take you to the definitions of airflow versus static pressure, their relationship, and the critical role of impedance.


Air Flow-Static Pressure Character Graph: Understanding Fan Performance

Manufacturers use the air flow-static pressure character graph, like a speed-torque curve in motors, to display fan performance, particularly indicating the sources of airflow and static pressure specifications.

Airflow Table

For some customers, this representation of ventilation products can appear quite unfamiliar. Many customers often select fans based on their dimensions and airflow alone. However, deeper insight is necessary to gauge how a fan will perform accurately in real-world conditions.

Max Air Flow Max Static Pressure
m³/min CFM Pa inH2O
21 742 320 1.28
25 883 390 1.57
25 883 410 1.65
24 848 340 1.36
24 848 1.45 24
21 742 310 1.24
24 848 360 1.45
21 742 320 1.28
24 848 360 1.45

In the table detailing ventilation fan specifications, "Maximum Air Flow" and "Maximum Static Pressure" are the key performance metrics.


refers to the air volume a fan can circulate over a given period, commonly measured in cubic meters per minute (m³/min) in metric units or cubic feet per minute (CFM) in imperial units.

Consider a fan with a capacity of 5 CFM in a 5 ft x 5 ft x 5 ft enclosure; theoretically, it would take about 25 minutes to ventilate the hot air completely from this space. However, the actual ventilation process is more complex

Static pressure

, however, represents the ventilation fan's ability to generate air pressure within an enclosure. This is typically measured in Pascals (Pa) or inches of water (inH2O). A Pascal, named after Blaise Pascal, is the SI unit for pressure, equivalent to one newton per square meter.

  static and airflow table  

Meanwhile, inches of water gauge (inH2O) measure the pressure exerted by a one-inch-high column of water at a specific temperature (4 °C, where water is densest) and is approximately equal to 249.082 Pascals.

It's crucial to understand that fans cannot simultaneously deliver their maximum airflow and static pressure values. The full specifications for each are distinct and cannot be achieved concurrently.

Airflow and static pressure in ventilation fans exhibit a negative correlation, meaning that an increase in one typically leads to a decrease in the other and vice versa. This relationship is crucial in understanding how fans perform in different scenarios, particularly ventilating an electronics enclosure.


Let's examine three illustrative examples:

1. Open Enclosure Scenario

Here, the enclosure is open at one end, allowing unobstructed airflow from the fan. This situation facilitates maximum airflow with zero static pressure, as all the air is expelled smoothly from the other end.

Arrow air flow table  

2. Partial Obstruction Scenario

The enclosure is almost sealed in this ventilation fan setup, save for a small exhaust hole smaller than the air intake. This limitation in the exhaust size impedes airflow, leading to a build-up of air inside the enclosure, thereby increasing static pressure. As a result, airflow is reduced from its maximum due to the heightened static pressure.

Air Intake Table  

3. Fully Sealed Enclosure Scenario

The enclosure is entirely closed in this example. Air flowing into the enclosure increases the static pressure since the air has no exit path. Once the static pressure exceeds the fan's specification, no additional air can be introduced, even if the ventilation fan continues to operate. Thus, at maximum static pressure, the airflow volume drops to zero.

Ventilation Fan Diagram  

In practical terms, scenarios 1 and 3 are extremes not typically encountered in real-life applications. Most ventilation scenarios, especially in electronics enclosures, closely resemble example 2.

The double chamber method is often employed to effectively illustrate the relationship between airflow and static pressure on a graph. This method helps visualise how a fan's performance varies under different air resistance and pressure build-up conditions.


The Importance of Impedance

Determining the precise airflow and static pressure requirements in a ventilation fan system hinges on understanding impedance. Impedance, in the context of airflow, refers to the resistance the air encounters as it moves. It can arise from various sources such as electronic components, walls, or any obstructions in the airflow path. This impedance ultimately dictates the actual airflow and static pressure a system will experience.

The' square law' is often applied to quantify this concept, particularly in forced air cooling applications. This principle states that static pressure varies as the square of the change in CFM (Cubic Feet per Minute).

In essence, minor alterations in airflow can result in disproportionately large changes in static pressure, highlighting the importance of accurately assessing impedance for effective system design.

The equation below can quantify static pressure in ventilation fans in Singapore:



    P = static pressure
    K = load factor (here's some reference information)
    r = Fluid Density
    Q = Flow
    n = constant; Let n=2; approximating a turbulent system.
  Impedance static pressure and airflow relevance to ventilation  

Understanding Impedance

The impedance curve in the impedance graph depicts distinct lines representing various impedance levels. These lines are crucial for understanding how impedance affects fan performance.

On the other hand, the performance curve simultaneously represents airflow and static pressure. The point where the impedance and performance curves meet indicates a scenario with different impedance levels.

In other words, the actual airflow and static pressure a ventilation product will achieve in any given system are identified at the intersection points of these impedance curves with the fan's performance curve.

Determining system impedance can sometimes be challenging. In such situations, a practical approach is to assume that the actual airflow will be approximately half of the fan's maximum capacity. Therefore, choosing a fan that can deliver twice the airflow needed for your specific requirements is advisable.

Beyond simply selecting the right ventilation fan, successful ventilation design for an enclosure also involves other critical factors. These include the size and location of intake and exhaust holes and the placement of internal components.

To illustrate how these elements influence the airflow of ventilation fan in Singapore, smoke traces airflow patterns visually. This demonstration highlights the impact of varying intake hole sizes and dividers within the enclosure, providing a clearer understanding of practical ventilation design principles.

Incorporating accessories like filters, screens, or finger guards can significantly enhance the durability and longevity of fans in environments prone to dust or moisture. But it's important to note that these additions can also alter the fan's airflow and static pressure properties.

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