Fan airflow and static pressure

What is fan air volume and static pressure?

The air volume of a fan is the amount of air that is blown out, and static pressure is the force with which the air pushes against the surroundings when it is stationary. The greater the static pressure, the farther the air can be blown.
maximum airflow of a fan refers to the airflow when there are no obstacles at the fan's intake and exhaust ports.
maximum static pressure of a fan is the static pressure that occurs when the fan's intake or exhaust port is completely blocked. However, since neither of these conditions can be achieved when the fan is installed, the fan mounted on the equipment will never reach maximum airflow or maximum static pressure.

Fan airflow and static pressure when implemented

Then, what will be the airflow and static pressure of the mounted fan?
If you look at the catalog, you will find an "airflow-static pressure characteristic" curve in addition to the fan specification table. The airflow and static pressure in the installed state are on that curve.
The "airflow-static pressure characteristic" is also called "P-Q performance" and shows the characteristics of a fan. In this article, we will use a typical axial flow fan as an example.

Looking at the "Air volume - static pressure characteristics," we can see that maximum airflow is the point where the static pressure is 0 Pa, and maximum static pressure is the point where the air volume is 0 m ³ /min. The air volume and static pressure when mounted are points between these two.
A fan's "airflow-static pressure characteristics" change depending on the rotational speed, and combining multiple fans also changes the airflow-static pressure characteristics of the entire device.

Relationship between fan air volume, static pressure and rotation speed

Basically, the airflow of a fan is proportional to the rotational speed, and the static pressure is proportional to the square of the rotational speed. In other words, doubling the rotational speed doubles the airflow and quadruples the static pressure. Using this law, you can roughly calculate the desired PQ characteristic based on the current airflow and static pressure values.

Changes due to combination of fan airflow and static pressure

When using multiple fans, the overall "air volume-static pressure characteristics" change depending on whether they are connected in series or parallel. For example, when two identical fans are combined, in theory, the static pressure will double when connected in series, and the air volume will double when connected in parallel.

However, in a real environment, the airflow between the two fans will interfere with each other, and it is rare for two fans to double the airflow and static pressure. If the fans are placed side by side with no gaps between them, the effects of interference will be particularly large, and the values will deviate significantly from the theoretical values mentioned above.

In addition, when multiple fan-equipped chassis are combined, the performance of the fans with low airflow capacity may be significantly reduced. For example, suppose chassis A and chassis B each have fans, and each has sufficient airflow capacity. However, when these are combined into a single chassis, the fan of chassis A may barely function at all, so care must be taken.

As in the example, in equipment that contains multiple components, it is common to set the thermal design for each case to the very limit. This can result in little air flow in areas where it is difficult to get air to flow. Also, the fan installation environment can change when components are installed, so be careful when designing the equipment.

A compact, lightweight "Airflow Tester" that measures and quantifies fan airflow-static pressure characteristics!

The industry's first portable double chamber, developed by SANYO DENKI, is small and lightweight, so it can be attached to large equipment that cannot be carried around for measurements.
Measurement is also easy; just attach a connecting duct to the ventilation hole.

For more information about the Airflow Tester, please see the downloadable materials.

Supervised by: SANYO DENKI CO., LTD. Cooling System Design Department

Update date: 2024-02-02 00:00 /release date: 2018-03-12 00:00