English
The simple and direct answer is: the wind speed generated by large exhaust fans is usually between level 5 and level 10, but their wind characteristics are fundamentally different from natural wind.
Below, I will explain in detail from several aspects:
1. Wind speed range (equivalent to what level of wind?)
The "level" we usually refer to is the Beaufort scale, which is a level that describes the impact of natural winds on ground objects.
Small/household exhaust fan: The air outlet speed is about 3-6 meters per second, equivalent to 3-5 levels of wind (light to cool).
Common industrial large exhaust fans (diameter 0.5-1.2 meters): The center wind speed of the air outlet can reach 10-15 meters per second, equivalent to 5-7 levels of wind (from cool to strong). This is a common situation.
Large and powerful exhaust fans (used in workshops and tunnels): The wind speed at the air outlet may reach 15-25 meters per second or even higher, equivalent to wind speeds of 7-10 levels (from gale to gale).
Special fans (such as for drying and cooling): The wind speed may be higher, but they are usually not used for conventional ventilation.
Key point: Exhaust fans are usually labeled with "air volume" (cubic meters per hour), not wind speed. The wind speed depends on the air volume divided by the area of the air outlet. The smaller the air outlet of the same fan, the higher the wind speed.
2. The fundamental difference between exhaust fan wind power and natural wind power
This is the core of understanding the problem. Although the wind speed is the same, there is a huge difference in sensation and effect:
Characteristics: Large exhaust fan with natural wind
The scope of action is very concentrated, mainly limited to the conical area directly in front of the air outlet. Leaving the core area, the wind speed drops sharply. The scope is extremely wide, serving as a "surface" that can cover the entire area with even wind force.
The nature of wind is turbulent and turbulent, with unstable airflow that feels "hard" and "rushing". Relatively uniform and continuous (under stable weather conditions), it feels more 'natural'.
Continuity remains constant, with no change in direction. There may be formation, direction, and speed changes.
The effect of local cooling and forced ventilation is excellent, but it can only be blown to specific locations. Capable of comprehensive ventilation, cooling, and driving the flow of air throughout the environment.
For example, a ventilation fan that generates level 7 wind (15 meters per second) will feel very strong and almost unstable at a distance of 1 meter from the air outlet. But as long as you take 2-3 steps to the side, you may only feel a 3-4 level breeze. And the level 7 wind in nature means that the entire environment is under that wind force, with nowhere to hide.
How to determine the wind speed of the exhaust fan in your hand?
View parameters: Find the air volume (m ³/h) and air outlet diameter (m) on the label.
Roughly estimated wind speed:
Air outlet area ≈ 3.14 × (radius) ²
Wind speed (m/s) ≈ Air volume (m ³/h) ÷ Air outlet area (m ²) ÷ 3600
*For example: air volume of 10000 m ³/h, diameter of 0.5 meters (area approximately 0.196 m ²), wind speed of ≈ 10000/0.196/3600 ≈ 14.2 m/s (approximately level 7 wind)*
Refer to the Beaufort Wind Scale:
Level 5 wind (8.0-10.7 m/s): Small trees sway and waves rise on the water surface.
Wind force 7 (13.9-17.1 m/s): Difficulty walking and shaking of the entire tree.
Level 9 wind (20.8-24.4 m/s): Roof tiles are blown away, causing minor damage.
summary
From the perspective of wind speed values, the wind speed at the outlet of large industrial exhaust fans is generally equivalent to natural wind of 5-7 levels, and strong models can reach 8-10 levels.
From the perspective of actual sensation and effect, it is more like a strong but limited range "wind column" or "wind cone", mainly used for local forced ventilation, cooling, drying or exhaust, and its effect cannot be compared to the impact of natural wind of the same level on the entire environment.
Therefore, when choosing an exhaust fan, in addition to paying attention to "equivalent to several levels of wind", it is also necessary to consider whether its air volume is sufficient to match your space volume, and whether the installation location can deliver the airflow to the target area.
