Direct answer: The basic calculation method of EFU face wind speed is: face wind speed = air volume ÷ effective filtration area. The air volume is usually in m³/h or m³/s, the effective filter area is in m², and the calculation result is m/s. During measurement, measuring points need to be arranged on the section at a predetermined distance from the wind outlet surface. After measuring the wind speed point by point, the arithmetic mean value is taken, and the wind speed distribution is evaluated based on the unevenness. Before calculation, you should first confirm the definition of effective filter area and avoid using the outer dimensions of the box instead.

Face wind speed is a common indicator in EFU performance confirmation and acceptance, but if the calculation and measurement methods are not unified, deviations may easily occur. The following starts from four aspects: calculation formula, effective filter area, measuring point arrangement and average method.

1. Basic calculation formula of surface wind speed

The calculation formula for surface wind speed is:

Face wind speed (m/s) = air volume (m³/s) ÷ effective filter area (m²)

If the air volume is in m³/h, it needs to be converted first:

Air volume (m³/s) = Air volume (m³/h) ÷ 3600

Example: The air volume of a certain EFU is 900 m³/h, and the effective filtration area is 0.5 m².

• Converted air volume: 900 ÷ 3600 = 0.25 m³/s

• Face wind speed: 0.25 ÷ 0.5 = 0.5 m/s

It should be noted that the air volume here should be the actual air volume on the air outlet surface of the filter, not the nominal air volume of the fan. The nominal air volume usually corresponds to zero static pressure or low static pressure conditions, and is different from the actual system conditions.

2. How to confirm the effective filtration area

The effective filtration area is the most prone to deviation in the calculation of face wind speed. A common misunderstanding is to directly use the outer dimensions of the cabinet to calculate and ignore the following factors:

1. The actual air outlet area of ​​the filter : should be based on the effective air supply area of ​​the filter, excluding the frame;

2. Filter border width : The area occupied by the border is not included in the effective filtering area;

3. Sealing strip occupancy : The area covered by the sealing strip is not included in the effective air supply area;

4. Structural obstruction : The part of the air outlet surface that is blocked by brackets, cables or equipment structures should be evaluated whether to be included;

5. Multi-filter configuration : When multiple filters are connected in parallel, the effective filtration area is the sum of the effective areas of each filter.

Therefore, before calculating the surface wind speed, you should first confirm the definition of the effective filtration area and agree on the calculation caliber with the project party.

3. Measurement point layout principles

Face wind speed measurement requires measuring points to be arranged on an agreed measurement plane. The layout of measuring points should follow the following principles:

1. Measuring plane : usually selected at a certain distance from the filter outlet surface, the specific distance is agreed upon by the project, and the common reference value is 100–300mm;

2. Number of measuring points : calculated based on the air supply area. The larger the area, the more measuring points. Each filter must measure at least 1 point;

3. Measuring point distribution : It should be evenly distributed, covering the center and edge areas, and avoid measuring only the center point;

4. Grid point layout : Measuring points can be arranged in a grid pattern for easy recording and comparison;

5. Avoid interference : Measuring points should avoid partially blocked locations such as brackets and cables, or be marked separately.

For EFUs configured with multiple filters, it is recommended to arrange separate measuring points for each filter to facilitate confirmation of whether the wind speed distribution of each filter is consistent.

4. Calculation method of average value and unevenness

After measuring the wind speed point by point, the following methods are commonly used to process the data:

4.1 Arithmetic mean

Average surface wind speed = sum of wind speeds at each measuring point ÷ number of measuring points

The arithmetic mean is a common method for determining face wind speed. It is simple to calculate and easy to compare.

4.2 Unevenness

Non-uniformity is used to evaluate the uniformity of wind speed distribution. The common calculation method is:

Unevenness = (maximum wind speed − minimum wind speed) ÷ average wind speed × 100%

The smaller the unevenness, the more uniform the wind speed distribution. Specific judgment criteria should be agreed upon with the project party.

4.3 Relative standard deviation (optional)

For more demanding projects, the relative standard deviation can be calculated:

Relative standard deviation = standard deviation ÷ average wind speed × 100%

The relative standard deviation can reflect the degree of dispersion of the wind speed at each measuring point relative to the average value, and is suitable for scenarios with high uniformity requirements.

5. Measurement precautions

During the face wind speed measurement process, the following factors will affect the results:

1. Types of anemometers : Different instruments such as hot-wire anemometers and impeller anemometers have different response characteristics;

2. Measuring direction : The probe should be perpendicular to the direction of air flow to avoid angular deviation;

3. Measurement time : Each measurement point should be read stably, and the average of multiple measurements should be taken if necessary;

4. Filter status : The resistance of the new filter and the filter after dust collection are different, and the wind speed will be different;

5. Fan operating status : It should be confirmed that the fan is measured in a stable operating status;

6. Environmental conditions : temperature, humidity, atmospheric pressure, etc. may affect the measurement results.

It is recommended to indicate the instrument model, measurement conditions and filter status in the measurement record to facilitate subsequent traceability.

6. Surface wind speed calculation and acceptance suggestions

Issues related to face wind speed should be agreed upon during the design stage to avoid deviations after delivery:

1. Calculation diameter : clarify the definition and calculation method of effective filter area;

2. Measurement plane : agreed distance from the wind outlet surface;

3. Measuring point layout : Agree on the number and distribution of measuring points;

4. Judgment value : clarify the average surface wind speed and allowable deviation range;

5. Unevenness : Agree on whether to evaluate unevenness and the criteria for determining it;

6. Measuring working conditions : Confirm filter status and fan operating status;

7. Recording method : Record the wind speed, average value and unevenness of each measuring point.

7. Information required for surface wind speed calculation

It is recommended to provide: when communicating with the project:

1. Equipment installation space and EFU installation method;

2. Target surface wind speed or volume;

3. Filter specifications and effective air supply area;

4. Air outlet size and structural occlusion;

5. Fan model and control method;

6. Acceptance measurement methods and judgment values;

7. Filter status, including new filter or after dust collection.

8. Aili Industrial EFU surface wind speed supporting capabilities

Aili Industrial has the following supporting conditions in terms of EFU surface wind speed:

• Fan matching : Self-produced EC/DC/AC motors and fans can match the air volume parameters according to the target surface wind speed;

• Self-produced filters : With HEPA/ULPA filter production capabilities, filter specifications and resistance consistency can be controlled;

• Structural design : The internal structure and diffusion space of the box can be designed according to the equipment space to improve wind speed distribution;

• Whole machine verification : conduct wind speed, air volume and operation tests before leaving the factory;

• Customization ability : The cabinet, air inlet and outlet methods and interfaces can be customized according to the equipment space.

For more EFU product systems, please refer toEquipment-side fan filter unit (EFU)、Custom EFU and70mm ultra-thin EFU。

FAQ

What is the formula for calculating EFU surface wind speed?

Face wind speed = air volume ÷ effective filter area. The air volume unit is m³/s, the effective filter area unit is m², and the result unit is m/s.

How to confirm the effective filtration area?

It should be based on the actual effective air supply area of ​​the filter, excluding the area occupied by the frame and sealing strips, and the structural obstruction should be taken into consideration.

Where should the surface wind speed measurement plane be selected?

Usually selected at a certain distance from the filter outlet surface, the common reference value is 100-300mm, and the specific distance is agreed upon by the project.

How to determine the number of measuring points?

Calculated based on the air supply area, the larger the area, the more measuring points. Each filter measures at least 1 point and evenly covers the center and edge areas.

How to calculate the average face wind speed?

The wind speed at each measuring point is added up and divided by the number of measuring points to obtain the arithmetic mean. Unevenness can be calculated at the same time if necessary.

How to calculate unevenness?

Unevenness = (maximum wind speed − minimum wind speed) ÷ average wind speed × 100%. The specific judgment standard is agreed with the project party.

Will the air velocity on the filter surface be different between the new filter and after dust collection?

meeting. After the filter contains dust, the resistance increases. If the fan speed remains unchanged, the air volume will decrease and the face wind speed will decrease accordingly.

What should we pay attention to when measuring face wind speed?

Pay attention to anemometer type, probe direction, measurement time, filter status, fan operating status and environmental conditions, and record the measurement conditions.