How to calculate the effective area of ​​ULPA filter?

This question will be asked during selection and on-site measurement, but the word 'effective area' itself may not refer to the same thing.

Windward area, air outlet area, effective ventilation area, unfolded filter material area - these concepts are often used interchangeably. One set is used when calculating air volume, and the other set is used when evaluating filter material load. If you use the wrong object, the calculated numbers will be meaningless.

The outer frame area is not equal to the effective ventilation area

The most common mistake is to directly multiply the length of the outer frame by its width.

Assuming a nominal 600×600 filter, the outer frame area is 0.36 square meters. But what parts should be deducted from the actual ventilation area?

Occupation of the outer frame itself. The bezel has width and this part is not ventilated.

Sealed edges. The position occupied by the gasket or liquid tank is not an effective ventilation surface.

Internal support structure. Protective nets and dividing strips will also take up part of the area.

Therefore, the real effective windward or windward area is usually smaller than the outer frame area. Products with different structures have different deduction ratios. If you calculate the surface wind speed based on the outer frame area when selecting a model, the result will be higher, and you may misjudge whether the actual wind speed meets the standard.

Expanding the filter media area is another concept

The windward area refers to the cross section of the airflow passing through the filter, and the expanded filter material area refers to the area of ​​the filter material itself.

A pleated filter in which the filter material is pleated. When the pleats are unfolded and flattened, the area obtained is the unfolded filter material area. This area is usually much larger than the windward area - the more tightly folded, the larger the unfolded area.

The expansion area affects the passing wind speed on the filter material. Under the same air volume, the larger the expansion area, the less airflow passes through the filter material per unit area, the lighter the filter material load, and the lower resistance.

This explains a common phenomenon: two products of the same size and grade may have very different resistance and dust holding capacity. The reason is often due to the difference in the unfolded filter material area, rather than the difference in filter material or grade itself. Please refer to the relevant instructions on the relationship between efficiency and resistance when making specific selections.

Pay attention to the units when calculating

The most common place for errors in on-site measurement is unit conversion.

Unit of length. Millimeters are usually used when measuring and converted to meters when calculating area. 600 millimeters is equal to 0.6 meters, not 600.

Air volume unit. The difference between cubic meters per hour (m³/h) and cubic meters per second (m³/s) is 3600 times. Which unit to use must match the area unit.

Unit of surface wind speed. Usually meters per second (m/s) are used. Divide the air volume (m³/h) by the area (m²) to get meters per hour, which must be divided by 3600 to convert to meters per second.

The formula can be recorded as follows: face wind speed (m/s) = air volume (m³/h) ÷ area (m²) ÷ 3600

Or conversely, if the surface wind speed and area are known, find the air volume: Air volume (m³/h) = Surface wind speed (m/s) × Area (m²) × 3600

If the conversion of these units is mixed up, the result may be thousands of times different.

It is necessary to see clearly in the report which area it is

The areas marked on different materials may have different meanings.

The dimensions on product samples are usually the dimensions of the outer frame, not the effective ventilation area.

For the effective area in the technical data , you need to confirm what the definition is - whether it is the effective area facing the wind or the area of ​​the unfolded filter material.

The test conditions on the air volume resistance curve usually indicate the surface wind speed in which area and where the measurement position is.

When you get an area data, first confirm what it is used for. The required area for air volume calculation and filter media load evaluation are not the same.

The calculation method of face wind speed should be explained clearly.

Face wind speed is an average value.

The results may be different depending on the location of the measuring point. The local wind speed may be different at the center, edge and four corners of the air outlet surface. The project document should indicate which cross section and which location the average surface wind speed is.

Measurement methods should be consistent. When comparing data before and after changing the filter element and between different equipment, the location of the measuring points and the measurement method must be consistent, otherwise the data will not be comparable.

When the air outlet distribution is uneven, a single point reading cannot represent the entire unit. It is necessary to average multiple measurements or evaluate according to the method agreed upon by the project.

Supporting In the FFU fan filter unit system, face wind speed measurement is usually recorded together with the unit gear; equipment-side applications include: The internal structure of the EFU equipment-side fan filter unit may affect the airflow distribution. The stability of the equipment status must be considered when measuring. involving For HEPA/ULPA air filter products of different grades, the effective area verification methods are the same.

Project judgment example

Assume that the effective ventilation area of ​​a filter is 0.5 square meters, and the measured average surface wind speed is 0.45 meters per second.

Calculate air volume: 0.5 × 0.45 × 3600 = 810 cubic meters per hour.

This is the arithmetic result in the example, not the product promise value. In actual projects, this number needs to be checked with other measurement data: compared with the design air volume, compared with the fan operating point, and correlated with the pressure difference record. Just looking at a calculation result cannot determine whether the system is normal.

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About Aili Industrial’s area accounting cooperation

If the effective area is clearly stated in the product information, there will be fewer disputes on site.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide ULPA ultra-high efficiency filter and supporting air supply equipment. The definition of size and effective area will be indicated in the product information to facilitate the project party to calculate the air volume and surface wind speed. filter with When FFU fan filter unit and EFU are used together, the area, air volume and surface wind speed can be checked together during the planning stage.

When enquiring, provide the target surface wind speed, design air volume and installation space to help confirm suitable specifications. Specific parameters are subject to the technical data of the corresponding model.