How to choose the rated air volume of high-efficiency filter?

The word rated air volume makes people think that there is a standard answer. When it comes to actual selection, it is more of a matching issue: how much air volume is required for this installation location, and how well the candidate product performs when bearing this air volume.

Select only by size or grade and ignore the air volume matching. After installation, the air speed may be insufficient or the resistance may be high. For matching The FFU fan filter unit system must also be calculated together with the fan operating point of the unit, not just the filter element itself.

First allocate the air supply demand of each location

Based on the required air supply volume in the target area and the layout of the air supply points, determine the air volume that a single filter can bear.

After the regional total air volume is determined, it will be distributed according to the number and location of air supply points. There are two points to note here:

The branch resistances are not necessarily the same. When multiple ends are connected in parallel, the length of the air duct, the number of elbows, and the position of the air valve in each branch may be different. Different resistances will lead to uneven distribution of air volume. The design cannot assume that each unit is naturally equally distributed.

Partial occlusion will affect the actual air supply. If there are structures, lamps or equipment near the air supply vents, the airflow distribution may be affected. In this case, a margin needs to be left in the design value of a single air volume.

Compare candidate products using the same air volume conditions

After determining the target air volume of a single unit, obtain the resistance data of the candidate product at that air volume from the supplier.

When comparing different products, use data under the same air volume conditions. The resistance of product A at the nominal rated air volume and the resistance of product B at another air volume cannot be directly compared. Also check whether the intended operating air volume is within the applicable range of the product description. Use outside the range may affect efficiency and lifespan.

For resistance data it is best to know both the initial resistance and the final resistance. The initial resistance is used to check the initial working point, and the final resistance is used to evaluate the fan's margin in the later stage of filter element dust accumulation. For device-side applications such as The internal space of the EFU equipment-side fan filter unit is limited, and the fan selection range is small. The final resistance conditions need to be taken into account when calculating.

Check the fan working points together

After selecting the filter element, you must also confirm whether the fan in the system can provide the target air volume under this resistance.

The initial resistance and final resistance of the filter, plus the resistance of the air duct and the resistance of other links, form the total resistance of the system. Compare the fan performance curve to find the corresponding operating point and confirm whether the air volume at this point meets the demand.

If the working point deviates far from the target air volume, adjustments may be needed: changing to a filter element with a larger effective filtration area, adjusting the fan configuration, or optimizing the air duct. It is a common omission in selection to only look at the rated air volume of the filter element and ignore the system resistance.

Calibrate based on actual measurements after installation

The calculation in the design stage is a prediction, and the actual status must be confirmed by measurement.

After completing the installation, measure the actual air supply volume and face velocity, and adjust the fan or damper if necessary. For systems with multiple terminals connected in parallel, it is recommended to measure each unit one by one to confirm whether the actual air volume of each branch is close to the design distribution value. If a certain unit is obviously low, check the branch air valve, filter element installation status and interface sealing.

After the adjustment is completed, record the actual measured data as a benchmark for subsequent operations. The equipment-side application must record the equipment operating gear as well, because the air volume requirements may be different under different operating conditions of the equipment. involving For HEPA/ULPA air filter products of different grades, the air volume matching verification method is the same, and the test data is checked according to the corresponding standards.

An idea for estimating air volume

Assume that a number of HEPA terminals are responsible for the total air supply volume of a group of terminals:

First determine the total air volume in the area according to the air flow coverage requirements. The target air volume of each unit is then allocated based on the branch structure and occlusion conditions. Then select the rated air volume one by one and check the corresponding resistance data. Finally, put the resistance into the system and confirm the working point by comparing it with the fan curve. Use measurements for leveling after installation.

After actual installation, if it is found that the air volume of a certain unit is low, do not directly divide the total air volume by the number of units to infer, but check the specific resistance of the branch.

About Aili Industrial’s air volume matching

Aili Industry also produces filters and clean air supply equipment, and can check the designed air volume based on the fan, filter element resistance and box structure. filter with FFU fan filter unit、The EFU equipment-end fan filter unit is matched in the same manufacturing system, and the filter element resistance and fan operating point can be calculated together during the planning stage.

The actual configuration is confirmed with project drawings and complete machine test results. It is recommended to provide the regional total air volume, air supply point layout and installation space to facilitate the judgment of single air volume and filter element selection.