Can reducing the surface wind speed of ULPA extend its life?

The answer to this question depends on how you implement 'lowering the face wind speed'.

If it is achieved by increasing the filtration area, the air volume remains unchanged and the passing wind speed is reduced, the load on the filter material is indeed reduced, and the resistance and dust accumulation speed may be slowed down. However, if the air supply volume is directly reduced, the face wind speed will decrease, and the air flow protection in the process area will also decrease. This approach is not considered a life extension, but a downgraded operation.

The relationship between face wind speed and lifespan is not unilinear. It depends on which way you drop, how much you drop, and what other conditions are at play upstream.

Let’s first look at how the passing wind speed affects the filter material

The impact of reduced face wind speed on the filter material can be seen from several aspects.

The particle impact velocity decreases. As the speed of air flowing through the filter material decreases, the inertial momentum of the particles decreases. For larger particles, the inertial collision efficiency may change slightly; for very small particles that rely on diffusion capture, the diffusion effect is favored by reducing the wind speed. Overall, the filtration efficiency at low passing wind speeds usually does not become worse, and in some cases is even more stable.

Dust accumulation is more evenly distributed. After the wind speed is reduced, the air flow is more evenly distributed on the surface of the filter material, and particles are not easily concentrated in certain local areas. Dust accumulation is dispersed, the risk of local blockage is reduced, and the overall utilization of the filter material is improved.

The rise in resistance slows down. Under the same particle concentration, the lower the passing wind speed, the amount of particles deposited on the filter material per unit time is relatively dispersed, and the pressure difference may rise slower. However, this effect is related to the properties of the particles - dry dust and viscous deposition behave differently. For details, please refer to the relevant instructions for oil mist airflow pretreatment.

These are analysis at the mechanism level, and the actual effect depends on the working conditions. If the upstream dust concentration is high, even if the passing wind speed is reduced, the dust accumulation speed will not be much slower.

However, the falling surface wind speed is not equal to the air reduction volume.

This is where the most confusion arises.

The correct approach is to reduce the passing wind speed by increasing the filter area. The air volume remains unchanged, the filter material area increases, and the passing wind speed naturally decreases. This approach does not sacrifice the air supply volume in the process area, and at the same time reduces the load of the filter material. The price is that the size of the filter element may increase, the cost will increase, and the installation space must be able to accommodate it.

The wrong approach is to directly reduce the air supply volume. When the fan speed is lowered, the air volume decreases, and the face wind speed also decreases. At this time, the load on the filter material is indeed reduced, but the process area also receives less clean air. If the number of air changes is insufficient and the unidirectional flow coverage is insufficient, the overall effectiveness of particle control may deteriorate. This approach does not extend life, but shifts the problem to cleanliness.

There is also an intermediate state: if the original system is operating at an excess air volume, the air volume is appropriately reduced to the design air volume, the face wind speed returns to a reasonable range, and the air volume is still within the process requirements. In this case, reducing the surface wind speed can indeed reduce the load on the filter material without affecting the protection effect. The key to judgment is: after the reduction is completed, whether the air volume and airflow organization in the process area are still within the design range.

Dust holding conditions are more critical than face wind speed

Face velocity is only one variable that affects longevity, with upstream dust loading often having a greater impact.

Whether the front-level protection is in place. If the primary and medium-efficiency filters are maintained normally and the concentration of particles entering the end is low, the dust accumulation speed of the filter element will naturally be slow. In the case of failure of the front stage, even if the face wind speed drops to a very low level, the end will still be blocked quickly. For specific configuration ideas, please refer to the instructions related to pre-filtering.

The nature of the contaminants. Dry dust, oil mist, and moisture agglomeration affect the filter material in different ways. Oil mist may form a sticky film on the surface of the filter material. Reducing the surface wind speed cannot solve the problem, and it needs to be dealt with from the source. The risk of moisture in a high-humidity environment cannot be eliminated by decreasing surface wind speed.

Run time and intermittent mode. The dust accumulation rules are different between continuous operation and intermittent operation. If the equipment has a downtime period, the state changes of the filter material during the downtime (such as moisture, particle settlement) will also affect the service life.

Therefore, it is said that 'lowering the surface wind speed can extend the service life' ignores a premise: the upstream load is controllable. If there is a problem upstream itself, the improvement brought about by reducing the surface wind speed will be limited.

How to judge the effect during operation

If a project decides to adopt an option to reduce passing wind speeds, operational data can help determine the effectiveness.

Record the rate of rise in differential pressure. Under the same working conditions, compare the pressure difference trends before and after adjustment. If the rate of increase slows down significantly, it means the plan is effective.

Check whether the air volume is maintained. If the solution is implemented by increasing the area, the air volume should be maintained near the design value. If the air volume also drops, confirm whether the process area can still meet the requirements. Supporting The system of FFU fan filter unit must record the unit gear and surface wind speed at the same time; the equipment-side application is as follows: For the EFU equipment-side fan filter unit , make sure that the operating status of the equipment has not changed due to air volume adjustment.

Check the surface condition of the filter media. Observe the dust distribution when replacing the filter element. If the dust accumulation is uniform and not locally concentrated, it means that the airflow distribution has been improved by reducing the wind speed. If there is still a local blockage, the airflow organization or upstream loading may need to be checked.

Evaluate overall costs. Increasing the filter area may increase the purchase cost, but if the replacement cycle is extended and the number of downtimes is reduced, the long-term cost may be lower. This account must be calculated based on actual project data. involving For HEPA/ULPA air filter selection, please refer to the corresponding product information.

Project judgment example

The replacement cycle of ULPA in a certain clean room was too short, so the operation and maintenance team considered reducing the face velocity to extend its life.

Option 1: Directly lower the fan gear, and the air volume is reduced from the design value to 80%. As a result, the rise in pressure difference did slow down, but particle monitoring in the process area fluctuated, and insufficient air exchanges caused particle recovery to slow down.

Option 2: Keep the air volume unchanged and switch to a ULPA structure with a larger effective filtration area. By reducing the wind speed by about 25%, the rise in pressure difference slowed down, the air volume in the process area was maintained at the design value, and there were no abnormalities in particle monitoring.

Both solutions are called 'reducing face wind speed', but the effects are completely different. The first option comes at the expense of process protection, while the second option is the real life extension measure. For device-side applications with limited space, increasing the area may be limited by installation conditions. At this time, other options need to be evaluated, such as optimizing front-end protection or adjusting replacement strategies.

Selection and Acceptance Checklist

About Aili Industrial’s face velocity solution adaptation

Whether it is feasible to reduce the passing wind speed depends on whether the product design can provide a larger effective area in a limited space, and whether the system can maintain stable operation after adjustment.

Aili Industrial has independent manufacturing capabilities in filters, fans, motors and control systems. It can evaluate the adjustment space of the passing wind speed in combination with the installation space, target air volume and filter material structure during the planning stage. For projects that require reducing the load of the filter material while maintaining air volume, you can check whether the filter element structure, box interface and fan working point match. When the filter is matched with equipment such as FFU and EFU, the air volume distribution and control parameters can also be confirmed uniformly.

Providing current operating data, replacement cycles and installation conditions when inquiring will help determine which surface wind speed reduction solution is more suitable. The specific configuration is subject to the technical documents and operating data confirmed by the project.