How to maintain air volume after FFU upgrades from HEPA to ULPA?

Replacing the filter element with FFU looks like replacing a part. However, when HEPA is replaced by ULPA, the resistance will change and the fan operating point will move accordingly. The air volume corresponding to the original speed may not be accurate.

'Maintaining air volume' is essentially about re-matching the working points of the fan and filter element, not just raising the speed.

Check the filter compatibility first, then the air volume

Whether the air volume can be maintained depends on whether the filter element can be installed and sealed correctly.

Thickness and structure. ULPA is usually thicker or has a denser internal structure than HEPA of the same size. The height of the original FFU box, the installation depth of the filter element, and the stroke of the compression piece must be able to accommodate the new filter element.

Sealing method. Gasket compression or liquid tank sealing, the interface conditions of the two structures are different. The blade edge and tank body size of the liquid tank must be checked item by item, not just the length and width of the outer frame. For the seal verification method, please refer to the instructions related to the knife edge size.

Maintain path. After the new filter element is installed, can it be taken out? Some FFUs are designed to be replaced from the bottom, and some are designed to be replaced from the top. Changes in the thickness of the filter element may affect the disassembly and assembly operations.

If the interfaces do not match, there is no need to talk about the air volume issue. First confirm that it can be installed and sealed, and then talk about the air volume.

The fan curve account needs to be recalculated

When HEPA is replaced by ULPA, the system resistance increases. At the same speed of the fan, the working point will move to the left - the air volume decreases and the static pressure increases.

The specific reduction depends on two data: the resistance curve of the new filter element at the target air volume, and the PQ curve of the original fan.

Put the initial resistance and final resistance of the new filter element into the total resistance of the system, and compare it with the fan curve to find the new working point. If the air volume corresponding to this working point is still within the target range, it means that the original speed can continue to be used; if the air volume has deviated, adjustment must be considered.

The final resistance condition must be calculated. The resistance of the filter element will rise after it has been running for a period of time. If the initial resistance is only calculated and the air volume is just enough after it is installed, it may not be enough after running for a few months. For specific calculation methods, please refer to the relevant instructions on initial resistance and final resistance. Product types can refer to ULPA ultra-high efficiency filter . Specifications of

Speed ​​regulation is not a panacea

When the air volume is not enough, the first reaction is often to increase the speed. But there are several boundaries to this matter.

Allowable range for fans and motors. As the speed increases, current, power, noise and vibration will all change. Operating beyond the design range may affect the life of the motor and may also trigger protection. The specific allowable range depends on the unit specifications.

The ability to control the system. EC fans or DC fans usually have limited speed ranges. If the output capability of the original controller is already close to the upper limit, continuing to increase the speed may not be effective.

Treating the symptoms rather than the root cause. If the resistance increases too much, compensation by speeding up is only temporary. When the filter element accumulates dust and reaches the final resistance, the rotation speed may have reached the top, but the air volume will still drop.

A more reasonable approach is to calculate the resistance clearly during the selection stage. If the resistance of the ULPA does exceed the capacity of the original fan, the solution may be to choose a ULPA structure with a larger effective filtration area, or adjust the fan configuration instead of blindly increasing the speed.

Multiple FFUs need to be rebalanced

Just because the air volume problem of a single FFU is solved, it does not mean that the entire system is normal.

For FFUs running in parallel, the difference in filter element resistance will affect the air volume distribution. If only part of the FFU filter element is replaced, or the resistance consistency of the new filter element is not good, the air volume between each unit may be uneven.

The gears in the group control system need to be recalibrated. The gear parameters originally adjusted according to HEPA may no longer be applicable after switching to ULPA. It is necessary to measure the air volume of each unit under actual operating conditions and re-confirm the gear settings.

Regional balance needs to be retested. After the upgrade, re-measure the surface wind speed in each area to confirm that the coverage of the protected area has not changed due to changes in wind volume. involving The group control configuration of the FFU fan filter unit and the corresponding relationship between control parameters and filter element data must also be updated. Device-side applications such as The internal space of the EFU equipment-side fan filter unit is limited, and there is less room for air volume adjustment, so more room should be left when selecting the model.

It must be tested after installation

No matter what the calculation results are, the actual measurement after installation is the final confirmation.

Measuring surface wind speed distribution is not just about measuring one point. The uniformity of wind speed on the FFU air outlet affects the actual protection effect. Just because the air volume at a single point reaches the standard does not mean that it is uniform over the entire surface.

Test working position and duty position. If the system has different operating modes, the air volume in both states must be confirmed.

Record new baseline data. The upgraded air volume, pressure difference and speed settings are the benchmark for subsequent maintenance. The original HEPA operating data should be retained for comparison before and after the upgrade.

On-site leak detection should also be done. After replacing the filter element and adjusting the air volume, the sealing status may change. Leak detection is a necessary step to confirm the integrity of the installation. involving For HEPA/ULPA air filter products of different grades, the testing methods and criteria are implemented in accordance with corresponding standards.

Project judgment example

A certain FFU has original H14 and plans to upgrade it to U15.

The calculation found that the initial resistance of the U15 filter element at the target air volume is about 25% higher than the original H14, and the final resistance is about 35% higher. According to the original fan curve, the air volume will decrease by about 15% at the original speed.

There are several options for handling: increase the speed to see if the air volume can be restored, but confirm the allowable range of the motor and controller; switch to a U15 structure with a larger effective filter area to reduce the resistance at the same air volume; or accept a moderate drop in air volume and re-evaluate the target surface wind speed.

Which solution is suitable depends on the actual air volume requirements of the project and the system margin. You can’t simply choose one and go with it, nor can you change it first.

Selection and Acceptance Checklist

About Aili Industrial’s FFU upgrade package

The core of FFU's upgrade to ULPA is to calculate filter element resistance, fan capacity and control parameters together.

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 FFU products. Since the core components are matched in the same system, the filter element resistance and fan operating point can be confirmed together during the planning stage, reducing air volume mismatch after installation.

When enquiring, provide the original FFU model, original filter element specifications, target air volume and installation space, which will help determine the upgrade plan. The specific configuration is subject to the technical documents and actual measurement results confirmed by the project.