Can ULPA and HEPA be mixed in the same clean room?

Yes, and this practice is not uncommon in semiconductor, precision manufacturing, and pharmaceutical projects.

But 'can be mixed' does not mean 'install as you like'. In the same clean room, the control objectives of different areas may be different - key workstations require stricter particle control, which can be met by HEPA in general areas. It is reasonable to configure them separately by region.

What really needs to be confirmed is whether the air volume distribution, pressure gradient and maintenance management can remain stable after mixing. If these links are not handled well, mixing them will cause new problems.

What is the basis for partition configuration?

Different grades of filters are used in the same clean room, usually due to the following situations.

Key workstations are partially strengthened. The entire room is designed according to HEPA, but a certain exposed workstation or equipment requires lower particle penetration, so a ULPA air supply unit is configured at that location. The entire room environment is maintained by HEPA and partially enhanced by ULPA. This configuration is common in precision electronic packaging and semiconductor equipment.

Different areas have different cleanliness levels. In the same factory, the core process area and peripheral areas have different control objectives, and the filtration levels can be set separately. ULPA is used in the core area and ULPA is used in the peripheral area.HEPA , separated by a pressure gradient.

Renovation project partially upgraded. The original system was all HEPA. Later, the process was adjusted and only some locations were upgraded to ULPA. This approach of 'partial replacement and partial non-replacement' is more risky than the first two, because the balance of the original system may be broken.

The premise of partition configuration is that the control objectives of each area are clear and there is reasonable physical isolation or pressure difference between areas. If you just mix them randomly without zoning logic, the air volume and pressure difference can easily get out of control.

The impact of mixed use on air volume distribution

This is the part of the hybrid plan that needs to be calculated in advance.

The resistance of the filter element is different, and the working point of the fan will change. The resistance of ULPA is usually higher than that of HEPA of the same size. If two types of filters share an air supply system, the difference in resistance will lead to uneven air volume distribution - the air volume will be larger where the resistance is smaller, and the air volume will be smaller where the resistance is greater.

The impact of parallel branches is more obvious. If HEPA and ULPA are installed on different branches of the same air conditioning box, the resistance differences of each branch need to be recalculated. If necessary, adjust or redistribute the designed air volume through the damper. For specific calculation methods, please refer to the relevant instructions on the filter resistance curve.

When FFU partitions are mixed, the problem is more direct. per unit The FFU fan filter unit comes with its own fan, and changes in filter element resistance will change the unit's working point. If there are both HEPA and ULPA units in the same area, the gear parameters may be different, and the group control settings need to be recalibrated.

Device-side applications should also pay attention. The internal space of the EFU equipment-end fan filter unit is compact, and the fan selection range is small. If HEPA and ULPA are mixed in different positions of the same equipment, the filter element resistance and fan matching must be confirmed one by one and cannot be set according to one parameter. involving For products of different grades of HEPA/ULPA air filters , the interface size and sealing method should also be checked separately.

The differential pressure gradient needs to be re-confirmed

Clean room partitions usually rely on pressure gradients to maintain the direction of air flow. When filters of different grades are mixed, the differential pressure relationship may change.

Changes in air supply volume will affect the room pressure difference. If the air volume in the ULPA area decreases due to increased resistance, the air supply volume in this area decreases, and the pressure difference may deviate from the original setting. The direction of airflow between adjacent areas may change.

The return air path should also be checked. If the return air in different areas shares a system, resistance changes will affect the return air distribution. The supply air and return air are linked, and adjusting only one side is often not enough.

The differential pressure monitoring points should cover the mixed use area. If differential pressure gauges were originally installed only in some locations, after mixed use, it is recommended to add monitoring at the boundaries of grade changes to facilitate timely detection of abnormalities. For specific troubleshooting ideas, please refer to the instructions related to abnormal pressure differences.

Maintenance and spare parts management should be separated

After mixing, the complexity of maintenance and management will increase.

Replacement intervals may vary. HEPA and ULPA have different resistance characteristics, dust holding capacity and replacement criteria. The maintenance records of the two types of filters should be separated and cannot be processed according to the same cycle.

Spare parts cannot be purchased based on appearance alone. Under the same dimensions, there may be both HEPA and ULPA, and the sealing structures may also be different. Spare parts management should match the product number with the installation location to avoid temporary use of filter elements that are similar in size but have the wrong grade or sealing structure.

Leak detection methods and judgment standards must be confirmed separately. The leak detection requirements of HEPA and ULPA may be different, and the instrument range and judgment limits must be implemented according to the corresponding levels. For specific differences, please refer to the relevant instructions for leak detection requirements.

Records must be traceable to a specific location. There must be records of what grade, model and when it was replaced at which location. When an abnormality occurs later, it can be quickly determined whether it is a product problem or a system problem.

Project judgment example

A certain clean room uses ULPA in the core area and HEPA in the peripheral area, sharing an air supply system.

After running for a period of time, it was found that the air volume in the core area was low, the air volume in the peripheral area was high, and the pressure gradient also deviated from the design value.

The investigation found that: the resistance of the filter element in the ULPA area was higher than estimated in the original design, resulting in a decrease in the air volume of the branch; the HEPA resistance in the peripheral area was lower and the air volume was larger. The total air volume of the system has not changed, but the distribution ratio has changed.

The solution is not to simply increase the fan speed - that will increase the air volume in the peripheral area. A more reasonable approach is to recalculate the resistance of each branch, restore the design distribution through air valve adjustment, and adjust the filter element structure or fan configuration in the ULPA area if necessary.

For a mixed-use plan, the air volume distribution must be calculated clearly at the design stage and cannot be adjusted after operation.

Selection and Acceptance Checklist

About Aili Industrial’s mixed solution package

When HEPA and ULPA are mixed, the core is to design the filtration needs, air volume distribution and system balance of each zone together.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide HEPA/ULPA products of different grades and supporting air supply equipment. Filter can be used with FFU fan filter unit、The EFU equipment-side fan filter unit checks the air volume, resistance and installation interface at the same time to facilitate unified accounting during partition configuration.

When enquiring, provide the control objectives, design air volume, available static pressure and installation conditions of each area, which will help determine whether the mixed solution is feasible. The specific configuration is subject to the technical documents and operating data confirmed by the project.