Can a chemical filtration retrofit retain the original HEPA filter?

Direct answer: Retention can usually be assessed, but not unconditionally.

The purpose of chemical filtration modification is to increase gaseous pollution treatment capacity. HEPA is responsible for particle control, and the two have different divisions of labor. Adding a chemical filtration section does not mean that the mission of HEPA has changed, nor does it mean that HEPA can be canceled or downgraded.

Whether the original HEPA can be retained depends on several conditions: whether the original HEPA itself still meets the particle requirements, whether the new chemical filter section will affect the air volume and sealing, and whether the system resistance after the modification is within the fan capacity. If these conditions are confirmed, it is reasonable to retain HEPA; if not confirmed, simultaneous adjustments may be needed.

Confirm original filtering status

Before renovation, perform a condition assessment on the original HEPA.

Model and grade. Confirm the model, efficiency level, size and sealing method of the original HEPA. If the project particle requirements do not change, the original HEPA rating remains valid. Specific product descriptions can be found in Information about HEPA high efficiency filters .

Use time and pressure difference. If the original HEPA has been running for a long time, the pressure difference is close to the final resistance, or it is close to the expected replacement cycle, you can consider replacing it together during the transformation to avoid repeated shutdowns in a short period of time. For specific life span judgment, please refer to Discussion of how long chemical filters last .

Leak detection records. View recent field leak test results. If the HEPA seal is in good condition and the leak test is qualified, the basis for retention is established. If there is a frame bypass or seal aging, it is recommended to deal with it during the renovation. For specific inspection methods, please refer to Discussion on how to check frame bypass after chemical filter installation .

Frame and seals. Check whether the HEPA frame is deformed and the seal is not aged. If the installation structure changes after modification, the sealing status may need to be re-confirmed.

Check the coordination of new segments

Keeping the original HEPA depends on how the new chemical filtration section works with it.

The medium loses powder and outgasses. Some chemical filter materials may produce trace amounts of dust or release organic matter during operation. If the chemical filter section is placed after the HEPA, this part of the dust and emissions will directly enter the clean side. When selecting, confirm whether the chemical medium meets the requirements for cleanliness and compatibility. For specific verification methods, please refer to Discussion on how to verify the low outgassing requirements of ULPA .

Installation sequence. Whether the chemical filtration section is placed before or after the HEPA affects the protection relationship and resistance distribution. A common configuration is that the chemical filter section is in the front and the HEPA is in the back, with the HEPA intercepting trace amounts of dust that may be generated by the chemical media. But the specific order must be confirmed according to the product and system. For specific differences, please refer to Discussion on whether the FFU chemical filter should be placed before or after the HEPA .

Resistance stacks up. Adding a new chemical filtration section will increase the total resistance of the system. Whether the original fan can overcome the resistance of the chemical filter section and HEPA at the same time needs to be calculated based on the actual working point. For specific methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Air volume distribution. If the original system has multiple branches, the air volume of each branch may change after adding a chemical filter section. The branch air valve or adjustment method needs to be rechecked. For specific methods, please refer to whether chemical filtration modification requires re-doing the air volume balance . Discuss

Re-verify related performance

After the transformation is completed, the particle and gas properties must be confirmed separately.

particle side. For the original HEPA or the replaced HEPA, installation sealing inspection and on-site leak detection shall be carried out according to the corresponding level. Particle cleanliness cannot be reduced due to modification. For specific testing requirements, please refer to Information about HEPA high efficiency filters .

gas side. The chemical filtration section detects the inlet and outlet concentrations according to the target components to confirm the removal effect. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Air volume and pressure difference. After the modification, measure the air volume and pressure difference of each section of the system to confirm that they are within the allowable range. If the air volume drops significantly, you need to check whether it is a problem with the resistance of the chemical filter section, the HEPA status, or the fan operating point.

Record archiving. Test data, replacement records and operating parameters before and after modification should be archived. During subsequent maintenance or renovation, you can quickly understand the system status.

Project judgment example

The original HEPA in a clean room has been running for two years, the leak detection has passed, and the pressure difference is still within the normal range. The project plans to add a chemical filtration section before the HEPA to process the externally input acid gas.

Check before transformation: the original HEPA is in good condition and can be retained; the initial resistance of the new chemical filtration section is about 60 Pa, and the final resistance is about 120 Pa, and the original fan margin can withstand it; the chemical filtration section is placed in front of the HEPA, and the HEPA can intercept possible trace powder loss. After re-testing, the particle leak detection was qualified, the gas outlet concentration reached the target, and the air volume was within the design range.

The original HEPA of another project was approaching its replacement cycle and the pressure difference was relatively high. During the renovation, it was decided to replace the HEPA simultaneously and adjust the installation frame to complete the update of the chemical filtration section and HEPA at one time. This avoids another downtime in the short term.

These two cases illustrate that the prerequisite for retaining the original HEPA is that the status is qualified, the system is matched, and the verification after modification is passed. involving When selecting a chemical filter product series , it is recommended to provide the original HEPA status, system data and target gas to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s transformation and HEPA matching

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide HEPA filters, chemical filter product series and supporting air supply equipment. For chemical filtration renovation projects, we can assist in checking the chemical filtration section configuration and retention plan based on the original HEPA status, system conditions, target gases, and installation space.

Related products:Chemical filter product series、HEPA high efficiency filter、MAU box chemical filter、FFU comes with chemical filter . Providing original system data and modification requirements when inquiring will help confirm the appropriate solution. The specific selection is subject to the technical documents and test results confirmed by the project.