How to avoid affecting the room pressure difference by modifying the chemical filter?

When modifying chemical filters, it is easy to focus on the filter section itself - what media to choose, where to place it, and how much resistance there is. But after the transformation is completed, what really affects production is often the change in room pressure difference.

Differential pressure is one of the core parameters of clean room operation. It determines the direction of air flow, whether external contamination penetrates, and whether there is cross-contamination between adjacent areas. Chemical filtration modification increases system resistance and may change the air supply volume; if the air supply volume changes, the balance of return air and exhaust air will also change, and the pressure difference may deviate from the original setting.

To avoid affecting the pressure difference, the key is not to 'turn the fan back after the transformation', but to clearly check the relationship between the supply air, return air and exhaust air before the transformation.

Record the airflow status before modification

Establish a baseline before the transformation, otherwise there will be no basis for comparison after the transformation.

Pressure difference in critical areas. Measure and record the pressure difference between the clean room and adjacent areas, corridors, and non-clean areas. The location of the measuring point, door status, and operating mode must be noted. Static single point pressure difference cannot reflect all dynamic conditions.

Supply and exhaust air volume. Record the supply air volume, return air volume, and exhaust air volume. The relationship between the three determines the room pressure difference. Merely recording the supply air volume is not enough; return air and exhaust air are equally important. For specific air volume measurement, please refer to Discussion on whether the chemical filter air volume should be selected based on the total air volume of the system or the air volume of a single unit .

operating conditions. Record the fan gear position, air valve opening, production status, and door zone status before the transformation. These conditions should be as consistent as possible during retesting after modification.

Baseline data should cover representative operating conditions. Static, dynamic, different shifts, and door opening status, if conditions permit, record them separately. For specific inspection record methods, please refer to Discussion of what items should be checked during daily inspection of chemical filters .

Assess the impact of new resistance

The increased resistance in the chemical filtration section will change the system operating point.

Resistance stacks up. Add the initial resistance and final resistance of the chemical filtration section to the total resistance of the original system. The total system resistance includes pre-filtration, surface cooler, heater, air duct, valve and terminal HEPA. For specific accounting methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

The fan operating point changes. When the system resistance increases, the fan operating point will move. If the original fan capacity is insufficient, the air supply volume may decrease. The air supply volume decreases and the room pressure difference may change.

Different branches have different impacts. If the chemical filter section is only added to some branches, the resistance changes of each branch will be different, and the air volume distribution may be offset. It needs to be checked branch by branch, not just the total air volume. For specific balancing methods, please refer to whether chemical filtration modification requires re-doing the air volume balance . Discuss

You cannot rely solely on restoring a certain fan speed. If the air supply volume decreases because the resistance of the chemical filter section increases, increasing the rotational speed may restore the total air volume, but the relationship between branch distribution and return air exhaust may not necessarily be restored. The pressure difference is the result of the joint action of supply air, return air, and exhaust air. If you only adjust one link, you may lose sight of one.

Synchronously check return air and exhaust air

Pressure balance is not a matter of air supply.

Return air volume changes. If the supply air volume changes due to renovation, the return air volume will also be affected. The return air valve opening, return air pipeline resistance, and return air fan status all need to be checked.

Changes in exhaust air volume. If the room has independent exhaust, changes in the exhaust volume will directly affect the pressure difference. The status of the exhaust fan, the opening of the exhaust valve, and the resistance of the exhaust pipeline should be checked together.

Door area and passing window. The door opening frequency, the use status of the transfer window, and the pressure difference between buffers will all affect the actual pressure difference performance of the room. Retesting after the transformation should cover these states.

Adjacent area relationships. If adjacent areas have also been renovated or share air supply and exhaust systems, the pressure difference relationship may be more complicated. Need to confirm area by area.

Temporary conditions during renovations should also be considered. During the construction period, the wind may be partially stopped, temporarily blocked or the operation may be adjusted. The impact of these temporary measures on the pressure difference should be stated in the construction plan.

Rebalance when finished

After the modification is completed, re-measure and adjust according to baseline conditions.

Review under normal operating and door zone conditions. The pressure difference measurement must cover the actual operating status and cannot only be measured under static and closed conditions. For specific methods, please refer to Discussion of what conditions should be evaluated first before adding a chemical filter to an existing clean room .

Adjustments item by item. Check the supply air, return air and exhaust air separately. First restore the total air volume, then adjust the branch distribution, and finally confirm the room pressure difference. Don't adjust multiple parameters at once, otherwise it will be difficult to tell which adjustment is working.

Verify target gas effect. Recovery of the pressure difference does not mean that gas treatment is up to standard. The outlet concentration needs to be tested separately. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Record the post-modification baseline. The air volume, pressure difference, fan gear and outlet concentration after modification should be recorded and archived as a basis for subsequent maintenance.

Project judgment example

A certain clean room added a chemical filtration section in the air-conditioning box. After the transformation, it only increased the fan speed by one gear, and it was considered that the recovery of the total air volume was complete.

After operation, it was found that the pressure difference in some areas was low and the air flow direction changed between adjacent areas. The investigation found that the chemical filter section was added to the main air supply branch, and the air volume distribution changed after the resistance of the branch increased. Return air and exhaust air are not adjusted simultaneously.

Treatment method: Re-measure the air volume according to the branch, adjust the air valve opening; check the return air volume and exhaust air volume, restore the original settings; re-measure the room pressure difference. After adjustment, the pressure difference in each area returned to the pre-renovation level.

In another project, the complete baseline of supply and exhaust air volume and pressure difference was recorded before the transformation. After the transformation, the baselines were retested one by one, and it was found that only the exhaust air volume changed slightly. After adjusting the exhaust valve, the pressure difference returned to the normal range.

These two cases illustrate that the chemical filtration transformation affects the pressure difference, which is usually not caused by a single link. The air supply, return air and exhaust air must be checked at the same time. involving When selecting a chemical filter product series , it is recommended to provide the system baseline, modification plan and target gas to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s transformation and pressure difference matching

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For renovation projects involving differential pressure control, the system baseline, air supply and exhaust relationship, target gas and installation space can be combined to assist in checking the chemical filtration section configuration and air volume balance plan.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Providing system baseline, modification requirements and target gases when enquiring, will help confirm the appropriate solution. The specific selection is subject to the technical documents and test results confirmed by the project.