Do I need to re-do the air volume balance after learning the filtration modification?

Direct answer: If a retrofit changes system resistance or branch distribution, the air volume balance usually needs to be rechecked.

Some people may think: Just adding a filter section and adjusting the total air volume back, there should be no need to balance it, right? The idea is risky. The recovery of the total air volume does not mean that the air volume distribution of each branch has also been restored.

When the resistance of the chemical filtration section is increased, the system operating point will move. If the filter section is only added to some branches, the resistance changes of each branch will be different, and the air volume may be redistributed. The original branch with large air volume may become smaller, and the original normal branch may deviate from the design value. These changes are not necessarily reflected in the total air volume.

Check the affected area

Before reconstruction, determine which areas and branch roads will be affected.

Add the location of the new filter segment. If a chemical filter section is added to the main supply duct, all ends will be affected. If added to a branch road, it will mainly affect the branch road and its downstream. Please refer to the specific location assessment Discussion of what conditions should be evaluated first before adding a chemical filter to an existing clean room .

A branch of a shared system. When multiple areas share one fan or one air duct, changes in the resistance of one branch will affect the air volume of other branches. It is necessary to clarify which branches are related.

Return the wind relationship. When the supply air volume changes, the return air volume will also change. If the return air branch is not adjusted synchronously, the room pressure differential may deviate. Please refer to the specific risks Discussion of how chemical filter modification can avoid affecting room pressure differential .

Don’t just measure the exit at the modified location. The outlet air volume at the modified location is normal, which does not mean that other areas are not affected. Associated branches and terminals need to be covered.

Use comparable operating states

Air volume balance measurement should be carried out under representative operating conditions.

Maintain normal valve status. During measurement, the air valve opening, door zone status, and production status should be consistent with daily operation. If the air volume is temporarily turned on or some areas are closed, the measured data cannot represent the actual status.

Record control settings. Fan gear, frequency converter frequency, and group control parameters must be recorded. These conditions should be consistent when comparing before and after the transformation. Please refer to the specific inspection records Discussion of what items should be checked during daily inspection of chemical filters .

Cover different working conditions. If the system has working mode and duty mode, the air volume in both states must be confirmed. You can't just test one gear.

Avoid changing other conditions at the same time. If dampers were also adjusted during the retrofit, other filters were replaced, or production schedules were changed, the causes of the data changes would be indistinguishable. Try to only change one variable at a time. For specific verification methods, please refer to Discussion of whether chemical filter validation is required to maintain consistent production loads .

Review filter targets after balancing

After adjusting the air volume, confirm the effect of the chemical filtration section.

The air volume passing through the filter section. Adjusting the branch changes the air volume through the chemical filtration section. If the air volume is too high, the contact time between the gas and the medium is insufficient, and the treatment effect may be reduced; if the air volume is too low, the processing capacity is insufficient. Please refer to the specific air volume selection. 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 .

outlet concentration. After the air volume is balanced, the target gas outlet concentration is detected according to project requirements to confirm that the protection objectives are met. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

pressure difference and resistance. Record the pressure difference in the chemical filtration section and compare it with the design value. If the pressure difference is high, it may be that the air volume is too large or the filter section resistance is abnormal. For detailed investigation, please refer to Discussion of what to check if the pressure difference before and after the chemical filter suddenly rises .

Qualified air volume is not proof of qualified gas effect. Both need to be verified separately.

Common misunderstandings

There are several common misunderstandings about air volume balancing.

The balance is considered complete when the total air volume reaches the standard. The total air volume is the sum of the air volumes of each branch. Some branches may be too large and some may be too small. The sum may look normal, but the actual distribution has deviated from the design.

Only the supply air is adjusted, not the return air. The supply air and return air are linked. If you only adjust the supply air valve, the return air volume may not match, and the room pressure difference will change. For specific control methods, please refer to Discussion of how chemical filter modification can avoid affecting room pressure differential .

Run according to the parameters before transformation. After adding a new filter section, the original fan gear and air valve opening may no longer be applicable. It needs to be recalibrated and the old parameters cannot be used.

Ignore the final resistance condition. When the filter material runs to a later stage, the resistance rises and the air volume may change again. Performance under final resistance conditions should be considered when balancing. For specific life assessment, please refer to Discussion of how long chemical filters last .

Project judgment example

A clean room adds a chemical filtration section to an air supply branch. After the transformation, the total air volume was adjusted to the original design value, and it was considered ok.

After running for a period of time, the air volume at the end of the branch is low and the air volume in the adjacent branch is high. The investigation found that the branch resistance of the newly added filter section increased, and the air volume shifted toward the branch with less resistance. The total air volume is normal, but the distribution has changed.

Treatment method: measure the air volume branch by branch, adjust the air valve opening, and restore the designed distribution of each branch. At the same time, check the return air volume and confirm that the room pressure difference is normal. After the adjustment, the air volume of each branch returned to the level before the transformation.

In another project, a complete branch air volume baseline was recorded before the renovation. After the renovation, the baselines were retested one by one and it was found that only two branches needed fine-tuning. After adjustment, the system runs normally.

These two cases illustrate that after the chemical filtration transformation, the air volume balance needs to be checked by branch, not just the total air volume. 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 air volume balance 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 that require air volume balance, the system structure, branch relationships, target air volume, and testing requirements can be combined to assist in checking the chemical filtration section configuration and balancing 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.